Posts Tagged ‘moon’

Eclipse

The obscuring of one celestial body by another either by passing directly in front of it or by casting a shadow. Solar eclipses can be total (whole Sun is obscured), partial (part of the Sun is obscured) or annular (a complete ring of sunlight is seen). Lunar eclipses are either total or partial. Quite often, during a total lunar eclipse, the moon is seen to become a coppery colour due to light refracting through the Earth’s atmosphere.

Book: Africa and Madagascar Total Eclipse 2001 & 2002

Draconic Month

The time that passes between successive passes of the Moon through its ascending node. Its average value is 27.21222 days.

Appennines

One of the most noticeable mountain ranges on the Moon, next to Mare Imbrium (Sea of Showers).

The first of the Apollo missions to use the Lunar Rover, Apollo 15 landed close to the Appennines. The site was chosen as it was felt that it would be possible to sample rocks from deeper in the Moon’s crust than previos missions and also that the feature known as Hadley Rille, a structure resembling a lava tube such as those seen on Hawaii, could be explored.

The range itself is about 225 miles in length and rise to a height of about 14000 feet above the Mare Imbrium.

Albedo

Albedo of an astronomical body

A measure of how reflective a body is. Albedo is expressed as a percentage, the higher the percentage, the higher the albedo and therefore the more reflective the object is.

On the face of it, albedo is a straightforward thing, however, the albedo of a planet varies from place to place. Dark surfaces absorb more light than light surfaces. Rough surfaces scatter light in all directions and therfore reflect less back to the observer. Thus when talking about the albedo of an astronomical body, one generally means the average albedo.

Cloudy planets like the gas giants and Venus have high albedos because clods are good reflectors whilst the rocky planets have lower albedos.

The light reaching your eye from an object is reduced thr further it has to travel so the albedo at the edge of a planet is less than at the centre, assuming the same surface composition. Accurate measurements of albedo need to take this into account and so there are two types of albedo, spherical and geometrical. The latter assumes the planet, asteroid, moon or whatever is a uniform sphere whilst the latter compares the reflecting power of the object with that of a flat white disc of the same diameter and distance as the object.

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