The Moon, just a couple days before new phase and the upcoming partial solar eclipse, joins Venus and Mars in the dawn sky on Thursday Sept. 10. Well below the triplet, look for returning Jupiter. Source: Stellarium
The dawn sky’s where it’s happening. With Saturn swiftly sinking westward at dusk, bright planets have become scarce in the evening hours. But if you get up early and look east, you’ll discover where the party is. Venus, Mars and now Jupiter have the dance floor.
Tale of two crescents. A montage of the thick crescent Moon and crescent Venus photographed earlier this month. Credit: Tom Ruen
What’s more, the sky gods have seen fit to roll a thin crescent Moon alongside Venus Thursday morning (Sept. 10). This lovely twinning of crescents is best seen about 75 minutes to an hour before sunrise. All you need is a pair of 10x binoculars to see the peewee Venusian version. Its waning crescent phase closely mimics the Moon’s.
From the U.S., the separation between the two will vary from 3° for the East Coast to 4.5° for the West. European and African skywatchers will witness the actual conjunction with the Moon gliding 2.5° north of the planet.
Venus is very bright, making it easy to see in the daytime if you know where to look. Try using the thin Moon soon after sunrise (7:30 a.m. local time shown here) to spot Venus. Aim and focus your binoculars on the Moon, then glide up and to the right to find Venus. If you succeed, lower the binoculars and see if you can spot it without optical aid. Source: Stellarium
Much fainter Mars, checking in at magnitude +1.8, lies 6° to the left or east of the Moon. It thrills me to see Mars begin a new apparition with its return to the morning sky. Next year, the Red Planet reaches opposition on May 22 in the constellation Scorpius, when it will be brighter than Sirius and more than 18 arc seconds across, its biggest and closest since 2005.
Remember Jupiter? We lost it in the solar glare more than a month ago, but if you can find a location with a nice, open eastern horizon, you can welcome the ever-jovial planet back Thursday. Bring binoculars just in case! Jove’s only a few degrees high in moderately-bright twilight.
The bright sunlit crescent contrasts with the darker lighting of twice-reflected light contributed by own planet. Credit: Bob King
When you look at the Moon Thursday, most of it will be illuminated not by sunlight but by Earth-light called earthshine. This smoky, dark glow results from sunlight bouncing off the globe into space to softly light the otherwise shadowed portion of the Moon. The effect is most pleasing to the eye and remarkable in binoculars, which reveal lunar seas and even larger craters shrouded in blue-dark. Don’t miss it!
The Universe is a very big place, and we occupy a very small corner of it. Known as the Solar System, our stomping grounds are not only a tiny fraction of the Universe as we know it, but is also a very small part of our galactic neighborhood (aka. the Milky Way Galaxy). When it comes right down to it, our world is just a drop of water in an endless cosmic sea.
Nevertheless, the Solar System is still a very big place, and one which is filled with its fair share of mysteries. And in truth, it was only within the relatively recent past that we began to understand its true extent. And when it comes to exploring it, we’ve really only begun to scratch the surface.
Discovery:
With very few exceptions, few people or civilizations before the era of modern astronomy recognized the Solar System for what it was. In fact, the vast majority of astronomical systems posited that the Earth was a stationary object and that all known celestial objects revolved around it. In addition, they viewed it as being fundamentally different from other stellar objects, which they held to be ethereal or divine in nature.
Although there were some Greek, Arab and Asian astronomers during Antiquity and the Medieval period who believed that the universe was heliocentric in nature (i.e. that the Earth and other bodies revolved around the Sun) it was not until Nicolaus Copernicus developed his mathematically predictive model of a heliocentric system in the 16th century that it began to become widespread.
Galileo (1564 – 1642) would often show people how to use his telescope to view the sky in Saint Mark’s square in Venice. Note the lack of adaptive optics. Credit: Public Domain
During the 17th-century, scientists like Galileo Galilei, Johannes Kepler, and Isaac Newton developed an understanding of physics which led to the gradual acceptance that the Earth revolves round the Sun. The development of theories like gravity also led to the realization that the other planets are governed by the same physical laws as Earth.
The widespread use of the telescope also led to a revolution in astronomy. After Galileo discovered the moons of Jupiter in 1610, Christian Huygens would go on to discover that Saturn also had moons in 1655. In time, new planets would also be discovered (such as Uranus and Neptune), as well as comets (such as Halley’s Comet) and the Asteroids Belt.
By the 19th century, three observations made by three separate astronomers determined the true nature of the Solar System and its place the universe. The first was made in 1839 by German astronomer Friedrich Bessel, who successfully measured an apparent shift in the position of a star created by the Earth’s motion around the Sun (aka. stellar parallax). This not only confirmed the heliocentric model beyond a doubt, but revealed the vast distance between the Sun and the stars.
In 1859, Robert Bunsen and Gustav Kirchhoff (a German chemist and physicist) used the newly invented spectroscope to examined the spectral signature of the Sun. They discovered that it was composed of the same elements as existed on Earth, thus proving that Earth and the heavens were composed of the same elements.
With parallax technique, astronomers observe object at opposite ends of Earth’s orbit around the Sun to precisely measure its distance. Credit: Alexandra Angelich, NRAO/AUI/NSF.
Then, Father Angelo Secchi – an Italian astronomer and director at the Pontifical Gregorian University – compared the spectral signature of the Sun with those of other stars, and found them to be virtually identical. This demonstrated conclusively that our Sun was composed of the same materials as every other star in the universe.
Further apparent discrepancies in the orbits of the outer planets led American astronomer Percival Lowell to conclude that yet another planet, which he referred to as “Planet X“, must lie beyond Neptune. After his death, his Lowell Observatory conducted a search that ultimately led to Clyde Tombaugh’s discovery of Pluto in 1930.
Also in 1992, astronomers David C. Jewitt of the University of Hawaii and Jane Luu of the MIT discovered the Trans-Neptunian Object (TNO) known as (15760) 1992 QB1. This would prove to be the first of a new population, known as the Kuiper Belt, which had already been predicted by astronomers to exist at the edge of the Solar System.
Further investigation of the Kuiper Belt by the turn of the century would lead to additional discoveries. The discovery of Eris and other “plutoids” by Mike Brown, Chad Trujillo, David Rabinowitz and other astronomers would lead to the Great Planet Debate – where IAU policy and the convention for designating planets would be contested.
The Sun contains 99.86% of the system’s known mass, and its gravity dominates the entire system. Most large objects in orbit around the Sun lie near the plane of Earth’s orbit (the ecliptic) and most planets and bodies rotate around it in the same direction (counter-clockwise when viewed from above Earth’s north pole). The planets are very close to the ecliptic, whereas comets and Kuiper belt objects are frequently at greater angles to it.
It’s four largest orbiting bodies (the gas giants) account for 99% of the remaining mass, with Jupiter and Saturn together comprising more than 90%. The remaining objects of the Solar System (including the four terrestrial planets, the dwarf planets, moons, asteroids, and comets) together comprise less than 0.002% of the Solar System’s total mass.
The Sun and planets to scale. Credit: Illustration by Judy Schmidt, texture maps by Björn Jónsson
Astronomers sometimes informally divide this structure into separate regions. First, there is the Inner Solar System, which includes the four terrestrial planets and the Asteroid Belt. Beyond this, there’s the outer Solar System that includes the four gas giant planets. Meanwhile, there’s the outermost parts of the Solar System are considered a distinct region consisting of the objects beyond Neptune (i.e. Trans-Neptunian Objects).
Most of the planets in the Solar System possess secondary systems of their own, being orbited by planetary objects called natural satellites (or moons). In the case of the four giant planets, there are also planetary rings – thin bands of tiny particles that orbit them in unison. Most of the largest natural satellites are in synchronous rotation, with one face permanently turned toward their parent.
The Sun, which comprises nearly all the matter in the Solar System, is composed of roughly 98% hydrogen and helium. The terrestrial planets of the Inner Solar System are composed primarily of silicate rock, iron and nickel. Beyond the Asteroid Belt, planets are composed mainly of gases (such as hydrogen, helium) and ices – like water, methane, ammonia, hydrogen sulfide and carbon dioxide.
Objects farther from the Sun are composed largely of materials with lower melting points. Icy substances comprise the majority of the satellites of the giant planets, as well as most of Uranus and Neptune (hence why they are sometimes referred to as “ice giants”) and the numerous small objects that lie beyond Neptune’s orbit.
Together, gases and ices are referred to as volatiles. The boundary in the Solar System beyond which those volatile substances could condense is known as the frost line, which lies roughly 5 AU from the Sun. Within the Kuiper Belt, objects and planetesimals are composed mainly of these materials and rock.
Formation and Evolution:
The Solar System formed 4.568 billion years ago from the gravitational collapse of a region within a large molecular cloud composed of hydrogen, helium, and small amounts of heavier elements fused by previous generations of stars. As the region that would become the Solar System (known as the pre-solar nebula) collapsed, conservation of angular momentum caused it to rotate faster.
The center, where most of the mass collected, became increasingly hotter than the surrounding disc. As the contracting nebula rotated faster, it began to flatten into a protoplanetary disc with a hot, dense protostar at the center. The planets formed by accretion from this disc, in which dust and gas gravitated together and coalesced to form ever larger bodies.
Due to their higher boiling points, only metals and silicates could exist in solid form closer to the Sun, and these would eventually form the terrestrial planets of Mercury, Venus, Earth, and Mars. Because metallic elements only comprised a very small fraction of the solar nebula, the terrestrial planets could not grow very large.
In contrast, the giant planets (Jupiter, Saturn, Uranus, and Neptune) formed beyond the point between the orbits of Mars and Jupiter where material is cool enough for volatile icy compounds to remain solid (i.e. the frost line).
The ices that formed these planets were more plentiful than the metals and silicates that formed the terrestrial inner planets, allowing them to grow massive enough to capture large atmospheres of hydrogen and helium. Leftover debris that never became planets congregated in regions such as the asteroid belt, Kuiper belt, and Oort cloud.
Within 50 million years, the pressure and density of hydrogen in the center of the protostar became great enough for it to begin thermonuclear fusion. The temperature, reaction rate, pressure, and density increased until hydrostatic equilibrium was achieved.
At this point, the Sun became a main-sequence star. Solar wind from the Sun created the heliosphere and swept away the remaining gas and dust from the protoplanetary disc into interstellar space, ending the planetary formation process.
The terrestrial planets of our Solar System at approximately relative sizes. From left, Mercury, Venus, Earth and Mars. Credit: Lunar and Planetary Institute
The Solar System will remain roughly as we know it today until the hydrogen in the core of the Sun has been entirely converted to helium. This will occur roughly 5 billion years from now and mark the end of the Sun’s main-sequence life. At this time, the core of the Sun will collapse, and the energy output will be much greater than at present.
The outer layers of the Sun will expand to roughly 260 times its current diameter, and the Sun will become a red giant. The expanding Sun is expected to vaporize Mercury and Venus and render Earth uninhabitable as the habitable zone moves out to the orbit of Mars. Eventually, the core will be hot enough for helium fusion and the Sun will burn helium for a time, after which nuclear reactions in the core will start to dwindle.
At this point, the Sun’s outer layers will move away into space, leaving a white dwarf – an extraordinarily dense object that will have half the original mass of the Sun, but will be the size of Earth. The ejected outer layers will form what is known as a planetary nebula, returning some of the material that formed the Sun to the interstellar medium.
Inner Solar System:
In the inner Solar System, we find the “Inner Planets” – Mercury, Venus, Earth, and Mars – which are so named because they orbit closest to the Sun. In addition to their proximity, these planets have a number of key differences that set them apart from planets elsewhere in the Solar System.
For starters, the inner planets are rocky and terrestrial, composed mostly of silicates and metals, whereas the outer planets are gas giants. The inner planets are also much more closely spaced than their outer Solar System counterparts. In fact, the radius of the entire region is less than the distance between the orbits of Jupiter and Saturn.
Generally, inner planets are smaller and denser than their counterparts, and have few to no moons or rings circling them. The outer planets, meanwhile, often have dozens of satellites and rings composed of particles of ice and rock.
The terrestrial inner planets are composed largely of refractory minerals such as the silicates, which form their crusts and mantles, and metals such as iron and nickel which form their cores. Three of the four inner planets (Venus, Earth and Mars) have atmospheres substantial enough to generate weather. All of them have impact craters and tectonic surface features as well, such as rift valleys and volcanoes.
Of the inner planets, Mercury is the closest to our Sun and the smallest of the terrestrial planets. Its magnetic field is only about 1% that of Earth’s, and it’s very thin atmosphere means that it is hot during the day (up to 430°C) and freezing at night (as low as -187 °C) because the atmosphere can neither keep heat in or out. It has no moons of its own and is comprised mostly of iron and nickel. Mercury is one of the densest planets in the Solar System.
Venus, which is about the same size as Earth, has a thick toxic atmosphere that traps heat, making it the hottest planet in the Solar System. This atmosphere is composed of 96% carbon dioxide, along with nitrogen and a few other gases. Dense clouds within Venus’ atmosphere are composed of sulphuric acid and other corrosive compounds, with very little water. Much of Venus’ surface is marked with volcanoes and deep canyons – the biggest of which is over 6400 km (4,000 mi) long.
Earth is the third inner planet and the one we know best. Of the four terrestrial planets, Earth is the largest, and the only one that currently has liquid water, which is necessary for life as we know it. Earth’s atmosphere protects the planet from dangerous radiation and helps keep valuable sunlight and warmth in, which is also essential for life to survive.
Like the other terrestrial planets, Earth has a rocky surface with mountains and canyons, and a heavy metal core. Earth’s atmosphere contains water vapor, which helps to moderate daily temperatures. Like Mercury, the Earth has an internal magnetic field. And our Moon, the only one we have, is comprised of a mixture of various rocks and minerals.
Mars, as it appears today, Credit: NASA
Mars is the fourth and final inner planet, and is also known as the “Red Planet” due to the oxidization of iron-rich materials that form the planet’s surface. Mars also has some of the most interesting terrain features of any of the terrestrial planets. These include the largest mountain in the Solar System (Olympus Mons) which rises some 21,229 m (69,649 ft) above the surface, and a giant canyon called Valles Marineris – which is 4000 km (2500 mi) long and reaches depths of up to 7 km (4 mi).
Much of Mars’ surface is very old and filled with craters, but there are geologically newer areas of the planet as well. At the Martian poles are polar ice caps that shrink in size during the Martian spring and summer. Mars is less dense than Earth and has a smaller magnetic field, which is indicative of a solid core, rather than a liquid one.
Mars’ thin atmosphere has led some astronomers to believe that the surface water that once existed there might have actually taken liquid form, but has since evaporated into space. The planet has two small moons called Phobos and Deimos.
Outer Solar System:
The outer planets (sometimes called Jovian planets or gas giants) are huge planets swaddled in gas that have rings and plenty of moons. Despite their size, only two of them are visible without telescopes: Jupiter and Saturn. Uranus and Neptune were the first planets discovered since antiquity, and showed astronomers that the solar system was bigger than previously thought.
The outer planets of our Solar System at approximately relative sizes. From left, Jupiter, Saturn, Uranus and Neptune. Credit: Lunar and Planetary Institute
Jupiter is the largest planet in our Solar System and spins very rapidly (10 Earth hours) relative to its orbit of the sun (12 Earth years). Its thick atmosphere is mostly made up of hydrogen and helium, perhaps surrounding a terrestrial core that is about Earth’s size. The planet has dozens of moons, some faint rings and a Great Red Spot – a raging storm that has happening for the past 400 years at least.
Saturn is best known for its prominent ring system – seven known rings with well-defined divisions and gaps between them. How the rings got there is one subject under investigation. It also has dozens of moons. Its atmosphere is mostly hydrogen and helium, and it also rotates quickly (10.7 Earth hours) relative to its time to circle the Sun (29 Earth years).
Uranus was first discovered by William Herschel in 1781. The planet’s day takes about 17 Earth hours and one orbit around the Sun takes 84 Earth years. Its mass contains water, methane, ammonia, hydrogen and helium surrounding a rocky core. It has dozens of moons and a faint ring system. The only spacecraft to visit this planet was the Voyager 2 spacecraft in 1986.
Neptune is a distant planet that contains water, ammmonia, methane, hydrogen and helium and a possible Earth-sized core. It has more than a dozen moons and six rings. NASA’s Voyager 2 spacecraft also visited this planet and its system by 1989 during its transit of the outer Solar System.
How many moons are there in the Solar System? Image credit: NASA
Trans-Neptunian Region:
There have been more than a thousand objects discovered in the Kuiper Belt, and it’s theorized that there are as many as 100,000 objects larger than 100 km in diameter. Given to their small size and extreme distance from Earth, the chemical makeup of KBOs is very difficult to determine.
However, spectrographic studies conducted of the region since its discovery have generally indicated that its members are primarily composed of ices: a mixture of light hydrocarbons (such as methane), ammonia, and water ice – a composition they share with comets. Initial studies also confirmed a broad range of colors among KBOs, ranging from neutral grey to deep red.
This suggests that their surfaces are composed of a wide range of compounds, from dirty ices to hydrocarbons. In 1996, Robert H. Brown et al. obtained spectroscopic data on the KBO 1993 SC, revealing its surface composition to be markedly similar to that of Pluto (as well as Neptune’s moon Triton) in that it possessed large amounts of methane ice.
Water ice has been detected in several KBOs, including 1996 TO66, 38628 Huya and 20000 Varuna. In 2004, Mike Brown et al. determined the existence of crystalline water ice and ammonia hydrate on one of the largest known KBOs, 50000 Quaoar. Both of these substances would have been destroyed over the age of the Solar System, suggesting that Quaoar had been recently resurfaced, either by internal tectonic activity or by meteorite impacts.
Keeping Pluto company out in the Kuiper belt are many other objects worthy of mention. Quaoar, Makemake, Haumea, Orcus and Eris are all large icy bodies in the Belt and several of them even have moons of their own. These are all tremendously far away, and yet, very much within reach.
Oort Cloud and Farthest Regions:
The Oort Cloud is thought to extend from between 2,000 and 5,000 AU (0.03 and 0.08 ly) to as far as 50,000 AU (0.79 ly) from the Sun, though some estimates place the outer edge as far as 100,000 and 200,000 AU (1.58 and 3.16 ly). The Cloud is thought to be comprised of two regions – a spherical outer Oort Cloud of 20,000 – 50,000 AU (0.32 – 0.79 ly), and disc-shaped inner Oort (or Hills) Cloud of 2,000 – 20,000 AU (0.03 – 0.32 ly).
The outer Oort cloud may have trillions of objects larger than 1 km (0.62 mi), and billions that measure 20 kilometers (12 mi) in diameter. Its total mass is not known, but – assuming that Halley’s Comet is a typical representation of outer Oort Cloud objects – it has the combined mass of roughly 3×1025 kilograms (6.6×1025 pounds), or five Earths.
The layout of the solar system, including the Oort Cloud, on a logarithmic scale. Credit: NASA
Based on the analyses of past comets, the vast majority of Oort Cloud objects are composed of icy volatiles – such as water, methane, ethane, carbon monoxide, hydrogen cyanide, and ammonia. The appearance of asteroids thought to be originating from the Oort Cloud has also prompted theoretical research that suggests that the population consists of 1-2% asteroids.
Earlier estimates placed its mass up to 380 Earth masses, but improved knowledge of the size distribution of long-period comets has led to lower estimates. The mass of the inner Oort Cloud, meanwhile, has yet to be characterized. The contents of both Kuiper Belt and the Oort Cloud are known as Trans-Neptunian Objects (TNOs), because the objects of both regions have orbits that that are further from the Sun than Neptune’s orbit.
Exploration:
Our knowledge of the Solar System also benefited immensely from the advent of robotic spacecraft, satellites, and robotic landers. Beginning in the mid-20th century, in what was known as “The Space Age“, manned and robotic spacecraft began exploring planets, asteroids and comets in the Inner and Outer Solar System.
All planets in the Solar System have now been visited to varying degrees by spacecraft launched from Earth. Through these unmanned missions, humans have been able to get close-up photographs of all the planets. In the case of landers and rovers, tests have been performed on the soils and atmospheres of some.
Photograph of a Russian technician putting the finishing touches on Sputnik 1, humanity’s first artificial satellite. Credit: NASA/Asif A. Siddiqi
The first artificial object sent into space was the Soviet satellite Sputnik 1, which was launched in space in 1957, successfully orbited the Earth for months, and collected information on the density of the upper atmosphere and the ionosphere. The American probe Explorer 6, launched in 1959, was the first satellite to capture images of the Earth from space.
Robotic spacecraft conducting flybys also revealed considerable information about the planet’s atmospheres, geological and surface features. The first successful probe to fly by another planet was the Soviet Luna 1 probe, which sped past the Moon in 1959. The Mariner program resulted in multiple successful planetary flybys, consisting of the Mariner 2 mission past Venus in 1962, the Mariner 4 mission past Mars in 1965, and the Mariner 10 mission past Mercury in 1974.
By the 1970’s, probes were being dispatched to the outer planets as well, beginning with the Pioneer 10 mission which flew past Jupiter in 1973 and the Pioneer 11 visit to Saturn in 1979.The Voyager probes performed a grand tour of the outer planets following their launch in 1977, with both probes passing Jupiter in 1979 and Saturn in 1980-1981. Voyager 2 then went on to make close approaches to Uranus in 1986 and Neptune in 1989.
Launched on January 19th, 2006, the New Horizons probe is the first man-made spacecraft to explore the Kuiper Belt. This unmanned mission flew by Pluto in July 2015. Should it prove feasible, the mission will also be extended to observe a number of other Kuiper Belt Objects (KBOs) in the coming years.
Orbiters, rovers, and landers began being deployed to other planets in the Solar System by the 1960’s. The first was the Soviet Luna 10 satellite, which was sent into lunar orbit in 1966. This was followed in 1971 with the deployment of the Mariner 9 space probe, which orbited Mars, and the Soviet Venera 9 which orbited Venus in 1975.
The Galileo probe became the first artificial satellite to orbit an outer planet when it reached Jupiter in 1995, followed by the Cassini–Huygens probe orbiting Saturn in 2004. Mercury and Vesta were explored by 2011 by the MESSENGER and Dawn probes, respectively, with Dawn establishing orbit around the asteroid/dwarf planet Ceres in 2015.
The first probe to land on another Solar System body was the Soviet Luna 2 probe, which impacted the Moon in 1959. Since then, probes have landed on or impacted on the surfaces of Venus in 1966 (Venera 3), Mars in 1971 (Mars 3 and Viking 1 in 1976), the asteroid 433 Eros in 2001 (NEAR Shoemaker), and Saturn’s moon Titan (Huygens) and the comet Tempel 1 (Deep Impact) in 2005.
Curiosity Rover self portrait mosaic, taken with the MAHLI camera while sitting on flat sedimentary rocks at the “John Klein” outcrop in Feb. 2013. Credit: NASA/JPL-Caltech/MSSS/Marco Di Lorenzo/KenKremer
To date, only two worlds in the Solar System, the Moon and Mars, have been visited by mobile rovers. The first robotic rover to land on another planet was the Soviet Lunokhod 1, which landed on the Moon in 1970. The first to visit another planet was Sojourner, which traveled 500 meters across the surface of Mars in 1997, followed by Spirit(2004), Opportunity (2004), and Curiosity (2012).
Manned missions into space began in earnest in the 1950’s, and was a major focal point for both the United States and Soviet Union during the “Space Race“. For the Soviets, this took the form of the Vostok program, which involved sending manned space capsules into orbit.
The first mission – Vostok 1 – took place on April 12th, 1961, and was piloted by Soviet cosmonaut Yuri Gagarin (the first human being to go into space). On June 6th, 1963, the Soviets also sent the first woman – Valentina Tereshvoka – into space as part of the Vostok 6 mission.
In the US, Project Mercury was initiated with the same goal of placing a crewed capsule into orbit. On May 5th, 1961, astronaut Alan Shepard went into space aboard the Freedom 7mission and became the first American (and second human) to go into space.
After the Vostok and Mercury programs were completed, the focus of both nations and space programs shifted towards the development of two and three-person spacecraft, as well as the development of long-duration spaceflights and extra-vehicular activity (EVA).
Bootprint in the moon dust from Apollo 11. Credit: NASA
This took the form of the Voshkod and Gemini programs in the Soviet Union and US, respectively. For the Soviets, this involved developing a two to three-person capsule, whereas the Gemini program focused on developing the support and expertise needed for an eventual manned mission to the Moon.
These latter efforts culminated on July 21st, 1969 with the Apollo 11 mission, when astronauts Neil Armstrong and Buzz Aldrin became the first men to walk on the Moon. As part of the Apollo program, five more Moon landings would take place through 1972, and the program itself resulted in many scientific packages being deployed on the Lunar surface, and samples of moon rocks being returned to Earth.
After the Moon Landing took place, the focus of the US and Soviet space programs then began to shift to the development of space stations and reusable spacecraft. For the Soviets, this resulted in the first crewed orbital space stations dedicated to scientific research and military reconnaissance – known as the Salyut and Almaz space stations.
The first orbital space station to host more than one crew was NASA’s Skylab, which successfully held three crews from 1973 to 1974. The first true human settlement in space was the Soviet space station Mir, which was continuously occupied for close to ten years, from 1989 to 1999. It was decommissioned in 2001, and its successor, the International Space Station, has maintained a continuous human presence in space since then.
Space Shuttle Columbia launching on its maiden voyage on April 12th, 1981. Credit: NASA
The United States’ Space Shuttle, which debuted in 1981, became the only reusable spacecraft to successfully make multiple orbital flights. The five shuttles that were built (Atlantis, Endeavour, Discovery, Challenger, Columbiaand Enterprise) flew a total of 121 missions before being decommissioned in 2011.
During their history of service, two of the craft were destroyed in accidents. These included the Space Shuttle Challenger – which exploded upon take-off on Jan. 28th, 1986 – and the Space Shuttle Columbia which disintegrated during re-entry on Feb. 1st, 2003.
In 2004, then-U.S. President George W. Bush announced the Vision for Space Exploration, which called for a replacement for the aging Shuttle, a return to the Moon and, ultimately, a manned mission to Mars. These goals have since been maintained by the Obama administration, and now include plans for an Asteroid Redirect mission, where a robotic craft will tow an asteroid closer to Earth so a manned mission can be mounted to it.
All the information gained from manned and robotic missions about the geological phenomena of other planets – such as mountains and craters – as well as their seasonal, meteorological phenomena (i.e. clouds, dust storms and ice caps) have led to the realization that other planets experience much the same phenomena as Earth. In addition, it has also helped scientists to learn much about the history of the Solar System and its formation.
As our exploration of the Inner and Outer Solar System has improved and expanded, our conventions for categorizing planets has also changed. Our current model of the Solar System includes eight planets (four terrestrial, four gas giants), four dwarf planets, and a growing number of Trans-Neptunian Objects that have yet to be designated. It also contains and is surrounded by countless asteroids and planetesimals.
Given its sheer size, composition and complexity, researching our Solar System in full detail would take an entire lifetime. Obviously, no one has that kind of time to dedicate to the topic, so we have decided to compile the many articles we have about it here on Universe Today in one simple page of links for your convenience.
There are thousands of facts about the solar system in the links below. Enjoy your research.
The Full Moon at 10:30 p.m. last night (Aug. 30). Even at 25 altitude, it glowed a deep, dark orange due to heavy smoke from western forest fires. Credit: Bob King
Did you see the Moon last night? I walked outside at 10:30 p.m. and was stunned to see a dark, burnt-orange Full Moon as if September’s eclipse had arrived a month early. Why? Heavy smoke from forest fires in Washington, California and Montana has now spread to cover nearly half the country in a smoky pall, soaking up starlight and muting the moonlight.
If this is what global warming has in store for us, skywatchers will soon have to take a forecast of “clear skies” with a huge grain of salt.
The Pacific Northwest is abundantly dotted with wildfires in Washington, Oregon, Idaho and Montana in this Aqua satellite image taken on August 25, 2015. Actively burning areas, detected by MODIS’s thermal bands, are outlined in red. Smoke from the fires has been drifting east, blanketing Midwestern skies and blotting out the stars at night. Credit: NASA image courtesy Jeff Schmaltz, MODIS Rapid Response Team
By day, the sky appears the palest of blues. By night, the stars are few if any, and the Moon appears faint, the color of fire and strangely remote. Despite last night’s clear skies, only the star Vega managed to penetrate the gloom. I never saw my shadow even at midnight when the Moon had climbed high into the southern sky.
Last night’s Full Moon seen through an 8-inch telescope at 11:30 p.m. The colors are true. Credit: Bob King
We’ve seen this smoke before. Back in July, Canadian forest fires wafted south and west and covered much of the northern half of the U.S., giving us red suns in the middle of the afternoon and leaving only enough stars to count with two hands at night. On the bright side, the Moon is fascinating to observe. I set up the telescope last night and spend a half hour watching this unexpected “eclipse”; sunsets appear positively atomic. The size of the smoke particles is just right for filtering out or scattering away blues, greens and even yellow from white light. Vivid reds, pinks and oranges remain to tint anything bright enough to penetrate the haze.
GOES-8 satellite view of the central U.S. taken at 8:15 a.m. CDT August 30, 2015 show a veil of grayish forest fire smoke covering much of the Midwest with clearer conditions to the southeast. The red line is the approximate border between the two. Credit: NOAA
But smoke can cause harm, too. Forest fire smoke contains carbon monoxide, carbon dioxide and soot. On especially smoky days, you can even smell the odor of burning trees in the air at ground level. Some may suffer from burning eyes, asthma or bronchitis on especially smoky days even a thousand miles from the source fires.
Wide-angle view of last night’s Moon. Notice that the smoke is thicker along the horizontal – left and right of the Moon. Above, at a higher elevation, we see through less smoke, so the moonlit sky is a bit brighter there. No stars are visible. Credit: Bob King
On clear, blue-sky days, I’ve watched the smoke creep in from the west. It begins a light haze and slowly covers the entire sky in a matter of several hours, often showing a banded structure in the direction of the Sun. A little smoke is OK for observing, but once it’s thick enough to redden the Moon even hours after moonrise, you can forget about using your telescope for stargazing. Sometimes, a passing thunderstorm and cold front clears the sky again. Sometimes not.
The only cures for fire soot are good old-fashioned rain and the colder weather that arrives with fall. In the meantime, many of us will spend our evenings reading about the stars instead of looking at them.
A Full Moon in all its horizontal glory. When near the horizon, refraction squeezes the lunar disk into an oval. Scattering removes the shorter wavelengths of white light, leaving the Moon a rich red or orange. Credit: Bob King
Who doesn’t love a Full Moon? Occurring about once a month, they never wear out their welcome. Each one becomes a special event to anticipate. In the summer months, when the Moon rises through the sultry haze, atmosphere and aerosols scatter away so much blue light and green light from its disk, the Moon glows an enticing orange or red.
At Full Moon, we’re also more likely to notice how the denser atmosphere near the horizon squeezes the lunar disk into a crazy hamburger bun shape. It’s caused by atmospheric refraction. Air closest to the horizon refracts more strongly than air near the top edge of the Moon, in effect “lifting” the bottom of the Moon up into the top. Squished light! We also get to see all the nearside maria or “seas” at full phase, while rayed craters like Tycho and Copernicus come into their full glory, looking for all the world like giant spatters of white paint even to the naked eye.
At full phase, the Moon lies directly opposite the Sun on the other side of Earth. Sunlight hits the Moon square on and fully illuminates the Earth-facing hemisphere. Credit: Bob King
Tomorrow night (August 29), the Full Sturgeon Moon rises around sunset across the world. The name comes from the association Great Lakes Indian groups made between the August moon and the best time to catch sturgeon. Next month’s moon is the familiar Harvest Moon; the additional light it provided at this important time of year allowed farmers to harvest into the night.
A Full Moon lies opposite the Sun in the sky exactly like a planet at opposition. Earth is stuck directly between the two orbs. As we look to the west to watch the Sun go down, the Moon creeps up at our back from the eastern horizon. Full Moon is the only time the Moon faces Sun directly – not off to one side or another – as seen from Earth, so the entire disk is illuminated.
The moon provides the perfect backdrop for watching birds migrate at night. Although a small telescope is best, you might see an occasional bird in binoculars, too. Credit: Bob King
If you’re a moonrise watcher like I am, you’ll want to find a place where you can see all the way down to the eastern horizon tomorrow night. You’ll also need the time of moonrise for your city and a pair of binoculars. Sure, you can watch a moonrise without optical aid perfectly well, but you’ll miss all the cool distortions happening across the lunar disk from air turbulence. Birds have also begun their annual migration south. Don’t be surprised if your glass also shows an occasional winged silhouette zipping over those lunar seas.
Because the Moon’s orbit is tilted 5.1° with respect to Earth’s, it normally passes above or below Earth’s shadow with no eclipse — either lunar or solar. Only when the lineup is exact, does the Moon pass directly behind Earth and into its shadow. Credit: Bob King
Next month’s Full Moon is very special. A few times a year, the alignment of Sun, Earth and Moon (in that order) is precise, and the Full Moon dives into Earth’s shadow in total eclipse. That will happen overnight Sunday night-Monday morning September 27-28. This will be the final in the current tetradof four total lunar eclipses, each spaced about six months apart from the other. I think this one will be the best of the bunch. Why?
The totally eclipsed moon on April 15, 2014 from Duluth, Minn. This was the first in the series of four eclipses called a tetrad. September’s totally eclipsed Moon will appear similar. The coloring comes from sunlight grazing the edge of Earth’s atmosphere and refracted by it into the planet’s shadow. Credit: Bob King
Convenient evening viewing hours (CDT times given) for observers in the Americas. Partial eclipse begins at 8:07 p.m., totality lasts from 9:11 – 10:23 p.m. and partial eclipse ends at 11:27 p.m. Those times mean that for many regions, kids can stay up and watch.
The Moon passes more centrally through Earth’s shadow than during the last total eclipse. That means a longer totality and possibly more striking color contrasts.
September’s will be the last total eclipse visible in the Americas until January 31, 2018. Between now and then, there will be a total of four minor penumbral eclipses and one small partial. Slim pickings.
Diagram showing the details of the upcoming total lunar eclipse. The event begins when the Moon treads into Earth’s outer shadow (penumbra) at 7:12 p.m. CDT. Partial phases start at 8:07 and totality at 9:11. Credit: NASA / Fred Espenak
Not only will the Americas enjoy a spectacle, but totality will also be visible from Europe, Africa and parts of Asia. For eastern hemisphere skywatchers, the event will occur during early morning hours of September 28. Universal or UT times for the eclipse are as follows: Partial phase begin at 1:07 a.m., totality from 2:11 – 3:23 a.m. with the end of partial phase at 4:27 a.m.
September 27-28, 2015 eclipse visibility map. Credit: NASA / Fred Espenak
We’ll have much more coverage on the upcoming eclipse in future articles here at Universe Today. I hope this brief look will serve to whet your appetite and help you anticipate what promises to be one of the best astronomical events of 2015.
During a 535-second test on August 13, 2015, operators ran the Space Launch System (SLS) RS-25 rocket engine through a series of tests at different power levels to collect engine performance data on the A-1 test stand at NASA's Stennis Space Center near Bay St. Louis, Mississippi. Credit: NASA
During a 535-second test on August 13, 2015, operators ran the Space Launch System (SLS) RS-25 rocket engine through a series of tests at different power levels to collect engine performance data on the A-1 test stand at NASA’s Stennis Space Center near Bay St. Louis, Mississippi. Credit: NASA Story/imagery updated
See video below of full duration hot-fire test[/caption]
With today’s (Aug. 13) successful test firing of an RS-25 main stage engine for NASA’s Space Launch System (SLS) monster rocket currently under development, the program passed a key milestone advancing the agency on the path to propel astronauts back to deep space at the turn of the decade.
The 535 second long test firing of the RS-25 development engine was conducted on the A-1 test stand at NASA’s Stennis Space Center near Bay St. Louis, Mississippi – and ran for the planned full duration of nearly 9 minutes, matching the time they will fire during an actual SLS launch.
All indications are that the hot fire test apparently went off without a hitch, on first look.
“We ran the full duration and met all test objectives,” said Steve Wofford, SLS engine manager, on NASA TV following today’s’ test firing.
“There were no anomalies.” – based on the initial look.
The RS-25 is actually an upgraded version of former space shuttle main engines that were used with a 100% success rate during NASA’s three decade-long Space Shuttle program to propel the now retired shuttle orbiters to low Earth orbit. Those same engines are now being modified for use by the SLS.
Spectators enjoy the view during the Aug. 13, 2015 test firing of the RS-25 engine for NASA’s Space Launch System (SLS) on the A-1 test stand at NASA’s Stennis Space Center near Bay St. Louis, Mississippi. Credit: NASA
“Data collected on performance of the engine at the various power levels will aid in adapting the former space shuttle engines to the new SLS vehicle mission requirements, including development of an all-new engine controller and software,” according to NASA officials .
The engine controller functions as the “brain” of the engine, which checks engine status, maintains communication between the vehicle and the engine and relays commands back and forth.
The core stage (first stage) of the SLS will be powered by four RS-25 engines and a pair of the five-segment solid rocket boosters that will generate a combined 8.4 million pounds of liftoff thrust, making it the most powerful rocket the world has ever seen.
Since shuttle orbiters were equipped with three space shuttle main engines, the use of four RS-25s on the SLS represents another significant change that also required many modifications being thoroughly evaluated as well.
RS-25 test firing in progress on the A-1 test stand at NASA’s Stennis Space Center near Bay St. Louis, Mississippi, on Aug. 13, 2015. Credit: NASA
The SLS will be some 10 percent more powerful than the Saturn V rockets that propelled astronauts to the Moon, including Neil Armstrong, the human to walk on the Moon during Apollo 11 in July 1969.
SLS will loft astronauts in the Orion capsule on missions back to the Moon by around 2021, to an asteroid around 2025 and then beyond on a ‘Journey to Mars’ in the 2030s – NASA’s overriding and agency wide goal.
Each of the RS-25’s engines generates some 500,000 pounds of thrust. They are fueled by cryogenic liquid hydrogen and liquid oxygen. For SLS they will be operating at 109% of power, compared to a routine usage of 104.5% during the shuttle era. They measure 14 feet tall and 8 feet in diameter.
They have to withstand and survive temperature extremes ranging from -423 degrees F to more than 6000 degrees F.
This video shows the full duration hot-fire test:
NASA has 16 of the RS-25s leftover from the shuttle era and they are all being modified and upgraded for use by the SLS rocket.
Today’s test was the sixth in a series of seven to qualify the modified engines to flight status. The engine ignited at 5:01 p.m. EDT and reached the full thrust level of 512,000 pounds within about 5 seconds.
The hot gas was exhausted out of the nozzle at 13 times the speed of sound.
Since the shuttle engines were designed and built over three decades ago, they are being modified where possible with state of the art components to enhance performance, functionality and ease of operation, by prime contractor Aerojet-Rocketdyne of Sacramento, California.
One of the key objectives of today’s engine firing and the entire hot fire series was to test the performance of a brand new engine controller assembled with modern manufacturing techniques.
“Operators on the A-1 Test Stand at Stennis are conducting the test series to qualify an all-new engine controller and put the upgraded former space shuttle main engines through the rigorous temperature and pressure conditions they will experience during a SLS mission,” says NASA.
“The new controller, or “brain,” for the engine, which monitors engine status and communicates between the vehicle and the engine, relaying commands to the engine and transmitting data back to the vehicle. The controller also provides closed-loop management of the engine by regulating the thrust and fuel mixture ratio while monitoring the engine’s health and status.’
Video caption: RS-25 – The Ferrari of Rocket Engines explained. Credit: NASA
“The RS-25 is the most complicated rocket engine out there on the market, but that’s because it’s the Ferrari of rocket engines,” says Kathryn Crowe, RS-25 propulsion engineer.
“When you’re looking at designing a rocket engine, there are several different ways you can optimize it. You can optimize it through increasing its thrust, increasing the weight to thrust ratio, or increasing its overall efficiency and how it consumes your propellant. With this engine, they maximized all three.”
Engineers will now pour over the data collected from hundreds of data channels in great detail to thoroughly analyze the test results. They will incorporate any findings into future test firings of the RS-25s.
NASA says that testing of RS-25 flight engines is set to start later this fall.
“The RS-25 engine gives SLS a proven, high performance, affordable main propulsion system for deep space exploration. It is one of the most experienced large rocket engines in the world, with more than a million seconds of ground test and flight operations time.”
NASA plans to buy completely new sets of RS-25 engines from Aerojet-Rocketdyne taking full advantage of technological advances and modern manufacturing techniques as well as lessons learned from this hot fire series of engine tests.
The maiden test flight of the SLS is targeted for no later than November 2018 and will be configured in its initial 70-metric-ton (77-ton) version with a liftoff thrust of 8.4 million pounds. It will boost an unmanned Orion on an approximately three week long test flight beyond the Moon and back.
Artist concept of the SLS Block 1 configuration. Credit: NASA
NASA plans to gradually upgrade the SLS to achieve an unprecedented lift capability of 130 metric tons (143 tons), enabling the more distant missions even farther into our solar system.
The first SLS test flight with the uncrewed Orion is called Exploration Mission-1 (EM-1) and will launch from Launch Complex 39-B at the Kennedy Space Center.
NASA’s first Orion spacecraft blasts off at 7:05 a.m. atop United Launch Alliance Delta 4 Heavy Booster at Space Launch Complex 37 (SLC-37) at Cape Canaveral Air Force Station in Florida on Dec. 5, 2014. Credit: Ken Kremer – kenkremer.com
Orion’s inaugural mission dubbed Exploration Flight Test-1 (EFT) was successfully launched on a flawless flight on Dec. 5, 2014 atop a United Launch Alliance Delta IV Heavy rocket Space Launch Complex 37 (SLC-37) at Cape Canaveral Air Force Station in Florida.
Stay tuned here for Ken’s continuing Earth and Planetary science and human spaceflight news.
NASA Administrator Charles Bolden officially unveils world’s largest welder to start construction of core stage of NASA’s Space Launch System (SLS) rocket at NASA Michoud Assembly Facility, New Orleans, on Sept. 12, 2014. SLS will be the world’s most powerful rocket ever built. Credit: Ken Kremer – kenkremer.comSTS-135: Last launch using RS-25 engines that will now power NASA’s SLS deep space exploration rocket. NASA’s 135th and final shuttle mission takes flight on July 8, 2011 at 11:29 a.m. from the Kennedy Space Center in Florida bound for the ISS and the high frontier with Chris Ferguson as Space Shuttle Commander. Credit: Ken Kremer/kenkremer.com
This animation shows images of the far side of the moon, illuminated by the sun, as it crosses between the DISCOVR spacecraft's Earth Polychromatic Imaging Camera (EPIC) camera and telescope, and the Earth - one million miles away. Credit: NASA/NOAA
This animation shows images of the far side of the moon, illuminated by the sun, as it crosses between the DISCOVR spacecraft’s Earth Polychromatic Imaging Camera (EPIC) camera and telescope, and the Earth – one million miles away. Credit: NASA/NOAA
See YouTube version and EPIC camera below[/caption]
An eye-poppingly ‘EPIC’ view of the sunlit far side of the Moon transiting the sunlit side of Earth was recently captured by NASA’s Earth Polychromatic Imaging Camera (EPIC) camera from one million miles away. “Wow!” – is an understatement!
The stunning animation of the Moon crossing in front of the Earth, shown above, and seemingly unlike anything else, was created from a series of images taken in July by NASA’s EPIC camera flying aboard the orbiting Deep Space Climate Observatory (DSCOVR), a space weather monitoring satellite, according to a NASA statement.
Have just witnessed NASA’s New Horizons flyby of the Pluto-Charondouble planet system, the similarity to what some call the Earth-Moon double planet system is eerie. You could imagine ones heart going out to Earth’s Australian continent as an upside down version of Pluto’s bright heart shaped ‘Tombaugh Regio’ region in the southern hemisphere.
EPIC is a four megapixel CCD camera and telescope mounted on DSCOVR and orbiting at the L1 Lagrange Point – a neutral gravity point that lies on the direct line between Earth and the sun.
The goal of the $340 million DSCOVR is to monitor the solar wind and aid very important forecasts of space weather at Earth from L1.
EPIC will capture “a constant view of the fully illuminated Earth as it rotates, providing scientific observations of ozone, vegetation, cloud height and aerosols in the atmosphere.”
L1 is located 1.5 million kilometers (932,000 miles) sunward from Earth. At L1 the gravity between the sun and Earth is perfectly balanced and the DSCOVR satellite orbits about that spot just like a planet.
The EPIC images “were taken between 3:50 p.m. and 8:45 p.m. EDT on July 16, showing the moon moving over the Pacific Ocean near North America,” NASA said.
This image shows images of the far side of the moon, illuminated by the sun, as it crosses between the DISCOVR spacecraft’s Earth Polychromatic Imaging Camera (EPIC) camera and telescope, and the Earth – one million miles away. Credits: NASA/NOAA
You can see Earth’s North Pole at the upper left side of the images which results from the orbital tilt of Earth from the vantage point of the spacecraft at the L1 Lagrange Point.
EPIC will take full disk color images of the sunlit side of Earth at least six times per day.
They will be made publically available by NASA at a dedicated website, when the camera starts its regular daily science observation campaign of the home planet in about a month during September.
NASA says the images will show varying views of the rotating Earth and they will be posted online some 12 to 36 hours after they are acquired.
Each image is actually a composite of three images taken in the red, green and blue channels of the EPIC camera to provide the final “natural color” image of Earth. Since the images are taken about 30 seconds apart as the moon is moving there is a slight but noticeable artifact on the right side of the moon, NASA explained.
Altogether, “ EPIC takes a series of 10 images using different narrowband spectral filters — from ultraviolet to near infrared — to produce a variety of science products. The red, green and blue channel images are used in these color images.”
EPIC should capture these Earth-Moon transits about twice per year as the orbit of DSCOVR crosses the orbital plane of the moon.
The closest analog according to NASA came in May 2008 when NASA’s Deep Impact spacecraft “captured a similar view of Earth and the moon from a distance of 31 million miles away. The series of images showed the moon passing in front of our home planet when it was only partially illuminated by the sun.”
We never see the far side of the moon from Earth since the bodies are tidally locked. And its quite apparent from the images, that the moon’s far side looks completely different from the side facing Earth. The far side lacks the large, dark, basaltic plains, or maria, that are so prominent on the Earth-facing side.
“It is surprising how much brighter Earth is than the moon,” said Adam Szabo, DSCOVR project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, in a statement.
“Our planet is a truly brilliant object in dark space compared to the lunar surface.”
DSCOVR is a joint mission between NOAA, NASA, and the U.S Air Force (USAF) that is managed by NOAA. The satellite and science instruments were provided by NASA and NOAA.
Technician works on NASA Earth science instruments and Earth imaging EPIC camera (white circle) housed on NOAA/NASA Deep Space Climate Observatory (DSCOVR) inside NASA Goddard Space Flight Center clean room in November 2014. Credit: Ken Kremer/kenkremer.com
DSCOVR was first proposed in 1998 by then US Vice President Al Gore as the low cost ‘Triana’ satellite to take near continuous views of the Earth’s entire globe to feed to the internet as a means of motivating students to study math and science. It was eventually built as a much more capable Earth science satellite that would also conduct the space weather observations.
But Triana was shelved for purely partisan political reasons and the satellite was placed into storage at NASA Goddard and the science was lost until now.
It was also dubbed “Goresat.’
Stay tuned here for Ken’s continuing Earth and planetary science and human spaceflight news.
Video caption: This animation shows images of the far side of the moon, illuminated by the sun, as it crosses between the DISCOVR spacecraft’s Earth Polychromatic Imaging Camera (EPIC) camera and telescope, and the Earth – one million miles away. Credit: NASA/NOAA
NOAA/NASA Deep Space Climate Observatory (DSCOVR) undergoes processing in NASA Goddard Space Flight Center clean room. Solar wind instruments at right. DSCOVER launched in February 2015 atop SpaceX Falcon 9 rocket. Credit: Ken Kremer/kenkremer.comLaunch of NOAA DSCOVR satellite from Cape Canaveral Air Force Station on Feb. 11, 2015 to monitor solar storms and space weather. Credit: Julian Leek
Enhanced-color image from Cassini showing red streaks on Tethys (NASA/JPL-Caltech/Space Science Institute)
Resembling what the skin on my arms looks like after giving my cat a bath, the surface of Saturn’s moon Tethys is seen above in an extended-color composite from NASA’s Cassini spacecraft showing strange long red streaks. They stretch for long distances across the moon’s surface following the rugged terrain, continuing unbroken over hills and down into craters… and their cause isn’t yet known.
According to a NASA news release, “The origin of the features and their reddish color is currently a mystery to Cassini scientists. Possibilities being studied include ideas that the reddish material is exposed ice with chemical impurities, or the result of outgassing from inside Tethys. The streaks could also be associated with features like fractures that are below the resolution of the available images.”
The images were taken by Cassini during a flyby of the 660-mile-wide (1,062 km) Tethys on April 11, 2015 at a resolution of about 2,300 feet (700 meters) per pixel. They were acquired in visible green, infrared, and ultraviolet light wavelengths and so the composite image reveals colors our eyes can’t directly perceive. The combination of this and the solar illumination needed to image this particular area as the spacecraft passed by are why these features haven’t been seen so well until now.
“The red arcs really popped out when we saw the new images,” said Cassini participating scientist Paul Schenk of the Lunar and Planetary Institute in Houston. “It’s surprising how extensive these features are.”
Extended color mosaic of Tethys from Cassini images acquired on April 11, 2015. The region where the streaks are is outlined. Click for original hi-res version. (NASA/JPL-Caltech/SSI)
While the nature of Tethys’ streaks isn’t understood, the observations do indicate a relatively young age compared to the surrounding surface.
“The red arcs must be geologically young because they cut across older features like impact craters, but we don’t know their age in years.” said Paul Helfenstein, a Cassini imaging scientist at Cornell University in Ithaca. “If the stain is only a thin, colored veneer on the icy soil, exposure to the space environment at Tethys’ surface might erase them on relatively short time scales.”
Reprocessed Galileo image of Europa’s streaked surface by Ted Stryk (NASA/JPL/Ted Stryk)
Could these arcs be signs of an underground ocean or reservoir of briny liquid, like Enceladus’ tiger stripes (aka sulcae) or the streaks that crisscross Europa’s ice? Or are they the results of infalling material from one of Saturn’s other moons? More observations with Cassini, now in its eleventh year in orbit at Saturn, are being planned to “study the streaks.”
“We are planning an even closer look at one of the Tethys red arcs in November to see if we can tease out the source and composition of these unusual markings,” said Linda Spilker, Cassini project scientist at JPL.
What would it take to destroy our moon, and eliminate the enemy of stellar astronomy for all time?
In the immortal words of Mr. Burns, “ever since the beginning of time, man has wished to destroy the Sun.” Your days are numbered, Sun.
But supervillains, being the practical folks they are, know that a more worthy goal would be to destroy the Moon, or at least deface it horribly. Nothing wrecks a beautiful night sky like that hideous pockmarked spotlight. What would it take to destroy it and eliminate the enemy of stellar astronomy for all time?
Crack out your Acme brand blueprint paper and white pencils, it’s Wile E. Coyote time.
The energy it takes to dismantle a gravitationally held object is known as its binding energy, we talked about it in a Death Star episode and inventive ways to overcome it.
For example, the binding energy of the Earth is 2.2 x 10^32 joules. It’s a lot. The binding energy of a smaller object, like our Moon is a tidy little 1.2 x 10^29 joules. It takes about 1800 times more energy to destroy the Earth than it takes to destroy the Moon.
It’s 1800 times easier. That’s downright doable, isn’t it? That’s almost 2000 times easier. Which, on the scale of easy to less easy, is definitely closer to easy.
Take the event that created the Caloris Basin on Mercury. It’s a crater, 1,500 km across. Astronomers think that a big fat asteroid, a fatsteroid(?) around 100 km in diameter crashed into Mercury billions of years ago. This event released 1.3 x 10^26 joules of energy, carving out this giant pit. It’s a thousandth of the binding energy of the Moon. We’ll need something more.
Our Sun produces 3.8 x 10^26 joules of energy every second, the equivalent of about a billion hydrogen bombs. If you directed the full power of the Sun at the Moon for 15 minutes, it’d tear apart.
That’s quite a superweapon you’ve got there, perhaps you’ll want to mount that on a space station and take it for a cruise through a galaxy far far away?
If that scene took that long, we’d have fallen asleep. It’s as if millions of voices gradually became a little hoarse from crying out for a quarter of an hour. There’s another way you could tear the Moon apart that doesn’t require an astral gate accident: gravity.
Astronomers use the Roche Limit to calculate how close an object – like a moon – can orbit another object – like a planet.
This is the point where the difference between the tidal forces on the “front” and “backside” are large enough that the object is torn apart, and if this sounds familiar you might want to look up “spaghettification”.
Spaghettification. Credit: Streeter
This is all based on the radius of the planet and the density of the planet and moon. If the Moon got close enough to the Earth, around 18,000 km, it would pull apart and be shredded into a beautiful ring.
And then the objects in the ring would enter the Earth’s atmosphere and rain down beautiful destruction for thousands of years.
Fortunately or unfortunately, depending your position in this “Die Moon, Die” discussion, the Moon is drifting away from the Earth. It’ll never be closer than it is right now, at almost 400,000 km, without a little nudge.
Phobos, the largest moon orbiting Mars is slowly approaching the planet, and astronomers think it’ll reach the Roche Limit in the next few million years.
It turns out that if we really want to destroy the Moon, we’ll need to destroy all life on Earth as well.
Now we know your new supervillain project, what’s your supervillain name? Tell us your handle in the comments below.
The waning gibbous moon was still the color of fire even at midnight last night due to heavy smoke from Canadian forest fires. Credit: Bob King
My eyes are burning. The morning Sun, already 40° high, glares a lemony-orange. It’s meteorologically clear, but the sky looks like paste. What’s going on here?
Forest fires! Many in the Midwest, northern mountain states and Canadian provinces have been living under a dome of high altitude smoke the past few days reflected in the ruddy midday Sun and bloody midnight Moon.
On June 29, 2015 NASA’s Terra satellite captured this image of a river of smoke pouring across the Canadian provinces and central U.S. from hundreds of wildfires (seen at upper left) in western Canada. The difference in color between clouds true clouds and smoke is obvious. Credit: NASA image courtesy Jeff Schmaltz, LANCE/EOSDIS MODIS Rapid Response Team at NASA GSFC
Fires raging in the forests of northern Alberta and Saskatchewan have poured tremendous amounts of smoke into the atmosphere. Favorable winds have channeled the fumes into a brownish river of haze flowing south and east across Canada and into the northern third of the U.S. If an orange Sun glares overheard at midday, you’ve got smoke. Sometimes you can smell it, but often you can’t because it’s at an altitude of 1.2 – 3 miles (2-5 km).
The Moon sits at lower right with the star Vega visible at the top of the frame in this 30-second time exposure made last night (July 2) under the pall of forest fire smoke. Credit: Bob King
But the visual effects are dramatic. Last night, the nearly full Moon looked so red and subdued, it could easily have been mistaken for a total lunar eclipse. I’ve never seen a darker, more remote-looking Moon. Yes, remote. Without its customary glare, our satellite looked shrunken as if untethered from Earth and drifting away into the deep.
And nevermind about the stars. Try as I might, I could only make out zero magnitude Vega last night. The camera and a time exposure did a little better but not much.
This image was taken by the Terra satellite on June 30, 2015. Residents of the states affected by the smoke will notice much more vivid sunsets during the time the smoke is in the air. The size of the smoke particles is just right for filtering out other colors meaning that red, pink and orange colors can be seen more vividly in the sky. NASA image courtesy Jeff Schmaltz, MODIS Rapid Response Team. Caption: NASA/Goddard, Lynn Jenner
These days of deep red suns in the middle of the day fiery moons at night are an occasional occurrence across Canada and the northern half of the U.S. during the summer. Our previous bout with fire haze happened in early June as a result of massive wildfires in the Northwest Territories and northern Alberta. A change in wind direction and thorough atmospheric-cleaning by thunderstorms returned our blue skies days later.
Using a prism, we can take white light and spread it apart into its component colors. Credit: NASA
While the downsides of fire haze range from poor air quality to starless nights, the upside is a more colorful Sun and Moon.
Back in grade school we all learned that white light is made up of every color of the rainbow. On a sunny day, air molecules, which are exceedingly tiny, scatter away the blue light coming from the Sun and color the sky blue. Around sunset and sunrise, when the Sun’s light passes through the lowest, thickest, haziest part of the atmosphere, greens and yellows are also scattered away, leaving an orange or red Sun.
Fire smoke adds billions of smoke particles to the atmosphere which scatter away purples, blues, greens and yellows to turn an otherwise white Sun into a blood red version smack in the middle of the day.
A ring-billed gull is silhouetted against a yellow sky and orange Sun in Duluth, Minn. a few weeks back during the previous series of smoky days.This photo was taken around 3 p.m. local time. Credit: Bob King
Keep an eye on the color of the blue sky and watch for red suns at midday. Forest fires are becoming more common and widespread due to climate change. If you’ve never seen this eerie phenomenon, you may soon. For more satellite images of forest fires, check out NASA’s Fires and Smoke site.
I’ve often wondered what it would look like if Earth orbited a red dwarf star instead of the Sun. These smoky days give us a taste.
Bootprint in the lunar regolith left behing by the Apollo 11 crew. Credit: NASA
On July 20th, 1969, history was made when men walked on the Moon for the very first time. The result of almost a decade’s worth of preparation, billions of dollars of investment, strenuous technical development and endless training, the Moon Landing was the high point of the Space Age and the single greatest accomplishment ever made.
Because they were the first men to walk on the Moon, Neil Armstrong and Edwin “Buzz” Aldrin are forever written in history. And since that time, only ten men have had the honor of following in their footsteps. But with plans to return to the Moon, a new generation of lunar explorers is sure to be coming soon. So just who were these twelve men who walked on the Moon?
Prelude to the Moon Landing:
Before the historic Apollo 11 mission and Moon Landing took place, NASA conducted two manned missions to test the Apollo spacecraft and the Saturn V rockets that would be responsible for bringing astronauts to the lunar surface. The Apollo 8 mission – which took place on Dec. 21st, 1968 – would be the first time a spacecraft left Earth orbit, orbited the Moon, and then returned safely to Earth.
During the mission, the three-astronaut crew – Commander Frank Borman, Command Module Pilot James Lovell, and Lunar Module Pilot William Anders – spent three days flying to the Moon, then completed 10 circumlunar orbits in the course of 20 hours before returning to Earth on Dec. 27th.
During one of their lunar orbits, the crew made a Christmas Eve television broadcast where they read the first 10 verses from the Book of Genesis. At the time, the broadcast was the most watched TV program in history, and the crew was named Time magazine’s “Men of the Year” for 1968 upon their return.
On May 18th, 1969, in what was described as a “dress rehearsal” for a lunar landing, the Apollo 10 mission blasted off. This involved testing all the components and procedures that would be used for the sake of the Moon Landing.
The crew – which consisted of Thomas P. Stafford as Commander, John W. Young as the Command Module Pilot, and Eugene A. Cernan as the Lunar Module Pilot – flew to the Moon and passed within 15.6 km (8.4 nautical miles) of the lunar surface before returning home.
Apollo 11:
On July 16th, 1969, at 13:32:00 UTC (9:32:00 a.m. EDT local time) the historic Apollo 11 mission took off from the Kennedy Space Center in Florida. The crew consisted of Neil Armstrong as the Commander, Michael Collins as the Command Module Pilot), and Edwin “Buzz” Aldrin as the Lunar Module Pilot.
Neil Armstrong and Buzz Aldrin plant the US flag on the Lunar Surface during the first human moonwalk in history on July 20, 1969. Credit: NASA
On July 19th at 17:21:50 UTC, Apollo 11 passed behind the Moon and fired its service propulsion engine to enter lunar orbit. On the following day, the Lunar Module Eagle separated from the Command Module Columbia, and Armstrong and Aldrin commenced their Lunar descent.
Taking manual control of the Lunar Module, Armstrong brought them down to a landing spot in the Sea of Tranquility, and then announced their arrival by saying: “Houston, Tranquility Base here. The Eagle has landed.” After conducting post-landing checks and depressurizing the cabin, Armstrong and Aldrin began descending the ladder to the lunar surface.
When he reached the bottom of the ladder, Armstrong said: “I’m going to step off the LEM now” (Lunar Excursion Module). He then turned and set his left boot on the surface of the Moon at 2:56 UTC July 21st, 1969, and spoke the famous words “That’s one small step for [a] man, one giant leap for mankind.”
About 20 minutes after the first step, Aldrin joined Armstrong on the surface, and the two men began conducting the planned surface operations. In so doing, they became the first and second humans to set foot on the Moon.
Apollo 12:
Four months later, on November 14th, 1969, the Apollo 12 mission took off from the Kennedy Space Center. Crewed by Commander Charles “Pete” Conrad, Lunar Module Pilot Alan L. Bean and Command Module Pilot Richard F. Gordon, this mission would be the second time astronauts would walk on the Moon.
Ten days later, the Lunar Module touched down without incident on the southeastern portion of the Ocean of Storms. When Conrad and Bean reached the lunar surface, Bean’s first words were: “Whoopie! Man, that may have been a small one step for Neil, but that’s a long one for me.” In the course of conducting a Extra-Vehicular Activities (EVAs), the two astronauts became the third and fourth men to walk on the Moon.
The crew also brought the first color television camera to film the mission, but transmission was lost after Bean accidentally destroyed the camera by pointing it at the Sun. On one of the two EVAs, the crew visited the Surveyor3 unmanned probe, which had landed in the Ocean of Storms on April 20th, 1967. The mission ended on November 24th with a successful splashdown.
Pete Conrad descends from the Lunar Module (LM). Credit: NASA
Apollo 14:
TheApollo 13 mission was intended to be the third lunar landing; but unfortunately, the explosion of the oxygen tank aboard the Service Module forced the crew to abort the landing. Using the Lunar Module as a “lifeboat”, the crew executed a single loop around the Moon before safely making it back to Earth.
As a result, Apollo 14 would be the third manned mission to the lunar surface, crewed by veteran Alan Shepard (as Commander), Stuart Roosa as Command Module Pilot, and Edgar Mitchell as Lunar Module Pilot. The mission launched on January 31st, 1971 and Shepard and Mitchell made their lunar landing on February 5th in the Fra Mauro formation, which had originally been targeted for the Apollo 13 mission.
During two lunar EVAs, Shepard and Mitchell became the fifth and sixth men to walk on the Moon. They also collected 42 kilograms (93 lb) of Moon rocks and conducted several surface experiments – which including seismic studies. During the 33 hours they spent on the Moon (9½ hours of which were dedicated to EVAs), Shepard famously hit two golf balls on the lunar surface with a makeshift club he had brought from Earth.
Shepard poses next to the American flag on the Moon during Apollo 14. Credit: NASA
Apollo 15:
The seventh and eight men to walk on the Moon were David R. Scott, and James B. Irwin – the Commander and Lunar Module Pilot of the Apollo 15 mission. This mission began on July 26th, 1971, and landed near Hadley rille – in an area of the Mare Imbrium called Palus Putredinus (Marsh of Decay) – on August 7th.
The mission was the first time a crew explored the lunar surface using a Lunar Vehicular Rover (LVR), which allowed them to travel farther and faster from the Lunar Module (LM) than was ever before possible. In the course of conducting multiple EVAs, the crew collected 77 kilograms (170 lb) of lunar surface material.
While in orbit, the crew also deployed a sub-satellite, and used it and the Scientific Instrument Module (SIM) to study the lunar surface with a panoramic camera, a gamma-ray spectrometer, a mapping camera, a laser altimeter, and a mass spectrometer. At the time, NASA hailed the mission as “the most successful manned flight ever achieved.”
Image from Apollo 15, taken by Commander David Scott at the end of EVA-1. Credit: NASA
Apollo 16:
It was during the Apollo 16 mission – the penultimate manned lunar mission – that the ninth and tenth men were to walk on the Moon. After launching from the Kennedy Space Center on April 16th, 1972, the mission arrived on the lunar surface by April 21st. Over the course of three days, Commander John Young and Lunar Module Pilot Charles Duke conducted three EVAs, totaling 20 hours and 14 minutes on the lunar surface.
The mission was also the second occasion where an LVR was used, and Young and Duke collected 95.8 kilograms (211 lb) of lunar samples for return to Earth, while Command Module Pilot Ken Mattingly orbited in the Command/Service Module (CSM) above to perform observations.
Apollo 16’s landing spot in the highlands was chosen to allow the astronauts to gather geologically older lunar material than the samples obtained in the first four landings. Because of this, samples from the Descartes Cayley Formations disproved a hypothesis that the formations were volcanic in origin. The Apollo 16 crew also released a subsatellite from the Service Module before breaking orbit and returning to Earth, making splashdown by April 27th.
John W. Young standing next to the LM Orion during the Apollo 16 mission, April 21, 1972. Credit: NASA
Apollo 17:
The last of the Apollo missions, and the final time astronauts would set foot on the moon, began at 12:33 am Eastern Standard Time (EST) on December 7th, 1972. The mission was crewed by Eugene Cernan, Ronald Evans, and Harrison Schmitt – in the roles of Commander, Command Module Pilot and Lunar Module Pilot, respectively.
After reaching the lunar surface, Cernan and Schmitt conducted EVAs and became the eleventh and twelve men to walk on the lunar surface. The mission also broke several records set by previous flights, which included the longest manned lunar landing flight, the longest total lunar surface extravehicular activities, the largest lunar sample return, and the longest time in lunar orbit.
While Evans remained in lunar orbit above in the Command/Service Module (CSM), Cernan and Schmitt spent just over three days on the lunar surface in the Taurus–Littrow valley, conducting three periods of extra-vehicular activity with an LRV, collecting lunar samples and deploying scientific instruments. Cernan, After an approximately 12 day mission, Evans, and Schmitt returned to Earth.
Astronaut Eugene A. Cernan, commander of the Apollo 17 mission, using a Lunar Roving Vehicle (LRV) for an EVA on December 11th 1972. Credit: NASA
Apollo 17 remains the most recent manned Moon mission and also the last time humans have traveled beyond low Earth orbit. Until such time as astronauts begin to go to the Moon again (or manned missions are made to Mars) these twelve men – Neil Armstrong, Edwin “Buzz” Aldrin, Charles “Pete” Conrad, Alan L. Bean, Alan Shepard, Edgar Mitchell, David R. Scott, James B. Irwin, John Young, Charles Duke, Eugene Cernan, and Harrison Schmitt – will remain the only human beings to ever walk on a celestial body other than Earth.
