Saturn appeared close in the sky to a Moon that was both a supermoon and a blue moon on the night of Wednesday, Aug. 30. While the conjunction of Saturn with the Moon occurs frequently, it is rare for it to align with a Super Blue Moon.
A supermoon occurs when the Moon is at its closest position to the Earth. Because the orbit of the Moon around the Earth is elliptical, there are positions that are closer to the Earth and farther away.
While the supermoon title corresponds to a full moon satisfying the physical requirement of close proximity to the earth, the blue moon simply refers to any moon which is the second full moon in a single month.
Saturn reached opposition on Aug. 27, meaning it was directly opposite of and illuminated by the Sun. Opposition marks Saturn’s peak brightness and visibility from Earth — however, it will continue to be visible until Feb. 2024.
“It [gave] people a perfect opportunity, when they [were] looking at the Moon, to use their [high quality] binoculars and see if they might be able to see the rings of Saturn,” said Prof. Gordon Stacey, astronomy.
After Wednesday’s sunset, the Moon and Saturn appeared in the night sky about five degrees apart. The two celestial objects were close enough to view with the naked eye but too far apart to see together with a telescope.
“There’s a lot of stuff where it’s hard to see it with your eyes, especially in a light polluted place, so it is a little bit special when there’s things you can see even from a city with just your eyes,” said Gillis Lowry ‘24, Cornell Astronomical Society president.
Because the Moon was in close proximity to the Earth, it appeared somewhat brighter and larger than normal, according to Stacey.
“That difference [in position] is modest, but it’s something like a total of [50,000] kilometers, so [about 12 percent] the distance to the Moon, so it gets [about] 12 percent larger when it’s close to us than when it’s away from us,” Stacey said. “It’s a 25 percent difference in brightness, but it’s hard for a person to remember how bright it was [on average].”
The Moon’s rotation and its orbit around the Earth are synchronized, meaning that the moon rotates once in the same time as it orbits once around the earth. Consequently, only one side of the Moon can ever be seen from Earth. The visible side reflects different amounts of sunlight, known as phases, depending on the Moon’s orbital position. For example, when the Moon is opposite the Sun, it is completely illuminated, and a full Moon will appear. However, when the Sun, Moon and Earth form a right angle, only half of the visible side is illuminated, creating a quarter moon.
The lunar month is the time between successive new moons, the phase when the visible side of the moon is not lit by the Sun. A lunar month is just 29.5 days, therefore, there are about 12.4 lunar months per year and 37.2 lunar months per three years. However, only 36 calendar months pass in three years. This discrepancy explains the existence of blue moons.
Stacey specified that because there are 12 months in a year, every three years there will be an extra full moon in one of the months on average.
A true supermoon occurs about every 413 days, and a full moon within 90 percent of the closest distance to the Earth can happen multiple times a year. Under this definition, the final supermoon in 2023 will occur on Sept. 29. However, the Super Blue Moon combination is less regular with the next two occurring in 2037.
“[A supermoon] is something that comes up a lot of times, so it’s not something you have to feel bummed about if you miss it,” Lowry said. “[But] it’s cool enough that it’s still somewhat rare. You can’t see it just every night.”
Laine Havens in a Sun contributor and can be reached at [email protected].
Clarification, Aug. 31, 12:12 p.m.: This article has been lightly edited to clarify some statements made by Prof. Gordon Stacey.