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24 February 2012

Ast. (P) #5 : Planet Saturn

So, earlier this morning I moved my telescope under the window in my dorm where Saturn appears to be bright and in the angle visible through the window. Windows open, telescope cover open and started to find that object.

Because my telescope is essentially Dobsonian mounted and no tracking motors are installed to the mount, so naturally tracking Saturn becomes a difficulty in high magnifications, this is because planets and other celestial objects will move in the sky due to the rotation of earth (The reason why sun rise and set).

# Explanation of the drift motion in high magnification. Skip this part if you are already familiar with this. #

The bigger the magnification ("zoom" of the object) we use to see the object, the faster the object appears to drift away from view if the telescope did not move to compensate earth's rotation. One might think the rotation of earth is slow, but think of it this way: a pilot is flying in a straight line due north from point A to point B and the distance between each other is far, say, 500 kilometers. Now instead of flying to point B as intended, the pilot accidentally changed the course of flight just one degree to the east. After flying 500 kilometers in the new course, he would realize the airplane is now about 8.7 kilometers off course.

Similarly, the magnification represents "how far we can zoom in" hence in bigger magnification, even slight changes in the angle of view will cause huge difference on where we are looking at in the sky (or planets moving away from view if we did not move the telescope according to the motion of the planets).

#Continue on post#

I used a cheap modified webcam (with lens removed) to take the photos directly from the focusser of the telescope, where the image will form on the detector without any lens - this is called prime focus imaging. As opposed to afocal imaging, this method will help in reducing light loss from the multiple lens system and also vignetting in afocal imaging.

After some really time consuming search on the planet Saturn (it's difficult to find the object when the image detector of the webcam is about the size of a few grains of coarse salt) I managed to find that planet. After some focusing to get a sharp image (which the motion of focusing actually moves the telescope so slightly it affects the location of the image on the webcam image detector, with the risk of relocating it!) finally allowed the telescope to stay at the spot where planet Saturn can be seen drifting across the webcam view through time.

So I took quite a few sets of photo each time I readjust the telescope to find Saturn. Out of 28 shots, I manage to find ONE with the best image quality. After little contrast adjustment and turning the picture black and white (the original coloured image has a purplish hue which is not Saturn's "true colour", this could due to the quality of the image detector) I finally manage to post this photo up!

In this photo, a few simple features can be seen. It is noted that the planet has a ring (obviously) and the gap between the ring and the planet sphere body can be clearly resolved. The shadow where the sphere castes on the ring can be seen on the right side of the ring and not sure if this is an image artifact or it could be two barely visible cloud bands of Saturn seen on the top hemisphere.

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