Baily's beads

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Baily's beads

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Timeline

1836 Francis Baily, during an eclipse of the sun, observes the phenomenon named after him as Baily's beads.

Encyclopedia

As the moonMoon

The Moon is Earth's only natural satellite....
"grazes" by the SunFacts About Sun

|+ The Sun |+|-| colspan="2" align="center" | |-...
during a solar eclipseSolar eclipse

A solar eclipse occurs when the Moon passes between Earth and the Sun, thereby totally or partially obscuring Earth's view o...
, the rugged lunar topography allows beads of sunlight to shine through in some places, and not in others. This effect is called Baily's beads, in honour of Francis BailyFrancis Baily

Francis Baily, English astronomer, was born at Newbury, Berkshire....
, who first noted the phenomenon in 1836.

Lunar topographyTopography of the Moon

The topography of the Moon has been measured by the methods of laser altimetry and stereo image analysis, most recently from...
has considerable reliefTerrain

Terrain, or relief, is the third or vertical dimension of land surface....
because of the presence of mountainsList of mountains on the Moon

This is a list of mountains on the Moon: ...
, craterImpact crater

An impact crater is a circular or oval depression on a surface, usually referring to a planet, moon, asteroid, or other cel...
s, valleysList of valleys on the Moon

The Moon's surface is covered in many interesting features....
, etc. The irregularities of the lunar limb profile (the "edge" of the Moon, as seen from a distance) are known accurately from observations of grazing occultationOccultation

An occultation is an astronomical event that occurs when one celestial object is hidden by another celestial object that pas...
s of starStar

A star is a massive, compact body of plasma in outer space that is held together by its own gravity and, unlike a planet, is...
s. Astronomers thus have a fairly good idea which mountains and valleys will cause the beads to appear in advance of the eclipse. While Baily's beads are seen briefly for a few seconds at the center of the eclipse path, their duration is maximized near the edges of the path of the umbraUmbra

The umbra is the darkest part of a shadow....
, reaching 1–2 minutes.

Baily's beads

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