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I want to introduce you today to Ligeia Mare (the Ligeian Sea), the second largest known body of liquid outside the Earth. It's on the surface of Saturn's moon Titan, the only moon in the solar system to have a thick atmosphere and, therefore, to have air pressure. It's air pressure that keeps liquids from evaporating and makes rivers, lakes, and seas possible.
And to our delight, Titan, despite the freezing cold temperatures in the Saturn System, has rivers, lakes, and seas. At Titan temperatures, water is frozen until it's harder than rock on Earth. So the bodies of liquid on Titan are not water, but methane and ethane, which can be liquid under Titan conditions. Methane is natural gas (and also what comes out of both ends of the cow after it has been digesting its food for a while.) Ethane is a chemical that is often found in natural gas and is also a product of refining oil.
Take a look at the picture. This is not a photograph, but an image that comes from bouncing radar beams off Titan, something we equipped our clever little Cassini spacecraft to do. On radar pictures, rough things show up light, smooth things (like bodies of liquid) show up dark. The colors are added artificially to make the picture more interesting.
The name Ligeia comes from one of the sirens of Greek mythology, beautiful creatures who lured sailors toward rocky shores and their certain death. Look at Ligeia on the image -- ain't she beautiful? Some people see the shape of a sleeping dog, with its head toward the bottom. But its size is what astounds. The sea is about the size of the Earth's Caspian sea and if you walked completely around it on the shore, you'd walk a total of 1,240 miles.
Where the radar picture is black, the sea is deep; where you see grey, the sea is more shallow, so the radar beam can hit the sea bottom and some of it bounces back. Already scientists have proposed a mission (not approved yet) to splash down a capsule in Ligeia Mare and either drift or purposely navigate around the sea, sending back images to Earth.
It's been winter in the North polar region of Titan since Cassini arrived in the neighborhood. Some scientists think that once the weather starts to warm up on Titan (it will still be outrageously cold compared to Earth,) the Titan winds might blow hard enough to make waves on this alien sea, and our radar might just pick up those waves. (Somebody should tell the Beach Boys that surf might soon be up another world!)
For more details about weather on Titan, see:
http://www.nasa.gov/mission_pages/cassini/whycassini/cassini20130522.html#.UjEPocYqh8E
A minor, but cute, pairing is visible in the sky tomorrow. It happens soon after sunset and you can only see it if you have an unobstructed view of the west-southwest horizon. (For many of us that means we will have to get high -- only in the geographical sense, mind you!! Typically, our view is blocked by buildings, trees, hills, etc. and we can't see the western horizon.) But if you get to a place where you can see low in the west Sunday evening, you will see a very thin crescent Moon and the bright planet Venus just to the right of it.
You can start looking about a half hour after the Sun sets on Sunday and you'll see it best about 45 minutes after sunset. But don't wait too long to catch it; soon both objects will set in the West, and disappear from your view.
When Venus is visible just after sunset, people call it the evening star. But it's not a star at all, but a planet -- our neighbor planet just sunward of the Earth. It reflects quite a bit of sunlight both because it's close to the Sun and because it's covered with clouds that are quite reflective. (In fact Venus is so cloudy, there hasn't been a clear day there in 3 billion years. I like to cheer up my friends in Seattle by telling them that.)
As you can see in the nice diagram, which I borrowed from the good people at Sky & Telescope magazine, if you look further up and to the left, you will also see the planet Saturn in the same part of the sky. The distance in the sky between the Moon and Saturn should be about the width of your clenched fist, if you hold out your hand at arm's length. If you have binoculars or a telescope, you can enhance your view, but if you don't have an instrument, it's still fun to look. If you have kids, bring them outside and show them the sight too. It couldn't hurt to impress them with your knowledge of the universe while they are young.
For more information, you can see the full story at the Sky & Telescope web site: http://www.skyandtelescope.com/observing/highlights/Crescent-Moon-and-Venus-Put-on-a-Show-222505621.html
A Japanese team of astronomers, using the giant Subaru telescope, atop an extinct volcano in Hawaii, have found further hints of the presence of water on a planet orbiting the star Gliese 1214, about 40 lightyears away.
The planet orbits its star in only 38 HOURS (not days, folks, but hours!) You might think that a planet this close to a star will soon be french fried, but, in this case, the star itself is much dimmer and cooler than the Sun -- it is what astronomers call a "red dwarf."
The planet circling the red dwarf is one of the few planets outside our own solar system which we have been able to find in two independent ways. We know it's there because its gravity makes the star wiggle a bit, and we also know it's there because we can see the planet move across the face of the star and cause a mini-eclipse (or transit).
This double identification is very helpful, since it lets us measure both the size of the planet and how much stuff (mass) it contains. That's how we know it's a "super-Earth" -- a kind of planet we don't have in the Sun's family. This super-Earth is about three times the size of Earth, and more than 6 times its mass. These characteristics make this alien world denser than Jupiter but less dense than Earth. It could be a little rocky planet with a giant atmosphere, or a planet with some rock and a lot of liquid water surrounding it.
The new Japanese study examined the planet's atmosphere and concluded that the way light of different colors scattered from it was consistent with either the presence of water vapor or with some kind of extensive cloud cover. Combining this work with other studies makes astronomers a bit more sure that this is a water-rich environment. That still doesn't help us pin down exactly what this super-Earth looks like, and it's probably too warm overall for life as we know it. Nevertheless, isn't it amazing that we can now discover not only planets out there in other parts of the Galaxy, but even something about the kind of air they have surrounding them?
(NOTE: The image above is an artist's conception of what the star might look like through a blue filter. The star itself would look red to your eye. The planet is the smaller black sphere on the left side of the star.)
If I had a dollar for every time someone in casual conversation had called me an astrologer or astrologist (instead of an astronomer), my retirement funding would be a lot more secure. Often, it's an honest mistake, where the speaker really does understand that astronomy is a science and simply isn't sure of the science's proper name. What's much worse is when I run into a "true believer" in astrology, who thinks that our personality, our character, and our destiny is shaped by the arrangement of stars and the position of celestial objects at the moment of our birth.
Some years ago, I wrote an article for Sky & Telescope magazine setting out an astronomer's reaction to astrology. A much revised and updated version is now on-line, thanks to the Astronomical Society of the Pacific. If you have wondered about astrology and what to say to those who believe in it, this short article may assist you. At the very least, you might find it amusing. In it, I also describe a new field for predicting things called "jetology" (where your future is determined by the position of all the jumbo jets at the moment of your birth.) The article is in PDF file format at:http://www.astrosociety.org/astrology.pdf
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It's a dizzying thought, but the solid ground beneath our feet is moving at great speeds through space. For example, our planet turns once a day. Every 24 hours, the place where you live on the surface of the Earth goes in a big circle around the center of our planet. In the San Francisco Bay Area, this motion happens at a speed of about 818 mph. (Children, you can do this without adult supervision, because gravity holds all of us firmly to the Earth's surface.)
Our planet turns around an imaginary stick that goes from the Earth's north pole through its south pole. We call the line of that imaginary stick the Earth's "axis." As our planet turns around its axis, the Sun appears to rise in the East and set in the West and we have day and night. At night, as we turn, we see everything in space slowly turning around us. But we know the Sun during the day and the stars at night are not really turning. They sit in space and mind their own business. The motions we see in the sky hour by hour just reflect the turning of planet Earth. Do you want to see this motion displayed?
On the magnificent photo I have attached to this little posting, you can actually see the turning of the stars (around the still point of the north pole of the sky). Master photographer Phil McGrew captured the turning of the sky above the Golden Gate Bridge. I was so enchanted with this photo, I asked him to give me permission to share it with all of you. You can see more of his photos at his web site: http://www.philmcgrew.com/
The photo is actually made up of more than 180 20-second exposures, skillfully added together. Instead of being a point, each star becomes a curved line as the Earth turns with the camera and photographer attached to it. Astronomers call the curved lines "star trails."
Can you think of other ways that you are moving even while sitting still in your favorite armchair? We'll discuss these other motions in future posts.
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The Silicon Valley Astronomy Lectures, which I have the pleasure of moderating, feature noted scientists giving nontechnical illustrated talks on recent developments in astronomy. I am happy to announce that they are now available on their own YouTube Channel, at:
http://www.youtube.com/SVAstronomyLectures/
The talks include:
* Frank Drake (the father of the search for radio signals from civilizations in space) discussing his modern view of the Drake Equation,
* Michael Brown explaining how his discovery of the dwarf planet Eris led to Pluto being kicked out of the planet club,
* Alex Filippenko (selected as the U.S. Professor of the Year, a few years ago) talking about the latest ideas and observations of black holes,
* Natalie Batalha (mission scientist for the Kepler Project) sharing the latest planet discoveries from outside the solar system, and
* Chris McKay updating the Cassini discoveries about Saturn's moon Titan (the only moon known to have an atmosphere thicker than Earths).
The lectures are taped at Foothill College near San Francisco (where I teach), and co-sponsored by NASA's Ames Research Center, the SETI Institute, and the Astronomical Society of the Pacific.
Note that the top page of the YouTube channel shows the lectures in the order they happened to be uploaded to YouTube. If you want to see them in chronological order, select the Playlist option.
Both new and older talks in the series will be added to the channel as time goes by. Many well-known astronomers have given talks in this series since its founding in 1999; recent lectures are being recorded so that people around the world can "tune in."
(About the picture: This is a false color image of the Helix Nebula, the last gasp of a dying star located about 650 lightyears away. A relatively low-mass star is collapsing and losing its outer layer in a final internal adjustment before it dies as a white dwarf. The material the star loses is excited by the energy of the shrinking star and set to glow. In this image, infrared radiation (as measured from the Spitzer telescope in space) is shown in green and red, ultraviolet radiation (as measured by the GALEX telescope in space) is shown in blue.)
Whenever small chunks of cosmic dust or dirt hit the Earth's atmosphere at high speed and heat up, they make a flash of light that's visible from the ground. We call these meteors or "shooting stars." When the Earth encounters an organized swarm of cosmic material, we call it a meteor shower.
The Perseids (one of our most reliable meteor showers) is best this year the night and morning of Sunday Aug. 11 to Monday Aug. 12, and the night and morning of Monday Aug. 12 to Tuesday Aug. 13th.
Watching for meteors is easiest for most people’s schedules in the evenings (before midnight). However, the meteor display is generally better after midnight (making night owls and early risers happy.)
The Perseids are better after midnight for two reasons this year:
a. The Earth turns after midnight to face the shower (so that the meteors are coming more directly at us)
b. The crescent Moon will set by then, so its light will not bother meteor shower fans. (On Aug. 11, the Moon sets at 10:32 pm, while on Aug. 12th the Moon sets at 11:10 pm.)
Whenever during those two nights you decide you want to watch, here are Fraknoi’s Friendly Meteor Shower Tips for best viewing:
1. It’s more important to decide WHERE to watch them, than WHEN to watch them. The crucial issue is that meteors are faint, so you need a location where the sky is DARK. That means getting away from city and car lights as much as possible. The darker your site, the more you will see.
2. Of course, if it’s foggy or cloudy, you won’t see a thing. So make sure you get to a place where the sky is not only dark but CLEAR.
3. Don’t use a telescope or binoculars. (Meteor showers are one of the most democratic of sky shows; those of us in the 99% can enjoy them as much as those in the 1%!).) Your eyes are the best tool, because the flash can be anywhere in the sky. So restricting your view to a small part of the sky makes it more likely you will miss many of the meteor flashes.
4. Dress warm for night-time temperatures and be patient. Meteor showers are far more subtle than fireworks. You will need to relax and wait for time to pass. First, it takes a while for your eyes to get adapted to the dark (I recommend at least 15 minutes) and, second, a minute or several minutes might pass without a single flash. Eventually, though, you should see significantly more shooting stars than on a regular night.
5. So (perhaps most important) try to take someone with you with whom you like to spend time in the dark.
The Perseid meteors are cosmic “garbage” (dust and dirt clumps) left over from a regularly returning comet, called Swift-Tuttle (after the two astronomers who first discovered it). When comets get near the Sun, their ice evaporates, leaving behind some of the dirt that was frozen inside them. Since comets are "left-overs" from the early days of our solar system, you can tell yourself that each flash you see is the “last gasp” of cosmic material that formed about 5 billion years ago.
(Our photo, by ESO Photo Ambassador Stéphane Guisard, shows a bright Perseid meteor in 2010 over the grouping called the Very Large Telescope at the European Southern Observatory in Chile.)
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