Sun

Summary

Sun Sun symbol.svg
Sun white.jpg
Pictured in visible light with solar filter in 2013 with sunspots and limb darkening.
The Sun by the Atmospheric Imaging Assembly of NASA's Solar Dynamics Observatory - 20100819.jpg
False-color image taken in 2010 as seen in ultraviolet light (wavelength of 30.4 nm)
NamesSun, Sol /ˈsɒl/,[1] Sól, Helios /ˈhliəs/[2]
AdjectivesSolar /ˈslər/[3]
Observation data
Mean distance
from Earth
AU1.496×108 km[4]
8 min 19 s at light speed
Visual brightness (V)−26.74[5]
Absolute magnitude4.83[5]
Spectral classificationG2V[6]
MetallicityZ = 0.0122[7]
Angular size31.6–32.7 minutes of arc[8]
≈ 0.5 degrees
Orbital characteristics
Mean distance
from Milky Way core
≈ 2.7×1017 km
29,000 light-years
Galactic period(2.25–2.50)×108 yr
Velocity≈ 220 km/s (orbit around the center of the Milky Way)
≈ 20 km/s (relative to average velocity of other stars in stellar neighborhood)
≈ 370 km/s[9] (relative to the cosmic microwave background)
Physical characteristics
Equatorial radius695,700 km,[10]
696,342 km[11]
109 × Earth[12]
Equatorial circumference4.379×106 km[12]
109 × Earth[12]
Flattening9×10−6
Surface area6.09×1012 km2[12]
12,000 × Earth[12]
Volume1.41×1018 km3[12]
1,300,000 × Earth
Mass1.9885×1030 kg[5]
333,000 Earths[5]
Average density1.408 g/cm3[5][12][13]
0.255 × Earth[5][12]
Center density (modeled)162.2 g/cm3[5]
12.4 × Earth
Equatorial surface gravity274 m/s2[5]
28 × Earth[12]
Moment of inertia factor0.070[5] (estimate)
Escape velocity
(from the surface)
617.7 km/s[12]
55 × Earth[12]
TemperatureCenter (modeled): 1.57×107 K[5]
Photosphere (effective): 5,772 K[5]
Corona: ≈ 5×106 K
Luminosity (Lsol)3.828×1026 W[5]
≈ 3.75×1028 lm
≈ 98 lm/W efficacy
Color (B-V)0.63
Mean radiance (Isol)2.009×107 W·m−2·sr−1
Age≈ 4.6 billion years[14][15]
Rotation characteristics
Obliquity7.25°[5]
(to the ecliptic)
67.23°
(to the galactic plane)
Right ascension
of North pole[16]
286.13°
19 h 4 min 30 s
Declination
of North pole
+63.87°
63° 52' North
Sidereal rotation period
(at equator)
25.05 d[5]
(at 16° latitude)25.38 d[5]
25 d 9 h 7 min 12 s[16]
(at poles)34.4 d[5]
Rotation velocity
(at equator)
7.189×103 km/h[12]
Photospheric composition (by mass)
Hydrogen73.46%[17]
Helium24.85%
Oxygen0.77%
Carbon0.29%
Iron0.16%
Neon0.12%
Nitrogen0.09%
Silicon0.07%
Magnesium0.05%
Sulphur0.04%

The Sun is the star at the center of the Solar System. It is a nearly perfect sphere of hot plasma,[18][19] heated to incandescence by nuclear fusion reactions in its core, radiating the energy mainly as visible light and infrared radiation. It is by far the most important source of energy for life on Earth. Its diameter is about 1.39 million kilometres (864,000 miles), or 109 times that of Earth. Its mass is about 330,000 times that of Earth; it accounts for about 99.86% of the total mass of the Solar System.[20] Roughly three quarters of the Sun's mass consists of hydrogen (~73%); the rest is mostly helium (~25%), with much smaller quantities of heavier elements, including oxygen, carbon, neon and iron.[21]

The Sun is a G-type main-sequence star (G2V) based on its spectral class. As such, it is informally and not completely accurately referred to as a yellow dwarf (its light is closer to white than yellow). It formed approximately 4.6 billion[a][14][22] years ago from the gravitational collapse of matter within a region of a large molecular cloud. Most of this matter gathered in the center, whereas the rest flattened into an orbiting disk that became the Solar System. The central mass became so hot and dense that it eventually initiated nuclear fusion in its core. It is thought that almost all stars form by this process.

The Sun's core fuses about 600 million tons of hydrogen into helium every second, converting 4 million tons of matter into energy every second as a result. This energy, which can take betw