During its brightest phase, at "full Moon", the Moon has an apparent magnitude of about −12.6. By comparison, the Sun has an apparent magnitude of −26.8. When the Moon is in a quarter phase, its brightness is not half of a full Moon, but only about a tenth. This is because the lunar surface is not a perfect Lambertian reflector. When the Moon is full the opposition effect makes it appear brighter, but away from full there are shadows projected onto the surface which diminish the amount of reflected light.
On average, the Moon covers an area of 0.21078 square degrees on the night sky.[74]
The Moon appears larger when close to the horizon. This is a purely psychological effect (see Moon illusion). It is actually about 1.5% smaller when the Moon is near the horizon than when it is high in the sky (because it is farther away by up to one Earth radius).
The Moon appears as a relatively bright object in the sky, in spite of its low albedo. The Moon is about the poorest reflector in the solar system and reflects only about 7% of the light incident upon it (about the same proportion as is reflected by a lump of coal). However, the Moon is not a Lambertian scatterer and reflects more light back towards the Sun (albedo of 12%) than in other directions because of the spherical glass beads in the moondust. This increases the brightness of a full Moon.[75] It also has the effect of making the edges of a full Moon seem about as bright as the centre. Besides this, color constancy in the visual system recalibrates the relations between the colours of an object and its surroundings, and since the surrounding sky is comparatively dark the sunlit Moon is perceived as a bright object.
The highest altitude of the Moon on a day varies and has nearly the same limits as the Sun. It also depends on the Earth season and lunar phase, with the full Moon being highest in winter. Moreover, the 18.6 year nodes cycle also has an influence, as when the ascending node of the lunar orbit is in the vernal equinox, the lunar declination can go as far as 28° each month (which happened most recently in 2006). This results that the Moon can go overhead on latitudes up to 28 degrees from the equator (e.g. Florida, Canary Islands or in the southern hemisphere Brisbane). Slightly more than 9 years later (next time in 2015) the declination reaches only 18° N or S each month. The orientation of the Moon's crescent also depends on the latitude of the observation site. Close to the equator, an observer can see a boat Moon.[76]
Like the Sun, the Moon can give rise to atmospheric effects, including a 22° halo ring, and the smaller coronal rings seen more often through thin clouds. For more information on how the Moon appears in Earth's sky, see lunar phase.
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