Category: Guide to Space

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The Andromeda galaxy is the closest spiral galaxy to the Milky Way (though it’s not the closest galaxy). It’s the most distant object you can easily see with the naked eye (under good observing conditions). Andromeda is 220,000 light years in diameter, and is one of the 35 objects that make up what is called the Local Group. Andromeda lies, of course, in Andromeda constellation.

The Andromeda galaxy (also known as  Messier 31, M31, or NGC 224) could be considered the big brother of the Milky Way, as it contains over a trillion stars (compared to our 200-400 billion), and is approximately 220,000 light years across to our 100,000. Andromeda and the Milky Way formed at roughly the same time – 13.5 billion years ago – near the beginning of the Universe. Our galaxy is thought to look much like Andromeda. Both Andromeda and the Milky Way got to their current size by eating up other galaxies they collide with. The expansion of the Universe causes most galaxies to move away from us, but Andromeda and the Milky Way are actually headed towards each other.

Andromeda and the Milky Way are good neighbors, but eventually our neighbor is going to move in with us – the Milky Way and Andromeda are approaching each other at 200 kilometers per second, and will eventually collide. There’s no need to panic, though, as Andromeda is over 2 million light years away, and the collision won’t happen for another 2 or 3 billion years. Astronomer John Dubinski of the University of Toronto has an excellent animated simulation from multiple perspectives of what this galactic dance could look like.

The collision between Andromeda and the Milky Way won’t be catastrophic, and after about 5 billion years from now the resulting galaxy will have settled down into an elliptical galaxy. There is a small chance, though, that the Sun won’t be part of this new “Milkomeda” galaxy.

Fraser and Pamela discuss how the collision between the Milky Way and Andromeda will look from Earth in the September 28th, 2008 episode of Astronomy Cast, and the Milky Way in Episode 99.

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The small constellation of Pictor resides just south of the ecliptic plane and was created by Nicolas Louis de Lacaille. It was adopted by the International Astronomical Union and accepted as one of the permanent 88 modern constellations. Pictor covers approximately 247 square degrees of sky and ranks 59th in size. It has 3 main stars in its asterism and contains 15 Bayer Flamsteed designated stars within its confines. Pictor is bordered by the constellations of Caelum, Carina, Columba, Dorado, Puppis and Volans. It is visible to all observers located at latitudes between +26° and ?90° and is best seen at culmination during the month of January.

Because Pictor is considered a “new” constellation, it has no mythology associated with it – but Nicolas Louis de Lacaille was a man of science and arts. The constellation names he chose to add to his southern star catalog – Coelum Australe Stelliferum – favored this love of technological advances and all things in the field, therefore Pictor was once added as “Equuleus Pictoris”, the “artist’s easel”, but was later shortened to just Pictor when added permanently to the modern constellation charts.

Let’s begin our tour of Pictor with binoculars and its brightest star – Alpha Pictoris – the “a” symbol on our map. It is a class A subgiant star which resides almost 100 light years away from Earth. At close to a billion years old, it is around 3 times larger than our own Sun, yet it rotates over 100 times faster. Alpha is a star that shouldn’t produce X-rays – but does. What’s going on? Perhaps it has a small companion star that’s waiting to be discovered!

Keep your binoculars in hand and hop to Beta Pictoris – the “B” symbol. Located about 64 light years from our solar system, Beta is the key player in a moving star group. This is a stellar association of young stars which share the same motion through space and have the same age. But that’s not all that Beta has going for it. The Beta Pictoris system is very young – only 8-20 million years old – and already in the main sequence stage of stellar evolution. While that in itself isn’t peculiar, what’s curious is an excess of infrared emission compared to normal stars of its type. It would appear that Beta has large quantities of dust! According to detailed studies, a large disk of dust and gas has been found orbiting Beta and was the first to ever be imaged. Inside they found the presence of several planetesimal belts and cometary activity… and there are indications that planets may have formed within this disk and that the processes of planet formation may still be occurring! In November 2008, the European Southern Observatory (ESO) published a press release announcing that a planet matching previous predictions may have been imaged in orbit around Beta Pictoris in the plane of the debris disk. If the physical association of the detected object with Beta Pictoris is confirmed, it would be the closest planet to its star ever photographed. How far apart you ask? Tthe observed separation between the parent star and the planet is roughly the same as the distance between Saturn and the Sun. Too cool….

Now, take out your telescope and have a look at Theta Pictoris – the figure “8” symbol. That’s right… We’ve got a multiple star system here! Theta Pictoris is a three part system, with each of the components all around 7th magnitude and well spaced enough to be easy for optics!

For a nice optical double star in binoculars, have a look at Eta Pictoris – the “n” symbol on our map. Although not gravitationally bound, it’s still a pretty pair!

While there is almost no deep sky to be observed in Pictor, you can still scope out Kapteyn’s Star. It is a class M0 subdwarf star which was discovered by Jacobus Kapteyn in 1897. Located just about 13 light years from Earth, this one has a high radial velocity, orbits the Milky Way in retrograde, and is the nearest halo star to the Sun! When Kapetyn first discovered it, it had the highest proper motion of any star known, later bowing to the discovery of Barnard’s star..

Don’t forget to have a look at variable star, R Pictoris, too!

Sources:
Chandra Observatory
Wikipedia
Chart provided by Your Sky.

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The mass of the Milky Way depends on what you consider this question to mean. If you are only talking about the visible part of the Milky Way – all the stars, gas and dust that make up the disk – then the Milky Way’s mass is between 200-600 billion times that of the Sun. We can’t just put the Milky way on a bathroom scale to get this number, however. This number is reached by counting the number of stars in the galaxy and assuming their mass is roughly that of the Sun. The mass varies depending on where one defines the edge of the Milky Way to be.

But there is another way to check the heft of the Milky Way – by measuring how fast stars are rotating around the disk, the mass of the disk itself can be determined. In other words, the heavier the Milky Way is, the more of an effect gravity will have on the rotation, and the faster the stars will move through the disk. This number comes up to be a whopping 1-2 trillion times the mass of the Sun!  The most recent estimate from a study using information from the Sloan Digital Sky Survey measuring the velocity of over 2,4oo stars put the mass of the Milky Way and its halo at 1 trillion solar masses. Though astronomers don’t use kilograms when measuring such large objects as the Sun or galaxies, the Milky Way and its halo would be about 6 x 10^42 kilograms.

Where is all of this matter, if not in the stars? As with many contemporary mysteries in astronomy, the answer is dark matter. The Milky Way is thought to be home to a halo of dark matter – matter that cannot be detected except through its gravitational influence – which makes up approximately 80-90% of its mass. That’s right, the mass of the Milky Way that can be seen (through visible, X-ray, infrared, etc.) makes up only about 10-20% of its mass. This halo may extend out to as far as 300,000 light years from the galactic center.

For more information about the Milky Way, you can refer to Episode 99 of Astronomy Cast, visit the rest of our section here in the Guide to Space, or Swinburne Astronomy Online.

Source:
Sloan Digital Sky Survey

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The Milky Way is pretty hard to map, given that we live inside of it and have to peer through all of the dust and gas that lie inside the disk. Though we can’t get a picture of our galaxy from outside, we can create images and maps from computer modeling of the stars we see in the disk.

The Milky Way – until recently – was thought to be a barred spiral with four star-forming arms, named  Norma, Scutum-Centaurus, Sagittarius and Perseus. In June of 2008, images from NASA’s Spitzer Space Telescope revealed that the Milky Way is a barred spiral with only two major arms, demoting the Sagittarius and Norma arms to minor arms. The Sun lies in a minor arm, named the Orion Arm, or Orion Spur, sandwiched between the Sagittarius minor arm and Perseus arm.

Our galaxy is a large disk approximately 100,000 light years across. There’s a bulge in the center that is 12,000-16,000 light years thick, and is home to a black hole named Sagittarius A*. Other areas of the disk range between 2,300 and 2,600 light years in thickness.

The image above is a representation of what the Milky Way would look like from above. Of course, there are plenty of maps of the Milky Way as we see it from the Earth. Also, you can go outside on a clear night and see it splashed across the sky. Below is an image in the infrared, with the various regions marked (named because of the constellation in which they lie).

Plenty of maps are available all over the web in a variety of spectrum. Here’s a gallery of 9 images of the Milky Way in different spectra to get you started, and An Atlas of the Universe has maps of the Milky Way and Universe from different perspectives and distances. If you’re looking for interactive maps of the sky and Milky Way, Sky-Map.org, Google Sky and the downloadable Stellarium are all great resources to familiarize yourself with our Galaxy.

If you’re interested in learning more about other aspects of the Milky Way, Astronomy Cast has a whole episode devoted to it. You can also check out the rest of our resources in the Milky Way section of the Guide to Space.

Sources: NASA, Wikipedia

[/caption]The size of Mars can not be given in one set of numbers. Scientists describe a planet by many factors. First there is radius, for Mars that is 3,389.5 km. Its circumference is 21,344 km. Next is volume, which is 1.63116 X 10¹¹ km³. Last is Mar’s mass at 6.4169 x 10²³ kg.

For comparison, Mars has 53% of the diameter of Earth. It has about 38% of the surface area of Earth. That sounds small, but that is equal to the total dry land here on Earth. The volume of Mars is equal to 15% of Earth’s and the Red Planet’s mass is 11% of Earth’s. As you can see, Mars is a small world, the second smallest in the Solar System.

Despite its small size, Mars has many interesting features that would seem larger than life. Olympus Mons is the tallest mountain in the Solar System and Valles Marineris is the deepest valley. Mars is home to hundreds of thousands of impact craters. Northern Polar Basin-Borealis Basin is largest at 10,500 km and Hellas Basin at 2,100 km is the third largest.

In addition to the extremes in topography, Mars is a world of weather extremes. Overall, it is a very cold world with an average surface temperature of about -47°C. During the summer, near the equator the temperatures can reach nearly 20°C during the day, but drop to -90°C at night. That 110° change in temperature can drive winds that reach tornado speeds. Once these winds start, they pick up the iron oxide dust that covers the planet, turning into a dust storm. There have been dust storms on Mars that have gotten large enough to engulf the entire planet for days at a time.

Scientists believe that Mars was a larger planet early in the history of the Solar System. The impact that created the Northern Polar Basin-Borealis Basin would have been large enough to eject a portion of the planet into space and beyond its gravitational pull; thus, the planet may have lost part of itself from the crash.

As you can see, the size of Mars is a minor fact amongst all of the interesting facts that you can discover about the Red Planet, but, hopefully, it is enough to get you to do more research.

Want information on other planets? Here’s an article about the size of Jupiter, and here’s one on the size of Saturn.

If you’d like more info on Mars, check out Hubblesite’s News Releases about Mars, and here’s a link to the NASA Mars Exploration home page.

We have recorded several podcasts just about Mars. Including Episode 52: Mars and Episode 92: Missions to Mars, Part 1.

Source:
NASA

The atmosphere of Mars is less than 1% of Earth’s, so it does not protect the planet from the Sun’s radiation nor does it do much to retain heat at the surface. It consists of 95% carbon dioxide, 3% nitrogen, 1.6% argon, and the remainder is trace amounts of oxygen, water vapor, and other gases. Also, it is constantly filled with small particles of dust(mainly iron oxide), which give Mars its reddish hue.

Scientist believe that the atmosphere of Mars is so negligible because the planet lost its magnetosphere about 4 billion years ago. A magnetosphere would channel the solar wind around the planet. Without one, the solar wind interacts directly with the ionosphere stripping away atoms, lowering the density of the atmosphere. These ionized particles have been detected by multiple spacecraft as they trial off into space behind Mars.

This leads the surface atmospheric pressure to be as low as 30 Pa(Pascal) with an average of 600 Pa compared to Earth’s average of 101,300 Pa. The atmosphere extends to about 10.8 km, about 4 km farther than Earth’s. This is possible because the planet’s gravity is slighter and does not hold the atmosphere as tightly.

A relatively large amount of methane has been found in the atmosphere of Mars. This unexpected find occurs at a rate of 30 ppb. The methane occurs in large plumes in different areas of the planet, which suggests that it was released in those general areas. Data seems to suggest that there are two main sources for the methane: one appears to be centered near 30° N, 260° W, with the second near 0°, 310° W.

It is estimated that Mars produces 270 ton/year of methane. Under the conditions on Mars, methane breaks down as quickly as 6 months(Earth time). In order for the methane to exist in the detected quantities, there must be a very active source under the surface. Volcanic activity, comet impacts, and serpentinization are the most probable causes. Methanogenic microbial life is a very remote alternative source.

The atmosphere of Mars will cause a great number of obstacles for human exploration of the planet. It prevents liquid water on the surface, allows radiation levels that humans can barely tolerate, and would make it difficult to grow food even in a greenhouse. NASA and other space agencies are confident that they will be able to engineer solutions for the problem within the next 30 years, though. Good luck to them.

Of course, we have written many articles about Mars’ atmosphere. Here’s an article about how the planet once held enough moisture for drizzle or dew. And here’s an article about the Mars methane mystery.

If you’d like more info on Mars, check out Hubblesite’s News Releases about Mars, and here’s a link to the NASA Mars Exploration home page.

We have recorded several podcasts just about Mars. Including Episode 52: Mars and Episode 92: Missions to Mars, Part 1.

Sources:
http://solarsystem.nasa.gov/planets/profile.cfm?Object=Mars&Display=OverviewLong
http://quest.nasa.gov/aero/planetary/mars.html
http://www.nasa.gov/home/hqnews/2009/jan/HQ_09-006_Mars_Methane.html

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You might be surprised to know that Venus is the hottest planet in the Solar System. With a global temperature of 735 Kelvin (462 degrees C), the surface of Venus is hot enough to melt lead. And if you could stand on the surface of Venus, you would experience atmospheric pressure 92 times greater than what you’re used to on Earth. Why is Venus so hot? The Venus greenhouse effect shows you what happens when this the process of trapping sunlight goes out of control into a runaway process.

As you probably know, carbon dioxide is a greenhouse gas. Various wavelengths can pass through this invisible gas, but it’s very effective at trapping heat. Light from the Sun strikes the ground of Venus, and warms it up. The ground tries to radiate heat back into space but the carbon dioxide traps much of it around the planet keeping it so warm. This is the same thing that happens when you keep your car windows closed on a hot day.

Scientists think that Venus used to be more similar to Earth, with lower temperatures and even liquid water on the surface of the planet. At some point, billions of years ago, the planet started to heat up. At some point, all the water on the surface evaporated into the atmosphere. Water vapor is an even more powerful greenhouse gas than carbon dioxide and this caused temperatures to rise even more. Then the surface of Venus got so hot that the carbon trapped in rocks sublimated into the atmosphere and mixed with oxygen to form even more carbon dioxide. And so today we have a carbon dioxide atmosphere on Venus which is 92 times more dense than Earth’s atmosphere at the surface.

Could this happen on Earth? Scientists think that if the same process happened on Earth, we would have temperatures with several hundred degrees C, and an atmosphere 100 times as dense as we have right now.

We have written articles on Universe Today about the Venus greenhouse effect. Here’s an article about the planet’s evolution over time, and here’s an article about how Venus could be colonized with floating cities.

Want more information on Venus? Here’s a link to Hubblesite’s News Releases about Venus, and here’s NASA’s Solar System Exploration Guide to Venus.

We have also recorded a whole episode of Astronomy Cast that’s just about planet Venus. Listen to it here, Episode 50: Venus.

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Even in ancient times, astronomers knew that Venus changed in brightness in the sky. Sometimes it’s like a dim star, and other times it becomes the brightest object in the sky (after the Moon); bright enough to cast shadows. But it wasn’t until Galileo first turned his rudimentary telescope on Venus in 1610 that astronomers first realized that Venus goes through phases, just like the Moon.

Think about the orbit of Venus for a moment. As you know, Venus orbits closer in to the Sun than Earth. One half of the planet is always in sunlight, and the other half of the planet is in shadow. It’s our view of Venus that changes. Sometimes we see Venus on one side of the Sun, and other times we see it on the other side. We can never see when Venus is completely illuminated because that’s when it’s on the opposite side of the Sun. We also can’t see when it’s completely in shadow because then it’s in between the Earth and the Sun, and the Sun obscures Venus from our view.

Just like the Moon, Venus goes through a full range of phases. When Venus has just passed out from behind the Sun, it’s almost a full circle, but it’s dim because it’s nearly at its most distant point from Earth. Then it “catches up” to Earth’s orbit as it travels around the Sun. Venus becomes brighter and brighter but also does into a half phase and eventually a slim crescent. You might be surprised to know that Venus is at its brightest when it’s a slender crescent.

The only way to see the phases of Venus is through a telescope. So find a friend with a telescope, ask them when Venus is going to be bright in the sky, and ask them for a chance to take a look.

We have written many articles on Universe Today about observing Venus. Here’s one article about a time when Venus, the Moon and Jupiter were all visible in the sky at the same time, and here’s one about Venus and Jupiter.

Want more information on Venus? Here’s a link to Hubblesite’s News Releases about Venus, and here’s NASA’s Solar System Exploration Guide to Venus.

We have also recorded a whole episode of Astronomy Cast that’s just about planet Venus. Listen to it here, Episode 50: Venus.

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One of the nicknames of Venus is “the Morning Star”. It’s also known as the Evening Star. Of course, Venus isn’t a star at all, but a planet. So why does Venus have these nicknames?

The orbit of Venus is inside the orbit of Earth. Unlike the outer planets, Venus is always relatively close to the Sun in the sky. When Venus is on one side of the Sun, it’s trailing the Sun in the sky and brightens into view shortly after the Sun sets, when the sky is dark enough for it to be visible. When Venus is at its brightest, it becomes visible just minutes after the Sun goes down. This is when Venus is seen as the Evening Star.

When Venus is on the other side of the Sun, it leads the Sun as it travels across the sky. Venus will rise in the morning a few hours before the Sun. Then as the Sun rises, the sky brightens and Venus fades away in the daytime sky. This is Venus the Morning Star.

The ancient Greeks and Egyptians thought that Venus was actually two separate objects, a morning star and an evening star. The Greeks called the morning star Phosphoros, “the bringer of light”; and they called the evening star Hesperos, “the star of the evening”. A few hundred years later, the Hellenistic Greeks realized that Venus was actually a single object.

We have done several articles on Universe Today encouraging readers to go out and see Venus the Morning Star. And here’s what Venus looks like in a telescope.

Want more information on Venus? Here’s a link to Hubblesite’s News Releases about Venus, and here’s NASA’s Solar System Exploration Guide to Venus.

We have also recorded a whole episode of Astronomy Cast that’s just about planet Venus. Listen to it here, Episode 50: Venus.

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Venus is one of the planets visible with the unaided eye. Because it has always been easy to see, it’s impossible to say who discovered Venus. In fact, after the Moon and the Sun, Venus is the brightest object in the sky – it’s likely ancient people thousands of years ago knew about it.

You can’t really talk about the discovery of Venus, but historians do know when observations of Venus were first written down. In fact, one of the oldest surviving astronomical documents is a Babylonian text that talks about Venus in 1600 BC. It contains a 21-year record of Venus’ appearances. Venus played a part in the mythology of many ancient peoples, including the Mayans and the Greeks.

The first person to point a telescope at Venus was Galileo Galilei in 1610. Even with his crude telescope, Galileo realized that Venus goes through phases like the Moon. These observations helped support the Copernican view that the planets orbited the Sun, and not the Earth as previously believed.

Astronomers predicted that Venus would transit across the surface of the Sun. The first time this was observed was on December 4, 1639, and later transits helped astronomers discover that Venus has an atmosphere, and helped calculate the distance from the Earth to the Sun with great accuracy. The last transit of Venus happened in 2004, and the next one will happen in 2012.

Although the surface of Venus is obscured by thick clouds, radar signals were bounced of the surface of the planet in 1961. This allowed astronomers to calculate its radius accurately, and measure its speed of rotation. They also discovered that its axis of rotation is almost zero.

The first spacecraft to actually visit Venus was NASA’s Mariner 2, which flew past Venus in 1962. More recently, NASA’s Magellan spacecraft visited Venus and extensively mapped it surface with radar. ESA’s Venus Express arrived at Venus in May, 2006.

You might be surprised to know that Russian spacecraft have actually landed on the surface of Venus. Although there were several failed attempts, the first spacecraft to actually land on the surface of Venus and survive was Venera 7; although, it was only able to transmit for about 35 minutes.

So, it’s hard to say who actually discovered Venus. The first caveman who stepped outside in the early evening would have noticed bright Venus. But since the discovery of the telescope, and the beginning of the space age, scientists have really been able to discover Venus.

Here are articles about two planets in the Solar System that were actually discovered in recent times. Here’s an article about the discovery of Uranus, and here’s an article about the discovery of Neptune.

Want more information on Venus? Here’s a link to Hubblesite’s News Releases about Venus, and here’s NASA’s Solar System Exploration Guide to Venus.

We have also recorded a whole episode of Astronomy Cast that’s just about planet Venus. Listen to it here, Episode 50: Venus.

References:
NASA: Transit of Venus
NASA Solar System Exploration: Venus