What makes the moon a super moon?

In its orbit around the Earth, the Moon particularly approaches us several times a year. This promises a particularly large and bright moon in the night sky. But although this effect is barely noticeable with the naked eye, the giant moon stuns many observers. Actually, this is due to a different effect.

It is mentioned over and over: Super Moon. The satellite is said to appear unusually large in the sky at certain times of the year. And if after that – assuming good weather – you get out and gaze at the moon, you might be truly amazed. The full moon hovers majestically over the horizon.

When the moon is especially close to us

In fact, “Super Moon” is not a historical, astronomical, or scientific term in general. Instead, it was astrologer Richard Knoll who first wrote in 1979 about the giant moon that was supposed to be responsible for earthquakes and volcanic eruptions – that is, when the satellite is particularly close to Earth during a full or new moon. the moon.

But even if Knoll’s considerations are not based on scientific principles, they cannot be completely ruled out. Because the tidal forces of the Moon and the Sun lead not only to tides, but also to movements in the Earth’s crust. If the sun, earth, and moon are roughly in a straight line, then the tidal forces of the sun and moon build up and cause especially strong spring waves. Floods, often colloquially referred to as spring tides, are about 20 percent higher than normal floods. In fact, increasingly powerful earthquakes are occurring in parallel with the spring tide, as a team led by geologist Satoshi Id showed in 2016 based on the analysis of more than 10,000 earthquakes.

Since the moon does not move in a circular orbit, but in a clear elliptical orbit around the Earth, not all tides are the same. The distance between Earth’s moon and our planet varies between 356,400 and 406700 kilometers. So it is quite evident that the tidal effects are stronger when the moon is also near the earth during the spring tide. However, this effect is very minimal: on average, the spring tides are about 2% stronger when the Moon is near Earth. Accordingly, the link between the giant moon and earthquakes has yet to be proven.

Bigger and brighter

However, the concept of a giant moon has been used more and more in recent years – albeit different from originally intended by Nolle: today the term no longer denotes the supposed effects of a near moon on earthquakes or volcanic eruptions. Instead, only the full moon is meant at a location close to Earth and the size and brightness associated with Earth’s moon in the night sky. Because when the moon is close to the earth, the apparent diameter of the moon is up to 14 percent larger than the diameter of the farthest from the earth – the so-called little moon. And with the greater area that the giant moon occupies in the night sky, the perceived brightness of the Earth satellite also increases. The Moon appears 30 percent brighter near Earth than farther away.

However, these are extreme values. The moon’s orbit is by no means static, but differs due to the gravitational pull of the sun and the larger planets. The distance between the Moon and Earth at perihelion, which is the closest point to Earth in each orbit, fluctuates between 356,400 and 370,400 kilometers. Therefore the theoretically possible maximum values ​​rarely occur. This begs the question of when is a full moon considered a supermoon. Noll himself has changed his definition over and over again over the decades – currently he uses an arbitrarily defined distance of less than 368 630 kilometers with a full moon as the maximum.

Just near a full moon is also a super moon

Distances of the moon from the earth to a super moon and a small moon

This means that there are two to four giant moons each year. On April 27, 2021, the satellite will be 357,378 kilometers from Earth. At the next full moon on May 26, the moon will be closer to Earth at an altitude of 357,309 kilometers – so only a month later there will be the next giant moon.

Another criterion often used is that the exact time of the full moon and the exact time of proximity to Earth fall on the same night. But this definition depends on the location of the observer: in Germany there is a full moon in the morning hours of April 27, 2021, but the proximity to Earth does not occur until evening – that is, the following night. Accordingly, this will be a supermoon in the US, but not in Germany. With a full moon on May 26, it’s the opposite.

A note worthy of attention?

Thus, whether or not the full moon is “wonderful” is debatable. The “Super Moon” phenomenon has no special scientific significance either. But is it still worth looking at Earth’s satellite if it is particularly close to us? After all, the differences in apparent size and brightness are quite large. In fact, in the night sky, the differences between a normal full moon and a supermoon are difficult to see with the naked eye due to the lack of things to compare. The super moon in the sky does not look much different to an observer than any other moon.

However, spurred by the reports about the giant moon, many people are out in the evening hours and amazed at the size of the Earth’s satellite when they see it near the horizon shortly after its ascent. However, the seemingly colossal size of the moon on the horizon depends on an entirely different phenomenon: an optical illusion leaves that out The moon is larger near the horizon It looks like it is high in the sky. So it has nothing to do with the giant moon.