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Sun

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The Sun Sun symbol.svg
The Sun by the Atmospheric Imaging Assembly of NASA's Solar Dynamics Observatory - 20100819.jpg
Observation data
Average distance
from Earth
1.496×108 km
8 min 19 s at light speed
Visual brightness (V) −26.74[1]
True brightness 4.83[1]
Angular size 31.6–32.7′[2]
Adjective Solar
Orbit and rotation
Average distance
from Milky Way center
≈ 2.7×1017 km
27,200 light-years
Velocity ≈ 220 km/s (orbit around the center of the Milky Way)
≈ 20 km/s (relative to average velocity of other stars nearby)
≈ 370 km/s[3] (relative to the cosmic microwave background)
Obliquity 7.25°[1]
(to the ecliptic)
67.23°
(to the galactic plane)
Rotation velocity 7.189×103 km/h[4]
Physical characteristics
Equatorial radius 696,342±65 km[5]
109 × Earth[4]
Equatorial circumference 4.379×106 km[4]
109 × Earth[4]
Flattening 9×10−6
Surface area 6.09×1012 km2[4]
12,000 × Earth[4]
Volume 1.41×1018 km3[4]
1,300,000 × Earth
Mass (1.98855±0.00025)×1030 kg[1]
333,000 × Earth[1]
Average density 1.408 g/cm3[1][4][6]
0.255 × Earth[1][4]
Surface gravity 274.0 m/s2[1]
27.94 g
27,542.29 cgs
28 × Earth[4]
Escape velocity
(from the surface)
617.7 km/s[4]
55 × Earth[4]
Temperature Center: 1.57×107 K[1]
Photosphere: 5,778 K[1]
Corona: ≈ 5×106 K
Luminosity (Lsol) 3.846×1026 W[1]
Age ≈4.6 billion years[7][8]
The Sun as it is seen from Earth

The Sun is the star at the center of the Solar System. It is seen in the sky and gives light to the Earth. When the Sun is in the sky, it is day. When the Sun is not in the sky, it is night. The planets, including Earth, orbit around it.

The Sun gives off energy as electromagnetic radiation. That includes light, infra-red energy (heat), ultraviolet light and radio waves. It also gives off a stream of particles, which reaches Earth as "solar wind". The source of all this energy is the reaction in the star which turns hydrogen into helium and makes huge amounts of energy.

The Sun is a star like many others in our Milky Way galaxy. It has existed for a little over 4.5 billion years, and is going to continue for at least as long. The Sun is about a hundred times as wide as the Earth. It has a mass of 1.9891×1030 kg, which is 333,000 times the mass of the Earth. The Earth can also fit inside the Sun 1.3 million times.

Physics of the Sun[change | change source]

Origin[change | change source]

Scientists think that the Sun started from a very large cloud of dust and small bits of ice about 4.567 billion years ago.[9]

At the center of that huge cloud, gravity caused the material to build up into a ball. Once this got big enough, the huge pressure inside started a fusion reaction. The energy this released caused that ball to heat and shine.

The energy radiated from the Sun pushed away the rest of the cloud from itself, and the planets formed from the rest of this cloud.

How it works[change | change source]

At its very center, hydrogen atoms collide together at great temperature and pressure so that they fuse to form atoms of helium. This process is called nuclear fusion. This fusion changes a very small part of the hydrogen atoms into a large amount of energy. This energy then travels from the core to the surface of the Sun. The Sun's surface is called the photosphere and is where it shines the energy into space. Energy can take thousands of years to reach the Sun's surface because the Sun is so huge and most of the way the energy is passed from atom to atom.

The sun can also be used as a source of energy.

Visible features[change | change source]

Since the Sun is all gas, surface features come and go. If the Sun is viewed through a special solar telescope, dark areas called sunspots can be seen. These areas are caused by the Sun's magnetic field. The sunspots only look dark because the rest of the Sun is very bright.

Some space telescopes, including the ones that orbit the Sun have seen huge arches of the Sun's matter extend suddenly from the Sun. These are called solar prominences. Solar prominences come in many different shapes and sizes. Some of them are so large that the Earth could fit inside of them, and a few are shaped like hands. Solar flares also come and go.

Sunspots, prominences and flares become rare, and then numerous, and then rare again, every 11 years.

Photosphere[change | change source]

This is the surface of the Sun. The light that the Earth receives from the Sun is radiated from this layer. Below this layer, the Sun is opaque, or not transparent to light.

Atmosphere[change | change source]

Five layers make up the atmosphere of the Sun. The chromosphere, transition region, and corona are much hotter than the outer photosphere surface of the Sun.[10] It is believed that Alfvén waves may pass through to heat the corona.[11]

The minimum temperature zone, the coolest layer of the Sun, is about 500 km above the photosphere. It has a temperature of about 4100 K.[10] This part of the Sun is cool enough to allow simple molecules such as carbon monoxide and water to form. those molecules can be seen on the Sun with special instruments called spectroscopes.[12]

The chromosphere is the first layer of the Sun which can be seen, especially during a solar eclipse when the moon is covering most of the Sun and blocking the brightest light.

The solar transition region is the part of the Sun's atmosphere, between the chromosphere and outer part called the corona.[13] It can be seen from space using telescopes that can sense ultraviolet light. The transition is between two very different layers. In the bottom part it touches the photosphere and gravity shapes the features. At the top, the transition layer touches the corona.

The corona is the outer atmosphere of the Sun and is much bigger than the rest of the Sun. The corona continuously expands into space forming the solar wind, which fills all the Solar System.[14] The average temperature of the corona and solar wind is about 1,000,000–2,000,000 K. In the hottest regions it is 8,000,000–20,000,000 K.[15] We do not understand why the corona is so hot.[14][15] It can be seen during a solar eclipse or with an instrument called a coronagraph.

The heliosphere is the thin outer atmosphere of the Sun, filled with the solar wind plasma. It extends out past the orbit of Pluto to the heliopause, where it forms a boundary where it collides with the interstellar medium.[16]

Eclipses[change | change source]

A solar eclipse appears when the moon is between the Earth and Sun. The last partial eclipse seen in Britain was on the 20th March 2015.

A Lunar eclipse happens when the moon passes through the shadow of the Earth which can only occur during a full moon.The number of lunar eclipses in a single year can range from 0 to 3. Partial eclipses slightly outnumber total eclipses by 7 to 6.[17]

Fate of the Sun[change | change source]

Astrophysicists say our Sun is a G-type main-sequence star in the middle of its life. In a billion years or so, increased solar energy will boil away the Earth's atmosphere and oceans. In a few more billion years, they think the Sun will get bigger and become a red giant star. The Sun would be up to 250 times its current size, as big as 1.4 AU and will swallow up the earth.

Earth's fate is still a bit of a mystery. In the long term, the Earth's future depends on the Sun, and the Sun is going to be fairly stable for the next 5 billion years.[18][19] Calculations suggest that the Earth might move to a wider orbit. This is because about 30% of the Sun's mass will blow away in the solar wind. However, in the very long term the Earth will probably be destroyed as the Sun increases in size. Stars like the Sun become red giants at a later stage.[20] The Sun will expand beyond orbits of Mercury, Venus, and probably Earth. In any event, the Earth's ocean and air would have vanished before the Sun gets to that stage.

After the Sun reaches a point where it can no longer get bigger, it will lose its layers and form a planetary nebula. Eventually, the Sun will shrink into a white dwarf. Then, over several hundred billion or even a trillion years, the Sun would fade into a black dwarf.

More reading[change | change source]

  • Lang, Kenneth R. (2001). The Cambridge Encyclopedia of the Sun. Cambridge University Press. ISBN 9780521780933.

References[change | change source]

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  1. 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 Williams, D. R. (1 July 2013). "Sun Fact Sheet". NASA Goddard Space Flight Center. http://nssdc.gsfc.nasa.gov/planetary/factsheet/sunfact.html. Retrieved 12 August 2013.
  2. "Eclipse 99: Frequently Asked Questions". NASA. http://education.gsfc.nasa.gov/eclipse/pages/faq.html. Retrieved 24 October 2010.
  3. Hinshaw, G. (2009). "Five-year Wilkinson Microwave Anisotropy Probe observations: data processing, sky maps, and basic results". The Astrophysical Journal Supplement Series 180 (2): 225–245. doi:10.1088/0067-0049/180/2/225.
  4. 4.00 4.01 4.02 4.03 4.04 4.05 4.06 4.07 4.08 4.09 4.10 4.11 "Solar System Exploration: Planets: Sun: Facts & Figures". NASA. Archived from the original on 2 January 2008. https://web.archive.org/web/20080102034758/http://solarsystem.nasa.gov/planets/profile.cfm?Object=Sun&Display=Facts&System=Metric.
  5. Emilio, M.; Kuhn, J. R.; Bush, R. I.; Scholl, I. F. (2012). "Measuring the Solar Radius from Space during the 2003 and 2006 Mercury Transits". The Astrophysical Journal 750 (2): 135. doi:10.1088/0004-637X/750/2/135.
  6. Ko, M. (1999). "Density of the Sun". In Elert, G.. The Physics Factbook. http://hypertextbook.com/facts/1999/MayKo.shtml.
  7. Bonanno, A.; Schlattl, H.; Paternò, L. (2008). "The age of the Sun and the relativistic corrections in the EOS". Astronomy and Astrophysics 390 (3): 1115–1118. doi:10.1051/0004-6361:20020749.
  8. "The Absolute Chronology and Thermal Processing of Solids in the Solar Protoplanetary Disk". Science 338 (6107): 651–655. 2 November 2012. doi:10.1126/science.1226919. PMID 23118187. //www.sciencemag.org/content/338/6107/651.full. Retrieved 17 March 2014.
  9. Connelly, James N. et al (2012). "The absolute chronology and thermal processing of solids in the solar protoplanetary disk". Science 338 (6107): 651–655. doi:10.1126/science.1226919. PMID 23118187.
  10. 10.0 10.1 Abhyankar K.D. (1977). "A survey of the solar atmospheric models". Bull. Astr. Soc. India 5: 40–44. http://prints.iiap.res.in/handle/2248/510.
  11. De Pontieu B. et al (2007). "Chromospheric Alfvénic waves strong enough to power the solar wind". Science 318 (5856): 1574–77. doi:10.1126/science.1151747. PMID 18063784.
  12. Solanki S.K; Livingston W. & Ayres T (1994). "New light on the heart of darkness of the solar chromosphere". Science 263 (5143): 64–66. doi:10.1126/science.263.5143.64. PMID 17748350.
  13. "The Transition Region". Solar Physics, NASA Marshall Space Flight Center. NASA. http://solarscience.msfc.nasa.gov/t_region.shtml.
  14. 14.0 14.1 Russell, C.T. (2001). "Solar wind and interplanetary magnetic filed: A tutorial". In Song, Paul; Singer, Howard J. and Siscoe, George L. (PDF). Space weather (Geophysical Monograph). American Geophysical Union. pp. 73–88. ISBN 978-0-87590-984-4. http://www-ssc.igpp.ucla.edu/personnel/russell/papers/SolWindTutorial.pdf.
  15. 15.0 15.1 Erdèlyi R. & Ballai I. 2007. Heating of the solar and stellar coronae: a review. Astron. Nachr. 328 (8): 726–733
  16. European Space Agency (2005). "The distortion of the Heliosphere: our interstellar magnetic compass". Press release. http://www.spaceref.com/news/viewpr.html?pid=16394. Retrieved 2006-03-22.
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