Magnitude of eclipse

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An annular solar eclipse has a magnitude of less than 1.0 Annular Solar Eclipse May 10 2013 Northern Territory Australia.JPG
An annular solar eclipse has a magnitude of less than 1.0

The magnitude of eclipse is the fraction of the angular diameter of a celestial body being eclipsed. [1] This applies to all celestial eclipses. The magnitude of a partial or annular solar eclipse is always between 0.0 and 1.0, while the magnitude of a total solar eclipse is always greater than or equal to 1.0, and has a theoretically maximum value of around 1.12.

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This measure is strictly a ratio of diameters and should not be confused with the covered fraction of the apparent area (disk) of the eclipsed body. Neither should it be confused with the astronomical magnitude scale of apparent brightness.

Effect of the magnitude on a solar eclipse

Each icon shows the view from the centre of its black spot, representing the Moon (not to scale) Solar eclipse visualisation.svg
Each icon shows the view from the centre of its black spot, representing the Moon (not to scale)

The apparent sizes of the Moon and Sun are both approximately 0.5°, or 30', but both vary because the distance between Earth and Moon varies. (The distance between Earth and Sun also varies, but the effect is slight in comparison.)

In an annular solar eclipse, the magnitude of the eclipse is the ratio between the apparent angular diameters of the Moon and that of the Sun during the maximum eclipse, yielding a ratio less than 1.0. As the magnitude of eclipse is less than one, the disk of the Moon cannot completely cover the Sun. When the centers of the two disks are sufficiently aligned, a ring of sunlight remains visible around the Moon. This is called an annular eclipse, from Latin annulus, meaning "ring". [2]

For a total solar eclipse to happen, the ratio of the apparent diameters of the Moon and of the Sun must be 1.0 or more, and the three celestial bodies (Sun, Earth and Moon) must be aligned centrally enough. When that is the case, the Moon's disk covers the Sun's disk in the sky completely. The path of totality (i.e. of the travelling shadow of the Moon cutting off all direct sunlight from reaching the Earth's surface) is a relatively narrow strip, at most a few hundreds of kilometers across.

In a partial solar eclipse, the magnitude of the eclipse is the fraction of the Sun's diameter occulted by the Moon at the time of maximum eclipse. As seen from one location, the momentary eclipse magnitude varies, being exactly 0.0 at the start of the eclipse, rising to some maximum value, and then decreasing to 0.0 at the end of the eclipse. When one says "the magnitude of the eclipse" without further specification, one usually means the maximum value of the magnitude of the eclipse.

The eclipse magnitude varies not only between eclipses, but also by viewing location. An eclipse may be annular in one location and total in another. These mixed-type eclipses are called hybrid. [2]

Effect of the magnitude on a lunar eclipse

The effect on a lunar eclipse is quite similar, with a few differences. First, the eclipsed body is the Moon and the eclipsing 'body' is the Earth's shadow. Second, since the Earth's shadow at the Moon's distance always is considerably larger than the Moon, a lunar eclipse can never be annular but is always partial or total. Third, the Earth's shadow has two components: the dark umbra and the much brighter penumbra. A lunar eclipse will have two geometric magnitudes: the umbral magnitude and the penumbral magnitude. If the three bodies are not aligned enough, the Moon does not reach into the Earth's umbra - it may still pass through the Earth's penumbra though, and such an eclipse is called a penumbral eclipse.

See also

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<span class="mw-page-title-main">March 2007 lunar eclipse</span> Total lunar eclipse of 3 March 2007

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<span class="mw-page-title-main">February 2008 lunar eclipse</span> Total lunar eclipse of 20 February 2008

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A partial lunar eclipse took place on 7 September 2006, the second of two lunar eclipses in 2006. The tables below contain detailed predictions and additional information on the partial lunar eclipse of 7 September 2006.

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A penumbral lunar eclipse took place on Tuesday, January 20, 1981, the first of two lunar eclipses in 1981. In a rare total penumbral eclipse, the entire Moon was partially shaded by the Earth, and the shading across the Moon should have been quite visible at maximum eclipse. The penumbral phase lasted for 4 hours and 24 minutes in all, though for most of it, the eclipse was extremely difficult or impossible to see. The moon's apparent diameter was larger because the eclipse occurred 5.2 days after perigee.

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<span class="mw-page-title-main">July 1963 lunar eclipse</span> Partial lunar eclipse July 6, 1963

A partial lunar eclipse took place on Saturday, July 6, 1963 with an umbral eclipse magnitude of 0.70602. The Moon was strikingly shadowed in this deep partial eclipse which lasted 3 hours exactly, with 71% of the Moon in darkness at maximum. A partial lunar eclipse occurs when the Earth moves between the Sun and Moon but the three celestial bodies do not form a straight line in space. When that happens, a small part of the Moon's surface is covered by the darkest, central part of the Earth's shadow, called the umbra. The rest of the Moon is covered by the outer part of the Earth's shadow called the penumbra. It was the second of three lunar eclipses in 1963, the first was a penumbral lunar eclipse on January 9, 1963 and the third and last was on December 30, 1963.

<span class="mw-page-title-main">November 1955 lunar eclipse</span> Partial lunar eclipse November 29, 1955

A partial lunar eclipse took place on Tuesday, November 29, 1955 with an umbral eclipse magnitude of 0.11899. A partial lunar eclipse happens when the Earth moves between the Sun and the Full Moon, but they are not precisely aligned. Only part of the Moon's visible surface moves into the dark part of the Earth's shadow. A partial lunar eclipse occurs when the Earth moves between the Sun and Moon but the three celestial bodies do not form a straight line in space. When that happens, a small part of the Moon's surface is covered by the darkest, central part of the Earth's shadow, called the umbra. The rest of the Moon is covered by the outer part of the Earth's shadow called the penumbra. It was the second of two lunar eclipses in 1955, first being the penumbral lunar eclipse on June 5. It also occurred near perigee, making such event a supermoon.

<span class="mw-page-title-main">June 1955 lunar eclipse</span> Penumbral lunar eclipse June 5, 1955

A penumbral lunar eclipse took place at the Moon's ascending of the orbit on Sunday, June 5, 1955, with a penumbral eclipse magnitude of 0.62181 (62.181%). A penumbral lunar eclipse takes place when the Moon moves through the faint, outer part of Earth's shadow, the penumbra. This type of eclipse is not as dramatic as other types of lunar eclipses and is often mistaken for a regular Full Moon. The Moon shines because its surface reflects the Sun's rays. A lunar eclipse happens when the Earth comes between the Sun and the Moon and blocks some or all of the Sun's light from reaching the Moon. A penumbral lunar eclipse occurs when the Sun, Earth, and the Moon are imperfectly aligned. When this happens, the Earth blocks some of the Sun's light from directly reaching the Moon's surface and covers all or part of the Moon with the outer part of its shadow, also known as the penumbra. Since the penumbra is much fainter than the dark core of the Earth's shadow, the umbra, a penumbral eclipse of the Moon is often difficult to tell apart from a normal Full Moon. Occurring only 0.5 days after apogee, the moon's apparent diameter was 6.5% smaller than average.

<span class="mw-page-title-main">Total penumbral lunar eclipse</span> Total penumbral lunar eclipse

A total penumbral lunar eclipse is a lunar eclipse that occurs when the Moon becomes completely immersed in the penumbral cone of the Earth without touching the umbra.

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<span class="mw-page-title-main">Solar eclipse of December 14, 1955</span> 20th-century annular solar eclipse

An annular solar eclipse occurred on December 14, 1955. A solar eclipse occurs when the Moon passes between Earth and the Sun, thereby totally or partly obscuring the image of the Sun for a viewer on Earth. An annular solar eclipse occurs when the Moon's apparent diameter is smaller than the Sun's, blocking most of the Sun's light and causing the Sun to look like an annulus (ring). An annular eclipse appears as a partial eclipse over a region of the Earth thousands of kilometres wide.

<span class="mw-page-title-main">Solar eclipse of November 4, 2078</span> Future annular solar eclipse

An annular solar eclipse will occur on Friday, November 4, 2078. A solar eclipse occurs when the Moon passes between Earth and the Sun, thereby totally or partly obscuring the image of the Sun for a viewer on Earth. An annular solar eclipse occurs when the Moon's apparent diameter is smaller than the Sun's, blocking most of the Sun's light and causing the Sun to look like an annulus (ring). An annular eclipse appears as a partial eclipse over a region of the Earth thousands of kilometres wide. The path of annularity will cross Pacific Ocean, South America, and Atlantic Ocean. The tables below contain detailed predictions and additional information on the Annular Solar Eclipse of 4 November 2078.

References

  1. "Glossary of Solar Eclipse Terms". NASA . Retrieved 2009-07-27.
  2. 1 2 Erickson, Robbi (2008). "Happy Living Magazine - Solar eclipse viewing schedule and information". Happy Living Magazine. Retrieved 2009-07-27.