The sun is the biggest object in our solar system. It is a star, similar in size and luminosity to many of the stars in the sky... except that it's a whole lot closer! The nearest other star, Proxima Centauri, is about 40,000,000,000,000 km away!
Almost all the mass (98%) of the solar system is represented by the sun. In diameter, it's equivalent to just over 100 earths. Its volume is about the same as one million earths. The sun rotates once every 27 days near the equator, but once every 31 days nearer the poles.

The sun is made up primarily of hydrogen (71%) and helium (27%), the major components of the interstellar gases from which the sun originally formed. The remaining 2% is composed of elements such as oxygen, carbon, nitrogen, neon, iron, silicon, magnesium, and sulphur. These latter elements (which make up the planets as well) also existed in the interstellar medium from which our solar system coalesced. All elements (other than hydrogen and helium) were originally made in massive stars undergoing hotter forms of fusion, (called supernovas), that exploded and scattered these elements throughout interstellar space. Elements on the periodic table higher than iron were made in stars that became supernovae.

The sun is about 4.5 billion years old, and will probably look a lot like it does now for another five billion years or so, until its supply of hydrogen runs out. Then it will swell to red giant size for about 500 million years, collapse to a white dwarf, and slowly begin to cool off over the next thousand billion years or so.

The process by which the sun gives off energy is called fusion; you can find out more this source of energy by visiting our nuclear fusion page. Every second in the sun, 700 million tons of hydrogen are converted to helium, and in the process, 5 million tons of energy are produced. This energy is generated deep in the sun's core, and is transferred upwards first by radiation, and then, closer to the surface, by convection currents. But the interior of the sun is under tremendous pressure, and the gases there are at millions of degrees. So the path this energy takes to get to the surface is tortuous; the time it takes to reach the surface is about one million years. It then becomes heat and light, which streams off and reaches us about eight minutes later!
This leads to the unusual fact that when you look at the sun, you are seeing the edge of the sun (the part near the surface) the way it was eight minutes ago, but the light from the middle is surface light (eight minutes old) AND from the core, a million years old! Much of what we perceive of the sun is the way it was one million years ago!


The inner layers of the sun are constantly churning, and they support vast and powerful magnetic fields. Great masses of plasma (hot, ionized gas) many times the size of the earth are constantly being pushed to the surface and then pulled under, just like a huge bubbling vat of pudding. Sometimes these huge masses of gas and electromagnetic radiation are even thrown off the surface; when they are, we get a solar flare. This material may follow the lines of magnetic force back to the surface, or escape entirely and eventually reach the earth. This makes up the solar wind, which, along with light and other forms of radiation, is constantly bombarding the earth. It interacts with the earth's magnetic field to cause auroras. It also can disrupt radio transmissions. Solar flares which cause material to escape and reach the earth happen more frequently during sunspot activity on the sun. Shown above, left, is a time-lapse image of a huge eruptive prominence, seen moving out from our Sun, that took place over a period of half an hour in early 2000. Ten Earths could easily fit in the 'claw' of this solar flare. The twisted figure eight shape indicates that a complex magnetic field runs through the emerging solar particles.

Sunspots appear to the eye as dark blotches on the bright surface of the sun. These spots are actually vast magnetic storms on the surface; they occur all the time, but their frequency peaks every 11 years (causing an increase in electromagnetic interference on earth). Like the edges of the sun, (see limb darkening), sunspots appear dark only because they are cooler than the surrounding surface gases; their temperature is still many thousands of degrees!



The sun gives off gases, and many types of 'light' as well. These types include x-rays, radio waves, gamma rays, infrared, ultraviolet, as well as visible light.
In the X-ray photograph of the sun at the right, regions with a strong magnetic field hold more X-ray producing gas and are bright, while areas producing fewer x-rays are dark.


Learn about the Parker Solar Probe, which in 2024 continues to orbit the sun closer and closer, sending us information about the corona and material ejected by the sun.

The sun's radiation furnishes directly or indirectly all of the energy supporting life on earth, because all foods and fuels are derived ultimately from plants using the energy of sunlight. Moreover, it is thought that the sun's x-rays and other radiation that are able to penetrate earth's atmosphere are the original cause of many genetic diseases, the radiation being responsible for damaging human genes. This may also be one of the driving forces of evolution, since genetic change can cause improvements as well as problems.

Ultraviolet radiation from the sun is normally absorbed by the ozone in the upper atmosphere. But as this gas disappears due to the environmental activity of mankind, more and more ultraviolet radiation can reach the surface. This radiation affects skin cells, causing them to turn brown, but too much will cause burns and even cancer.


For a convenient table of facts about the sun you can print out, click here.

A simple calculation you can do to measure the size of the sun.


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