# Measuring the sizes of the moon crates

Last Edited By Krjb Donovan
Last Updated: Mar 11, 2014 07:56 PM GMT

## Question

Hello. I was going to do a project on the impact of the moon craters but my teacher suggested me to do it on the measuring the sizes of the moon craters. I researched the ways calculating the sizes but those were so complicated and i was so confused. Now I feel frustrated. What can i do? How can I measure the sizes of moon craters? Please help me.

Hi, QED. Quite easily done. The size of the moon is known. Its diameter is known. Unless the crater is very large, one can get an approximation by knowing at what angle its rims are facing you.

Case 1

Say a crater is directly opposite you on the moon's disk, and it appears perfectly circular, Then knowing that the moons disk represents say 2*1738.14=approx 3476 km. refer:- http://en.wikipedia.org/wiki/Moon

Then knowing that the width of the crater is a certain %age of the apparent width of the moon's disk, one can get a fairly accurate size (diameter) of the crater.

Case 2

A crater is located off center and the plane representing the rim of the crater is at an oblique angle to you. Then depending on the offset, the offset equals R*cosine (theta). The angle subtended by a line passing through the center of that crater radially from the moon's center. Rcos(theta)= the observed offset, from the center of the flattened disk of the moon. (in any direction). Then theta = cosinverse(Offset/R) where R is 1738 km. (approx) Once theta is known, the angle at which the crater plane is inclined to the plane of the disk image is 90-theta in degrees. Let alpha be 90-theta in degrees. then image of the crater is shortened to z where z/actual width = cos(90-theta) = sin(theta) or z (apparent width of crater = actual width * sin(theta). here you must measure apparent width of crater along a line bisecting the image of the crater, and running thru the center of the disk.

Converth the actual width to %age of width of disk and calculate size in km.

regards Jayen