The average distance from the Earth to the Moon is 384,400 km. On Saturday, March 19, 2011, the Moon will be 356,577 km away. It will of course maintain it's diameter of 3,474 km. Using the small angle formula, we can determine how much bigger the moon will appear.
Here is the small angle formula: (angular diameter in arcseconds times the distance of the object) divided by (206,265) equals the diameter of the object.
Entering in the appropriate figures, we find that normally the Moon's angular diameter in the sky is 31.07 arcminutes or about half a degree, or what a dime would look like at a distance of 2 meters. On Saturday, the Moon's angular diameter will be about 33.49 arcminutes, bringing in that dime about 15 centimeters closer.
That difference of 2.42 arcminutes, by the way, is equivalent to what our dime would look like at 25.5 meters; or to put it another way, if the Moon looks like a dime at 2 meters, a difference of 2.42 arcminutes is less than the thickness of a dime from that same distance. So add that on to what the Moon normally looks like, and you begin to appreciate what a wondrous celestial event awaits us on March 19.
You will love the Supermoon on Saturday if you are impressed by the size of a dime from 1.85 meters away, but for most of us, we won't even notice the change...no pun intended.