How come during the day the radio only gets AM from near but at night you can hear AM radio stations from a distance?

Answer 1

There's a whole lot to it, actually, and real scientific. But basically, you can get AM radio from a distance at night, and only local during the day, because the straight waves of radio bounce from the ionosphere back to earth. The ionosphere is composed differently, depending on if it's day or night. When it's nighttime, the ionosphere reflects much better, thus you can hear stations from farther away.

Answer 2

Yes. They can. but not always.

FM signals travel in a straight line (Line of sight). Under very special conditions the FM signal can bounce the troposphere and be received very far away. This is known as "skip". It is very rare to have a good skip. In very rare instances, the signal can be carried quite far by two ionized layers of the atmosphere in what is known as tropospheric ducting. FM Signals can travel halfway around the world, but can only be received in a small area and for a very short time.

AM signals also travel line of sight. However at night the AM signal usually bounces off of the ionosphere and can be received reliably very far away (this signal is called a sky wave). For this reason most AM stations in the US and Canada must reduce their transmission power at sunset so they do not interfere with radio stations in other distant cities. AM signals can also go over mountains and be received on the other side of a mountain from a transmission tower due to another phenomenon called a ground wave. The ground wave follows the contours of the terrain over moderate distances. This also adds to the ability of AM to reach areas where an FM signal would be blocked.