Wednesday, May 18, 2011

Measuring the Sun's Altitude with an Objective Lens

I tried a simple way to measure the Sun's altitude this afternoon by mounting the objective lens of a small telescope on a tripod. The 50mm lens and holder come from a Jason Star Search Telescope 100. It was held in place by a small Phillips head screw which is easy to remove. The shade on the end of telescope just slides off.

An image of the Sun was projected onto a 8 1/2 x 11 inch sheet of paper lying on the ground near the focal length of the lens. You can see the index card which was used to stop down the lens. By placing a watch in the image one can keep track of the time. The time on the watch needed resetting but this was just a test of the method. To find the correct time you can go the Official US Time page at NIST or use their widget on the sidebar to the right. Both clocks can be adjusted to display the time in US Time Zones or UTC.

The image seen above is a little blurred by internal reflections in the lens but changing the angle the lens helps. This method works better than with the lens on the telescope since it allows the image of the Sun to move freely across the screen as the time changes.

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