Monthly Archives: June 2010

stargazing, ursa major

Looking Up

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There’s a Bear Up There!

The constellation of Ursa Major, with the Big Dipper outlined in red.

The other night we decided to do a little late spring stargazing. The sky was fairly dark and clear, and the stars were bright.  We went out on the deck and looked up. There, almost directly overhead was the Big Dipper.

Back when I used to give star lectures in the planetarium, I’d always start the audience out at the Big Dipper and work my way around the sky from there. For northern hemisphere stargazers, it’s one of the most recognizable star patterns.

The Big Dipper is really an asterism — that’s because it’s part of a larger constellation called Ursa Major, the Greater Bear. The figure here sort of looks like a bear striding across the sky and the dipper is on his back. In other parts of the world, people call the Dipper by the name of “the Plough. Other cultures throughout time have assigned meaning to the stars, from the Greeks to various Asian cultures and even throughout the native groups living in North America.

There are a couple of useful things you can do with the Dipper — well, three actually. The first thing you can do is admire it. It’s a pretty striking shape that our human brains have assigned to it.  The second thing you can do with it is test your eyesight. After you’ve gotten good and dark-adapted to the night sky (which takes around 10-2o minutes, look up at the bend in the handle of the Dipper. There are two stars there, and if your eyesight is good, you should be able to make them out. They’re called Alcor and Mizar.  There are actually six stars in that little region of space, but they’re too faint to make out with the naked eye.  Try checking out this pair with binoculars or a telescope.

The third thing you can do is find north. The way to do this is to locate the end stars in the cup. These are called Mirak and Dubhe.  If you start at Merak and trace a line through Dubhe and continue it on out, you will eventually run into the North Star, also known as Polaris.  That’s the star that our north pole appears to point to and indicates true north.

The Big Dipper is often the first star pattern that people learn (at least in the Northern Hemisphere) when they begin stargazing. It’s not a bad start. Once you learn it, you can branch your way out to other constellations pretty easily.  Over the next few entries, I’ll share a few more with you! In the meantime, point your browser here if you want to know more about Ursa Major and the Big Dipper.

amateur astronomy, astronomy, astronomy news, impact site, Jupiter

Something Smacked Jupiter… Again

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Is it Rare, or Not?

The June 3 impact of something on Jupiter, courtesy of Anthony Wesley of Broken Hill, Australia, and posted on spaceweather.com

The planet Jupiter got smacked again by an object this past week.  Recall that in 1994, pieces of Comet Shoemaker-Levy 9 blasted their way into the Jovian cloud tops.  At the time, people called it a once-in-a-lifetime event. That is, they did until something else plowed into Jupiter on July 19, 2009.

In an amazing coincidence, a major research paper came out this week, explaining just what it was that impacted Jupiter in 2009.  In another coincidence to THAT coincidence, the same observer who first chronicled the 2009 impact — Australian amateur observer Anthony Wesley — also saw the one that occurred a few days ago.  Christopher Go of the Phillippines captured a video of the event that sent a flash of light out from the Jovian cloud tops. Both are posted at Spaceweather.com, along with frequent updates.

You might be tempted to ask, doesn’t it seem like Jupiter’s getting hit a lot more lately?  The answer is: probably not.  In fact, Jupiter maybe getting less whacked NOW than it was in the past, back when the solar system had a LOT more debris flying around in orbit around the Sun and amongst the planets.  The difference is that we have people watching Jupiter all the time — well-equipped and qualified amateurs — and they’re bound to see these things happening, simply as a consequence of having more people pay attention. And, Jupiter being what it is — massive, strong gravity, and surrounded by debris in various orbits — it’s bound to get whacked pretty frequently.  We just haven’t always had the chance to see it happen.

Think of it this way: if trees fall in the forest on an average of once a day and nobody’s there to see it happening, we could come to the conclusion that trees falling in the forest are rare things. But that would be only because we aren’t looking. It’s an erroneous assumption, of course.  And, once we start putting people in the forest to watch the trees fall, we’d then find out that they’re falling once a day.  But, that doesn’t mean that more trees are falling. It just means we’re watching more. It’s probably the same with Jupiter. We’re watching it more and catching more of these events that could be very commonplace out in the Jovian neighborhood.

Jupiter has a long history of sucking up and sweeping in debris (comets, asteroids, etc.) throughout the life of the solar system.  In the beginning, it probably saved Earth’s skin more than once, by intercepting larger bodies that could have whacked the young Earth and changed it into something that might not be the planet we know and love today.  It’s still picking off debris today, and we’re fortunate enough to now have the technology to see it happen.

Now, about that paper explaining the 2009 collision.  When the impact occurred last year, scientists immediately turned their attention to the aftermath of the collision. They used a whole host of observatories on (and orbiting above) Earth. They mapped the thermal changes in the impact site (in other words, the temperature changes) and searched out spectral evidence of chemical elements that were part of the impactor (that is, they examined the planet in different wavelengths of light to tease out the fingerprints of chemical elements given off during the collision).  It now turns out that the evidence points toward an asteroid plowing into the cloudtops of Jupiter.  Critical examination of the impact debris suggests that the asteroid came from a family of bodies called the Hildas — a secondary asteroid belt that orbits near Jupiter and has about 1,100 members. Hildas are mainly rocky bodies that may also contain some ice.

This past February, when I was out at NASA Jet Propulsion Laboratory for a meeting, I had dinner with an old friend — Padma Yanamandra-Fisher — who was part of the team working on the data analysis of the impact debris. We talked about the event and I asked her if the impact could have been an asteroid. At that time, she was just finishing analysis, but she thought that it sure looked like an asteroid had been the culprit in the collision.

What about the impactor last week?  What’s it made of? It’s too soon to tell. Scientists are busily studying the impact site. There’s not much of an impact cloud to study, but they can take infrared measurements of the zone where the event occurred and get some idea of what the incoming debris could have been.  As with all ongoing science, stay tuned!