Baily's beads
Encyclopedia
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
"grazes" by the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
during a solar eclipse
Solar eclipse
As seen from the Earth, a solar eclipse occurs when the Moon passes between the Sun and the Earth, and the Moon fully or partially blocks the Sun as viewed from a location on Earth. This can happen only during a new moon, when the Sun and the Moon are in conjunction as seen from Earth. At least...
, the rugged lunar limb
Lunar limb
The lunar limb is the edge of the visible surface of the Moon as viewed from Earth. Libration of the Moon, with its irregular surface, leads to small changes in its profile, and this complicates the task of precisely calculating eclipse times and durations...
topography allows beads of sunlight to shine through in some places, and not in others. This effect is called Baily's beads in honor of Francis Baily
Francis Baily
Francis Baily was an English astronomer, most famous for his observations of 'Baily's beads' during an eclipse of the Sun.-Life:Baily was born at Newbury in Berkshire in 1774...
who first provided an exact explanation of the phenomenon in 1836.
Lunar topography
Topography of the Moon
The topography of the Moon has been measured by the methods of laser altimetry and stereo image analysis, most recently from data obtained during the Clementine mission. The most visible topographic feature is the giant far side South Pole-Aitken basin, which possesses the lowest elevations of the...
has considerable relief
Terrain
Terrain, or land relief, is the vertical and horizontal dimension of land surface. When relief is described underwater, the term bathymetry is used...
because of the presence of mountains, crater
Impact crater
In the broadest sense, the term impact crater can be applied to any depression, natural or manmade, resulting from the high velocity impact of a projectile with a larger body...
s, valleys and other topographical features. The irregularities of the lunar limb profile (the "edge" of the Moon, as seen from a distance) are known accurately from observations of grazing occultation
Occultation
An occultation is an event that occurs when one object is hidden by another object that passes between it and the observer. The word is used in astronomy . It can also refer to any situation wherein an object in the foreground blocks from view an object in the background...
s of star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
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 umbra
Umbra
The umbra, penumbra and antumbra are the names given to three distinct parts of a shadow, created by any light source. For a point source only the umbra is cast.These names are most often used to refer to the shadows cast by celestial bodies....
, reaching 1–2 minutes.
The Baily's beads phenomenon is seen during the credit opening sequence of the NBC TV show Heroes
Heroes (TV series)
Heroes is an American science fiction television drama series created by Tim Kring that appeared on NBC for four seasons from September 25, 2006 through February 8, 2010. The series tells the stories of ordinary people who discover superhuman abilities, and how these abilities take effect in the...
.