Elizabeth Howell, Author at Universe Today

January 22, 2015December 23, 2015 by Elizabeth Howell

10 Amazing Facts About Black Holes

An artists illustration of the central engine of a Quasar. These "Quasi-stellar Objects" QSOs are now recognized as the super massive black holes at the center of emerging galaxies in the early Universe. (Photo Credit: NASA)

Imagine matter packed so densely that nothing can escape. Not a moon, not a planet and not even light. That’s what black holes are — a spot where gravity’s pull is huge, ending up being dangerous for anything that accidentally strays by. But how did black holes come to be, and why are they important? Below we have 10 facts about black holes — just a few tidbits about these fascinating objects.

Fact 1: You can’t directly see a black hole.

Because a black hole is indeed “black” — no light can escape from it — it’s impossible for us to sense the hole directly through our instruments, no matter what kind of electromagnetic radiation you use (light, X-rays, whatever.) The key is to look at the hole’s effects on the nearby environment, points out NASA. Say a star happens to get too close to the black hole, for example. The black hole naturally pulls on the star and rips it to shreds. When the matter from the star begins to bleed toward the black hole, it gets faster, gets hotter and glows brightly in X-rays.

Fact 2: Look out! Our Milky Way likely has a black hole.

A natural next question is given how dangerous a black hole is, is Earth in any imminent danger of getting swallowed? The answer is no, astronomers say, although there is probably a huge supermassive black hole lurking in the middle of our galaxy. Luckily, we’re nowhere near this monster — we are about two-thirds of the way out from the center, relative to the rest of our galaxy — but we can certainly observe its effects from afar. For example: the European Space Agency says it’s four million times more massive than our Sun, and that it’s surrounded by surprisingly hot gas.

*Sagittarius A in infrared (red and yellow, from the Hubble Space Telescope) and X-ray (blue, from the Chandra space telescope). Credit: X-ray: NASA/UMass/D.Wang et al., IR: NASA/STScI*

Fact 3: Dying stars create stellar black holes.

Say you have a star that’s about 20 times more massive than the Sun. Our Sun is going to end its life quietly; when its nuclear fuel burns out, it’ll slowly fade into a white dwarf. That’s not the case for far more massive stars. When those monsters run out of fuel, gravity will overwhelm the natural pressure the star maintains to keep its shape stable. When the pressure from nuclear reactions collapses, according to the Space Telescope Science Institute, gravity violently overwhelms and collapses the core and other layers are flung into space. This is called a supernova. The remaining core collapses into a singularity — a spot of infinite density and almost no volume. That’s another name for a black hole.

Fact 4: Black holes come in a range of sizes.

There are at least three types of black holes, NASA says, ranging from relative squeakers to those that dominate a galaxy’s center. Primordial black holes are the smallest kinds, and range in size from one atom’s size to a mountain’s mass. Stellar black holes, the most common type, are up to 20 times more massive than our own Sun and are likely sprinkled in the dozens within the Milky Way. And then there are the gargantuan ones in the centers of galaxies, called “supermassive black holes.” They’re each more than one million times more massive than the Sun. How these beasts formed is still being examined.

A binary black hole system, viewed from above. Image Credit: Bohn et al. (see http://arxiv.org/abs/1410.7775) — *A binary black hole system, viewed from above. Credit: Bohn et al. (see http://arxiv.org/abs/1410.7775)*

Fact 5: Weird time stuff happens around black holes.

This is best illustrated by one person (call them Unlucky) falling into a black hole while another person (call them Lucky) watches. From Lucky’s perspective, Unlucky’s time clock appears to be ticking slower and slower. This is in accordance with Einstein’s theory of general relativity, which (simply put) says that time is affected by how fast you go, when you’re at extreme speeds close to light. The black hole warps time and space so much that Unlucky’s time appears to be running slower. From Unlucky’s perspective, however, their clock is running normally and Lucky’s is running fast.

Fact 6: The first black hole wasn’t discovered until X-ray astronomy was used.

Cygnus X-1 was first found during balloon flights in the 1960s, but wasn’t identified as a black hole for about another decade. According to NASA, the black hole is 10 times more massive to the Sun. Nearby is a blue supergiant star that is about 20 times more massive than the Sun, which is bleeding due to the black hole and creating X-ray emissions.

Illustration of Cygnus X-1, another stellar-mass black hole located 6070 ly away. (NASA/CXC/M.Weiss) — *Illustration of Cygnus X-1, another stellar-mass black hole located 6070 ly away. Credit: NASA/CXC/M.Weiss*

Fact 7: The nearest black hole is likely not 1,600 light-years away.

An erroneous measurement of V4641 Sagitarii led to a slew of news reports a few years back saying that the nearest black hole to Earth is astoundingly close, just 1,600 light-years away. Not close enough to be considered dangerous, but way closer than thought. Further research, however, shows that the black hole is likely further away than that. Looking at the rotation of its companion star, among other factors, yielded a 2014 result of more than 20,000 light years.

Fact 8: We aren’t sure if wormholes exist.

A popular science-fiction topic concerns what happens if somebody falls into a black hole. Some people believe these objects are a sort of wormhole to other parts of the Universe, making faster-than-light travel possible. But as this Smithsonian Magazine article points out, anything is possible since we still have a lot to figure out about physics. “Since we do not yet have a theory that reliably unifies general relativity with quantum mechanics, we do not know of the entire zoo of possible spacetime structures that could accommodate wormholes,” said Abi Loeb, who is with the Harvard-Smithsonian Center for Astrophysics.

*Diagram of a wormhole, or theoretical shortcut path between two locations in the universe. Credit: Wikipedia*

Fact 9: Black holes are only dangerous if you get too close.

Like creatures behind a cage, it’s okay to observe a black hole if you stay away from its event horizon — think of it like the gravitational field of a planet. This zone is the point of no return, when you’re too close for any hope of rescue. But you can safely observe the black hole from outside of this arena. By extension, this means it’s likely impossible for a black hole to swallow up everything in the Universe (barring some sort of major revision to physics or understanding of our Cosmos, of course.)

Fact 10: Black holes are used all the time in science fiction.

There are so many films and movies using black holes, for example, that it’s impossible to list them all. Interstellar‘s journeys through the universe includes a close-up look at a black hole. Event Horizon explores the phenomenon of artificial black holes — something that is also discussed in the Star Trek universe. Black holes are also talked about in Battlestar: Galactica, Stargate: SG1 and many, many other space shows.

Here on Universe Today we have a great article about a practical use for black holes: as spacecraft engines. No one can get to a black hole without space travel. Astronomy Cast offers a good episode about interstellar travel.

January 22, 2015December 23, 2015 by Elizabeth Howell

Why Is Our Galaxy Called The Milky Way?

This annotated artist's conception illustrates our current understanding of the structure of the Milky Way galaxy. Image Credit: NASA

We have a lot of crazy informal names for space sights. Sometimes they’re named after how they are shaped, like the Horsehead Nebula. Sometimes they have a name “borrowed” from their constellation, such as the Andromeda Galaxy. But what about our own galaxy, the Milky Way? Why does this band of stars across Earth’s sky have a name associated with food?

First, let’s back up a bit and talk a bit about what the Milky Way actually is. Astronomers believe it is a barred spiral galaxy — a galaxy with a spiral shape that has a line of stars across its middle, as you can see in the picture above. If you were to fly across the galaxy at the speed of light, it would take you an astounding 100,000 years.

The Milky Way is part of a collection of galaxies called the Local Group. We’re on a collision course with the most massive and largest member of that collection, which is the Andromeda Galaxy (also known as M31). The Milky Way is the second-largest galaxy, and the Triangulum Galaxy (M33) the third-largest. There are roughly 30 members of this group all told.

To get a sense of its immense size, you’ll be glad to hear the Earth is nowhere near the Milky Way’s center and its powerful, supermassive black hole. NASA says we’re roughly 165 quadrillion miles from the black hole, which is found in the direction of the constellation Sagittarius.

The magnetic field of our Milky Way Galaxy as seen by ESA’s Planck satellite. Credit: ESA and the Planck Collaboration.

As for how our galaxy got its name, it is indeed because of its milky appearance as it stretches across the sky. While spotting the galaxy’s arms is a challenge from our current light-polluted centers, if you get out to a more rural area it really begins to dominate the skies. The ancient Romans called our galaxy the Via Lactea, which literally means “The Road of Milk.”

And according to the Astronomy Picture of the Day website, the Greek word for “galaxy” also derives from the word “milk”. It’s hard to say if it was a coincidence, because the origin of both the Milky Way’s name and the Greek word for galaxy are long lost to prehistory, although some sources say that it was inspired by the Milky Way’s appearance.

It took thousands of years for us to understand the nature of what we were looking at. Back in the time of Aristotle, according to the Library of Congress, the Milky Way was believed to be the spot “where the celestial spheres came into contact with the terrestrial spheres.” Without a telescope, it was hard to say much more, but that began to change in the early 1600s.

Beautiful view of our Milky Way Galaxy. If other alien civilizations are out there, can we find them? Credit: ESO/S. Guisard

One important early observation, the library adds, was from the noted astronomer Galileo Galilei. (He’s best known for being credited for the discovery of four of Jupiter’s moons — Io, Europa, Callisto and Ganymede — which he spotted through a telescope.) In his 1610 volume Sidereus Nuncius, Galileo said his observations showed the Milky Way was not a uniform band, but had certain pockets with more star densities.

But the true nature of the galaxy eluded us for some time yet. Other early observations: the stars were a part of our Solar System (Thomas Wainwright, 1750 — a claim that was later shown as erroneous) and that the stars appeared to be denser on one side of the band than the other (William and John Herschel, in the late 1700s).

It took until the 20th century for astronomers to figure out that the Milky Way is just one of a large number of galaxies in the sky. This came, the library says, through a few steps: doing observations of distant “spiral nebulas” that showed their speeds were receding faster than the escape velocity of our own galaxy (Vesto Slipher, 1912); observations that a “nova” (temporary bright star) in Andromeda was fainter than our own galaxy (Herber Curtis, 1917); and most famously, Edwin Hubble’s observations of galaxies showing that they were very far from Earth indeed (1920ish).

The Hubble Ultra Deep Field seen in ultraviolet, visible, and infrared light. Image Credit: NASA, ESA, H. Teplitz and M. Rafelski (IPAC/Caltech), A. Koekemoer (STScI), R. Windhorst (Arizona State University), and Z. Levay (STScI)

There are in fact more galaxies out there than we could have imagined even a century ago. Using the Hubble Space Telescope, periodically astronomers have used the powerful observatory to gaze at a tiny patch of the sky.

This has produced several “deep fields” of galaxies billions of light-years away. It’s hard to estimate just how many there are “out there”, but estimates seem to say there are at least 100 billion galaxies. That’ll keep astronomers busy observing for a while.

We have written many articles about the Milky Way for Universe Today. Here are some facts about the Milky Way, and here’s an article about the stars in the Milky Way. We’ve also recorded an episode of Astronomy Cast about galaxies. Listen here, Episode 97: Galaxies.

January 20, 2015December 23, 2015 by Elizabeth Howell

How Big Is The Milky Way?

The summertime Milky Way from Scorpius to Cygnus is broader and brighter than the winter version because we look into the direction of its center. Credit: Stephen Bockhold

The Milky Way is our home galaxy, the spot where the Earth resides. We are not anywhere near the center — NASA says we’re roughly 165 quadrillion miles from the galaxy’s black hole, for example — which demonstrates just how darn big the galaxy is. So how big is it, and how does it measure up with other neighborhood residents?

The numbers are pretty astounding. NASA estimates the galaxy at 100,000 light-years across. Since one light year is about 9.5 x 10¹²km, so the diameter of the Milky Way galaxy is about 9.5 x 10¹⁷ km in diameter. The thickness of the galaxy ranges depending on how close you are to the center, but it’s tens of thousands of light-years across.

Our galaxy is part of a collection known as the Local Group. Because some of these galaxies are prominent in our sky, the names tend to be familiar. The Milky Way is on a collision course with the most massive member of the group, called M31 or the Andromeda Galaxy. The Milky Way is the second-largest member, with M33 (the Triangulum Galaxy) the third-largest, NASA says. Andromeda appears much brighter in the night sky due to its size and relatively closer distance. There are about 30 members of this group.

The Andromeda Galaxy will collide with the Milky Way in the future. Credit: Adam Evans

Because we are inside the Milky Way’s arms, it appears as a band of stars (or a fuzzy white band) across the Earth’s sky. Casting a pair of binoculars or a telescope across it shows a mix of lighter areas and darker areas; the darker areas are dust that obscures any light from stars, galaxies and other bright objects behind it. From the outside, however, astronomers say the Milky Way is a barred spiral galaxy — a galaxy that has a band of stars across its center as well as the spiral shape.

If you’re looking for the center of the galaxy, gaze at the constellation Sagittarius, which is low on the summer sky horizon for most northern hemisphere residents. The constellation contains a massive radio source known as Sagittarius A*. Astronomers using the Chandra space telescope discovered why this supermassive black hole is relatively weak in X-rays: it’s because hot gas is being pulled inside the nebula, and most of it (99%) gets ejected and diffused.

Based on observing globular clusters (star clusters) in the galaxy, astronomers have estimated the Milky Way’s overall age at 13.5 billion years old — just 200 million years younger than the rest of the universe.

However, scientists are beginning to think that different parts of the galaxy formed at different times. In 2012, for example, astronomers led by Jason Kalirai of the Space Telescope Science Institute pinned down the age of the Milky Way’s inner halo of stars: 11.5 billion years old. They used white dwarfs, the burned-out remnants of Sun-like stars, to make that measurement.

Kalirai’s group’s research indicates that the Milky Way formed in the following sequence: the halo (including globular star clusters and dwarf galaxies), the inner halo (whose stars were born as a result of this construction) and the outer halo (created when the Milky Way ate up nearby ancient dwarf galaxies).

Artist's impression of the structure of the Milky Way's halo. Credit: NASA, ESA, and A. Feild (STScI) — Artist’s impression of the structure of the Milky Way’s halo. Credit: NASA, ESA, and A. Feild (STScI)

While we’ve been focusing on the parts of the galaxy that you can see, in reality most of its mass is made up of dark matter. NASA estimates that there is about 10 times the mass of dark matter than the visible matter in the universe. (Dark matter is a form of matter that we cannot sense with conventional telescopic instruments, except through its gravitational effect on other things such as galaxies. When masses gather in high enough concentrations, they can bend the light of other objects.)

We have written many articles about the Milky Way for Universe Today. Here’s an article about the rotation of Milky Way, and here are some facts about the Milky Way. We’ve also recorded an episode of Astronomy Cast about galaxies. Listen here, Episode 97: Galaxies.

January 19, 2015December 23, 2015 by Elizabeth Howell

How Long Have Humans Been On Earth?

Lights from the United States glow in this night image based on data taken from the Suomi NPP satellite in April and October 2012. Credit: NASA Earth Observatory/NOAA NGDC

While our ancestors have been around for about six million years, the modern form of humans only evolved about 200,000 years ago. Civilization as we know it is only about 6,000 years old, and industrialization started in the earnest only in the 1800s. While we’ve accomplished much in that short time, it also shows our responsibility as caretakers for the only planet we live on right now.

The effects of humans on Earth cannot be understated. We’ve been able to survive in environments all over the world, even harsh ones such as Antarctica. Every year, we fell forests and destroy other natural areas, driving species into smaller areas or into endangerment, because of our need to build more housing to contain our growing population.

With seven billion people on Earth, pollution from industry and cars is a growing element in climate change — which affects our planet in ways we can’t predict. But we’re already seeing the effects in melting glaciers and rising global temperatures.

Enormous chuck of ice breaks off the Petermann Glacier in Greenland. Credit: NASA.

The first tangible link to humanity started around six million years ago with a primate group called Ardipithecus, according to the Smithsonian Institution. Based in Africa, this group began the path of walking upright. This is traditionally considered important because it allowed for more free use of the hands for toolmaking, weaponry and other survival needs.

The Australopithecus group, the museum added, took hold between about two million and four million years ago, with the abilities to walk upright and climb trees. Next came Paranthropus, which existed between about one million and three million years ago. The group is distinguished by its larger teeth, giving a wider diet.

The Homo group — including our own species, Homo sapiens — began arising more than two million years ago, the museum said. It’s distinguished by bigger brains, more tool-making and the ability to reach far beyond Africa. Our species was distinguished about 200,000 years ago and managed to survive and thrive despite climate change at the time. While we started in temperate climates, about 60,000 to 80,000 years ago the first humans began straying outside of the continent in which our species was born.

GOCE view of Africa.. Credits: ESA/HPF/DLR, anaglyph by Nathanial Burton-Bradford.

“This great migration brought our species to a position of world dominance that it has never relinquished,” reads a 2008 article in Smithsonian Magazine, pointing out that eventually we obviated the competition (most prominently including Neanderthals and Homo erectus). When the migration was complete,” the article continues, “Homo sapiens was the last—and only—man standing.”

Using genetic markers and an understanding of ancient geography, scientists have partially reconstructed how humans could have made the journey. It’s believed that the first explorers of Eurasia went there using the Bab-al-Mandab Strait that now divides Yemen and Djibouti, according to National Geographic. These people made it to India, then by 50,000 years ago, southeast Asia and Australia.

A little after this time, another group began an inland journey across the Middle East and south-central Asia, positioning them to later go to Europe and Asia, the magazine added. This proved important for North America, as about 20,000 years ago, some of these people crossed over to that continent using a land bridge created by glaciation. From there, colonies have been found in Asia dating as far back as 14,000 years ago.

A teensy-tiny Neil Armstrong is visible in the helmet of Buzz Aldrin during the Apollo 11 landing in July 1969. Credit: NASA

Since this is a space website, it’s also worth noting when humans began leaving Earth. The first human mission to space took place April 12, 1961 when Soviet cosmonaut Yuri Gagarin made a single orbit of Earth in his spacecraft, Vostok 1. Humanity first set foot on another world on July 20, 1969, when Americans Neil Armstrong and Buzz Aldrin walked on the Moon.

Since then, our colonization efforts in space have focused mostly on space stations. The first space station was the Soviet Salyut 1, which launched from Earth April 19, 1971 and was first occupied by Georgi Dobrovolski, Vladislav Vokov, and Viktor Patsayev on June 6. The men died during re-entry June 29 due to spacecraft decompression, meaning no further flights went to that station.

There have been other space stations since. A notable example is Mir, which hosted several long-duration missions of a year or more — including the longest single spaceflight duration of any human to date, 437 days, by Valeri Polyakov in 1994-95. The International Space Station launched its first piece Nov. 20, 1998 and has been continuously occupied by humans since Oct. 31, 2000. The first humans to start the continuous occupation included Expedition 1 members Bill Shepard (U.S.) and Russian cosmonauts Sergei Krikalev and Yuri Gidzenko.

January 19, 2015December 23, 2015 by Elizabeth Howell

What is the Zodiac?

A chart of the constellations and signs that make up the zodiac. Credit: NASA

The zodiac represents the constellations that the Sun passes through in its apparent path across Earth’s sky. Because the Sun (and the planets) are all on about the same plane in the Solar System, they pass through the same constellations and at times, can even eclipse each other.

While traditionally the zodiac is considered to have 12 constellations, technically the Sun passes through 13, according to this NASA page. In order, the constellations are Sagittarius, Capricornus, Aquarius, Pisces, Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpius and Ophiuchus.

The reason there are now 13 constellations that the Sun passes through is that the axis of the Earth has changed over the millennia. Earth’s axis precesses or moves in a cycle that takes about 26,000 years. Over time, this means the direction of north has changed with respect to the sky. Vega was the North Star several thousand years ago, and will become it again in about 13,000 years, according to NASA. Today, the North Star is Polaris.

Time exposure centered on Polaris, the North Star. Notice that the closer stars are to Polaris, the smaller the circles they describe. Stars at the edge of the frame make much larger circles. Credit: Bob King

Because different cultures see different shapes in the stars of the sky, the number of constellations varied in ancient definitions of the zodiac. It has been used in cultures ranging from Greece to Babylon to China to India. It should also be noted that the constellations are of different size, so the Sun does not spend the same amount of time in each.

The number of constellations was fixed at 12 when mathematics was added to astronomy, according to Encyclopedia Britannica. While we don’t know when the symbols were first used, the first known instance is in Greek manuscripts used during the late Middle Ages, the encyclopedia added. Briefly, according to the encyclopedia, these are what each of the constellations are:

Aries (the ram), which has no bright stars and traditionally governs the period from March 21 to April 19. In Greek mythology, it represents the ran with the golden fleece. Phrixus sacrificed a ram to Zeus (the chief god) after safely fleeing Thessaly to Colchis on its back. Jason (the chief of the Argonauts) later recovered the fleece.

Venus within the Pleiades on April 4, 2012, as seen from New Jersey in the US. Credit and copyright John Anton.

Taurus (the bull), whose brightest star Aldebaran is the 14th-brightest in the sky. Also in Taurus are two bright star clusters (the Pleiades and the Hyades) and the Crab Nebula. It traditionally governs April 20 to May 20. In Greek mythology, Taurus represents the bull form that Zeus (the chief god) took upon to abduct Europa.

Gemini (the twins), whose brightest stars are Castor and Pollux. It’s the current location of the northern summer solstice, when the Sun reaches its highest point in the sky. It traditionally represents May 21 to June 21. In Greek mythology, the twins were gods who “succored shipwrecked sailors and received sacrifices for favorable winds,” the encyclopedia stated.

Cancer (the crab), which also has no bright stars but contains a prominent star cluster known as the Beehive (Praesepe). It traditionally governs June 22 to July 22. In Greek mythology, it refers to a crab that was crushed after pinching Heracles while he was fighting a hydra. Hera (an enemy of Heracles) rewarded the crab by immortalizing it in the sky.

Beehive Cluster. Image credit: Tom Bash and John Fox/Adam Block/NOAO/AURA/NSF

Leo (the lion), whose brightest star is Regulus — sometimes called the “little king.” It traditionally governs July 23 to August 22 and in Greek mythology, represents a lion that Heracles killed.

Virgo (the virgin), whose brightest star is Spica — the 15th-brightest seen in Earth’s sky. It’s also known for the Virgo cluster of galaxies and the pulsar PSR 1257+12, where astronomers found the first confirmed extrasolar planets in 1992. It traditionally represents August 23 to September 22 and in Greek mythology, is associated with the harvest maiden (Persephone).

Libra, which has no bright stars. It traditionally governs Sept. 22 to Oct. 23 and is associated with balance or justice, such as with the Roman goddess Astraea.

Scorpius, whose brightest star Antares is known as the “rival of Mars” due to its red color and similar appearance to the Red Planet. It also contains Scorpius X-1, the brightest X-ray source in the sky. It traditionally governs Oct. 24 to Nov. 21 and in Greek mythology, refers to one of two legends. The first is said to be a scorpion that killed Orion, and the second refers to one that spooked horses being controlled by Phaeton as the young man was trying to drive the Sun.

Globular Cluster — A Hubble Space Telescope image of the typical globular cluster Messier 80, an object made up of hundreds of thousands of stars and located in the direction of the constellation of Scorpius. The Milky Way galaxy has an estimated 160 globular clusters of which one quarter are thought to be ‘alien’. Image: NASA / The Hubble Heritage Team / STScI / AURA. Click for hi-resolution version.

Sagittarius (the archer), which contains a prominent radio source known as Sagitarrius A. It is considered to govern Nov. 22 to Dec. 21, and is considered a mounted archer in several cultures (starting with the Babylonians in the 11th century).

Capricornus (the goat), which has no bright stars. It traditionally governs Dec. 22 to Jan. 19. In Greek mythology, it is associated with the god Pan. He leaped into the water to get away from a monster called Typhon, just as Pan was changing shape. This made him a goat with a fish tail.

Aquarius (the water bearer), which has no bright stars. It is considered to rule over Jan. 20 to Feb. 18 and is traditionally associated with a man pouring water out of a jug. The symbolism likely arises from the Middle East, whose astronomers noted that the constellation rises with the rainy season.

Pisces (the fish), which has no bright stars. It traditionally rules over Feb. 19 to March 20 and in Greek mythology, refers to Aphrodite and Eros. They went into a river to avoid a monster called Typhon. Some versions of the myth say they changed into fish, while others say they rode fish to get away.

Universe Today has articles on zodiac signs and their dates. Astronomy Cast also has an episode on constellations.

January 15, 2015December 23, 2015 by Elizabeth Howell

What Is The Gibbous Moon?

Astrophoto: The Moon by Logan Mancuso — The Moon. Credit: Logan Mancuso

What does it mean when you hear the term “gibbous moon”? It’s when the Moon is more than half full, but not quite fully illuminated, when you look at it from the perspective of Earth. The reason the light changes has to do with how the Moon orbits the Earth.

The average distance between the Earth and the Moon is about 382,500 km (237,675 miles). As the Moon orbits our planet, the illumination of the Sun changes on its surface. The Moon takes about 29.5 days to go from a new moon to a full moon and then back again. This is called a “synodic period” or sometimes, a “synodic month.”

It’s slightly longer than the “sidereal period” or “sidereal month” (27.3 days) for the Moon to return to the same position relative to the stars. That’s because the Earth is moving at the same time along its orbit of the Sun, requiring the Moon to “catch up” to reach the same illumination, according to NASA.

How the phases of the Moon work. Credit: NASA/Bill Dunford

So as the Moon orbits the Earth, the illumination of the Sun changes. When the Moon is in between the Earth and the Sun — with the three objects perfectly aligned — the angle between the Moon and the Sun is 0 degrees. This produces a “new moon”, which is when the Moon is not illuminated or barely illuminated at all.

The first quarter occurs when the Moon is at a 90-degree angle with the Sun, as seen from Earth. Once the Moon’s angle exceeds 90 degrees, that’s when it enters the waxing gibbous phase. At 180 degrees from the Sun, the Moon is fully illuminated (a full moon). Then after it reaches 180 degrees, when the Moon and the Sun are on the opposite sides of the Earth, it becomes a waning gibbous moon.

At 270 degrees, the Moon finishes its gibbous phase, enters the third quarter of its synodic period and becomes a waning crescent, until it reaches the new moon phase and starts the cycle anew. And actually, the Moon’s position around the Earth plays a role in solar and lunar eclipses.

Total solar eclipse in 1999. The alignment of the nearby Moon and massive Sun, the weightiest body in the Solar System by far, didn't cause anyone to float off the ground. To my knowledge. Credit: Luc Viatour — Total solar eclipse in 1999. Credit: Luc Viatour

A solar eclipse can only happen when the Moon is in its “new phase”. This is, again, because of geometry — because the Moon is in between the Sun and the Earth. From time to time, the position of the Moon lines up with the position of the Sun in Earth’s sky. Coincidentally, the Sun and the Moon appear to be about the same size from Earth’s surface, which makes it possible for the Moon to completely (or almost completely) block the Sun. This creates a solar eclipse. The full eclipse phase can last anywhere from seconds to minutes.

By contrast, a lunar eclipse happens when the Moon is in its “full phase.” At this time, the Earth is in between the Moon and the Sun. When the Moon enters the Earth’s shadow, the shadow can completely or partially fall across the Moon’s surface. A total lunar eclipse phase tends to last anywhere from minutes to over an hour. It creates a ruddy (red or brown) glow due to the effect of sunsets and sunrises all around the Earth shining on the Moon at the same time, according to Bad Astronomy’s Phil Plait.

You’ll notice that as the Moon goes through its various phases, it keeps the same side of itself turned towards Earth. This is due to an effect called tidal locking. After the Moon was formed (likely through a near-cataclysmic collision with Earth), its rotation period didn’t align with that of Earth’s. But over millions of years, the tug of the Earth’s gravity produced a bulge in the Moon’s interior on the side closest to Earth.

Tidal locking results in the Moon rotating about its axis in about the same time it takes to orbit the Earth (left side). If the Moon didn't spin at all, then it would alternately show its near and far sides to the Earth while moving around our planet in orbit, as shown in the figure on the right. Credit: Wikipedia — Tidal locking results in the Moon rotating about its axis in about the same time it takes to orbit the Earth (left side). If the Moon didn’t spin at all, then it would alternately show its near and far sides to the Earth while moving around our planet in orbit, as shown in the figure on the right. Credit: Wikipedia

As Discovery News explains, over time that bulge was pulled back and forth as the Moon orbited Earth. If the rotation is much slower than the orbit, the bulge “lags behind” while the smaller body orbits. Eventually, this causes one side to always face the larger body.

Tidal locking, by the way, is a fairly common phenomenon in our Solar System — particularly at Jupiter and Saturn, which are massive gas giants that (compared to their immense size) have nat-sized moons orbiting close by. Tidal locking also likely takes place with exoplanets that are orbiting close in to their parent stars.

We have done many stories on Universe Today about the Moon. Here’s one about the phases of the Moon. Want to know when the next full moon is going to be? Here’s a handy guide from NASA that covers the phases of the Moon for 6000 years. And here’s a good explainer on the phases of the Moon. We also discussed the formation of the Moon on Astronomy Cast, Episode 17: Where Did the Moon Come From?

January 14, 2015December 23, 2015 by Elizabeth Howell

What Are The Biggest Telescopes in the World (and Space)?

Artist's impression of the European Extremely Large Telescope. Credit: ESO/L. Calçada

When you want to watch the sky, size really matters. The more light a telescope can collect, the more information we can get about stars, galaxies, quasars, or whatever the heck else we want to take a look at.

We’ve been fortunate in recent years to see bigger and bigger telescopes on the drawing board. Here are some of the monsters (present and future) of the astronomy world — and why their huge size really matters.

In Space

A large optical telescope we we have in orbit right now is NASA’s Hubble Space Telescope, which was launched in in 1990. It has a 2.4-meter (7.9-foot) mirror that, along with other instruments, has allowed it to refine the age of the Cosmos and show that the universe’s expansion is accelerating.

NASA's Hubble Space Telescope as seen during the second servicing mission to the observatory in 1997. (Credit: NASA) — NASA’s Hubble Space Telescope as seen during the second servicing mission to the observatory in 1997. (Credit: NASA)

The largest current infrared space telescope is Herschel, which has a 3.5-meter (11.5-foot) primary mirror. The European observatory launched in 2009 and has racked up several achievements since making it to space. It has observed frantic star formation in galaxy clusters, spotted a molecule required for water in expiring stars like our Sun, and completed an immense cosmic dust survey.

While Hubble has helped us chart the universe’s expansion and peered deep into time, a bigger NASA telescope is on its way. Called the James Webb Space Telescope, it is expected to launch in 2018. The telescope will observe in infrared and have a 6.5-meter (21.3-foot) mirror, giving even higher resolution to our cosmic searches.

There are of course many space telescopes out there, but those are representative of some of the bigger ones. Wikipedia has a list of space observatories, but be sure to double-check the information there for authenticity.

Comparison of the largest optical telescopes in the world. Click for a larger version. Credit: Wikimedia Commons

On the ground

The largest optical reflector in the world is the Gran Telescopio Canarias in the Canary Islands, whose individual mirror segments create an equivalent light collecting surface to a 10.4-meter (34-foot) mirror. It has been used to examine comets and asteroids, exoplanets and even supernovas.

Close behind are the twin Keck telescopes at Mauna Kea in Hawaii, which each have a diameter of 10 meters (33 feet). Their discoveries include refining the Andromeda galaxy’s size and nabbing the first picture of an exoplanet system.

One method of enhancing an individual telescope’s collecting power is to pair it with others. This is something that is used, for example, with the Atacama Large Millimeter/submillimeter Array (ALMA), which uses 66 radio telescopes in Chile’s Atacama Desert to do observations of the universe. It’s the largest interferometer of its type in the world. It’s made some of the most distant observations of water to date.

Another example of an interferometer is the Very Large Telescope at the Paranal Observatory in Chile. It has four 8.2-meter (27-foot) mirrors and four movable 1.8 meter (5.9-foot) auxiliary telescopes. It did the first image of an extrasolar planet and also saw the afterglow of the furthest gamma-ray burst astronomers have found.

In the future

We’ve also included a small list of large telescopes yet to come. The European Extremely Large Telescope (E-ELT) at Cerro Armazones in Chile is expected to have a working mirror equivalent of nearly 40 meters (131 feet), large enough to probe exoplanet atmospheres in detail. First light date is currently set at 2024.

Also under consideration is the Thirty Meter Telescope, which would have a collecting area of 30 meters (98 feet). Construction has begun at Mauna Kea, Hawaii and first light is expected in the 2020s. Scientists may be able to use the observatory to look at giant structures in the Universe, and how planets were formed, among other things.

The Giant Magellan Telescope, set to be used at Las Campanas Observatory in Chile, will have a resolving power of 24.5 meters, or 80 feet. Commissioning is set for 2021. It will be used to probe matters such as what dark energy and dark matter are really made of, and how the Universe is expected to end.

January 13, 2015December 23, 2015 by Elizabeth Howell

What Other Worlds Have We Landed On?

As of November 2014, these are all of the planetary, lunar and small body surfaces where humanity has either lived, visited, or sent probes to. Composition by Mike Malaska, updated by Michiel Straathof. Image credits: Comet 67P/C-G [Rosetta/Philae]: ESA / Rosetta / Philae / CIVA / Michiel Straathof. Asteroid Itokawa [Hayabusa]: ISAS / JAXA / Gordan Ugarkovic. Moon [Apollo 17]: NASA. Venus [Venera 14]: IKI / Don Mitchell / Ted Stryk / Mike Malaska. Mars [Mars Exploration Rover Spirit]: NASA / JPL / Cornell / Mike Malaska. Titan [Cassini-Huygens]: ESA / NASA / JPL / University of Arizona. Earth: Mike Malaska

Think of all the different horizons humans have viewed on other worlds. The dust-filled skies of Mars. The Moon’s inky darkness. Titan’s orange haze. These are just a small subset of the worlds that humans or our robots landed on since the Space Age began.

It’s a mighty tribute to human imagination and engineering that we’ve managed to get to all these places, from moons to planets to comets and asteroids. By the way, for the most part we are going to focus on “soft landings” rather than impacts — so, for example, we wouldn’t count Galileo’s death plunge into Jupiter in 2003, or the series of planned landers on Mars that ended up crashing instead.

The Moon

Al Shepard raises the American flag during Apollo 14 in February 1971. Below is the shadow of his crewmate, Ed Mitchell. Credit: NASA

Our instant first association with landings on other worlds is the human landings on the Moon. While it looms large in NASA folklore, the Apollo landings only took place in a brief span of space history. Neil Armstrong and Buzz Aldrin were the first crew (on Apollo 11) to make a sortie in 1969, and Apollo 17’s Gene Cernan and Jack Schmitt made the final set of moonwalks in 1972. (Read more: How Many People Have Walked on the Moon?)

But don’t forget all the robotic surveyors that came before and after. In 1959, the Soviet Union’s Luna 2 made the first impact on the lunar surface; the first soft landing came in 1966, with Luna 9. The United States set a series of Ranger and Surveyor probes to reach the moon in the 1960s and 1970s. The Soviet Union also deployed a rover on the moon, Lunakhod 1, in 1970 — the first remote-controlled robot controlled on another world’s surface.

In 2013, China made the first lunar soft landing in a generation. The country’s Chang’e-3 not only made it safely, but deployed the Yutu rover shortly afterwards.

Mars

Mars is a popular destination for spacecraft, but only a fraction of those machines that tried to get there actually safely made it to the surface. The first successful soft landing came on Dec. 2, 1971 when the Soviet Union’s Mars 3 made it to the surface. The spacecraft, however, only transmitted for 20 seconds — perhaps due to dust storms on the planet’s surface.

Less than five years later, on July 20, 1976, NASA’s Viking 1 touched down on Chryse Planitia. This was quickly followed by its twin Viking 2 in September. NASA has actually made all the other soft landings to date, and expanded its exploration by using rovers to move around on the surface. The first one was Sojourner, a rover that rolled off the Pathfinder lander in 1997.

NASA also sent a pair of Mars Exploration Rovers in 2004. Spirit transmitted information back to Earth until 2010, while Opportunity is still roaming the surface. The more massive Curiosity lander followed them in 2012. Another stationary spacecraft, Phoenix, successfully landed close to the planet’s north pole in 2008.

Venus

Venera 7 — one of a series of Soviet probes sent in the 1960s and 1970s — was the first to make it to the surface of Venus and send data back, on Dec. 15, 1970. It lasted 23 minutes on the surface, transmitting weakly towards Earth. This may have been because it came to rest on its side after bouncing through a landing.

The first pictures of the surface came courtesy of Venera 9, which made it to Venus on Oct. 22, 1975 and sent data back for 53 minutes. Venera 10 also successfully landed three days later and sent back data from Venus as planned. Several other Venera probes followed, most notably including Venera 13 — which sent back the first color images and remained active for 127 minutes.

Titan

Humanity’s first and only landing on Titan so far came on Jan. 14, 2005. The European Space Agency’s Huygens probe likely didn’t come to rest right away when it arrived on the surface, bouncing and skidding for about 10 seconds after landing, an analysis showed almost a decade later.

A fish-eye view of Titan's surface from the European Space Agency's Huygens lander in January 2005. Credit: ESA/NASA/JPL/University of Arizona — A fish-eye view of Titan’s surface from the European Space Agency’s Huygens lander in January 2005. Credit: ESA/NASA/JPL/University of Arizona

The probe managed to send back information all the way through its 2.5-hour descent, and continued transmitting data for an hour and 12 minutes after landing. Besides the pictures, it also sent back information about the moon’s wind and surface.

The orangey moon of Saturn has come under scrutiny because it is believed to have elements in its atmosphere and on its surface that are precursors to life. It also has lakes of ethane and methane on its surface, showing that it has a liquid cycle similar to our own planet.

Comets and asteroids

Images from the Rosetta spacecraft show Philae drifting across the surface of its target comet during landing Nov. 12, 2014. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Robots have also touched the ground on smaller, airless bodies in our Solar System — specifically, a comet and two asteroids. NASA’s NEAR Shoemaker made the first landing on asteroid Eros on Feb. 12, 2001, even though the spacecraft wasn’t even designed to do so. While no images were sent back from the surface, it did transmit data successfully for more than two weeks.

Japan made its first landing on an extraterrestrial surface on Nov. 19, 2005, when the Hayabusa spacecraft successfully touched down on asteroid Itokawa. (This followed a failed attempt to send a small hopper/lander, called Minerva, from Hayabusa on Nov. 12.) Incredibly, Hayabusa not only made it to the surface, but took off again to return the samples to Earth — a feat it accomplished successfully in 2010.

The first comet landing came on Nov. 12, 2014 when the European Space Agency’s Philae lander successfully separated from the Rosetta orbiter and touched the surface of Comet 67P/Churyumov–Gerasimenko. Philae’s harpoons failed to deploy as planned and the lander drifted for more than two hours from its planned landing site until it stopped in a relatively shady spot on the comet’s surface. Its batteries drained after a few days and the probe fell silent. As of early 2015, controllers are hoping that as more sunlight reaches 67P by mid-year, Philae will wake up again.

January 12, 2015December 23, 2015 by Elizabeth Howell

NASA Space Shots Inspire This Brilliant Video Of Universal Wonders

A still from Lucas Green's video "Space Suite", on Vimeo.

Moons pass by Saturn’s rings. An eclipse takes place on Jupiter. We see these shots every day in images from space agencies, but how would it be to actually float in a nearby spacecraft and watch these in action?

An incredible new Vimeo video called “Space Suite” shows off what it actually could be like. And here’s the neat thing — it is heavily based on those very same jaw-dropping shots space agencies regularly release.

“I created the video above as a visual proof-of-concept for a project I’m currently working on with Two Story Productions. The project relies heavily on space visuals, and I wanted to demonstrate that compelling footage could be created quickly and easily by mining the impressive image libraries of NASA (and others) for stunning photography, and then bringing them to life with simple 3d ‘tricks’,” wrote creator Lucas Green in a blog post last week.

Editor’s note: It has come to our attention that some of the visuals used in this video were taken from previously pre-processed files by Stephen van Vuuren, who used a painstaking proprietary method for creating the feature I-MAX Film, “In Saturn’s Rings.” The files were acquired and re-purposed by Lucas Green, without permission.

Green has now added notation on his webpage that ” In addition to the libraries of NASA and ESA, some of the more striking imagery was created by Stephen van Vuuren, who meticulously stitched together thousands of raw images to use in his film ‘In Saturn’s Rings’. Watch some clips on his website – his work makes ‘Space Suite’ look like a fuzzy picture on an old television screen.”

“In Saturn’s Rings” is still in production, scheduled for release this year, and Universe Today will provide updates on the film.

“The demo footage probably won’t make it into the final project, so I wanted to show it off here, and give a short breakdown of some of my favorite shots. All of the imagery in the video is sourced directly from actual photographs, with minimal retouching. Most of the shots make use of photogrammetry, or ‘projection-mapping’, in order to rapidly block out the source images as virtual scenes.”

His blog includes details of the shots he chose and how he converted them to the incredible 3-D effects you can see in the video above. Enjoy!

January 9, 2015December 23, 2015 by Elizabeth Howell

SpaceX’s Rocket Explained So Simply A Kid Could Understand

"Bird 9", a SpaceX parody of a famous xkcd cartoon called "Up Goer Nine." SpaceX used it to demonstrate its Falcon 9 rocket. Click for full image. Credit: SpaceX/Twitter/Imgur

Rocket science is difficult stuff, but we don’t always necessarily have to explain it that way. It’s important at times to break science down as simply as we can, for purposes ranging from simple understanding to making it accessible to children.

A couple of days ago, SpaceX posted a brilliant parody of a famous xkcd cartoon to describe the organization’s Falcon 9 rocket. Called “Bird 9”, it describes the components of the rocket using only the words that are used most often in speech.

The result is brilliant, with the top of the rocket called “stuff going into space” and the rocket stage aiming for a drone landing soon nicknamed “part that folds out when the first part is just above the big boat”. We won’t spoil any more for you; click on the infographic below so you can see it in its full glory. We’ve also included the original xkcd cartoon for reference.