Shoot the Moon

[TCampbell]

The moon's angular size is about 1/2º. It varies in distance from the earth by roughly 10% from apogee to perigee. BTW... it gets this close EVERY lunar month... there's nothing special about any specific perigee that makes one closer than any other. The only difference is when the perigee happens to occur during a full moon -- then everyone makes a big deal about it.

As Neil DeGrasse Tyson says... it's only "super" if you think getting a 13" Pizza when you're normally used to getting a 12" pizza is "super."

Hold your thumb out at arms length. The moon is about 1/3rd of the width of your thumb and this tends to work for both adults and children alike. It is not larger at the horizon than it is up in the sky.

To create a large moon in any photo, just use a VERY long lens, but walk back quite a considerable distance from some object on the ground. At a long distance, the moon will "seem" larger in comparison to things on land (such as buildings or mountains in the distance) because those objects on land will seem "smaller" but the moon wont appear to change size at all (that's because it's so friggin' far away that you changing where you stand by a few miles makes no perceptible difference.) With the "long" lens everything is magnified... the buildings "seem" closer and the moon "seems" bigger in comparison.

We haven't done this at the planetarium where I present, but a nearby planetarium does this for fun: They ask people to estimate the size of the moon on the sky (with the moon hidden) and then reveal the moon on the planetarium dome in true size. People will make their hands huge... like they're holding a basketball. When you tell them about the thumb trick they don't believe it.

You can also ask about distance and relative size -- the average person has no idea. The moon's diameter is roughly 1/4 of Earth's. Turns out if the Earth were the size of a men's regulation size basketball (10" diameter) then the moon would be the size of a Tennis ball. The moon is 27% of the Earth diameter (just barely over 1/4). A tennis ball is 2.63"... so not perfect but extremely close.

You can then have fun asking people to estimate the distance from Earth to the moon in that same scale. Most people seem to think about 10' is more than far enough. Turns out at that scale (where the Earth is the size of a basketball and the moon is the size of a tennis ball) the moon needs to be about 25' away. At 25' away, just about everyone thinks it's much much too far -- even though that's actually true to scale.