Mercury is the closest planet to the sun. In fact the sun would look two and one-half times larger if you were standing on Mercury. You wouldn't survive long if you were standing on Mercury. Because of its closeness to the sun, the temperature rises to 800F. That's hotter than an oven. However, strange as it sounds, the dark side of Mercury can fall to - 300 degrees below zero. This is because Mercury does not have an atmosphere (Gasses surrounding it) to retain heat and it takes 180 days to make a revolution (spin). This means that 90 days are spent facing away from the sun (What we call night). During this long time without the Sun's direct radiation (energy), it cools down a lot. The lack of gasses would also mean you have no oxygen to breath. Don't expect humans to be colonizing Mercury any time soon.
Mercury is about two-fifth the size of Earth. The lack of mass is one reason Mercury does not have an atmosphere. The gravity is not strong enough due to this lack of mass to hold onto any gasses. Less gravity means that you would also weigh less. If you weighed a hundred pounds on Earth, you would weigh about 37 pounds on Mercury. Mercury takes about 88 Earth days to orbit the sun. Since a year is measure by an orbit of the sun, you would be about 4 times older on Mercury than Earth (In birthday numbers only, you'd still have lived the same amount of time.)
Mercury was named by the Romans after their swift messenger of the Gods. This was because Mercury has a much shorter orbit around the sun than Earth because it is closer to the sun. To the Romans, Mercury appeared to move quickest of all the regular heavenly bodies. Mercury is on of the four innermost rocky planet. In fact, Mercury has more iron than any other planet. http://planetfacts.net/Mercury-Facts.html