ELI5: Explain Like I'm 5

Air mass coefficient

Air mass coefficient is a number that tells us how much sunlight is reaching the Earth's surface from the Sun. It's highest when the Sun is directly overhead and lowest when the Sun hits the Earth's surface at an angle. The air mass coefficient is used to calculate how much energy from the Sun is available for things like photosynthesis and heating. This number helps us know how much sunlight we will get in different regions of the world!