The bad news is that our sun will not exist forever, unfortunately like everything in the universe it 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 hydrogen fusion in its core. This is the longest phase in the life of a star which lasts billions of years, in the case of our sun around 10 billion years. After this time the sun will run out of hydrogen, it will begin expanding to hundreds of times its original size and its surface will cool down turning it into a red giant (pictured left). This will result in the destruction of Mercury, Venus and Earth. It will exist as a red giant for around one billion years until eventually it will begin to lose its mass until only the core remains, this is called a white dwarf. It will remain in this state for billions of years until eventually it cools down and dies.

Our sun is part of a single star system but actually this is not the norm in the galaxy. The majority of stars are part of a binary system which is two nearby suns orbiting each other. Our closest stellar neighbour Proxima Centauri (pictured left) is actually part of a multiple star system with Alpha Centauri A and 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 and are usually much smaller in comparison, Proxima Centauri is only around one seventh the size of our sun with only 10% of its mass. Whereas stars like our sun last only around 10 to 12 billion years red dwarfs exist for trillions of years. They are much cooler than our own sun and it seems unlikely they could support life in any orbiting planets.

One of the other stars in the Alpha Centuari system, Alpha Centauri A, is much more like our own sun. Planets orbiting close to this sun could enjoy habitable 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 much smaller and dimmer orange coloured Centauri B and and the even smaller red dwarf star.

Solar flare

Sun Rotation (NASA)

Sun in our sky

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

Maximium Temperatures: 15 million C (27 million F) (Core)
Minumum 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%.

Diameter: 7,926 miles (12,756 km)
Average Distance from Sun: 93 million miles (150 million km)
Orbital Period: 365.24 days
Rotation Period: 23.934 hours

Maximium Surface Temperatures: 58C (136F)
Minumum Surface Temperatures: -88C (-126F)

Gravity: 9.766 m/s²
Density: 5.515 g/cm³
Mass: 5.9737 x 10²⁴ kg
Volume: 1.0832 x 10¹² km³

Atmosphere: 78.08% nitrogen, 20.95% oxygen, 0.93% argon, 0.038% carbon dioxide, water vapour makes up on average around 0.4% of Earth's atmosphere depending on climatic conditions.