Mean Diameter: 1,392,530 km (865,278 miles)
Mean distance from Earth: 149,597,870.7 km (92,955,807 miles)
Mean axial rotation period: 25.38 days
Composition: Hydrogen 74.9% and helium 23.8%, with heavier elements, mainly oxygen, carbon, neon and iron.
The Sun is one of the 300 billion stars in the Milky Way galaxy.
“Sun” and “star” mean the same thing. The Sun is the star at the center of our Solar System. It looks large and round instead of little and twinkly because we're close to it. The stars we see in the night sky are a long way off. The nearest sun-like star is Alpha Centauri and it's 4.4 light years away. That's over 40 trillion kilometers (26 trillion miles).
The Sun is BIG.
The Sun is bigger than 85% of the stars in the Milky Way. Its diameter is about 1,400,000 km. If you lined up a hundred Earths, that would almost give you the diameter of the Sun. The Sun's mass is 99.8% of the mass of the whole Solar System. All of the planets, moons, asteroids, comets, Kuiper belt objects, meteoroids, etc. are made of what's left over.
There are stars much bigger than the Sun.
The Sun is big, but there are bigger stars out there. For example, if someone could put Antares in the middle of the Solar System, its outer edge would be between the orbits of Mars and Jupiter. The mass of Antares is over 15 times that of the Sun. Click to see the Sun compared to some larger stars.
The Sun rotates on its axis.
Different parts of the Sun rotate at different speeds. It takes 25 days for the area around the equator to turn once, but 33.5 days for the polar regions. Remember, it's a gas, so it doesn't all have to turn together.
The Sun is a giant nuclear reactor.
Until the 20th century no one understood what kept the Sun shining. We now know that the Sun gets most of its energy from squeezing hydrogen atoms together to make helium – this is called thermonuclear fusion. (Hydrogen bombs give out energy in this way.) Thermonuclear fusion happens in the Sun's core, which is the Sun's center. The pressure is extremely high there and the temperature is millions of degrees.
Helium was seen in the Sun before it was discovered on Earth.
You've probably seen a rainbow made by light coming through a prism or crystal. This is called a spectrum. Astronomers use something similar on a telescope to break up the light coming from stars. They can also see lines in the spectrum which tells them about the chemical elements in the stars. In 1868 some astronomers found a spectral line for an element that they didn't recognize. They called it helium after the Greek word for sun, helios. It then took almost thirty years to find helium on Earth.
The Sun has spots sometimes.
Sunspots seem to be dark spots on the Sun's surface. Actually, they are very bright and very hot, about 3500 degrees Celsius (6300 degrees Fahrenheit). But the rest of the surface is even hotter, so they look dark. Sunspots are areas of magnetic activity and the number goes up and down in a cycle of about eleven years. Many sunspots are the size of the Earth, but some are as big as Jupiter.
A wind blows from the Sun through the Solar System.
It isn't the kind of wind we have on Earth. Instead of moving air, the solar wind is a stream of atomic particles from the Sun. They have an electrical charge, so they are also affected by magnetic fields such as Earth's. Usually, our magnetic field keeps the solar wind from causing damage on Earth.
Watch out for geomagnetic storms!
Sometimes the solar wind is very strong because of extra activity on the Sun which sends out massive amounts of gas and plasma. If it comes our way, it can disrupt Earth's magnetic field – we call this a geomagnetic storm. Most of the time this just means that we get bright aurorae (northern lights), which are very beautiful if you can see them. However if the storm is very strong, it can damage satellites and power plants. Astronauts in space also need to stay safely inside.
There are images connected to this article on my Pinterest board "The Sun".