How does the sun emit energy?

The age of our sun is 4.6 billion years. The surface temperature of the sun is 5,778 Kelvin (K) which is nothing compared with the temperature of the core. Sun’s core temperature is 15 million K. Yes million.

Thanks to this temperature, in every second, 600 million tons of hydrogen is being converted to helium by undergoing a reaction called “Fusion”. Fusion is the opposite of fission that breaks down nuclear of atoms and release energy in agreement with the famous equation E = ∆mc². In fusion, tritium and deuterium which are isotopes of hydrogen are merged and forms helium and a neutron. Now we should get familiar with the term “Binding Energy” to fully understand the reason for releasing energy in fusion.

Mass of a proton	1.007277 amu
Mass of a neutron	1.008665 amu
Number of protons in tritium	1
Number of neutrons in tritium	2
Therefore, the total mass of tritium should be:	3.024607 amu
But the actual mass of tritium is:	3.016049 amu
Mass difference	0.008557 amu
Let’s apply this to E = ∆mc2	E = (0.0085578 ×1.66×10-27)× (3×108)2 E = 1.27853532×10-12 J E = 7.98 MeV

This is called “Binding Energy” of tritium which is the amount of energy that keep protons and neutrons in the nucleus. Similarly binding energy of deuterium and helium are 2.22 MeV and 28.3 MeV respectively. This amount of energy should be added to break the nuclear apart.

	Tritium	+	Dutirum	→	Helium	+	neutron
Binding Energy	7.98 MeV (Absorb)		2.22 MeV (Absorb)		28.3 MeV (Release)		0 MeV
Net Release	18 MeV

In every second, about 10⁸ such fusion reactions are happening in the sun, and it releases 3.85×10³⁸ W of power to the universe.