How do scientist know the internal temperature of the sun?
The following excerpt taken from www.popularmechanics.co.za website can be your answer. “By analyzing the color of the visible light emitted by the Sun, scientists have determined that its surface temperature is about 5 500 degrees Celsius. The halo surrounding the surface is harder to see and much more dynamic, with solar flares and magnetic loops that are measured with X-ray and ultraviolet-detecting telescopes. Temperatures here can top 1 million degrees. The hottest part of the Sun – its core – is impossible to measure directly. However, in recent years space- and ground-based telescopes have been able to measure patterns of vibrations on the solar surface. Those patterns indicate internal fusion reactions powerful enough to generate temperatures of 15 million degrees at the very center of the Sun.” The following link will take you to the source site of the above excerpt.