This event makes the Moon appear slightly brighter and closer to us than usual, although the difference is difficult to see with the naked eye.
The term “supermoon” has only come into use in the last 40 years, but it gained a lot of attention in late 2016 when three supermoons occurred in a row.
The supermoon in November 2016 was the biggest supermoon in 69 years, although the moon will be even bigger in the 2030s.
How Supermoons Happen
The Moon’s orbit around the Earth is not a perfect circle. Its average distance is 382,900 km from Earth, but its apogee and perigee its closest and furthest approaches from Earth change each lunar month.
“The main reason the Moon’s orbit is not a perfect circle is because there are a lot of tidal or gravitational forces pulling on the Moon,” said NASA‘s Noah Petro, LRO lunar mission officer.
He added that the different gravity forces of the Earth, the Sun and the planets affect the Moon’s orbit. “You have all these different gravitational forces pulling and pushing the moon, but it gives us the ability to observe these close passages.”
A supermoon needs two key ingredients. The Moon must be on its closest approach to the Earth (perigee) in its 27-day orbit.
The moon must also be in its full phase, which happens every 29.5 days when the sun fully illuminates the moon. A supermoon only happens a few times a year (at most) because the moon’s orbit changes direction while the earth revolves around the sun.
The moon will look 30 percent brighter and 14 percent larger than usual, but it’s very hard to see the difference with the naked eye.
However, a supermoon can seem especially large to you when it happens very close to the horizon. But this has nothing to do with astronomy and is connected only with the work of the human brain. This effect is called “moon illusion” and can occur due to at least a few different things.
The scientists speculate that perhaps the brain is comparing the moon to nearby buildings or objects, or perhaps our brains are just wired to process things on the horizon as more than things in the sky.
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