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


Crescent Moon with Earthshine
Crescent Moon and Venus
Observing the Moon There are few things in nature more beautiful than the sight of a darkening twilight sky adorned with an Earthshine- blue-tinted crescent Moon, surrounded by a sprinkling of stars and one or two bright planets nearby. When magnified through binoculars the crescent Moon becomes a gleaming sickle with a dented edge, and through a telescope our satellite is transformed into a spectacular alien landscape. Even small binoculars will show a wealth of lunar detail.

During the four centuries since the telescope was invented, watchers of the Moon have discovered that lunar observing is the most visually rewarding branch of amateur astronomy. The constantly changing vistas of the Moon’s surface are every bit as stimulating as the greatest artistic masterpieces. Lots can be learned about the Moon through careful observation, even using the unaided eye.

Following the Moon
The Moon’s orbit around the Earth is tilted by just 5 degrees to the ecliptic – the path followed by the Sun during the year – and the Moon slowly moves from west to east (right to left in the northern hemisphere), covering the distance of a little more than its own diameter each hour. The Moon therefore travels just over 13° each day – about the width of your outstretched hand. 

Phases of the Moon
The phases of the Moon, with new Moon
at right and full Moon at left

Because of the changing angle of lighting by the Sun, the Moon goes through a complete set of phases from new Moon, through full Moon and back again to new Moon in 29.5 days. This period is called a synodic month, or lunation. Because the Moon’s orbital plane is so close to the ecliptic, its monthly path among the stars is similar to that followed by the Sun during a whole year.

When the Moon is increasing in phase or illumination it is said to be waxing, and when it is decreasing in phase it is waning. The waxing half Moon is known as first quarter because at this point the Moon is a quarter of the way round its orbit, while the waning half moon is last quarter. The phases between the quarters and full Moon are known as gibbous phases.

The Moon’s visibility and its height above the horizon change according to its phase and the time of the year. Full Moon is always on the opposite side of the sky to the Sun, in the same region of sky where the Sun will be in six months’ time. From the UK, the Sun of the winter solstice is at its most southerly and climbs to its lowest point above the southern horizon. Around the same time, the mid winter full Moon rides very high in the early morning skies. At summer solstice the Sun reaches its highest point above the southern horizon, which means that the mid summer full Moon barely clears the southern horizon.

For UK-based observers, the range of intervals between successive Moonrises varies from a quarter of an hour up to as much an hour and a half because of the varying angle at which the ecliptic (and the Moon’s orbital plane nearby) intersects the horizon. Around the days of full Moon in autumn the ecliptic makes a very shallow angle with the eastern horizon, causing the Moon to rise just 15 to 20 minutes later each evening. 

Astronomers often refer to the age of the Moon in days. This means the number of days that have elapsed since new Moon. First quarter is about seven days, and full Moon is about 14 days.

Moon lighting >

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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 6 November 2008
International Year of AstronomySociety for Popular AstronomySociety for Popular Astronomy