We never get to see a brightly illuminated, perfectly full moon. The phase defect is best seen when the Moon’s orbit carries if off the ecliptic circle (the Sun’s apparent “orbit” in the sky, over the course of a year) and we see a little around to the night side, near either the Moon’s north pole or its south pole. The Sun is almost fully illuminating the hemisphere facing Earth a telescope can show the slight “phase defect” around the “limb” (disk edge) of a full moon. The Moon is exactly 180 degrees opposite the Sun, as measured in celestial longitude, though its angular separation from the Sun may be less than 180 degrees because of its tilted orbit. A full moon occurs in a syzygy wherein the order of alignment in space is Sun-Earth-Moon. Scientists have used the brightness of earthshine to gauge the cloudiness of Earth’s dayside visible from the Moon.įull Moon. Most easily observed when the Moon is a relatively narrow crescent, sunlight reflecting from Earth’s day side is the earthshine illuminating the Moon’s night side. “Dark side of the Moon” could refer to the Moon’s night side, but this is not common usage.Įarthshine. “Far side of the Moon” or “lunar far side” are correct phrases to use. Dark Side of the Moon is not just an album by the English rock band Pink Floyd-it’s also an incorrect description used by some when referring to the hemisphere of the Moon invisible from Earth. This is a recently coined term for the new moon each month.ĭark side of the Moon. We view a crescent between new moon and first quarter (half moon) in the evening sky and between third quarter (also a half moon, facing the other direction) and new moon in the morning sky.ĭark Moon. This is the phase of the Moon when the Earth-facing hemisphere is illuminated over less than 50 percent of its area. The color ranges from bright orange to brick to the complete disappearance of the Moon in the sky (temporarily).Ĭrescent. The atmosphere acts like a lens and bends the rays far enough that Earth’s sunrises and sunsets all illuminate the Moon. When the Moon is inside Earth’s shadow, with the Sun completely blocked as seen everywhere on the lunar surface, the Sun’s rays bend as they go through Earth’s atmosphere. This is a recently coined term for a full moon during a total lunar eclipse. The equivalent point for Earth’s orbit around the Sun is called aphelion (ap-he-lee-un or af-he-lee-un).īlood Moon.
This is the most distant point (ap-) on an elliptical orbit around Earth (-gee).
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