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The Sun is the star at the center of the Solar System.It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light and infrared radiation with 10% at ultraviolet energies.
Solar cycles are nearly periodic 11-year changes in the Sun's activity that are based on the number of sunspots present on the Sun's surface. The first solar cycle conventionally is said to have started in 1755. The source data are the revised International Sunspot Numbers (ISN v2.0), as available at SILSO. [1]
Sun path, sometimes also called day arc, refers to the daily (sunrise to sunset) and seasonal arc-like path that the Sun appears to follow across the sky as the Earth rotates and orbits the Sun. The Sun's path affects the length of daytime experienced and amount of daylight received along a certain latitude during a given season.
Sun's habitable zone moves outside of the Earth's orbit, possibly shifting onto Mars's orbit. [120] 7 billion years 2.4 billion years in the future The Milky Way and Andromeda Galaxy begin to collide. Slight chance the Solar System could be captured by Andromeda before the two galaxies fuse completely. [137] Post–main sequence
The Sun has a radiative core surrounded by a convective envelope, and at the boundary of these two is the tachocline. However, brown dwarfs lack radiative cores and tachoclines. Their structure consists of a solar-like convective envelope that exists from core to surface.
The core of the Sun is considered to extend from the center to about 0.2 of the solar radius (139,000 km; 86,000 mi). [1] It is the hottest part of the Sun and of the Solar System . It has a density of 150,000 kg/m 3 (150 g/cm 3 ) at the center, and a temperature of 15 million kelvins (15 million degrees Celsius; 27 million degrees Fahrenheit).
This will rise to 10 −6 M ☉ /year on the asymptotic giant branch, before peaking at a rate of 10 −5 to 10 −4 M ☉ /year as the Sun generates a planetary nebula. By the time the Sun becomes a degenerate white dwarf, it will have lost 46% of its starting mass. [15] The mass of the Sun has been decreasing since the time it formed.
In the spectral class label, G2 indicates its surface temperature, of approximately 5770 K ( the UAI will accept in 2014 5772 K) and V indicates that the Sun, like most stars, is a main-sequence star, and thus generates its energy via fusing hydrogen into helium. In its core, the Sun fuses about 620 million metric tons of hydrogen each second.