The sun is constantly radiating energy and yet its surface temperature is nearly constant at 6000°C. The constancy of solar temperature is due to

The Sun maintains a nearly constant surface temperature of approximately 6000°C (photosphere) due to the continuous generation of energy in its core through nuclear fusion [2]. In this process, hydrogen nuclei fuse to form helium under extreme temperatures (around 15 million °C) and pressures, releasing vast amounts of energy [3]. This energy is transported outward through the radiative and convective zones to the surface. The constancy of the solar temperature is a result of hydrostatic equilibrium, where the inward pull of gravity is balanced by the outward thermal pressure generated by these thermonuclear reactions [t2][t4]. Unlike fission or radioactivity, fusion provides a sustained and massive energy output that has powered the Sun for billions of years and will continue to do so as long as hydrogen fuel remains in the core [t6].

Sources

1. [1] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 2: The Solar System > Photosphere > p. 23
2. [2] Certificate Physical and Human Geography , GC Leong (Oxford University press 3rd ed.) > Chapter 14: Climate > lnsolation > p. 131
3. [3] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 1: The Universe, The Big Bang Theory, Galaxies & Stellar Evolution > Protostar > p. 9