Tonight marks day 18 of the lunar cycle, meaning the Moon is in its waning gibbous phase. More than half of its surface is still illuminated, but it’s slowly shrinking each night as it moves toward the New Moon. Keep reading to find out what this means.

What is today’s moon phase?

As of Monday, Dec. 8, the moon phase is Waning Gibbous. This means 83% of the moon is lit up tonight, according to NASA’s Daily Moon Observation.

There’s still more than half of the moon on display, so with just you naked eye you can see the Mare Tranquillitatis, Tycho Crater, and Copernicus Crater. If have binoculars to hand, pull these out to see the Gassendi Crater, Endymion Crater, and the Alps Mountains. And a telescope will help you see the you can catch a glimpse of the Apollo 16 landing spot, Rima Ariadaeus, and the Linne Crater.

When is the next full moon?

The next full moon will be on Jan. 3.

What are moon phases?

NASA explains that the lunar cycle (which is about 29.5 days long) is made up of the Moon’s phases, which describe how the Moon looks from Earth as it travels around us. We view the same side of the Moon at all times, but the sunlight hitting its surface shifts as it moves through its orbit. That changing illumination is what makes the Moon appear full, half-lit, or not visible at all. The cycle includes eight distinct phases:

New Moon – The moon is between Earth and the sun, so the side we see is dark (in other words, it’s invisible to the eye).

Mashable Light Speed

Waxing Crescent – A small sliver of light appears on the right side (Northern Hemisphere).

First Quarter – Half of the moon is lit on the right side. It looks like a half-moon.

Waxing Gibbous – More than half is lit up, but it’s not quite full yet.

Full Moon – The whole face of the moon is illuminated and fully visible.

Waning Gibbous – The moon starts losing light on the right side. (Northern Hemisphere)

Third Quarter (or Last Quarter) – Another half-moon, but now the left side is lit.

Waning Crescent – A thin sliver of light remains on the left side before going dark again.