In simple terms, the Sun is a very hot ball of gas. It’s made up primarily of hydrogen and helium. The temperature at its core is 15 million degrees Celsius (27 million degrees Fahrenheit). That’s hot enough to fuse hydrogen into helium and release tremendous amounts of energy — so much that it accounts for 99 percent of the total mass in the solar system.

The Sun’s surface is about 5,800 degrees Celsius (10,000 degrees Fahrenheit), which is cooler than its core but still extremely hot compared with Earth’s 15-degree Celsius (59-degree Fahrenheit) average temperature. But even this temperature isn’t constant. During its 11-year solar cycle, the Sun’s surface can vary by as much as 1 million degrees Celsius (1.8 million degrees Fahrenheit).

So how hot would you have to cool the Sun in order for it not to be able to give off light? That depends on how much energy it releases per second — known as luminosity — and how much surface area you want to cover with whatever substance you’re using to block out all that radiation.

Last modified: July 29, 2022