One Moon and another

Typical. The weather front that came in yesterday caused a cloudy night making it impossible to see the total lunar eclipse. The previous night started off badly but improved during the night. The undergraduates got some very nice images of the Orion Nebula (M42) and Saturn. Talking of Saturn, the Cassini-Huygens mission has been taking some nice shots of Titan - a moon of Saturn - while on a fly-by. The images show continent-like structures on the surface of the moon.

The images of Titan also contain doughnut shapes, which conspiracy theorists will probably claim are alien spaceships. They are actually caused by out-of-focus specks of dust in the camera and are imaginatively called dust doughnuts. The easy way to see that they are related to the camera, and not the object being imaged, by comparing two or three different view. The dust doughnuts don't move even though the camera is looking at a different object at a different time. They are usually removed by taking an image called a flat field. A flat field is essentially an image of something very boring and uniform. Usually this will be the inside of the telescope dome or a patch of evening sky before stars become visible. As Cassini is in space, I imagine a flat field image is a little harder to organise. With some knowledge of the camera optics it is even possible to work out where the dust is relative to the CCD chip (the bit of a digital camera that takes the picture).

Posted in astro blog by Stuart on Thursday 28th Oct 2004 (16:21 UTC) | Permalink
[an error occurred while processing this directive]
[an error occurred while processing this directive]