Why are East and West reversed in astrophotos?

[Mark Geary]

When you look at most ordinary maps of the earth, North is up, and East is to the right.  Right?  And West is to the left.  When you look at a map of the sky, however, and most professional astrophotos, the conventional directions are reversed.  With North up in an astrophoto or a star map, West is to the right, and East is to the left.  Why is that?

Here's a thought experiment to explain why that is:  imagine laying on your back in the grass in your backyard (or in a park or wherever) at night, with your head pointing North-wards, and your feet pointing South-wards.  From that position, which direction is West?  It's to your right, isn't it?  And East would be to the left, wouldn't it?

The reason for the reversal is that you're essentially reversing your direction of view...when you look at a map of the Earth, you're looking "down" on the surface which is depicted in the map.  When you look at an astrophoto, or a celestial map, you're looking "up" from the surface of the Earth.

Clear as mud?  :D  It's the best I can do, hope it works for you as an explanation.  It's a little bit of astronomy trivia, but it helps to understand astrophotos and star maps a little better.