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- al-Kāshī
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- Georg von Peuerbach
Eclipse
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What is an eclipse in astronomy?
In astronomy, an eclipse occurs when one celestial body obstructs the light from another, creating a shadow. From Earth, a solar eclipse happens when the Moon passes between the Sun and Earth, blocking the Sun's light. A lunar eclipse occurs when the Earth passes between the Sun and Moon, casting a shadow on the Moon.
Solar eclipses can be total, where the Sun is completely covered, or annular, where a ring of sunlight remains visible. Lunar eclipses can be partial, where only part of the Moon is in Earth's shadow, or total, where the entire Moon is in shadow, often appearing red due to refracted sunlight.
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What are the main types of eclipses?
Eclipses occur when an astronomical body blocks light from another. The two main types are solar eclipses and lunar eclipses.
Solar Eclipse
Occurs when the Moon passes between the Sun and Earth, blocking the Sun's light. Types of solar eclipses are:- Partial The Sun is only partly covered by the Moon.
- Total The Sun is completely covered by the Moon.
- Annular The Moon doesn't completely cover the Sun, leaving a visible outer ring.
Lunar Eclipse
Occurs when the Earth passes between the Sun and Moon, casting a shadow on the Moon. Types of lunar eclipses are:- Penumbral The Moon passes through the penumbra (outer part of Earth’s shadow), causing a slight dimming.
- Partial Part of the Moon passes through the umbra (central part of Earth’s shadow), darkening part of the Moon.
- Total The entire Moon passes through the umbra, often giving it a reddish color.
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How does a solar eclipse occur?
A solar eclipse happens when the Moon passes between the Sun and Earth, blocking some or all of the Sun's light from reaching Earth.
The Moon's shadow has two parts: the umbra, where direct sunlight is completely blocked, causing a total solar eclipse, and the penumbra, where sunlight is only partially blocked, resulting in a partial solar eclipse.
During a total solar eclipse, the Moon completely covers the Sun. In an annular solar eclipse, the Moon appears smaller than the Sun, leaving a visible ring of sunlight. Observers within the umbra experience a total eclipse, while those in the penumbra see a partial eclipse.
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How does a lunar eclipse happen?
A lunar eclipse occurs when the Earth passes between the Sun and the Moon, casting a shadow on the Moon. This can only happen at the time of the full moon, when the Moon is on the opposite side of the Earth from the Sun.
The eclipse begins when the Moon enters the penumbra, the outer part of Earth’s shadow, causing a slight dimming. As the Moon moves further into the umbra, the central and darkest part of Earth's shadow, a partial eclipse occurs. When the entire Moon is within the umbra, the eclipse is total and the Moon often appears reddish due to the refraction of sunlight through Earth's atmosphere. A lunar eclipse is visible from anywhere on Earth where the Moon is above the horizon.
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Why don’t we see eclipses every month?
Eclipses don't occur every month because the Moon's orbit is inclined about 5° to Earth's orbit around the Sun, known as the ecliptic. Therefore, the Sun, Earth, and Moon are not in a straight line at most new and full moons.
Solar eclipses happen when the Moon passes between the Earth and Sun, while lunar eclipses occur when the Earth passes between the Sun and Moon. Solar eclipses may be total, partial, or annular, depending on the distances between the three bodies. Lunar eclipses can be total, partial, or penumbral.
Solar eclipses happen two to five times a year. Lunar eclipses happen about once per year at any given location.
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How have eclipses been important for scientific discoveries?
Eclipses have played a significant role in advancing scientific knowledge. During a total solar eclipse, the Sun's corona is visible, allowing astronomers to study its details.
Notably, observations made during the eclipse of May 29, 1919, provided experimental support for Einstein's theory of general relativity by measuring the deflection of starlight as it passed near the Sun. Also, spectra of the solar corona obtained at a total eclipse led to the discovery that the Sun’s corona is exceedingly hot.
Lunar eclipses offer insights into the cooling and composition of the lunar surface. Ancient civilizations in China and the Middle East also used eclipses to record data and predict future events, contributing to our understanding of the Earth-Moon system.
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Eclipse, in astronomy, complete or partial obscuring of a celestial body by another. An eclipse occurs when three celestial objects become aligned.
From the perspective of a person on Earth, the Sun is eclipsed when the Moon comes between it and Earth, and the Moon is eclipsed when it moves into the shadow of Earth cast by the Sun. Eclipses of natural satellites (moons) or of spacecraft orbiting or flying past a planet occur as the bodies move into the planet’s shadow. The two component stars of an eclipsing binary star move around each other in such a way that their orbital plane passes through or very near Earth, and each star periodically eclipses the other as seen from Earth.
In 2026–28 there will be 14 eclipses. Learn all about them in our list.
When the apparent size of the eclipsed body is much smaller than that of the eclipsing body, the phenomenon is known as an occultation. Examples are the disappearance of a star, nebula, or planet behind the Moon or the vanishing of a natural satellite or spacecraft behind some body of the solar system.
A transit occurs when, as viewed from Earth or another point in space, a relatively small body passes across the disk of a larger body, usually the Sun or a planet, eclipsing only a very small area. Mercury and Venus, for example, periodically transit the Sun, and a natural satellite may transit its planet. Extrasolar planets (e.g., HD 209458b) have been discovered when they perform a transit of their stars.
Phenomena observed during eclipses
Lunar eclipse phenomena
The Moon, when full, may enter the shadow of Earth. The motion of the Moon around Earth is from west to east. For an observer facing south, the shadowing of the Moon begins at its left edge (if the Moon were north of the observer, as, for example, in parts of the Southern Hemisphere, the opposite would be true).
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If the eclipse is a total one and circumstances are favourable, the Moon will pass through the umbra, the darkest part of the shadow, in about two hours. During this time the Moon is usually not completely dark. A part of the sunlight, especially the redder light, penetrates Earth’s atmosphere, is refracted into the shadow cone, and reaches the Moon. Meteorological conditions on Earth strongly affect the amount and colour of light that can penetrate the atmosphere. Generally, the totally eclipsed Moon is clearly visible and has a reddish brown, coppery colour, but the brightness varies strongly from one eclipse to another.
Before the Moon enters the umbra and after it leaves the umbra, it must pass through the penumbra, or partial shadow. When the border between umbra and penumbra is visible on the Moon, the border is seen to be part of a circle, the projection of the circumference of Earth. This is a direct proof of the spherical shape of Earth, a discovery made by the ancient Greeks. Because of Earth’s atmosphere, the edge of the umbra is rather diffuse, and the times of contact between the Moon and the umbra cannot be observed accurately.
During the eclipse the surface of the Moon cools at a rate dependent on the constitution of the lunar soil, which is not everywhere the same. Many spots on the Moon sometimes remain brighter than their surroundings during totality—particularly in their output of infrared radiation—possibly because their heat conductivity is less, but the cause is not fully understood.
An eclipse of the Moon can be seen under similar conditions at all places on Earth where the Moon is above the horizon.