Lunar Eclipses
A lunar eclipse is a phenomenon that occurs when the Earth is between the Sun and the Moon, or Sun-Earth-Moon, and only occurs during a full moon. However, it does not always occur on the full moon each month.
This is because the ecliptic plane, the plane of the Moon’s orbit, is tilted about 5° from the ecliptic plane, the plane of the Sun’s orbit, making it less likely that the Sun, Earth, and Moon will be in a straight line.
There are two intersections of the ecliptic with the celestial sphere, and solar and lunar eclipses occur when the Sun is near these intersections. These are called eclipse seasons, and they occur twice a year. Eclipse seasons usually include lunar eclipses, but sometimes they don’t.
Solar eclipses occur more frequently than lunar eclipses, but lunar eclipses are observed more often because solar eclipses are visible from a very limited area of the Earth, whereas lunar eclipses are visible from anywhere on Earth where it is night.
Total and partial lunar eclipses
A total lunar eclipse occurs when all of the Moon is in the Earth’s bosom, and a partial lunar eclipse occurs when part of the Moon is in the Earth’s bosom. A penumbral lunar eclipse occurs when part of the Moon is in the Earth’s reflection. During a penumbral lunar eclipse, the brightness of the Moon does not decrease much, so it cannot be detected from Earth.
Progression of a total lunar eclipse
Every total lunar eclipse begins with a perigee, when the Moon enters Earth’s reflection. The moment the edge of the Moon enters the Earth’s bosom is called first contact. Over time, the Moon enters the Earth’s bosom more and more, until it is obscured by the shadow of the round Earth. Perigee is when the Moon is completely inside the Earth’s bosom.
A total lunar eclipse lasts about 1 hour and 40 minutes if the center of the moon passes through the center of Earth’s bosom. During a total lunar eclipse, light scattered by the Earth’s surrounding atmosphere shines on the lunar surface, giving the Moon a dark reddish color instead of being completely dark.
At perigee, when the Moon begins to leave the Earth’s celestial sphere, lunar light is visible on the eastern edge of the lunar surface, and at penumbral, when the Moon is completely out of the celestial sphere. During a lunar eclipse, the sun’s rays are blocked, causing the lunar surface to cool rapidly. The temperature difference is observed as infrared or microwave radiation, and the thermal conductivity of the lunar material can be measured.
What is a partial lunar eclipse?
A lunar eclipse is when the Moon enters the Earth’s shadow, causing part or all of the Moon to appear to disappear. The Earth’s shadow has two parts: the penumbra, where no sunlight is visible, and the annulus, where some sunlight is visible.
A partial lunar eclipse occurs when the Sun, Earth, and Moon don’t line up exactly in a straight line, but are slightly offset so that the Moon doesn’t fully enter the Earth’s umbra. A lunar eclipse occurs when the Sun, Earth, and Moon line up in a straight line, so the Moon is in its full phase. The lunar eclipse starts on the left side of the Moon, and the part of the Moon that is covered will be colored red.
Both total and partial lunar eclipses last relatively longer than solar eclipses because the Earth’s shadow is about seven times larger than the Moon’s. Lunar eclipses occur as the Moon passes through the Earth’s shadow from west to east, due to the Moon’s rotational motion.
Eclipses and lunar eclipses do not occur every month because the ecliptic and the ecliptic are tilted by about 5°. There are two intersections of the ecliptic and the ecliptic, and solar and lunar eclipses occur when the Sun is near those intersections.
Solar eclipses occur more frequently than lunar eclipses, but they are observed much more frequently because solar eclipses are visible from a very limited area of the Earth, while lunar eclipses are visible everywhere on Earth’s night side. A total lunar eclipse occurs when all of the moon is in the Earth’s celestial sphere, while a partial lunar eclipse occurs when only part of the moon is in the Earth’s celestial sphere.