A Star With Two Very Different Temperatures
When people ask how hot the Sun is, the answer depends on which part of the Sun they mean. The Sun is not a solid object with a single temperature — it is a giant ball of hot gas, and its temperature changes dramatically from its surface to its center. The visible surface, called the photosphere, is around 5,500 degrees Celsius. That is hot enough to vaporize any known material on Earth, yet it is actually the coolest major layer of the Sun.
The Blazing Core
The true furnace of the Sun lies deep in its center. The core reaches a staggering temperature of roughly 15 million degrees Celsius. Under this extreme heat and the crushing pressure of the Sun’s own gravity, hydrogen atoms are forced together in a process called nuclear fusion. Fusion converts hydrogen into helium and releases an enormous amount of energy. This energy is what ultimately powers the Sun and provides the light and warmth that reaches Earth. Every bit of sunlight began its journey as energy created in this blazing core.
The Mystery of the Outer Atmosphere
One of the strangest facts about the Sun is what happens above its surface. The Sun’s outer atmosphere, called the corona, is far hotter than the surface beneath it — reaching temperatures of one to three million degrees Celsius. This is surprising, because moving away from a heat source would normally mean things get cooler, not hotter. Scientists call this the coronal heating problem, and it remains an active area of research. Magnetic activity and waves of energy travelling through the Sun are thought to play a major role.
How We Measure a Star We Cannot Touch
No instrument could ever be placed directly on the Sun, so scientists measure its temperature from a distance. They study the light the Sun emits, because the color and spectrum of light reveal how hot the source is. Different elements glow in distinct patterns at different temperatures, allowing astronomers to read the Sun’s heat almost like a fingerprint. Spacecraft such as solar observatories have also flown closer to the Sun than ever before, gathering data that helps confirm and refine these measurements.
Source
This article was written using information from Wikipedia.