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Saturday, February 27, 2010


This blob is Mars

This blob is Mars. It's a blob because we are having lovely warm weather here in Adelaide (no point in clicking to embiggen, it doesn't get any better).

You would think that warm weather would be ideal for astronomy, as you don't have to dress up in multiple layers like the Michelin Man or run the risk of losing favourite extremities to frost bite. On the other hand, the warm air and ground means atmospheric turbulence, and to an astronomer, the atmosphere is the enemy.

Warm air rises from the warm ground, cooler air percolates down, and all this happens chaotically, rather than smoothly. These bubbles of warm and cold air act as lenses magnifying or reducing the image of the Moon or planet, unfortunately, they do it chaotically, and ever changeingly, so the image of the planet (and its focus) jiggles around like a diseased chicken (see the video of the Moon down below to see what I mean). Now, there are ways to get around this, using a video-type camera taking tens of frames in one exposure, you can use a program like registax to sift through the frames, eliminate the real stinkers and average out the rest to give an acceptable image.

But when things are really bad nothing will help. The bubbles twinkle faster than the shutter speed of your video camera (in my case a Phillips ToUCam web cam) and the image is hopelessly blurred beyond all the help of fast Fourier transforms or wavelet analysis. It is then that sketching comes in handy, your eye has better time resolution than any web cam, and you can catch the fleeting moments when the planet is in focus and set them down.

Mars changes in size over the month (click to embiggen).

Where in the sky the planet is matters as well. From Adelaide, Mars is barely 30 degrees (5 handspans) above the horizon. Mars is still close to all the murk that hangs around close to the horizon. And because of line of sight effects, the light from Mars has to travel through a whole lot more atmosphere (with a whole lot more chance to get bumped and bubbled around. That's why winter oppositions when the ecliptic is high in the sky and the air is cold and still, is the best for observing planets.

Twinkle, twinkle little star? It looks great in the sky, but if the stars near the planet you want to observe are twinkling furiously, forget getting the telescope out, the planet will be jiggling like demented jelly in your eyepieces.

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