The Moon Guide
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U. S. N. O.
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The phase of the Moon right now

Phase
 
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This is the place where we explain terms which you might not be familiar with.

15 x 80, 8 x 20 These are binocular specifications and simply refer to their magnification and size (said 'Eight by twenty' and so on). The first figure is the magnification while the second one is the size of the objective (the big lens at the front) in millimetres. So 8 x 20 binoculars have lenses just 20 mm across and are easy to hold, while 15 x 80s have giant lenses and really need some sort of additional support. Almost all types of binoculars have a use in astronomy and are often regarded as being a good way to begin observing before you get a telescope, or even in place of one.

50x, 200x etc These figures refer to magnifications of a telescope and are usually provided by changing the telescope eyepiece. Said 'Fifty times' and so on.

Earthshine is the faint light on the Moon's dark area seen when the Moon is a crescent, and sometimes even at first quarter. It's caused by light reflected from Earth. When the Moon is new as seen from Earth, Earth is full as seen from the Moon and the Moon is bathed in Earthlight.

refractor A type of telescope with a lens at the top end as distinct from a mirror at the bottom end, which is a reflector. In other words, the traditional type of telescope, and often used as a starter telescope where the main lens is 70 mm or so in diameter, as well as more advanced telescopes which have main lenses are 100 mm to 150 mm or more across.

Sun's selenographic colongitude A mouthful of a term which actually refers to the position of the shadow line (terminator) on the Moon's surface. It is 0º at first quarter, 90º at full Moon, 180º at last quarter and 270º at new Moon. 

UT Stands for Universal Time. Though there is a much more precise definition, for general purposes this is the same as Greenwich Mean Time – the time in the time zone of Greenwich, UK, which constitutes the zero point of the world's grid system of longitude. Bear in mind, however, that during the summer, the UK is not on Greewich Mean Time but is one hour ahead of this.


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Crescent Moon

Observing the Moon

Moon lighting

'Seas' and mountains

How much can you see?

Using binoculars and telescopes

Drawing the Moon

Getting to know the Moon

Three-day crescent Moon

Six-day crescent Moon

First-quarter Moon

Gibbous Moon

Interactive Moon map

 
spacerMaintained by SPA Webmaster: Last modified 8 November 2008
 
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