You probably know that wind chill temperatures could reach a record -70F during the polar vortex sweeping the United States right now. But what exactly is wind chill and how do they calculate it? Here are some answers:

According to Wikipedia, "wind chill is the perceived decrease in air temperature felt by the body on exposed skin due to the flow of air." Obviously, wind chill is always going to be lower than the air temperature, but it's affected by many things. If you are using the right clothes, you are protected from the wind, or you are under the sun, the wind chill temperature will not be as low as the weatherman says. It will vary depending on those factors.

The formula to calculate that perceived decreaseâ€”what it feels to be outside if you are not properly protectedâ€”is:

Wind Chill = 35.74 + 0.6215T â€“ 35.75(V^0.16) + 0.4275T(V^0.16)

Where V is the wind speed and T is the air temperature as registered by a weather station. This formula was created by the National Weather Service in 2001 following tests on volunteers who "walked on treadmills in a refrigerated wind tunnel. Using sensors on the subjects' skin, scientists calculated a more accurate formula. You can read one of the test subjects' thoughts on the experiments here." Learn more about wind chills here.