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ECLIPSE FAQ

A list of some of the most frequently asked questions about eclipses.




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SOLAR ECLIPSES

Q. What is a solar eclipse?

A. A solar eclipse occurs when the Moon passes directly between the Earth and the Sun and the Moon blocks the Sun for a viewer on Earth.


Q. What is a total solar eclipse?

A. During a total solar eclipse, the Moon lines up perfectly to fully obscure the Sun, resulting in "totality."


Q. What is a partial solar eclipse?

A. During a partial solar eclipse, the Moon and the Sun are not perfectly aligned and only part of the Sun is obscured by the Moon.


Q. What is an annular solar eclipse?

A. During an annular solar eclipse, the Moon and the Sun are perfectly aligned but the Moon is too far away from the Earth in its orbit to fully obscure the Sun.


Q. What is a hybrid solar eclipse?

A. A hybrid solar eclipse occurs when a solar eclipse morphs between a total eclipse and an annular eclipse along its path. Only about five percent of all solar eclipses are hybrid eclipses.


Q. What is totality?

A. Totality is the very brief period of time during a total solar eclipse when the Sun is 100 percent blocked by the Moon and only the soft wisps of the solar corona can be seen.


Q. What is the solar corona?

A. The solar corona is the outer part of the Sun's atmosphere. While the corona is usually hidden by the bright light of the Sun's surface, it becomes visible during a total solar eclipse when the surface of the Sun is completely blocked by the Moon.


Q. What is the "diamond ring" effect?

A. Lasting for only a few moments, the diamond ring effect occurs when just a single point of bright sunlight shines past the edge of the Moon shortly before totality during a total solar eclipse. This point of light, combined with the emergence of the solar corona around the edge of the Moon, creates what looks like a giant diamond ring in the sky when captured by eclipse photographers using proper photographic techniques and exposures. The diamond ring effect also occurs shortly after totality ends.


Q. What are "Baily's beads"?

A. Baily's beads are small individual points of light frequently observed in the moments immediately before totality during a total solar eclipse. Named for English astronomer Francis Baily who described them in 1836, the phenomenon is caused by the very last rays of sunlight streaming through lunar valleys along the edge of the Moon. Baily's beads are also seen immediately after totality ends and during annular solar eclipses as well.


Q. What is the "path of totality"?

A. The path of totality is the narrow track across the Earth along which the darkest part of the Moon's shadow, the umbra, travels during a total solar eclipse. On either side of the path of totality an eclipse is only partial.


Q. What is the "duration of totality"?

A. The duration of totality is the amount of time that the Sun is 100 percent blocked by the Moon for any specific point within the path of totality during a total solar eclipse.


Q. How long does a total solar eclipse last?

A. While the partial phases of a total solar eclipse can last for several hours, the total phase, or totality, usually lasts for only a few minutes. Every total solar eclipse has a maximum duration of totality, which can be any length of time up to the theoretical maximum duration for a total solar eclipse on Earth, about 7 minutes and 30 seconds. The actual duration of totality for any specific point within the path of totality depends on the location within the path of totality, with the longest durations along the centerline.


Q. Where can a total solar eclipse be seen from?

A. The total phase of a total solar eclipse, or totality, can be seen only from the narrow path of totality. Areas outside the path of totality will experience a partial solar eclipse only.


Q. Why is an annular solar eclipse sometimes called a "ring of fire" eclipse?

A. Since during an annular solar eclipse the Moon obscures all of the Sun except for the outer edge of the Sun's surface, this results in what looks like a ring of fire in the sky.


Q. How often do solar eclipses occur?

A. A solar eclipse occurs somewhere on Earth at least twice, and as many as five times, per year. A total solar eclipse occurs, on average, about once every 18 months.


Q. If the Moon orbits the Earth about once per month, why doesn't a solar eclipse occur every month?

A. Although the Moon orbits the Earth about once per month, a solar eclipse doesn't occur every month because the Moon's orbit is tilted five degrees to the Earth's orbit around the Sun. Therefore, a new Moon usually occurs when the Moon is above or below the plane of the Earth's orbit.


Q. How often does a total solar eclipse occur in the same place?

A. There is no universally accepted answer to this question, but the general consensus is that, on average, a total solar eclipse occurs in the same place on Earth only about once every 375 years, although the timeframe can also be a lot longer or a lot shorter.


Q. How much can the temperature drop during a total solar eclipse?

A. Although the temperature will usually drop about 10 degrees during a total solar eclipse, drops of as much as 20 degrees have been reported.


Q. What are "shadow bands"?

A. Shadow bands are rippling patterns of light and dark that are sometimes seen on the ground shortly before and after totality during a total solar eclipse. Although there is still some debate over what actually causes this visual phenomenon, the generally accepted hypothesis is that shadow bands are caused by turbulence in the Earth's atmosphere that refracts the light coming from the narrow solar crescent.


Q. If the Sun is so much larger than the Moon, how can the Moon completely block the Sun during a total solar eclipse?

A. Although the Sun is 400 times larger than the Moon, it's also 400 times farther away, making total solar eclipses possible due to the apparently identical sizes of the Sun and the Moon in the sky.


Q. Is it safe to view a solar eclipse?

A. It's perfectly safe to view a solar eclipse but only if you follow safe eclipse viewing procedures. Attempting to view a solar eclipse incorrectly can cause permanent eye damage or even blindness. You must use special eclipse safety glasses or viewers to view a partial eclipse, an annular eclipse, and the partial phases of a total eclipse. The only time it's safe to look at a total eclipse without proper eye protection is during the very brief period of totality when the Sun is 100 percent blocked by the Moon. (For more detailed information about how to view a solar eclipse safely, please see our Safety page.)


Q. What is the difference between a solar eclipse and a lunar eclipse?

A. A solar eclipse is the obscuration of the Sun by the Moon; a lunar eclipse is the obscuration of the Moon by the Earth. The name of the eclipse type (solar or lunar) refers to the body being obscured. A solar eclipse can only occur during a new Moon, when the Earth is on the opposite side of the Moon from the Sun; a lunar eclipse can only occur during a full Moon, when the Moon is on the opposite side of the Earth from the Sun.


Q. Where is the best place to view the 2024 total solar eclipse?

A. There is no single "best" place to view a total eclipse. Every observer needs to evaluate what's most important to them and then decide where their own personal "best" place is. Among others factors, travel distance, local attractions, weather prospects, and distance to the centerline should all be considered.


Q. How can I learn more about solar eclipses?

A. If you'd like to learn more about solar eclipses in general, or about the 2024 total solar eclipse in particular, Solar Eclipses 101 is a 60-minute on-demand program that covers solar eclipse basics and provides viewing tips for the 2024 eclipse.

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LUNAR ECLIPSES

Q. What is a lunar eclipse?

A. A lunar eclipse occurs when the Sun, the Earth, and the Moon are aligned and the Earth casts a shadow across the Moon that can be seen by a viewer on Earth.


Q. What is a total lunar eclipse?

A. During a total lunar eclipse, the Sun, the Earth, and the Moon line up perfectly and the Earth's shadow fully covers the Moon, resulting in "totality."


Q. What is a partial lunar eclipse?

A. During a partial lunar eclipse, the Sun, the Earth, and the Moon are not perfectly aligned and the Earth's shadow covers only part of the Moon.


Q. What is a penumbral lunar eclipse?

A. During a penumbral lunar eclipse, only the faint outer edge of the Earth's shadow falls on the Moon, resulting in a very subtle dimming of the lunar disc.


Q. Why is a total lunar eclipse sometimes called a "blood moon"?

A. A total lunar eclipse is sometimes called a blood moon because of the reddish tint exhibited by the Moon during totality.


Q. What causes the Moon to have a reddish tint during a total lunar eclipse?

A. Although the Earth blocks all direct sunlight from striking the Moon during a total lunar eclipse, a small amount of indirect light reaches the Moon after passing around the edge of the Earth. After Earth's atmosphere filters and refracts this light, scattering non-red wavelengths, it's reflected back from the Moon to the Earth with a reddish hue.


Q. How long does a total lunar eclipse last?

A. Unlike during a total solar eclipse, when totality is visible for just a few short minutes, the total phase of a total lunar eclipse can last for up to almost two hours.


Q. Where can a total lunar eclipse be seen from?

A. Unlike during a total solar eclipse, when totality is visible only from the narrow path of totality, the total phase of a total lunar eclipse can be seen by almost everyone on the nighttime side of the Earth.


Q. How often do lunar eclipses occur?

A. A lunar eclipse occurs somewhere on Earth at least twice, and as many as five times, per year. A total lunar eclipse occurs, on average, about once every 18 months.


Q. If the Moon orbits the Earth about once per month, why doesn't a lunar eclipse occur every month?

A. Although the Moon orbits the Earth about once per month, a lunar eclipse doesn't occur every month because the Moon's orbit is tilted five degrees to the Earth's orbit around the Sun. Therefore, a full Moon usually occurs when the Moon is above or below the plane of the Earth's orbit.


Q. Is it safe to view a lunar eclipse?

A. While a solar eclipse requires special eclipse safety glasses or viewers, a lunar eclipse can be viewed safely with just the naked eye.


Q. What is the difference between a solar eclipse and a lunar eclipse?

A. A solar eclipse is the obscuration of the Sun by the Moon; a lunar eclipse is the obscuration of the Moon by the Earth. The name of the eclipse type (solar or lunar) refers to the body being obscured. A solar eclipse can only occur during a new Moon, when the Earth is on the opposite side of the Moon from the Sun; a lunar eclipse can only occur during a full Moon, when the Moon is on the opposite side of the Earth from the Sun.

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TRANSITS

Q. What is a transit?

A. A transit occurs when a celestial body passes directly between a larger body and a viewer. On Earth, planetary transits occur when Mercury or Venus pass between the Sun and the Earth, appearing as tiny black dots traveling across the face of the Sun. In a way, a transit can be thought of as a "mini solar eclipse," although the sunlight blocked by the distant planet equals just a tiny fraction of that which is blocked when the Moon obscures the Sun during an actual solar eclipse.


Q. How long does a transit last?

A. A transit of Mercury or Venus can last for several hours.


Q. Where can a transit be seen from?

A. A transit of Mercury or Venus can be seen by almost everyone on the daytime side of the Earth.


Q. How often do transits occur?

A. A transit of Mercury or Venus is much rarer than a solar eclipse. A transit of Mercury only occurs about 13 or 14 times per century in either May or November. A transit of Venus is even rarer, with two transits occurring in June or December within eight years of each other, but with gaps of over 100 years in between pairs.


Q. Is it safe to view a transit?

A. As with solar eclipses, transits require that safe solar viewing procedures are followed. Attempting to view a transit incorrectly can cause permanent eye damage or even blindness. Because Mercury and Venus appear so small against the solar disc, binoculous or telescopes with special front-mounted (the Sun side) solar filters are used for safe viewing. (For more detailed information about safe solar viewing, please see our Safety page.)

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