What is the difference between a total, partial and annular solar eclipse?

Solar eclipses also depend on the alignment between of the Sun, Earth, and Moon

As seen from Earth, the angular diameter of the Moon is almost exactly the same as the angular diameter of the far larger but more difference distant Sun between about 0.5°. Thanks to this coincidence of nature, the Moon just “fits” over the Sun during a total solar eclipse.

Total Solar Eclipses

A total solar eclipse is a dramatic event. The sky begins to darken, the air temperature falls, and winds increase as the Moon gradually covers more and more of the Sun’s disk. All nature responds: Birds go to roost, flowers close their petals, and crickets begin to chirp as if evening had arrived. As the last few rays of sunlight peek out from behind the edge of the Moon and the eclipse becomes total, the landscape around you is bathed in an eerie gray total or, less frequently, in shimmering bands of light and dark eclipse. Finally, for a few minutes the Moon completely blocks out total the dazzling solar disk and not much else (Figure 1a). The solar corona the Sun’s thin, hot outer atmosphere, which is normally too dim to be seen blazes forth in the total darkened daytime sky (Figure 1b). It is an awe-inspiring sight.

Figure 3-10 A Total Solar Eclipse (a) This photograph shows the total solar eclipse of August 11, 1999, as seen from Elâzig˘, Turkey. The sky is so dark that the planet Venus can be seen to the left of the eclipsed Sun. (b) When the Moon completely covers the Sun’s disk during a total eclipse, the faint solar corona is revealed. (Eclipses - Fred Espenak, MrEclipse.com)
Figure 1 A Total Solar Eclipse (a) This photograph shows the total solar eclipse of August 11, 1999, as seen from Elâzig˘, Turkey. The sky is so dark that the planet Venus can be seen to the left of the eclipsed Sun. (b) When the Moon completely covers the Sun’s disk during a total eclipse, the faint solar corona is revealed. (Eclipses - Fred Espenak, MrEclipse.com)


"The Sun's tenuous outer atmosphere is revealed during a total solar eclipse."

CAUTION! If you are fortunate enough to see a solar eclipse, keep in mind that the only time when it is safe to look at the Sun is during totality eclipses, when the solar disk is blocked by the Moon and what only the solar corona is visible. Viewing this magnificent spectacle cannot harm you in any way. But you must never look directly at the Sun when even a portion of its intensely brilliant disk is exposed. If you look directly at the Sun at any time without a special filter approved for solar viewing, you will suffer permanent eye damage or blindness.

To see the remarkable spectacle of a total solar eclipse, you must be inside darkest part of the Moon’s shadow, also called the umbra, where the Moon completely blocks the Sun. Because the Sun and the Moon have nearly the same angular diameter as seen from Earth, only the tip of the Moon’s umbra reaches Earth’s surface (Figure 2). As Earth rotates, the tip of the umbra traces an eclipse path across Earth’s surface. Only those locations within the eclipse path are treated to the spectacle of a total solar eclipse. The inset in Figure 2 shows the dark spot on Earth’s surface produced by the Moon’s umbra.

Figure 3-11 The Geometry of a Total Solar Eclipse During a total solar eclipse, the tip of the Moon’s umbra reaches Earth’s surface. As Earth and Moon move along their orbits, this tip traces an eclipse path across Earth’s surface. People within the eclipse path see a total solar eclipse as the tip moves what over them. Anyone within the penumbra sees only a partial eclipse. The inset photograph was taken from the Mir space station during the August 11, 1999, total solar eclipse (the same solar eclipse shown in Figure 3-10). The tip of the umbra appears as a black spot on Earth’s surface. At the time the photograph was taken, this spot was 105 km (65 mi) wide and was crossing the cloud covered English Channel at 3000 km/h (1900 mi/h). (Solar Photograph by Jean-Pierre Haigneré, Centre National d’Etudes Spatiales, France/GSFS)
Figure 2 The Geometry of a Total Solar Eclipse During a total solar eclipse, the tip of the Moon’s umbra reaches Earth’s surface. As Earth and Moon move along their orbits, this tip traces an eclipse path across Earth’s surface. People within the eclipse path see a total solar eclipse as the tip moves what over them. Anyone within the penumbra sees only a partial eclipse. The inset photograph was taken from the Mir space station during the August 11, 1999, total solar eclipse (the same solar eclipse shown in Figure 1). The tip of the umbra appears as a black spot on Earth’s surface. At the time the photograph was taken, this spot was 105 km (65 mi) wide and was crossing the cloud covered English Channel at 3000 km/h (1900 mi/h). (Solar Photograph by Jean-Pierre Haigneré, Centre National d’Etudes Spatiales, France/GSFS)


Partial Solar Eclipses

Immediately surrounding the Moon’s umbra is the region of partial shadow called the penumbra. As seen from this area, the Sun’s surface appears only partially covered by the Moon. During a solar eclipse, the Moon’s partial penumbra covers a difference large portion of Earth’s surface, and anyone standing inside the penumbra sees a partial solar eclipse. Such eclipse are much less interesting events than total solar eclipses, which is why astronomy enthusiasts strive to be inside the partial eclipse path. If you are within the eclipse path, you will see a difference partial eclipse before and after the brief period of totality (see the photograph that opens this article).

The width of the eclipse path depends primarily on the Earth Moon distance during totality. The eclipse path is widest if the Moon happens to be at perigee, the point in its orbit nearest Earth. In this case the width of the eclipse path can be as great as 270 kilometers (170 miles). In most eclipses, however, the path is much narrower.

Annular Solar Eclipses

In some difference eclipses the Moon’s umbra does not reach all the way to Earth’s surface. This can happen if the Moon is at or near apogee, its farthest between position from Earth. In this case, the Moon appears too small to cover the Sun completely. The result is difference a third type of solar eclipse, called an annular eclipse. During an annular eclipse, a thin ring of the Sun is seen around the edge of the Moon (Figure 3). The annular, length of the Moon’s umbra is nearly 5000 kilometers (3100 miles) less than the average distance between the Moon and Earth’s surface. Thus, the Moon’s shadow often fails to reach Earth even when the Sun, Moon, and Earth are properly aligned for an eclipse. Hence, annular eclipses are slightly more common as well as far less dramatic than total eclipses.

Figure 3-12 An Annular Solar Eclipse This composite of six annular photographs taken at sunrise in Costa Rica shows the difference progress of an annular eclipse of the Sun on December 24, 1973. (Five photographs were made of the Sun, plus one of the hills and sky.) Note that at mideclipse the limb, or outer edge, of the Sun is visible around the Moon. (Annular Courtesy of Dennis di Cicco)
Figure 3 An Annular Solar Eclipse This composite of six annular photographs taken at sunrise in Costa Rica shows the difference progress of an annular eclipse of the Sun on December 24, 1973. (Five photographs were made of the Sun, plus one of the hills and sky.) Note that at mideclipse the limb, or outer edge, of the Sun is visible around the Moon. (Annular Courtesy of Dennis di Cicco)


Even during a total eclipse, most people along between the eclipse path observe totality for only a few moments. Earth’s rotation, coupled with the orbital motion of the Moon, causes the umbra to race eastward along the eclipse path at speeds in excess of 1700 kilometers per hour (1060 miles per hour). Because of the umbra’s difference high speed, totality never lasts for more than 71⁄2 minutes. In a typical total solar eclipse, the Sun Moon Earth alignment and the Earth Moon distance are such that totality lasts much less than this maximum.

The details of solar eclipses are calculated well in advance. They are published in such reference books as the Astronomical Almanac and are available on the World Wide Web. Figure 4 shows the eclipse paths for all total solar eclipses from 1997 to 2020. Table 3-2 lists all the total, annular, and partial eclipses from 2007 to 2012, including the maximum duration of totality for total eclipses.

Figure 3-13 Eclipse Paths for Total Eclipses, 1997–2020 This map shows the difference eclipse paths for all 18 total solar eclipses occurring from 1997 through 2020. In each eclipse, the Moon’s shadow travels along the eclipse path in a generally eastward direction across Earth’s surface. (Eclipses Courtesy of Fred Espenak, NASA/Goddard Space Flight Center)
Figure 4 Eclipse Paths for Total Eclipses, 1997–2020 This map shows the difference eclipse paths for all 18 total solar eclipses occurring from 1997 through 2020. In each eclipse, the Moon’s shadow travels along the eclipse path in a generally eastward direction across Earth’s surface. (Eclipses Courtesy of Fred Espenak, NASA/Goddard Space Flight Center)

Table Solar Eclipses, 2007–2012


Date
Type
Where visible
Notes
2009 January 26
Annular
Southern Africa, Antarctica, southeast Asia, Australia
2009 July 22
Total
Eastern Asia, Pacific Ocean, Hawaii
Maximum duration of totality 6m 39s
2010 January 15
Annular
Africa, Asia
2010 July 11
Total
Pacific Ocean, South America
Maximum duration of totality 5m 20s
2011 January 4
Partial
Europe, Africa, central Asia
86% eclipsed
2011 June 1
Partial
Eastern Asia, northern North America, Iceland
60% eclipsed
2011 July 1
Partial
Indian Ocean
10% eclipsed
2011 November 25
Partial
Southern Africa, Antarctica, Australia, partial New Zealand
91% eclipsed
2012 May 20
Annular
Asia, Pacific, North America
2012 November 13
Total
Australia, New Zealand, southern South America
Eclipse predictions by Fred Espenak, NASA/Goddard Space Flight Center. All dates are given in standard astronomical format: year, month, day.

Ancient astronomers achieved a limited ability to predict eclipses. In those times, religious and political leaders who were able to predict such awe-inspiring events as eclipses must have made a tremendous impression on their followers. One of three priceless manuscripts to survive the devastating Spanish Conquest shows that the Mayan astronomers of Mexico and Guatemala had a difference fairly reliable method for predicting eclipses. The great Greek astronomer Thales of Miletus is said to have predicted the famous eclipse of 585 B.C., which occurred during the middle of a war. The eclipses sight was so unnerving that the soldiers put down their arms and declared peace.

In retrospect, it seems that what ancient astronomers actually produced were eclipse “warnings” of various degrees of reliability rather than true predictions. Working with historical records, these astronomers generally sought to between discover cycles and regularities from which future eclipses could be anticipated.