Is the Moon really larger when you see it on the horizon?
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Carrying out your exploration Carrying out your exploration


Carrying out your exploration
Now you're ready to put your prediction to the test, by taking images of the Moon and comparing their size at different altitudes above the horizon. Suggested telescope settings for imaging the Moon are listed below. Be sure to record your measurements carefully on the DATA PAGE below.
'Scope it out: Taking images of the Moon
When to take images: The Moon is near the horizon TWICE every day: once when it rises, and once when it sets. For this exploration, you can take images of the Moon EITHER shortly after it rises and then a few hours later OR shortly before it sets and a few hours before that.
When does the Moon rise (or set) at the telescope site you selected?
You can find out at the U.S. Naval Observatory Website:
Or go directly to their moonrise page at:
Make sure you use the right day (remember that midnight starts a new day). For the location, enter the telescope site you are using (either Boston, MA; Tucson, AZ; or Hilo, Hawaii).
IMPORTANT: Schedule your Moonrise observation for about 1 hour after the Moon actually rises. This will allow enough time for the Moon to rise above buildings at the site. The telescope will not take images that are too close to the horizon.
Selecting your target: Use the pull-down menu to select the Moon as a target.
Filter: Use the grey ("neutral density") filter to cut down on the Moon's bright reflected light..
Exposure time: Use a 0.5 second exposure or less.
Saving your image: Be certain to download the image to your computer as soon as it is ready. Remember, images are deleted from the Web server after a week. Download the image in GIF-format (just click and hold on the image with your mouse button, and select "Save this Image" or "Download this Image").
IMPORTANT: Be sure to label your images carefully so you are certain which image was taken at which time!
IMPORTANT: Be sure to download (or print) the Image Info file with each image as well. This tells you how high the Moon was above the horizon.
Printing your image: You can print your images directly from your browser. Or, after you have downloaded the images to your computer, you can open them in an image-viewing program and print them from there. You can invert your image so that the Moon is black and the background is white. This will save toner and may make it easier to measure your image.


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This document reflects the views only of the author, and the Commission cannot be held responsible for any use which may be made of the information contained therein.