The Sun is the star at the centre of the solar system. It is nearly perfect sphere of hot plasma. It is by far the most important source of energy of life on Earth. Roughly three quarter of the Sun’s mass consist of hydrogen (75%), helium (25%) and smaller quantities of heavier elements such as oxygen, carbon, neon and iron.

Life phases of Sun


Sun is informally and not completely accurately referred as yellow dwarf. It was formed approximately 4.6 billion years ago from gravitational collapse of matter within a region of large molecular cloud. The sun is roughly halfway through the most stable part of its life and will remain stable for more than 5 billion years.

Main Sequence

Sun is about halfway through its main sequence stage. During this stage nuclear fusion reaction in its core fuse hydrogen into helium. Each second, more than 4 million tonnes of matter are converted into energy with Sun’s core, producing neutrinos and solar radiations. At this time sun has so far converted around 100 times the mass of Earth into energy, about 0.03% of the total mass of the Sun. The Sun will spend a total of approximately 10 billion years in main sequence star.

After core hydrogen exhaustion

Sun doesn’t have enough mass to explode as supernova. Instead it will exit in main sequence for 5 billion years and star will turn into red giant as a result Sun will grow so large that will engulf Mercury, Venus and most probably Earth.

Orbit and location

Sun lies close to the inner rim of the Milky Way’s Orion Arm, in the Local Interstellar cloud at a distance of 7.5 - 8.5 kpc (25,000-28,000 light years) from the Galactic Centre. The solar apex is the direction that the Sun travels relative to other nearby stars. This motion is towards a point in the constellation Hercules, near the star Vega. The Sun takes 235 million years to go once around the galaxy and thus remain in the same vicinity. The Sun orbits the centre of the Milky Way, and it is presently moving in the direction of the constellation Cygnus.

Structure of Sun


Innermost of Sun’s radius where temperature and pressure are sufficient for nuclear fusion to occur. The fusion process releases energy and helium gradually accumulates to for to form inner core of helium within core itself.

Radioactive Zone

Radioactive Zone in which energy transfer occurs by means of radiation (photons) rather than by convection.


Boundary between the radioactive and convective zones.

Convective Zone

Between about 70% of the Sun’s radius and a point close to the visible surface, the Sun is cool and diffuse enough for convection to occur, and this becomes the primary means of outward heat transfer, similar to weather cells which from in the Earth’s atmosphere.


Deepest part of the Sun which we can see with visible light. Because Sun is a gaseous object it does not have definite surface, its visible surface is divided into photosphere and atmosphere.


A gaseous halo of the sun which comprises of chromospheres, corona, solar transition region and heliosphere.

Amazing facts

1. The Sun accounts for 99.86% of the mass in the solar system. It has a mass of around 330,000 times that of Earth. It is three quarters hydrogen and most of its remaining mass is helium.

2. The Sun is almost a perfect sphere. Considering the sheer size of the Sun, there is only a 10 km difference in its polar and equatorial diameters – this makes it the closest thing to a perfect sphere observed in nature.

3. The Sun is travelling at 220 km per second. It is around 24,000-26,000 light-years from the galactic centre and it takes the Sun approximately 225-250 million years to complete one orbit of the centre of the Milky Way.

4. The distance between Earth and Sun changes. This is because the Earth travels on an elliptical orbit path around the Sun. The distance between the two ranges from 147 to 152 million km. This distance between them is one Astronomical Unit (AU).

5. The Sun rotates more quickly at its equator than it does close to its poles. This is known as differential rotation.

Home | Explore | Units

Curated by: Radhika Bangar