<P> The Sun is about halfway through its main - sequence stage , during which nuclear fusion reactions in its core fuse hydrogen into helium . Each second , more than four million tonnes of matter are converted into energy within the Sun 's core , producing neutrinos and solar radiation . At this rate , the 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 as a main - sequence star . The Sun is gradually becoming hotter during its time on the main sequence , because the helium atoms in the core occupy less volume than the hydrogen atoms that were fused . The core is therefore shrinking , allowing the outer layers of the Sun to move closer to the centre and experience a stronger gravitational force , according to the inverse - square law . This stronger force increases the pressure on the core , which is resisted by a gradual increase in the rate at which fusion occurs . This process speeds up as the core gradually becomes denser . It is estimated that the Sun has become 30 % brighter in the last 4.5 billion years . At present , it is increasing in brightness by about 1 % every 100 million years . </P>
what stage of the star life cycle is the sun in
about halfway through its main - sequence stage