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!
First, the bad news. This weekend’s partial solar eclipse only touches down across the very southern tip of the African continent, Madagascar, a few remote stations in Antarctica, and a few wind-swept islands in the southern Indian Ocean. More than likely, the only views afforded humanity by Sunday’s partial solar eclipse will come out of South Africa, where the eclipse will be about 40% partial around 5:30 Universal Time (UT).
An animation of the September 13th eclipse. Image credit: NASA/GSFC/A.T. Sinclair
It’s the curious circumstances surrounding the September 13th eclipse that conspire to hide it from the majority of humanity. First, the Moon reaches its ascending node along the plane of the ecliptic at 4:38 UT on Monday, September 14th, nearly 22 hours after New phase. The umbra, or dark inner core of the shadow of Earth’s Moon ‘misses’ the Earth, passing about 380 kilometres or 230 miles above the South Pole. The outer penumbra of the Moon’s shadow just brushes the planet Earth, assuring a 79% maximum obscuration of the Sun over Antarctica around 6:55 UT.
Second, the Moon also reaches its most distant apogee for 2015 on September 14th at 11:29 UT, 406,465 kilometers from the Earth. This is just over 28 hours after New, assuring that the umbra of the Moon falls 25,000 kilometres short of striking the Earth. The eclipse would be an annular one, even if we were in line to see it.
Observers will see the eclipse begin at sunrise over South Africa and the Kalahari Desert, great for photography and catching the eclipse along with foreground objects. Observers will need to follow solar observing safety protocols during all stages of the eclipse. A high value neutral density filter will bring out the silhouette of foreground objects while preserving the image of the partially eclipsed Sun, but remember that such a filter is for photographic use only.
Maximum obscuration of the Sun, with times and solar elevation for four selected sites. Image credit: Stellarium
P1, or the first contact of the Moon’s penumbra with the Earth occurs on the morning of the 13th over the Angola/South Africa border at 4:41 UT, and the shadow footprint races across the southern Indian Ocean to depart Earth near the Antarctic coast (P4) at 09:06 UT.
New Moon occurs on September 13th at 6:43 UT, marking the start of lunation 1147.
A close-up of the eclipse circumstances for southern Africa. Image credit: Michael Zeiler/TheGreatAmericanEclipse.com
For saros buffs, this eclipse is a part of saros series 125 (member 54 of 73). Saros 125 started on February 4th, 1060 and produced just four total eclipses in the late 13th and early 14th centuries. Mark your calendars, as this saros will end with a brief partial eclipse on April 8th, 2358. The final total eclipse for this particular saros crossed over central Europe on July 16th, 1330, when an observation by monks near Prague noted “the Sun was so greatly obscured that of its great body, only a small extremity like a three night old Moon was seen.”
A partially eclipsed Sun rising over the Vehicle Assembly Building at the Kennedy Space Center. Image credit: Dave Dickinson
Missing out on the eclipse? The good folks over at Slooh have got you covered, with a live webcast set to start at 4:30 UT/12:30 AM EDT.
Planning an ad-hoc webcast of your own from the eclipse viewing zone? Let us know!
There are also some chances to nab the eclipse from space via solar observing satellites in low Earth orbit:
The European Space Agency’s Proba-2 will see eclipses on the following passes – 5:01 UT (partial)/6:31 UT (annular) 8:00 UT (partial).
The view from ESA’s Proba-2 spacecraft at 6:31 UT. Image credit: Starry Night Education Software
And JAXA’s Hinode mission will see the same at the following times: 5:56 UT (Partial)/7:46 UT (partial). Unfortunately, there are no good circumstances for an ISS transit this time around, as the ISS never passes far enough south in its orbit.
Looking for more? You can always participate in the exciting pastime of slender moonspotting within 24 hours post or prior to the New Moon worldwide. This feat of extreme visual athletics favors the morning of Saturday, September 12th to sight the slim waning crescent Moon the morning before the eclipse, or the evenings of September 13th and 14th, to spy the waxing crescent Moon on the evenings after.
Predicted locations worldwide for the first sightings of the thin waxing/waning crescent Moon. Image credit: Dave Dickinson
And this eclipse sets us up for the grand finale: the last total lunar eclipse of the ongoing tetrad on September 28th, visible from North America and Europe. And yes, the Moon will be near perigee to boot… expect Super/Blood Moon wackiness to ensue.
Watch for our complete guide to the upcoming lunar eclipse, with observational tips, factoids, eclipse lunacy and more!
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.
Artist's impression of Pluto and its moons. Credit: NASA / Johns Hopkins University Applied Physics Laboratory / Southwest Research Institute
Over the course of the past decade, many amazing discoveries have been made at the edge of the Solar System. Thanks to the work of astronomers working out of Earth-based observatories, with the Hubble Space Telescope, and those behind the recent New Horizons mission, not only have new objects been discovered, but additional discoveries have been made about the ones we already knew about.
For example, in 2005, two additional satellites were discovered in orbit of Pluto – Hydra and Nix. The discovery of these moons (which has since been followed by the discovery of two more) has taught astronomers much about the far-flung system of Pluto, and helped to advance our understanding of the Kuiper Belt.
Discovery and Naming:
Nix was discovered in June of 2005 by the Hubble Space Telescope Pluto Companion Search Team, using discovery images that were taken on May 15th and 18th, 2005. The team was composed of Hal A. Weaver, Alan Stern, Max J. Mutchler, Andrew J. Steffl, Marc W. Buie, William J. Merline, John R. Spencer, Eliot F. Young, and Leslie A. Young.
The discovery images of Nix (and Hydra) obtained by the Hubble Space Telescope. Credit: NASA, ESA, H. Weaver (JHU/APL), A. Stern (SwRI)
Nix and Hydra were also independently discovered by Max J. Mutchler on June 15th, 2005, and by Andrew J. Steffl on August 15th, 2005. At the time, Nix was given the provisional designation of S/2005 P 2 and casually referred to as “P2”. Once pre-recovery images from 2002 were confirmed, the discoveries were announced on October 31st, 2005.
In accordance with IAU guidelines concerning the naming of satellites in the Solar System, the moon was named Nix. Derived from Greek mythology, Nix is the goddess of darkness and night, the mother of Charon and the ferryman of Hades (the Greek equivalent of Pluto) who brought the souls of the dead to the underworld.
The name was officially announced on June 21st, 2006, in an IAU Circular, where the designation “Pluto II” is also given. The initials N and H (for Nix and Hydra) were also a deliberate reference to the New Horizons mission, which would be conducting a flyby of the Pluto system in less than ten years time after the announcement was made.
Images acquired by the New Horizon’s probe of Nix (left) and Hydra (right) on July 14th, 2015. Credit: NASA/JHUAPL/SWRI
Size, Mass and Orbit: Based on observations with the Hubble Space Telescope of Nix’s geometric albedo and shape, the satellite was estimated to measure 56.3 km (35 mi) along its longest axis and 25.7 km (16 mi) wide. However, images provided by the New Horizons’ Ralph instrument on July 14th, 2015, indicated that Nix measures 42 km (26 mi) in length and 36 km (22 mi) wide.
Nix follows a circular orbit with very little eccentricity (0.0020) and a low inclination of approximately 0.13°. It is in the same orbital plane as Charon, is in a 3:2 orbital resonance with Hydra, and a 9:11 resonance with Styx. Its orbital period is roughly 24.9 days, meaning it takes about 25 days to complete a single orbit of Pluto.
As with Hydra and perhaps the other small Plutonian moons, Nix rotates chaotically, which is due mainly to its oblong shape. This means that the moon’s axial tilt and day length vary greatly over short timescales, to the point that it regularly flips over.
Composition: Early observations conducted by Marc W. Buie and William M. Grundy at the Lowell Observatory appeared to show that Nix has a reddish color like Pluto, but unlike any of its other moons. However, more-recent studies conducted by S. Alan Stern et al. using the Hubble Space Telescope’s Advanced Camera for Surveys (ACS), have indicated that it is likely as grey as the remaining satellites.
From these observations, it is likely that the surface of Nix is composed primarily of water ice (like Hydra) and may or may also have trace amount of methane ice on its surface. If true, then the exposure of these deposits of methane ice to ultra-violet radiation from the Sun would result in the presence of tholins, which would give it a reddish hue.
However, when the New Horizons space probe photographed Hydra and Nix during its flyby of the Pluto system, it spotted a large region with a distinctive red tint, probably a crater. The appearance of this surface region – a spot of red against an otherwise grey landscape – may explain these conflicting results.
Exploration: Thus far, only one mission has been performed to the Pluto system that resulted in close-up and detailed photographs of Nix. This would be the New Horizons mission, which flew through the Pluto-Charon system on July 14th, 2015 and photographed Hydra and Nix from an approximate distance of 640,000 km (400,000 mi).
Until July 13th, 2015, when NASA’s Long Range Reconnaissance Imager (LORRI) on board New Horizons determined Nix’s dimensions, its size was unknown. More images and information will be downloaded from the spacecraft between now and late 2016.
Prior to the discovery of Hydra and Nix in 2005, Pluto was believed to share its orbit with only the satellite of Charon – hence why astronomers often refer to it as the “Pluto-Charon system”. However, since the discovery of these two additional satellites in 2005, two more have been discovered – Kerberos in July of 2011 and Styx in July of 2012.
This raises the number of bodes in the Pluto-Charon system to one primary and five satellites. And thanks to the recent New Horizons flyby, we got to see all of them up close for the first time!
Like most large bodies in the Kuiper Belt (not to mention their satellites) much remains to be learned about Nix and its companions. In time, and with more missions to the outer Solar System, we are sure to address many of the mysteries surrounding this particular satellite, and will probably find many more waiting for us!
We have written many interesting articles on Pluto, its system of moons and the Kuiper Belt here at Universe Today.
An artist's conception of 2007 OR10, nicknamed Snow White. Astronomers suspect that its rosy color is due to the presence of irradiated methane. [Credit: NASA]
Over the course of the past decade, more and more objects have been discovered within the Trans-Neptunian region. With every new find, we have learned more about the history of our Solar System and the mysteries it holds. At the same time, these finds have forced astronomers to reexamine astronomical conventions that have been in place for decades.
Consider 2007 OR10, a Trans-Neptunian Object (TNO) located within the scattered disc that at one time went by the nicknames of “the seventh dwarf” and “Snow White”. Approximately the same size as Haumea, it is believed to be a dwarf planet, and is currently the largest object in the Solar System that does not have a name.
Discovery and Naming:
2007 OR10 was discovered in 2007 by Meg Schwamb, a PhD candidate at Caltech and a graduate student of Michael Brown, while working out of the Palomar Observatory. The object was colloquially referred to as the “seventh dwarf” (from Snow White and the Seven Dwarfs) since it was the seventh object to be discovered by Brown’s team (after Quaoar in 2002, Sedna in 2003, Haumea and Orcus in 2004, and Makemake and Eris in 2005).
Comparison of Sedna with the other largest TNOs and with Earth (all to scale). Credit: NASA/Lexicon
At the time of its discovery, the object appeared to be very large and very white, which led to Brown giving it the other nickname of “Snow White”. However, subsequent observation has revealed that the planet is actually one of the reddest in the Kuiper Belt, comparable only to Haumea. As a result, the nickname was dropped and the object is still designated as 2007 OR10.
The discovery of 2007 OR10 would not be formally announced until January 7th, 2009.
Size, Mass and Orbit:
A study published in 2011 by Brown – in collaboration with A.J. Burgasser (University of California San Diego) and W.C. Fraser (MIT) – 2007 OR10’s diameter was estimated to be between 1000-1500 km. These estimates were based on photometry data obtained in 2010 using the Magellan Baade Telescope at the Las Campanas Observatory in Chile, and from spectral data obtained by the Hubble Space Telescope.
However, a survey conducted in 2012 by Pablo Santos Sanz et al. of the Trans-Neptunian region produced an estimate of 1280±210 km based on the object’s size, albedo, and thermal properties. Combined with its absolute magnitude and albedo, 2007 OR10 is the largest unnamed object and the fifth brightest TNO in the Solar System. No estimates of its mass have been made as of yet.
2007 OR10 also has a highly eccentric orbit (0.5058) with an inclination of 30.9376°. What this means is that at perihelion, it is roughly 33 AU (4.9 x 109 km/30.67 x 109 mi) from our Sun while at aphelion, it is as distant as 100.66 AU (1.5 x 1010 km/9.36 x 1010 mi). It also has an orbital period of 546.6 years, which means that the last time it was at perihelion was 1857 and it won’t reach aphelion until 2130. As such, it is currently the second-farthest known large body in the Solar System, and will be farther out than both Sedna and Eris by 2045.
Composition:
According to the spectral data obtained by Brown, Burgasser and Fraser, 2007 OR10 shows infrared signatures for both water ice and methane, which indicates that it is likely similar in composition to Quaoar. Concurrent with this, the reddish appearance of 2007 OR10 is believed to be due to presence of tholins in the surface ice, which are caused by the irradiation of methane by ultraviolet radiation.
The presence of red methane frost on the surfaces of both 2007 OR10 and Quaoar is also seen as an indication of the possible existence of a tenuous methane atmosphere, which would slowly evaporate into space when the objects are closer to the Sun. Although 2007 OR10 comes closer to the Sun than Quaoar, and is thus warm enough that a methane atmosphere should evaporate, its larger mass makes retention of an atmosphere just possible.
Also, the presence of water ice on the surface is believed to imply that the object underwent a brief period of cryovolcanism in its distant past. According to Brown, this period would have been responsible not only for water ice freezing on the surface, but for the creation of an atmosphere that included nitrogen and carbon monoxide. These would have been depleted rather quickly, and a tenuous atmosphere of methane would be all that remains today.
However, more data is required before astronomers can say for sure whether or not 2007 OR10 has an atmosphere, a history of cryovolcanism, and what its interior looks like. Like other KBOs, it is possible that it is differentiated between a mantle of ices and a rocky core. Assuming that there is sufficient antifreeze, or due to the decay of radioactive elements, there may even be a liquid-water ocean at the core-mantle boundary.
Classification:
Though it is too difficult to resolve 2007 OR10’s size based on direct observation, based on calculations of 2007 OR10’s albedo and absolute magnitude, many astronomers believe it to be of sufficient size to have achieved hydrostatic equilibrium. As Brown stated in 2011, 2007 OR10 “must be a dwarf planet even if predominantly rocky”, which is based on a minimum possible diameter of 552 km and what is believed to be the conditions under which hydrostatic equilibrium occurs in cold icy-rock bodies.
That same year, Scott S. Sheppard and his team (which included Chad Trujillo) conducted a survey of bright KBOs (including 2007 OR10) using the Palomar Observatory’s 48 inch Schmidt telescope. According to their findings, they determined that “[a]ssuming moderate albedos, several of the new discoveries from this survey could be in hydrostatic equilibrium and thus could be considered dwarf planets.”
Currently, nothing is known of 2007 OR10’s mass, which is a major factor when determining if a body has achieved hydrostatic equilibrium. This is due in part to there being no known satellite(s) in orbit of the object, which in turn is a major factor in determining the mass of a system. Meanwhile, the IAU has not addressed the possibility of accepting additional dwarf planets since before the discovery of 2007 OR10 was announced.
Alas, much remains to be learned about 2007 OR10. Much like it’s Trans-Neptunian neighbors and fellow KBOs, a lot will depend on future missions and observations being able to learn more about its size, mass, composition, and whether or not it has any satellites. However, given its extreme distance and fact that it is currently moving further and further away, opportunities to observe and explore it via flybys will be limited.
However, if all goes well, this potential dwarf planet could be joining the ranks of such bodies as Pluto, Eris, Ceres, Haumea and Makemake in the not-too-distant future. And with luck, it will be given a name that actually sticks!
Reentry of Kosmos-1315 captured by Joshua Lambus. Click here to see the full video.
A relic of the Cold War surprised beach-goers and Hawaiian islands residents Sunday night, as Kosmos-1315 reentered the Earth’s atmosphere in a dramatic display.
The reentry occurred right around 11:00 PM Sunday night on August 30th local time (Hawaii is 10 hours behind Universal Time). Folks in the satellite tracking community had been following the predicted reentry for some time, which was projected for August 31st at 10:56 UT +/- an hour. That puts the Hawaii sighting right at the beginning of the window.
Kosmos-1315 reenters over the Pacific Ocean near Hawaii. Image credit: Lance Owens
“We were outside, about 11:00. I have a TV outside on our lanai (deck) and we had watched the 10:00 news, when we were just wrapping it up for the evening,” Hawaiian resident Lance Owens told Universe Today. “My wife sees this unreal thing in the sky. Our first description was it looked like someone dragging a “sparkler” across our sky like those old spaceship movies. It took at least a minute to get across our skyline. It appeared to be breaking up right in front of our eyes. I did not hear any boom, but the visuals were incredible!”
A close-up of the reentry of Kosmos 1315 from Sunday night. Image credit: Lance Owens
Kosmos 1315 (Sometimes listed as Cosmos 1315) was an electronic signal intelligence (ELINT) satellite launched from the Plesetsk Cosmodrome in the then Soviet Union on October 13th, 1981. First developed in the late 1960s, Kosmos 1315 was a typical Tselina-D type component of the two-satellite Tselina ELINT system. Kosmos 1315 was launched atop a Vostok-2M rocket, the booster for which still remains in orbit today as NORAD ID 1981-103B. Kosmos 1315 was in a 533 x 574 km low Earth orbit.
Long-time satellite tracker Ted Molczan has been compiling a list of reentries that goes back to the dawn of the Space Age, and notes that this was the 256th reentry sighting he’s confirmed in his cataloging effort.
“Objects launched by Russia account for 205 sightings or 80 percent, followed by the U.S., which accounts for 40 sightings or 16 percent. China, Europe and Japan account for the remaining 4 percent,” Molczan told Universe Today. “Considering the vast areas of the Earth that have been under-reported, the total number of reentries seen during the Space Age probably is between 500 and 1000, the large majority lost to history.”
This was a fine example of a classic reentry versus a typical fireball or meteor train. Satellites typically have a slower reentry velocity, and you can see this in several of the videos captured of the event. Most fireball captures come from security and dashboard cams (remember Chelyabinsk?) or cameras that are already up and running recording another event, such as a concert or a football game. The famous Peekskill meteor in 1992 was captured in the background during a high school football game. Remember, during Chelyabinsk, the very first images of the event were from dashcams; minutes later, after everyone rushed to aim their hastily deployed mobile phone cameras at the contrail, we got the recordings of the blast wave. The very fact that several folks grabbed their phones and managed to capture the reentry in progress on Sunday night (how fast can YOU have your phone out, camera running?) speaks to the slow, stately traverse typical of a satellite reentry.
The position of Kosmos-1315 at 9:17 UT. Image credit: Orbitron
…and folks on social media often try to get in on the hype during a breaking story involving a meteor train or fireball event. Feel free to try to be creative, but trust us, we’ve seen ‘em all. Some ‘meteor wrongs’ (to paraphrase Meteorite Man Geoff Notkin) that typically get recycled and advertised as new videos are: the reentries of Mir, Hayabasa, the aforementioned Peekskill event, Chelyabinsk, and screen grabs from the film Armageddon.
“As is common with reentries, a few people reported the phenomenon as a UFO. A couple of witnesses perceived the glowing fragments as individual craft of some kind,” Molczan told Universe Today. “Satellite orbits closely follow the curvature of the Earth’s surface, and they continue to do so as they begin their final descent during reentry. As reentry proceeds, velocity is lost due to drag, causing the descent to gradually become steeper, but to an observer, the motion appears to be nearly horizontal. By the time an object descends below about 30 kilometers, it will have lost nearly all of its forward velocity, and from there, any surviving fragments will descend almost vertically to the Earth.”
This final descent is similar to what’s known as ‘dark flight’ prior to a meteorite impact.
And though we usually get a few high interest reentries such as Phobos-Grunt or UARS every year, space junk is reentering worldwide weekly. The Aerospace Corp. keeps a running list of upcoming reentries, and the See-Sat-L message board is a great source of fast-breaking news.
It’s definitely a space junk shooting gallery out there. Keep those smartphones charged up and handy, and keep watching the skies!
How about that perigee Full Moon this past weekend? Thus begins ‘Supermoon season’ for 2015, as this month’s Full Moon occurs even closer to perigee — less than an hour apart, in fact — on September 28th, with the final total lunar eclipse of the ongoing tetrad to boot. Keep an eye on Luna this week, as it crosses into the early AM sky for several key dates with destiny just prior to the start of the second and final eclipse season for 2015.
The big event later this week is a passage of the waning gibbous Moon through the Hyades open cluster on the morning of Saturday, September 5th, climaxing with a dramatic occultation of the bright star Aldebaran on the same morning. This is part of a series of 49 ongoing occultations of Aldebaran by the Moon, one for each lunation extending out to September 2018.
The visibility footprint for the September 5th occultation of Aldebaran by the Moon. Image credit: Occult 4.1
This weekend’s event will occur at moonrise under nighttime skies for the northeastern United States and the Canadian Maritimes, and near dawn and under daytime skies for observers in Western Europe and Northern Africa eastward. We observed an occultation of Aldebaran by the Moon under daytime skies from Alaska back in the late 1990s, and can attest that the star is indeed visible near the limb of the Moon in binoculars. A good deep blue sky is key to spotting +1 magnitude Aldebaran in the daytime.
The view from London UK at 7:11 AM local. Image Credit: Starry Night Education software
During waning phase, the bright edge of the Moon is always leading, meaning Aldebaran will ingress (wink out) on the bright limb of the 52% illuminated Moon, and egress (reappear) along its dark limb.
Here are some key times for ingress/egress by location (all times quoted are local and incorporate daylight saving/summer time):
Washington D.C.
Moonrise: 11:53 PM
Ingress: N/A (before Moonrise)
Egress: 12:38 AM (altitude = 8 degrees)
Boston
Moonrise: 11:22 PM
Ingress 11:57 PM (altitude = 6 degrees)
Egress: 12:41 AM (altitude = 14 degrees)
Gander, Newfoundland
Moonrise: 11:26 PM
Ingress: 1:37 AM (altitude = 20 degrees)
Egress: 2:26 AM (altitude = 28 degrees)
London
Moonrise: 11:04 PM
Ingress: 5:50 AM (altitude = 53 degrees)
Sunrise: 6:18 AM
Egress: 7:07 AM (altitude = 54 degrees)
Paris
Moonrise: 12:02 AM
Ingress: 6:53 AM (altitude = 56 degrees)
Sunrise: 7:12 AM
Egress: 8:10 AM (altitude = 57 degrees)
Occultations of bright stars by the Moon are one of the few times besides a solar or lunar eclipse when you can actually discern the one degree per every two and half hours orbital motion of the Moon in real time. The Moon moves just a little more than its own apparent diameter as seen from the Earth every hour. This also sets us up for four more fine occultations of Aldebaran by the Moon alternating between Europe and North America on October 2nd, October 29th, November 26th, and December 23rd.
The final four occultations of Aldebaran by the Moon for 2015. Image credit: Occult 4.1
The bright stars Antares, Spica and Regulus also lie along the path of the Moon, which is inclined about five degrees relative to the ecliptic. A series of occultations of Regulus by the Moon begins in late 2016.
Fun fact: The Moon used to occult the bright star Pollux in the constellation Gemini until about 2100 years ago in 117 BC. The 26,000 year cycle known as the Precession of the Equinoxes has since carried the star out of the Moon’s path.
Observations of occultations — especially dramatic grazes spied right from the edge of the path — can be used to construct a profile of the lunar limb. A step-wise ‘wink out’ of a star during an occultation can also betray the existence of a close binary.
Recording an occultation of a star by the Moon is as easy as running video while shooting the Moon. The dark limb egress of Aldebaran will be much easier to record during the September 5th event than the ingress of the star against the bright limb. I typically run video with a DLSR directly coupled to a Celestron 8” SCT telescope, with WWV radio running in the background for a precise audio timing of the event. Remember, the Moon will also be transiting the Hyades star cluster as well, covering and uncovering many fainter stars for observers worldwide around the same time frame.
The Last Quarter Moon versus Aldebaran and the Hyades on September 5th at ~5:00 UT. Image credit: Stellarium
Now for the ‘wow’ factor. The Moon is about 240,000 miles (400,000 km), or 1 1/4 light seconds distant. Aldebaran is 65 light years away, and said light left the star around 1950, only to have its light ‘rejected’ during the very last second by the craggy mountains along the lunar limb. And though Aldebaran appears to be a member of the Hyades, it isn’t, as the open cluster sits 153 light years from Earth.
The Moon crosses through the Hyades in January 2015. Image credit and copyright: Nell Ghosh
And watch that Moon, as it then heads for a partial solar eclipse as seen from South Africa and the southern Indian Ocean on September 13th, and a total lunar eclipse visible from North America and Europe on September 28th.
Expect more to come, with complete guides to both on Universe Today!
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.
Artist's impression of the Trans-Neptunian Object (TNO) 90482 Orcus. Credit: NASA
Since the early 2000s, more and more objects have been discovered in the outer Solar System that resemble planets. However, until they are officially classified, the terms Kuiper Belt Object (KBO) and Trans-Neptunian Object (TNO) are commonly used. This is certainly true of Orcus, another large object that was spotted in Pluto’s neighborhood about a decade ago.
Although similar in size and orbital characteristics to Pluto, Orcus is Pluto’s opposite in many ways. For this reason, Orcus is often referred to as the “anti-Pluto”, a fact that contributed greatly to the selection of its name. Although Orcus has not yet been officially categorized as a dwarf planet by the IAU, many astronomers agree that it meets all the requirements and will be in the future.
Discovery and Naming: Orcus was discovered on February 17th, 2004, by Michael Brown of Caltech, Chad Trujillo of the Gemini Observatory, and David Rabinowitz of Yale University. Although discovered using images that were taken in 2004, prerecovery images of Orcus have been identified going back as far as November 8th, 1951.
Provisionally known as 90482 2004 DW, by November 22nd, 2004, the name Orcus was assigned. In accordance with the IAU’s astronomical conventions, objects with a similar size and orbit to that of Pluto are to be named after underworld deities. Therefore, the discovery team suggested the name Orcus, after the Etruscan god of the underworld and the equivalent of the Roman god Pluto.
90482 Orcus. The location of Orcus is shown in the green circle (top, left). Credit: NASA
Size, Mass and Orbit: Given its distance, estimates of Orcus’ diameter and mass have varied over time. In 2008, observations made using the Spitzer Space Telescope in the far infrared placed its diameter at 958.4 ± 22.9 km. Subsequent observations made in 2013 using the Herschel Space Telescope at submillimeter wavelengths led to similar estimates being made.
In addition, Orcus appears to have an albedo of about 21% to 25%, which may be typical of trans-Neptunian objects approaching the 1000 km diameter range. However, these estimates were based on the assumption that Orcus was a singular object and not part of a system. The discovery of the relatively large satellite Vanth (see below) in 2007 by Brown et al. is likely to change these considerably.
The absolute magnitude of Vanth is estimated to be 4.88, which means that it is about 11 times fainter than Orcus itself. If the albedos of both bodies are the same at 0.23, then the diameter of Orcus would be closer to 892 -942 km, while Vanth would measure about 260 -293 km.
In terms of mass, the Orcus system is estimated to be 6.32 ± 0.05 ×1020 kg, which is about 3.8% the mass of the dwarf planet Eris. How this mass is partitioned between Orcus and Vanth depends of their relative sizes. If Vanth is 1/3rd the diameter Orcus, its mass is likely to be only 3% of the system. However, if it’s diameter is about half that of Orcus, then its mass could be as high as 1/12 of the system, or about 8% of the mass of Orcus.
Orcus compared to Earth and the Moon. Credit: Wikipedia Commons
Much like Pluto, Orcus has a very long orbital period, taking 245.18 years (89552 days) to complete a single rotation around the Sun. It also is in a 2:3 orbital resonance with Neptune and is above the ecliptic during perihelion. In addition, it’s orbit has a similar inclination and eccentricity as Pluto’s – 20.573° to the ecliptic, and 0.227, respectively.
In short, Orcus orbits the Sun at a distance of 30.27 AU (4.53 billion km) at perihelion and 48.07 AU (7.19 billion km) at aphelion. However, Pluto and Orcus are oriented differently. For one, Orcus is at aphelion when Pluto is at perihelion (and vice versa), and the aphelion of Orcus’s orbit points in nearly the opposite direction from Pluto’s. Hence why Orcus is often referred to as the “anti-Pluto”.
Composition: The density of the primary (and secondary assuming they have the same density) is estimated to be 1.5 g/cm3. In addition, spectroscopic and near-infrared observations have indicated that the surface is neutral in color and shows signs of water. Further infrared observations in 2004 by the European Southern Observatory and the Gemini Observatory indicated the possible presence of water ice and carbonaceous compounds.
This would indicate that Orcus is most likely differentiated between a rocky core and an icy mantle composed of water and methane ices as well as tholins – though not as much as other KBOs which are more reddish in appearance. The water and methane ices are believed to cover no more than 50% and 30% of the surface, respectively – which would mean the proportion of ice on the surface is less than on Charon, but similar to that on Triton.
Another interesting feature on Orcus is the presence of crystalline ice on its surface – which may be an indication of cryovolcanism – and the possible presence of ammonia dissolved in water and/or methane/ethane ices. This would make Orcus quite unique, since ammonia has not been detected on any other TNO or icy satellite of the outer planets (other than Uranus’ moon Miranda).
Moon: In 2011, Mike Brown and T.A. Suer detected a satellite in orbit of Orcus, based on images taken by the Hubble Space Telescope on November 13th, 2005. The satellite was given the designation S/2005 (90482) before being renamed Vanth on March 30th, 2005. This name was the result of an opinion poll where Mike Brown asked readers of his weekly column to submit their suggestions.
The name Vanth, after the Etruscan goddess who guided the souls of the dead to the underworld, was eventually chosen from among a large pool of submissions, which Brown then submitted to the IAU. The IAU’s Committee for Small Body Nomenclature assessed it and determined it fit with their naming procedures, and officially approved of it in March of 2010.
Vanth orbits Orcus in a nearly face-on circular orbit at a distance of 9030 ± 89 km. It has an eccentricity of about 0.007 and an orbital period of 9.54 days. In terms of how Orcus acquired it, it is not likely that it was the result of a collision with an object, since Vanth’s spectrum is very different from that of its primary.
Therefore, it is much more likely that Vanth is a captured KBO that Orcus acquired in the course of its history. However, it is also possible that Vanth could have originated as a result of rotational fission of the primordial Orcus, which would have rotated much faster billions of years ago than it does now.
Much like most other KBOs, there is much that we still don’t know about Orcus. There are currently no plans for a mission in the near future. But given the growing interest in the region, it would not be surprising at all if future missions to the outer Solar System were to include a flyby of this world. And as we learn more about Orcus’ size, shape and composition, we are likely to see it added to the list of confirmed dwarf planets.
For more information on Orcus, Vanth, check out the Planetary Society’s page on Orcus and Vanth. To learn more about how they were discovered, consult Mike Brown’s Planets.
Astronomy Cast also has a great interview with Mike Brown from Caltech.
Levi Joraanstad, a student at North Dakota State University displays his telescope, which police mistook for a rifle. Image via WDAY TV, Fargo, North Dakota.
One more thing amateur astronomers might need to worry about besides clouds, bugs, and trying to fix equipment malfunctions in the dark – and this one’s a little more serious.
Earlier this week, two students at North Dakota State University (NDSU) in Fargo, North Dakota were settting up a telescope and camera system to take pictures of the Moon when armed police approached them. The police officers had mistaken the telescope for a rifle.
Students Levi Joraanstad and Colin Waldera told WDAY TV in Fargo that they were were setting up their telescope behind their apartment’s garage when they were blinded by a bright light and told to stop moving.
Initially, they thought it was a joke, that fellow students were pulling a prank, and because police were shining a bright light at them, the two students were blinded.
Police said that an officer patrolling the area had seen what he thought was suspicious activity behind the garage, thinking that one of the students’ dark sweater with white lettering on the back looked like a tactical vest, and that the telescope might be a rifle.
Police added that their response was a “better safe than sorry” approach, and they said the two students were never in any danger of being shot.
However, Joraanstad and Waldera said since they thought it was a joke, they initially ignored the order to stop moving and kept digging in their bags for equipment.
“I was kind of fumbling around with my stuff and my roommate and I were kind of talking, we were kind of wondering, what the heck’s going on? This is pretty dum that these guys are doing this,” WDAY quoted Joraanstad, a junior at NDSU. “And then they started shouting to quit moving or we could be shot. And so at that moment we kind of look at each other and we’re thinking we better take this seriously.”
If the police had acted more aggressively, the outcome could have been tragic. Joraanstad said the officers were very apologetic when they realized their mistake, and they explained what had happened.
So, watch where and how you point your telescope.
This is a rare occurrence, of course, and is nothing like risks amateur astronomers in Afghanistan regularly take to look through a telescope and share their views with local people. We wrote an article — which you can read here — about how they have to deal with more serious complications, such as making sure the area is clear of land mines, not arousing the suspicions the Taliban or the local police, and watching out for potential bombing raids by the US/UK/Afghan military alliance.
UPDATE: Maybe incidents like this aren’t quite as rare as I thought. Universe Today’s Bob King told me that just two weeks ago he was out observing in the countryside, when a very similar event happened to him. “A truck pulled up fast, with bright lights blinding my eyes and then the sheriff walked out of the car,” Bob said. “I quickly identified myself and explained what I was up to. He thought I was burying a dead body! No kidding.”
