The 15th of August welcomes the last supermoon of 2023

The supermoon on September 29 is called the "harvest moon" and coincides with the Mid-Autumn Festival on the 15th of the 8th lunar month. When the supermoon occurs, the moon is at its closest point to Earth in its orbit, called perigee, according to NASA. At that time, the moon will fly 361,552 km from Earth, and can appear up to 14% larger and 30% brighter than the dimmest moon of the year.

According to ancient beliefs, the full moon in the eighth lunar month (ie the Mid-Autumn Festival night) is always the roundest and brightest of the year, but experts say this is not correct.

Mr. Dang Vu Tuan Son, Chairman of the Vietnam Astronomy and Cosmology Association (VACA), explained that when the Moon moves around the Earth, the illuminated part is sometimes completely directed towards the Earth, sometimes only partially, and sometimes not at all. Therefore, we see the full - waning - semi-moon - crescent phases of the Moon. In each lunar cycle, there is always a time when the entire illuminated part of the Moon is directed towards the Earth, astronomers call it the Full Moon point.

"This point can fall on the 15th or 16th day of the lunar month. There are no exceptions among such full moons, or in other words, the full moon on the Mid-Autumn Festival night is not rounder than other months," said Mr. Son.

Explaining why the full moon in the eighth lunar month appears larger and brighter than other months, Mr. Son said that the average distance from the Moon to Earth is 384,000 km, but because its orbit is actually elliptical, the Moon is sometimes closer and sometimes a little farther than this distance.

Typically, there are 1, 2, or maybe 3 full moons each year that fall right when the Moon is near its perigee (the closest point to Earth in its orbit). At that time, from Earth, the Moon can be seen to be slightly larger and brighter, and this phenomenon is called a supermoon. However, the supermoon does not have any priority for the 8th lunar month, and so there is absolutely no such thing as the moon being brighter every 15th day of the 8th lunar month.

The supermoon on September 29 won’t be the biggest of the year—that title goes to August’s super blue moon—but it will still be larger than average. While it won’t be as close or as bright as August’s supermoon, it could take on a deep yellow, orange, or red hue, especially as it rises above the horizon.

Observing this event is exactly the same as for a normal full moon, that is, the sky only needs to be slightly cloudy, enough to see the Moon. Observers also do not need to prepare any eye protection when observing.