The Sun
Our Sun
Ultraviolet image taken of the sun by a NASA solar imaging satellite.
Sun Facts
  • The sun is a star at the center of our solar system and is thought to be around 4.5 billion years old.
  • It has a diameter of around 865,000 miles (1.4 million km), which is 109 times larger than Earth.
  • The mass of the sun accounts for 99.86% of all the mass in the solar system.
  • Three quarters of the sun is composed of hydrogen with helium making up most of the rest.
  • The sun is actually bigger and brighter than the vast majority of stars in our galaxy.
  • Charged particles that stream from the sun's upper atmosphere create a solar wind.
  • Sunspots are cooler areas on the sun's surface as large as 50,000 miles (80,000 km) making them visible from Earth with the naked eye.
  • The sun is actually white, the Earth's atmosphere makes it appear yellow.
  • In around 5 billion years time the sun will become a red giant, destroying the planets Mercury, Venus and Earth in the process.

Sun from Earth orbit
The sun as seen from the space shuttle in orbit around the Earth
Sun's Orbit
The sun orbits around the center of our galaxy, the milky way, at a distance of around 25 thousand light years taking about 250 million years to make one orbit.
Sun's Atmosphere
The atmosphere of the sun consists of several layers called the photosphere, chromosphere, transition region and corona. The photosphere is the lowest layer and the visible surface of the sun we see. The corona is the outer layer of the sun's atmosphere and is much hotter than it's surface.
Sun's Temperature
Temperatures at the photosphere are around 5,500C (10,000F), the corona can reach temperatures of almost 2 million C (3.6 million F). At the sun's core temperatures are over 15 million C (27 million F).

Life of our Sun

Sun in our sky
The sun lighting up our sky
The sun produces its energy through a process called nuclear fusion, in its core hydrogen atoms are fused together which produces helium, during this process a small amount of mass is lost which emerges as energy. The sun burns around 600 million tonnes of hydrogen in its core every second, the energy produced slowly makes its way to its surface and is released into the solar system.

The bad news is that this process cannot exist forever, unfortunately like everything in the universe the sun has a life span. The good news is that it will continue in its current state for another 5 or 6 billion years. At the moment our sun is in the middle of its main sequence phase, meaning it is producing all its energy from this hydrogen fusion process. This is the longest phase in the life of a star, in the case of our sun around 10 billion years. After this time nuclear fusion will stop in its core and the sun will instead begin fusing hydrogen in an outer shell surrounding the core, it will begin expanding to hundreds of times its original size and its surface will cool down turning it into a red giant. This will result in the destruction of Mercury, Venus and bring an end to all life on Earth. It will exist as a red giant for only a few million years before it eventually loses its outer layers leaving only its core remaining. The sun would now be a small but incredibly dense object called a white dwarf, over many billions of years it would cool down and darken until it no longer emits any energy.

The Sun Compared to Earth in Size
sun compared to earth in size

Our Nearest Neighbors

Sun in our sky
Artist's impression of the red dwarf star Proxima Centauri
Our sun is part of a single star system but around half of all stars in our galaxy are part of a binary or multiple system, that’s where two or more stars orbit around each other. Our closest stellar neighbor Proxima Centauri (pictured left) is part of a three star system with Alpha Centauri A and Alpha Centauri B. Proxima Centauri is 25 trillion miles (40 trillion km) from our sun, even if we could travel at the speed of light it would still take over 4 years to reach it.

Proxima Centauri is a red dwarf star and these are by far the most common types of star in our galaxy. Red dwarfs have less than half the mass of the sun, are much smaller in comparison and emit far less energy. Proxima Centauri is only around one seventh the size of our sun with only 12% of its mass. Whereas stars like our sun last only around 10 to 12 billion years in their main sequence red dwarfs can exist over a trillion years. This is because they burn their hydrogen fuel at a much slower rate than larger stars.

The other stars in the Alpha Centauri system are more like our own sun. Planets orbiting in the habitable zone around these stars could enjoy conditions similar to what we have on Earth. Any inhabitants living on this planet would have the striking image of three suns in its sky, the very bright Centauri A, the smaller and dimmer orange colored Centauri B and the even smaller red dwarf star.

Solar eclipse
A solar eclipse
Sun Statistics

Diameter: 864,000 miles (1.4 million km)
Distance from center of Galaxy: 25,000 light years
Orbital Period: 250 million years
Rotation Period: 25.38 days

Maximum Temperatures: 15 million C (27 million F) (Core)
Minimum Temperatures: 5,500C (10,000F) (Photosphere)

Gravity: 274 m/s2 (28 x Earth's Gravity)
Density: 1.409 g/cm3 (25.5% Earth's Density)
Mass: 1.989 x 1030 kg (333,000 x Earth's Mass)
Volume: 1.412 x 1018 km3 (1.3 million x Earth's Volume)

Atmosphere (Photosphere): Hydrogen 73.46%, Helium 24.85%, Oxygen 0.77%, Carbon 0.29%, Iron 0.16%, Sulfur 0.12%, Neon 0.12%, Nitrogen 0.09%, Silicon 0.07%, Magnesium 0.05%.

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