Phenomena in the night sky Super moon, blue moon - please what?

There are always spectacular things to observe in the night sky. The appearance of a supermoon or a "blue moon" is somewhat more common than events such as the visit of a distant comet. But what exactly do these terms actually mean? blue News explains the lunar phenomena.

What is a blue moon?

The Blue Moon is not a space spectacle in which the Earth's satellite glows blue. Rather, the term refers to the phenomenon that, statistically speaking, a full moon can be seen twice within a month on average every 2.5 years.

The European Space Agency (ESA) explains that a lunar cycle lasts around 29.5 days, but our calendar months are between 28 and 31 days long. This means that there are normally three full moons per season. Because the two cycles do not quite coincide, there are occasionally two full moons in one calendar month - and the second full moon is then called the "blue moon".

Because of its rarity, the expression "once in a Blue Moon" is used in English to express that something occurs rarely, i.e. once in a blue moon

This event last occurred on August 19, 2024.

Is the "blue moon" really blue?

The ESA emphasizes on its website that there is "no scientific basis" for the colloquial expression "blue moon": "Our moon is certainly not turning blue." From space, however, the moon looks the same as it always has. From a scientific point of view, the blue moon is therefore not a significant event, but it is rare.

What is a supermoon?

A "supermoon" occurs when the full moon coincides with the moon's closest point to Earth in its elliptical orbit, a location known as perigee.

During each 27-day orbit around Earth, the moon reaches both its perigee, about 363,300 kilometers from Earth, and its farthest point, or apogee, about 405,500 kilometers from Earth. Because the Moon's orbit varies and depends on the position of the Sun and Earth in their orbits, the exact distance of these closest and farthest points varies, and some supermoons are closer or farther away than others.

"Supermoon" is not an official astronomical term, but is typically used to describe a full moon that comes particularly close to the Earth at a distance of around 363,300 kilometers, according to the US space agency NASA. The full moon therefore appears slightly larger than on other full moon nights.

Is the supermoon bigger?

At its closest point, the full moon can appear up to 14 percent larger and 30 percent brighter than when it is furthest away from the Earth in its orbit. In fact, the moon is not "bigger" - it just appears that way. In general, the moon appears particularly powerful when it is low - and not high in the sky. This "moon illusion" or "lunar illusion" is due to the fact that viewers place it in relation to earthly objects on the horizon, such as mountains, trees or buildings, explains Pilz.

It can be difficult to recognize a supermoon visually, but it does have an effect on the Earth. For example, it can cause higher tides than usual.

Even though 14 percent doesn't make a big difference in visible size, a full supermoon is slightly brighter than other moons throughout the year.

What are super-supermoons?

Incidentally, the moon's distance from the Earth is slightly different at each perigee. This means that not all supermoons are equally "super". The record holder is currently the full moon of 14 November 2016. This full moon was "only" 356,510 kilometers away from us. The last time the full moon was this close to us was on 26 January 1948. And the eEarth satellite will only come similarly close again on 13 January 2036 at 356,531 kilometers. A closer and larger full moon will not occur again until 6 December 2052, when it will be just 356,429 kilometers away.