This is a really simple one, and a very popular misconception. Try this on a night when a nearly full moon is close to the eastern horizon shortly after sunset. You can learn when the next Full Moon occurs by clicking on our AOAS "Calendar" link in the top toolbar of our home page, then choose the current month and open that month in your browser. Do this no sooner, nor later than, 2 days either side of the time listed for Full Moon in the calendar.

About the simplest and most accurate way to determine the moon's diameter is to roll up a piece of paper into a tube and tighten the tube until it is as close to the size of the moon as you can make it when looking through it. Next, use a little tape to keep it the same size and shape for checking the diameter again later. When the moon is overhead 4 or 5 hours later, check it again........does the moon look smaller than the diameter of your tube now?