You can also view previously answered questions in the HSW Question Archive . This question has been pondered for hundreds if not thousands of years. This problem is commonly referred to as the moon illusion . Some have speculated that there is some effect that causes the atmosphere to act like a magnifying glass making the moon look bigger. It turns out that any distortion caused by the atmosphere would actually make the moon look a little smaller.
Most scientists agree that the reason the moon looks bigger is purely in our minds.
Our mind interprets the things we see in interesting ways. For instance, if you look at any door frame you can see that it is rectangular. But if you were to sketch the outline of the door frame from the angle that you are looking at it, most likely you would sketch a trapezoid. Your mind adjusts the door so that you perceive it as a rectangle from whatever angle you look at it. That theory is called shape constancy .