On Tuesday evening, the sky will be lit up by a double lunar phenomenon: the supermoon and a partial lunar eclipse.

Supermoons are full moons that appear larger because they occur simultaneously with the moon’s closest orbit to Earth.

According to NASA, this means the moon will appear 30% brighter and 14% larger than when the moon is at its dimmest.

Tuesday’s supermoon is called the Harvest Supermoon because it is the full moon closest to the autumnal equinox. The name goes back hundreds of years, when farmers sometimes used the moonlight to work later in the evening.

But the clear sky is not the only thing the spectators can see.

The full moon — the second in four consecutive months of supermoons — coincides with a partial lunar eclipse, which occurs when the Earth passes between the sun and the moon, casting a shadow on the moon.

In this case, about 3.5% of the Moon appears obscured by the Earth’s umbra. This term describes the darkest part of the Earth’s shadow.

Unlike the April eclipse, no special glasses are required to safely view this eclipse.

In Southern California, the moon rises at 6:52 p.m. The largest chunk of Earth appears at 7:44 p.m. and gradually fades over 31 minutes. The moon is at its brightest at 9:48 p.m.

Tuesday’s moon follows the super blue moon of August 19. The phrase does not describe the color of the moon; instead, it refers to the second full moon to occur in a single calendar month.

According to experts, supermoons are moons that are at a distance of 90% of the distance from the Moon to the Earth.

August’s supermoon was about 224,000 miles from Earth. This month is a little closer: 222,000 miles.

The next supermoons are on October 17 and November 15.