How to find the moon tonight (and why it looks different every night)

There’s a small, specific disappointment that belongs to beginner astronomers. You step outside on a clear night, ready to see the moon, and the moon isn’t there.

It happens more than people expect. The moon isn’t out every night. And even when it is, it’s often not in the part of the sky you thought to look first. Once you understand why, the moon stops surprising you. You’ll be able to guess roughly where it is at any given hour, in any month, for the rest of your life.

The moon moves like the sun does

Every object you can see from Earth’s surface rises somewhere in the east and sets somewhere in the west. That’s not really the sky moving. It’s us, spinning. The moon does the same thing. It rises in the east, climbs through the southern part of the sky if you’re in the northern hemisphere (or the northern part if you’re in the south), and sets in the west.

What changes from one night to the next is when. The moon takes roughly 29.5 days to orbit Earth, and that orbit means it doesn’t rise at the same clock time every night. It rises about 50 minutes later each night than the night before.

The phase tells you when the moon is up

Here’s the part most people never learn in school. The phase of the moon tells you, almost exactly, when it’s in the sky.

New moon. The moon is lined up between Earth and the sun. It rises around sunrise and sets around sunset. You can’t see it because the lit side is facing away from you, and the sky around it is too bright anyway. On a new-moon night, the moon is not there. Don’t go looking.

First quarter (a half-moon, lit on the right side from the northern hemisphere). Rises around noon, reaches its highest point at sunset, sets around midnight. This is the evening moon. Look south after dinner.

Full moon. Rises at sunset, crosses the sky all night, sets at sunrise. A full moon is somewhere up there every hour between dusk and dawn. This is the one night a month the moon is your reliable companion.

Last quarter (a half-moon, lit on the left side). Rises around midnight, highest at sunrise, sets around noon. The morning moon, mostly seen by early risers, commuters, and dog walkers.

Everything in between these is some shade of crescent or gibbous, and the rising time drifts by roughly 50 minutes each night. If tonight’s moon is rising at 9pm, tomorrow it’ll rise closer to 10.

One rule covers it all: the lit side of the moon faces the sun. Always. Once you know the phase, you can work out which half of the night will have the moon, and where in the sky to look for it relative to where the sun just was.

Why it looks different every night

Two things are changing. The phase (what fraction is lit) and the orbital position (when it rises).

Phase changes because the geometry changes. Earth is going around the sun, the moon is going around Earth, and from our vantage point the angle between sun and moon shifts a little each day. When the sun and moon are on opposite sides of Earth, we see the whole lit face: full moon. When they’re on the same side, we see the dark face: new moon. Every angle in between gives us crescents, quarters, and gibbous shapes.

The rising time changes because the moon has moved about 12 degrees eastward along its orbit each day. Earth has to spin for an extra 50 minutes or so before the moon clears the horizon again. Hence the drift.

A cheat sheet you can memorise

If you only remember one thing, let it be this:

• Want to see the moon after dinner? Aim for the week before the full moon. It’ll be high in the evening sky and won’t set until late.
• Want it all night? Go out on a full-moon night.
• Want a dark sky with no moon at all? The week of the new moon. The moon will either be invisible or a faint sliver at dawn.
• Morning person? The week after the full moon is yours. The moon will still be high at sunrise.

You don’t need an app. You just need to notice tonight’s phase, even for a second, and you’ll know when to try next.

The moon in daylight

Most people think of the moon as a night object. It isn’t. Roughly half the time, some portion of the moon is above the horizon while the sun is still up. That pale half-moon you sometimes spot hanging in a blue afternoon sky is a first-quarter moon, rising around noon and just sitting there as the sun marches past it. Perfectly normal. Nothing wrong with your eyes.

The moon is the easiest, most reliable astronomical object you have. Once you’re friends with it, the rest of the sky starts to make sense. Step outside tonight, whatever phase it’s in, and see if you can find it. If you can’t, you now know why. And roughly when to try again.