The impact diaries
The team
Ellen McCallie's diary about the challenge for the Impact programme, from the BBC/OU series Rough Science 4
Day One
Challenge: Measure the diameter of a crater on the moon. We can’t get to the moon - unlike Kathy, Iain and Kate, who are going to Meteor Crater in Arizona - so Jonathan and I are going to make a telescope out of mirrors from the trunk.
Strategy:
We've been given good mirrors - something we couldn’t make in three days.
Collect a lot of light - bright so we are able to see detail.
Increase magnification - big mirror and an eyepiece.
Secondary challenge: Make soft-light candles to work by at night while making measurements of the diameter of a crater on the moon.
Strategy:
Collect pine resin, make a wick out of sagebrush bark.
Discuss telescope and mount design with Jonathan. We decided there was no need to enclose the telescope because we are using it in the dark. Plus, having it open allows everyone to see exactly how the telescope works. The stability of the mount is crucially important because when we magnify stuff even the littlest shake makes a big difference. We want an accurate measurement of the diameter of a crater on the moon - no wiggle allowed.
Setting up the telescope: First, we found the focal length of the telescope. Then, using similar triangles, Jonathan and I figured out where to put the small (1 inch) mirror, which will divert the image to the eyepiece, where it will be magnified further. (Yes, we are using inches. Some areas of science just haven’t switched over yet.)
The 6 inch mirror has a focal length of 48 inches. Our 6 inch mirror is a concave mirror, a parabolic shape that collects light. Light travels in straight lines, hits the mirror and comes to a point—the focal point of the mirror.
We use strips of an old California car license plate to hold the small mirror in place. Because we are looking far, far away (the moon) and because light travels in straight lines from all points, it is okay to have the thin metal strips in front of the mirrors. They don’t block very much light and they are much better than putting one’s head in front of the mirror—which would make the telescope completely ineffective!
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Content last updated: 19/07/2006
