The Sun is a star in the centre of our Solar System. It is the largest object and the only star in our Solar System. It is one of billions of stars in our galaxy, the Milky Way.
It looks bigger than the other stars we see in the night sky because it is far closer to Earth. It is only 150 million kilometres away! Alpha Proxima is the next nearest star, 40,000 billion km from Earth!
Without the energy and heat from the Sun, life would not exist on Earth, and we wouldn't have daytime or seasons.
The Sun is the only object in our Solar System that makes its own light. Everything else, like the Earth and our Moon, can be seen when it reflects light from the Sun.
Remember, the Sun's light is powerful. Never look directly at the Sun, not even when wearing dark glasses. The light could damage your eyes.
You may have noticed that the Sun appears to move across the sky each day, rising in the east and setting in the west. The Sun actually stays where it is in the centre of the Solar System. The Earth's rotation on its axis makes it look like the Sun is moving!
- How big is the Sun?
It is 1.4 million kilometres wide, more than 100 times wider than Earth. It contains more than 99.8% of all the mass in the Solar System, with the gas giant planet Jupiter containing most of the rest.
Because it is so massive, the Sun's gravity is very strong—strong enough to influence objects across huge distances. The Sun's gravity keeps every object in our Solar System (planets, asteroids, dwarf planets) in orbit around the Sun.
The Sun is a hot spherical ball of glowing gas we call plasma. The Sun is 75% hydrogen, and most of the rest (24%) is helium. These are the lightest chemical elements. They are also the most common elements in the Universe. The Sun also has small amounts of oxygen, carbon, neon and iron. Nuclear reactions deep inside the Sun made these heavier elements.
There are three main parts to the Sun. The core at its centre is the hottest part. Deep in the Sun's core, temperatures reach 15 million degrees Celsius! Around the core is the radiative zone. Energy is carried through this area, away from the core, as thermal radiation. Around that is the convective zone. Heat moves around this zone like soup bubbling in a pot.
The visible layer of the Sun is called the photosphere. The photosphere's temperature is about 6,000 degrees Celsius, giving it its yellow colour. The Sun also has an atmosphere. Some of the Sun's atmosphere escapes into space - we call this the solar wind. It takes 50 million years for the Sun's energy to travel from the core to the surface. And then another 8 minutes for the light to reach us here on Earth!
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CreditThis work by The Schools' Observatory is licensed under All rights reservedThe different layers of the Sun. - How old is the Sun?
Scientists have worked out that the Sun is about 4,500 million years old. It was made from part of a giant cloud of gas and dust. The pull from the cloud's gravity caused it to clump together and collapse inwards.
As the gas and dust fell to the centre of the cloud, the temperature and pressure increased. When the temperature got as high as 1 million degrees Celsius, the Sun began to shine.
The Sun, like all stars, shines and releases energy through a process called nuclear fusion. The hot, high pressure in the cores of stars creates the right conditions for nuclear fusion to take place.
- Does the Sun change?
You might think that the Sun stays the same and does not change. Yet, research shows us that the Sun is an active star that changes with time. Like the Earth, the Sun has a magnetic field. This magnetic field varies with time because the Sun rotates. The Sun's equator spins at a faster rate than its poles do, making the magnetic field lines curve and twist. This twisting causes changes in the Sun's activity.
For 100s of years, scientists have measured this solar activity. The data lets them predict when the Sun's activity will peak. We call these peaks solar maximums. A solar maximum takes place about every 11 years. There are many ways of measuring solar activity. One way is to count the number of sunspots and solar flares on the Sun over time.
- Sunspots and Solar Flares
- What will happen to the Sun?
The Sun will carry on shining for another 5,000 million years. This period of time is called its main sequence. It will then begin to run out of nuclear fuel, which powers its core, and expand to become a red giant star.
Some stars explode once they run out of fuel. The Sun is not big enough to explode. Instead, it will lose its outer layers over a long time - we call this a planetary nebula. The central mass of the Sun will shrink to a dense white dwarf. Finally, it will dim, stop shining, and become a black dwarf.
