Whats it called when both the sun and the moon appear on opposite horizons? and how often does it occur?

Question

Every once in a great while I see the sun setting and the moon is already in the visibal sky. While I'd like a picture of this happening I never have my camera at the right time. Can someone help?

Answer 1

As someone else mentioned, this can happen only at the time of Full Moon (which is not surprising, if you try to model the situation with a flashlight and a ping-pong ball).  There is a technical term for any alignment of the three bodies in a more or less straight line, called "syzygy."

If you want to capture this, you'll need a special setup for your camera (such as a convex reflector), or else do a photomosaic.  The times you should be checking are the dawns and dusks around Full Moon.  It's hard to be more precise than that, because the exact days and times depend on your latitude and the declinations of the Moon and Sun (essentially, how far up in the sky they get at their highest).  If you're curious, I can go further into that, but I think the easiest thing to do is to go to an online almanac and look up rising and setting times for the Sun and Moon, around the dates of the Full Moon, and look for the Moon to rise before the Sun sets, or vice versa.

If you're wondering about the convex reflector, you get one of those reflectors that you use on your right-hand side view mirror (the ones that are even more "objects may be closer than they appear" than the one already there), maybe three inches across.  You put it flat on a table with a full view of the horizon, and then you mount the camera above the reflector so that it's pointed down at it.  It should then have a full 360° view of the horizon, and you can capture your shot.  The Sun's light will be bright, but it should be sufficiently attenuated at the horizon, provided you set the exposure short.  You should bracket the exposure times to make sure you get a good shot in there somewhere (especially as the circumstance is not all that common).

Answer 2

Happens every month.  When they match exactly it is called an eclipse.  Otherwise it is called a "Full Moon"

Answer 3

On the day of Full Moon (once a month), the Moon rises over the East horizon at the same time as the Sun sets at the West horizon.

A few days before that, you can see an almost-full Moon rising in the East an hour or two before sunset.

A few days after Full Moon, you can see the almost-full Moon setting in the West an hour or two after sunrise.