All posts for the month December, 2007

Snow Good

One of the consequences of living on a planet that orbits a star is that we get seasons. Every planet in the solar system has reasons for seasons:

  • the tilt of the planet on its axis—which determines the angle of the incoming sunlight that strikes the surface (or upper atmosphere) of the planet;
  • the number of hours of daylight experienced on any given part of the planet (more hours of sunlight mean more warmth)

For those of us in northern hemisphere winter, right now we’re having shorter days and colder weather because our part of the planet is tilted away from the Sun and we have fewer hours of sunlight per day than the folks in the southern hemisphere, who are enjoying the height of summer weather.

This is all academic if you’re looking at some other planet, like Mars or Venus or Neptune, and trying to figure out what time of year it is on various places on those planets. It’s not so academic if you’re in the “middle of the experiment” so to speak.

Where I live it’s winter. There’s no question about it. We’ve had cold weather for some weeks now, and the Sun is much lower in the southern part of our sky than it is the rest of the year. Nighttime comes around 5 p.m. And, it has been snowing.

Today I looked out the window and saw these huge snowflakes falling. So, I did what anybody who’s been stuck in front of a computer all day indoors on a cold winter day would do: I grabbed my camera and started taking pictures to show to the folks I know in warmer climes. I even managed to capture a few short movies with my digital still camera (alas, I was shooting through screened windows, but hey— you grab your chances when and where you can).

So, here’s today’s real-life flash video demonstration of a seasonally caused weather pattern and what it looks like from indoors, in the form of a little music and visual-arts video. Click on the snowflake and enjoy!

To see this video here, you need to tell your browser not to block active content, or you need to get the Flash player. RSS readers who can’t access the video can download it here.

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See Mars for the Holidays (originally posted for Dec. 2007)

Star chart by C.C. Petersen/

The holidays (all kinds of them) are upon us. Whatever you celebrate at this time of year, take a few moments to step outside and look up at the night sky. Orion should be prominent, and not far away, one horn of the Hyades (in Taurus) seem to point at the planet Mars. If you have binoculars or a small telescope, check out the Orion Nebula not far from the three stars that make up Orion’s belt. And, don’t forget to include the Pleiades in your stellar and planetary travels!

(Note: this post and map refer to the sky and Mars as seen in December 2007.)

Happy Holidays from

Smacking Mars

Ever hear of 2007 WD5? It’s all over the news right now, so I’m probably not telling you anything new about it, but just in case you’ve been out holiday shopping or traveling or hiding under a rock, here’s the scoop. 2007 WD5 is a 164-foot-wide asteroid that is moving in an orbit that will cross Mars’s orbital path in late January. It comes close enough to Mars that it will pass within 30,000 miles (48,000 kilometers) of the planet. It’s possible, although not likely, that this thing could actually smack into Mars’s surface. The chances are about 1 in 75. If it did, this rock (traveling at 30,000 miles per hour) would dig out a crater about the same size as the one that the Opportunity rover is exploring right now.

Victoria Crater on Mars

Over the next few weeks astronomers will get a better idea of the asteroid’s orbit and whether it will actually hit Mars or sail on by. You can follow the action by visiting NASA’s Near Earth Object Program web page for updates.