Astronomy for Beginners
Here’s where you’ll find observing guides, how-to articles and great astronomy hints and tips. Don’t forget to also check out our comprehensive astronomy dictionary.
'How To' Guides
Astronomy Dictionary
Exosphere
The upper part of an atmosphere where gas is very tenuous and rarefied. Earth’s exosphere lies about 500km above its surface. Mercury has no substantial atmosphere, but does have a very thin layer of gas extending around it that is essentially an exosphere
Ray (moon)
When a large meteoroid or asteroid impacts the Moon it forms a crater. In doing so it blasts vast amounts of material over the surface. This material then falls back on to the lunar surface, showing up as a bright ‘ray’ extending out from the centre of the crater.
