The Sun

The Sun - in the prime of its life

The Sun - in the prime of its life.
Source: SOHO (ESA & NASA)

Average Distance from the Earth: 149.6 million km (1.0 AU)

Size (Equatorial Diameter):

1 392 000 km (109 x that of Earth)

Mass:

1.989 x 1030 kg (333 000 x that of Earth)

Rotation Period:

27.28 days (Synodic Period)
25.38 days (Sidereal Period)

Temperature:

5 500°C (surface)
15 000 000°C (core)

Gravity:

273 m/s2 (27.9 x that of Earth)

The Sun is the star at the centre of our Solar System. It is the largest object in the Solar System, containing 99.86% of its total mass. Due to its great mass, the Sun's gravity dominates the Solar System and holds all of the planets in orbit. The energy it produces through nuclear fusion provides the light and heat for our family of planets.

The Sun is located in an outer spiral arm of the Milky Way Galaxy, approximately 28,000 light-years from the Galaxy's centre. The Sun goes around the Galaxy once every 220 million years. This length of time is known as a Cosmic Year. The Sun's path around the Galaxy is not flat, but goes up and down like a merry-go-round, passing through the plane of the Galaxy every 30 million years.

The Sun is an average yellow, main sequence star of spectral type G2 V. It is middle-aged, at least 4.6 billion years old with an expected lifespan of 10 - 12 billion years.

Atmosphere

The Sun is a massive ball of very hot gasses held together by gravity. It is composed mostly of hydrogen (70% by mass) and helium (28%), as well as small amounts of other elements such as oxygen, nitrogen and carbon. It has no solid surface but its atmosphere has several layers.

The Inner Core has only 1.5% of the Sun's volume but half of its mass, and it is here that the nuclear fusion reactions which power the Sun occur. Deep within the Sun hydrogen atoms are fused to form helium, a process which releases incredible amounts of energy.

The energy produced in the inner core must travel out through the Sun's interior. During this journey, which can take millions of years, the energy is transformed into the light and heat that is essential for life on Earth.

The heat and light finally escape from a thin shell called the Photosphere. It is this region of the Sun we can observe and it is sometimes referred to as the surface. The photosphere has a granulated appearance arising from convection currents, like boiling water in a saucepan. There are dark, cooler patches on the photosphere called sunspots, and sometimes large eruptions, called solar flares, send energy and material out into space. Both are associated with the Sun's magnetic field.

Surrounding the photosphere are two more regions. The first is a thin shell called the chromosphere. The other is the outermost part of the Sun's atmosphere called the corona which extends far out into space and is very hot. Both of these regions were first seen during total solar eclipses.

Comments (10)

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Natali 20 April, 2009 17:17
What does G2 V stand for or mean.
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Discovery Centre 21 April, 2009 10:22
Hi Natali, "G2V" describes the different aspects of the spectral type as given in the infosheet above. "G2" means average yellow, "V" means "main sequence". A more indepth explanation of spectral types is available at the following website: http://astronomy.swin.edu.au/cosmos/H/Harvard+Spectral+Classification
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meaghan 7 July, 2009 12:20
When is the next solar eclipse?
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Discovery Centre 10 July, 2009 14:18

Hi Meaghan,

Thanks for your question. According to NASA, the next total eclipse of the Sun will take place on Wednesday 22nd July 2009. This eclipse will not be visible from Australia however the NASA website will tell you where it can be seen.

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Spike 16 November, 2010 16:08
what is the suns original name and were did it come from?
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Discovery Centre 21 November, 2010 16:23
Hi Spike, ancient cultures had various names for the sun, such as Ra in ancient Egypt, Marduk in the Babylonian culture, or Apollo (or Helios) in the Greco/Roman world. Neither of these names translates to the word ‘sun’.  However, the Romans sometimes used the word ‘Sol’ instead of the name Apollo when referring to the sun god, and this word is closely related to the Italian word for a sun: ‘sole’. So there is some connection between the word sun and Sol. At present, the word sun is just a generic term for a bright light in the sky during the day. Thus, our sun does not have any special name. See the following here and here for more information.
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Nipuna 29 December, 2010 20:27
when will the sun engulf the earth !!!!
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Discovery Centre 30 December, 2010 11:41

Hi Nipuna, you might find this Question of the Week interesting!

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Jet Allstar 4 January, 2013 16:14
how long will it take for the sun to die? and will we be abel to survive it?
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Discovery Centre 5 January, 2013 10:56
Hello Jet, as the information above says, the Sun has an expected lifespan of 10 - 12 billion years, and is currently at least 4.6 billion years old. It is quite unlikely that Humans will still inhabit Earth by the time the Sun is thought to 'die', so I think you can rest easy!