When the moon hits your eye like a big pizza pie ... that's a supermoon.
On Thursday, for the second time this month, the moon's orbit will bring it unusually close to Earth. Don't fret, it's not that close. The moon will still be about 225,000 miles away.
Also, don't expect a full, bright disc. Thursday's supermoon is a new moon, meaning it will be in alignment between the Earth and the sun, and so will appear as a thin crescent. A full moon is when the Earth is aligned between the sun and the moon.
According to the National Aeronautics and Space Administration, supermoons can appear to be 14 percent larger and 30 percent brighter because of their closeness to the Earth.
The first supermoon this month was Jan. 1, also a new moon. This second supermoon is also known as a "black moon" because it happens within 30 days of the first one.
The term supermoon was coined about 30 years ago by astrologer Richard Nolle of Arizona. He defined a supermoon as a new or full moon which occurs with the moon at or near (within 90 percent of) its closest approach to Earth.
Before Nolle defined that close point in an orbit as a supermoon, astronomers called them "perigee full moons." Perigee means "near Earth."
Bear in mind an astrologer is someone who studies the positions and movements of the planets, in the belief that they influence peoples' lives and characters. An astronomer scientifically observes the heavenly bodies.
Scientists expect five supermoons this year: The two new moons in January, and full moons in July, August and September.
Astronomy expert Bruce McClure, writing for EarthSky.org, noted that the supermoons will likely affect the Earth's oceans, and that people living on coastlines can expect large tides.
But it won't be a bad moon rising. This week's supermoon won't cause tidal waves or unleash lunatics.
"The Earth has stored a tremendous amount of internal energy within its outer shell, or crust, and the small differences in the tidal forces exerted by the moon (and sun) are not enough to fundamentally overcome the much larger forces within the planet due to convection (and other aspects of the internal energy balance that drives plate tectonics)," wrote Dr. James Garvin, chief scientist at NASA's Goddard Space Flight Center.
The next time we have two supermoons in the same calendar month will be in 2018, he wrote. On Aug. 10, we'll see the closest supermoon of the year. Then, the moon is expected to come within 221,765 miles of Earth.