Between last year's historic November supermoon and August's partial solar eclipse, a lunar event that's coming on Dec. 3 has taken a bit of a back seat. But 2017's first and only visible supermoon is nothing to sneeze at.
The term "supermoon" is popular vernacular. Its scientific name is perigee syzygy. University of Arizona professor Gurtina Besla says the phrase means two specific things in reference to the moon's placement and phase.
"Perigee refers to the moon being at its closest distance to the Earth, and syzygy refers to the alignment of multiple bodies — the moon, Earth and sun need to be aligned for us to see a full moon," Besla told NPR. "So it translates to the closest separation between the moon and Earth when the Earth, moon and sun are aligned."
Because the moon is closer to Earth, it can appear about 14 percent larger than an apogee moon, or micromoon, which is when the moon is at its farthest distance from our planet. NPR's Bill Chappell reported that last November's supermoon was the closest Earth's moon had been to the planet since 1948, and it's not scheduled to get that close again until 2034.