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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.
Passive solar techniques include selecting materials with favorable thermal properties, designing spaces that naturally circulate air, and referencing [clarification needed] the position of a building to the Sun. Active solar technologies increase the supply of energy and are considered supply side technologies, while passive solar technologies ...
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).
Properties and parameters Artist's rendition of the Earth's plasma fountain , showing oxygen, helium, and hydrogen ions that gush into space from regions near the Earth's poles. The faint yellow area shown above the north pole represents gas lost from Earth into space; the green area is the aurora borealis , where plasma energy pours back into ...
The Sun is composed primarily of the chemical elements hydrogen and helium; they account for 74.9% and 23.8%, respectively, of the mass of the Sun in the photosphere.All heavier elements, colloquially called metals in stellar astronomy, account for less than 2% of the mass, with oxygen (roughly 1% of the Sun's mass), carbon (0.3%), neon (0.2%), and iron (0.2%) being the most abundant.
The age of the Sun cannot be measured directly; one way to estimate it is from the age of the oldest meteorites, and models of the evolution of the Solar System. [1] The composition in the photosphere of the modern-day Sun, by mass, is 74.9% hydrogen and 23.8% helium. [2]
The SoLEXS is an X-ray spectrometer designed to continuously measure the solar soft X-ray flux (1 keV-22 keV) from the Sun-Earth Lagrangian point L1. These measurements can be used to better understand the properties of the Sun's corona, in particular, why the temperature of the corona is so high.
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.