Éclipse
An eclipse is an astronomical phenomenon in which a celestial body passes into theshadow of another, or obscures a third body from an observer’s perspective. On Earth, two types of eclipses have fascinated people sinceAntiquity: solar eclipses, when the Moon passes in front of the Sun, and lunar eclipses, when the Moon enters the Earth’s shadow.
The solar eclipse
A solar eclipse occurs during a new moon, when the Moon passes precisely between the Earth and the Sun. There are three types. The total eclipse is one of nature’s most breathtaking spectacles: the Moon completely blocks the Sun, revealing the solar corona for a few minutes in broad daylight. A partial eclipse blocks only a fraction of the Sun’s disk. An annular eclipse occurs when the Moon is too far from Earth to completely cover the Sun—a bright ring remains visible.
The lunar eclipse
A lunar eclipse occurs during a full moon, when the Moon enters the shadow cone cast by the Earth. During a total lunar eclipse, the Moon takes on a coppery-red hue— this is known as a blood moon—due to sunlight filtered and refracted by Earth’s atmosphere. Lunar eclipses generally last longer than solar eclipses (up to several hours) and are visible from across the entire night hemisphere.
Why don’t eclipses occur every month?
The Moon’s orbit around the Earth is tilted by about 5 degrees relative to the plane of the Earth’s orbit. Most of the time, the Moon passes above or below the Earth-Sun line. Eclipses occur only when a new or full Moon coincides with the Moon’s passage through the Earth’s orbital plane— at the orbital nodes. This happens 4 to 7 times a year in total.
Significance in Astronomy
Total solar eclipses have historically allowed scientists to study the solar corona, which is normally invisible due to the glare of the Sun’s disk. It was during an eclipse in 1919 that the deflection of starlight by the Sun was measured, confirming Einstein’s general theory of relativity. Today, onboard coronagraphs enable these observations to be made continuously from space.
Did you know?
The coincidence that makes total solar eclipses possible is extraordinary: the Sun is about 400 times larger than the Moon, but also about 400 times farther away, which makes them appear to be almost the same size in the sky. This coincidence will not last forever: the Moon is moving away from Earth at a rate of 3.8 cm per year, and in about 600 million years, total eclipses will have disappeared.
Frequently Asked Questions
Is it dangerous to watch a solar eclipse?
Yes, except during the total phase of a total eclipse. Looking at the Sun without protection, even when it is partially obscured, can cause irreversible eye damage. You must use special ISO 12312-2-certified eclipse glasses or an indirect projector.
How often do total solar eclipses occur?
A total solar eclipse occurs on average every 18 months somewhere on Earth, but for a given location, the average interval is about 360 years. The next total solar eclipse visible in metropolitan France will be on September 3, 2081.
Why does the Moon turn red during a lunar eclipse?
Earth’s atmosphere filters sunlight and primarily scatters the blue light (which is why the sky is blue). Red light passes through the atmosphere and is refracted into theEarth’s shadow, illuminating the Moon with a coppery red hue—like all of Earth’s sunsets seen from the Moon at the same time.