How cold is space? And how hot is the sun? These are both excellent questions. Unlike our mild habitat here on Earth, our solar system is full of temperature extremes. The sun is a bolus of gas and fire measuring around 27 million degrees Fahrenheit at its core and 10,000 degrees at its surface. Meanwhile, the cosmic background temperature—the temperature of space once you get far enough away to escape Earth’s balmy atmosphere—hovers at -455 F.