The temperatures on Mercury range from 430` in the day to -170` at night. Please explain why the temperature varies so much..

Mercury receives intense solar radiation because it is so close to the sun. The sun beats down on it, heating it to, as you note, an insanely high temperature. However, Mercury really doesn't have an atmosphere. Earth's atmosphere is what allows it to retain solar radiation. Mercury doesn't have that, so any part of the planet that isn't in direct sun quickly loses its heat, radiating back into the vacuum. Mercury has a very long night, and that means the planet has lots of time to lose heat. The result? Very extreme temperatures.