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Treebeard's Stumper
12 September 2003

Close Encounters

It's hard to miss the planet Mars in the eastern sky after sundown. It's so bright because it's so close. Mars was closest to us on August 27, but it's still plenty bright and even easier to see now because it's rising a bit earlier every day. We've all heard that this was the closest approach to Earth in 60,000 years. Should we worry that Mars is getting closer? Earth orbits the sun in 365 days, and Mars orbits in 687 days, so why aren't these close encounters more common? What kind of natural cycle in the solar system takes 60,000 years to repeat?

At it's closest approach last month, Mars was a "mere" 34,647,397 miles from Earth. It's still plenty bright. If you haven't noticed it yet, get outside tonight!

I did my duty as a science teacher on the night of August 27, 2003 and went out at 1:30 A.M. PDT to get a photo of Mars at closest approach. (See this NASA page.) My method was brute force: set my Olympus 2040Z digital camera up on a tripod at full telephoto and take the longest manual exposure possible, F2.6 @ 16 seconds. It`s still just a (over-exposed) red dot, so I enlarged the 30x30 pixel planet to fill the frame. Kind of pretty. I also pasted the original size image in the upper right corner for comparison.

Mars at closest approach, August 27, 2003 at 1:30 A.M. "Black frame" photo with lens covered for 16 second exposure. .

A problem with such long exposures is that digital photo sensors fire off +/- random pixels over time. Astronomers use elaborate schemes to keep their cameras VERY COLD. Another way is to put your hand over the lens and take a "black frame" shot and then subtract it from your image using a program like the free MediaChance Black Frame Noise Reduction utility. This works because the hot pixels aren`t quite random, they will most likely be in the same place during a short period at the same temperature. (I have three hot pixels that show up in every photo.) The photo on the right is a 360x360 pixel section of my 16 second "black frame" exposure with the lens covered. Looks pretty busy for nothing!

I got another photo last week on September 10, 2003 showing the almost full Moon and the bright planet Mars rising above the trees at my home. They were even closer together two nights before, but lost in the fog. The exposure is F2 @ 1 second, short enough that noise is not a problem.


The Moon and Mars on September 10, 2003

This photo raises another stumper. Mars and the Moon are barely above the trees. Last winter, Saturn and Jupiter were much higher and easier to see. Why the difference?

Answer


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Copyright © 2003 by Marc Kummel / mkummel@rain.org