Jump to content

Narrowband

How do they measure the size of a crater?


Recommended Posts

I suppose the question then is how we know the distance to the Moon. This can be measured using parallax: the principle can be demonstrated by holding a pencil in front of you and looking at it with one eye, alternating between left and right. You see the pencil apparently move in relation to the background. The amount that it "moves" depends on the distance between your eyes and the distance to the object. Two observers far apart on Earth can measure this sort of effect by timing an event such as an eclipse (when the Moon passes in front of the Sun) or occulation (when the Moon passes in front of a star). This was first realised by the ancient Greeks. In modern times the distance has also been measured directly by bouncing electromagnetic signals (radio, laser etc) from the Moon's surface.

Link to comment
Share on other sites

The modern methods, I think, involve redar and, more recently, lasers directed at a mirror left by the Apollo astrononauts. No doubt a more knowledgeable reply will follow.

On an UCLAN course we estimated the height of lunar mountains using trig and the shadows of the mountains.

Olly

Link to comment
Share on other sites

The modern methods, I think, involve redar and, more recently, lasers directed at a mirror left by the Apollo astrononauts.

Yes, but you don't need to know the distance to the Moon to the nearest millimetre to get a good estimate of crater sizes.

The best measures now come from images sent back by lunar mapping satellites rather than from ground based photos but the principle is the same. You know the distance (or can work it out by parallax), you know how big a feature appears to be in angular measures, and basic trigonometry fills in the missing numbers.

Link to comment
Share on other sites

Yes, but you don't need to know the distance to the Moon to the nearest millimetre to get a good estimate of crater sizes.

The best measures now come from images sent back by lunar mapping satellites rather than from ground based photos but the principle is the same. You know the distance (or can work it out by parallax), you know how big a feature appears to be in angular measures, and basic trigonometry fills in the missing numbers.

No, but I was replying to the question immediately before mine! I should have used the quote thngy. Sorry.

Olly

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.

  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.