12.9 day old moon
96.3 percent lit
July 17, 2016
By Dennis Mammana
There are few things (click here) in nature I enjoy more than watching a massive full moon rising over the horizon. This is truly a treat everyone should experience at least once, and when you do you’ll surely raise the same question as every other moon gazer: “Why does the moon appear so large when it’s rising, and smaller when overhead?”
A simple question without a simple answer.
Many believe the Earth’s atmosphere somehow acts like a lens and magnifies the moon’s appearance, but this is just as wrong now as it was when Ptolemy suggested it 20 centuries ago.
More likely is that it’s related to how we humans have evolved to perceive rigid objects appearing near the horizon.
Whatever the cause, try estimating the moon’s size the last time you saw it rising in the east and compare it to a familiar object — say, your hand. For example, hold your little finger at arm’s length and it will subtend to your eye an approximate angle of one degree; your fist also at arm’s length will appear about 10 degrees across....
