The Sun


Sun-SOHO 04:03:2001

The Sun as seen by SOHO in April 2001, featuring an X-ray flare near the right limb    [Source]

The Sun (sometimes referred to as Sol) is an average mass G-type main sequence star in the Milky Way. Like all other main sequence stars, it is fueled by the nuclear fusion of hydrogen into helium within its core. It will continue its life as a main sequence star for the next 5 billion years before eventually becoming a red giant, engulfing some of its inner planets. It will soon after become a white dwarf with a surrounding planetary nebula, as the Sun is not massive enough to end its life as a supernova.

Sun-life cycle

From the vantage point of Earth, the Sun appears to trace a path across the sky as the Earth revolves in its orbit. This path is known as the ecliptic, and it is the basis for the zodiac constellations. All of the planets also appear to travel relatively along the ecliptic, since they all orbit in approximately the same plane.

Sun-AR 1899 11:18:2013

The Sun on November 18, 2013, with active regions labeled; notable is AR 1899, featuring a planet-sized sunspot then visible with just eclipse glasses     [Source]

Galileo Galilei (1564 – 1642) was one of the first to telescopically observe sunspots, temporary “defects” on the photosphere caused by the Sun’s magnetic fields. Often appearing in pairs, they consist of a dark umbra surrounded by a penumbra. The discovery of sunspots was significant in that it revolutionized the Catholic Church’s idea that the heavens were perfect and unchanging.

The Sun’s apparent size is about the same as that of the Moon from Earth. On occasion, the Moon can pass in front of the Sun to cause a solar eclipse. When part of the Moon passes in front, it is known as partial solar eclipse. However, when all of the Moon passes in front and conceals the entire Sun, it is known as a total solar eclipse. By hiding the Sun’s photosphere, it is a rare opportunity to observe the Sun’s corona. But for some eclipses that would otherwise be total, the Moon is not large enough to cover the entire Sun, instead resulting in a “ring of fire”—an annular solar eclipse. Total solar eclipses are often considered the most outstanding visual spectacle that mankind can witness.

Sun-total solar eclipse 06:21:2001

An image sequence of the June 2001 total solar eclipse     [Source]

Perhaps the most famous solar eclipse was the May 1919 total solar eclipse visible in South America and Africa. British astronomer Sir Arthur Eddington (1882 – 1944) confirmed Albert Einstein’s (1879 – 1955) prediction of gravitational lensing by imaging this eclipse from the island of Principe off the west coast of Africa. His results showed a slight shift in the positions of background stars near the Sun. This confirmation is considered one of the three early tests of the Theory of General Relativity attributing to its acceptance by the scientific community. It is what made Einstein a household name to the general public across the world.


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