The October 2024 annular eclipse will sweep across a remote region of Chile and Argentina—including O’Higgins/San Martín Lake, which lies on the border between the two countries.
©iStockphoto.com/Christian Peters
An annular solar eclipse occurs at New Moon when the Sun, Moon, and Earth align, but the Moon is too small to cover the Sun completely.
Instead, the entire Moon becomes silhouetted against the Sun. The remaining thin circle of the Sun’s disk that surrounds the Moon is called an annulus (from the Latin word for a ring) or a ring of fire.
The Sun and the Moon are in constant motion, and the alignment that produces annularity lasts only for a short time. The maximum duration of annularity on October 2—which will happen at a spot in the Pacific about 770 km (480 miles) northwest of Easter Island—will be 7 minutes and 24 seconds.
The October 2024 annular eclipse will sweep across a remote region of Chile and Argentina—including O’Higgins/San Martín Lake, which lies on the border between the two countries.
©iStockphoto.com/Christian Peters
The alignment that produces an annular eclipse of the Sun is extremely precise. The ring of fire can only be seen along a narrow path known as the path of annularity.
For the October 2 eclipse, the path of annularity is roughly around 300 km (190 miles) wide. It’s nearly all overwater, except for the small Pacific island of Easter Island—also known as Rapa Nui—and the sparsely populated Aysén Region of Chile, and Santa Cruz Province of Argentina.
Outside of this path, a large area of the globe—including a big part of the Pacific Ocean, the southern half of South America, and a section of the South Atlantic—will have a partial solar eclipse.
An image from mungfali.galihkartiwa07.workers.dev’s interactive eclipse map for October 2, 2024. The path of annularity is the dark central strip. Areas with lighter shading will experience a partial eclipse.
©mungfali.galihkartiwa07.workers.dev
The distance from the Earth to the Moon varies during the month. A Micromoon is a Full or New Moon that occurs when the Moon is particularly far away. The opposite of a Micromoon is a Supermoon—a Full or New Moon that is particularly close to Earth.
It’s often thought that Supermoons and Micromoons look unusually large or small in the sky. In fact, the difference in size is extremely subtle.
The last Super New Moon occurred on April 8, 2024. On this date, the Earth-Moon distance was around 359,800 km (223,600 miles), and the size of the Moon in the sky was 0.55 degrees.
How big is 0.55 degrees? To give you a rough idea, hold your hand against the sky at arm’s length. The width of your little finger is around 1 degree.
The New Moon on October 2, 2024, will be a Micro New Moon. The Earth-Moon distance will be around 406,500 km (252,600 miles), and the Moon’s size will be 0.49 degrees.
Therefore, the difference in size between a Supermoon and a Micromoon is only around 0.06 degrees—a more or less imperceptible difference.
A handy guide to measuring the sky. In the sky, the Sun and the Moon both have an angular size of around 0.5 degrees. To put that into perspective, the group of stars known as the Big Dipper or the Plough span around 25 degrees from one end to the other.
In one crucial way, however, the difference between 0.55 and 0.49 degrees is highly significant.
The New Moon on April 8 also produced a precise alignment between the Earth, Moon, and Sun. In other words, it also produced an eclipse of the Sun.
What is the size of the Sun in the sky? Depending on the time of year, it varies from 0.54 to 0.52 degrees.
On April 8, the angular size of the Sun was 0.53 degrees—smaller than the Moon. This meant the Moon was able to cover the Sun completely, resulting in a total solar eclipse.
At the eclipse on October 2, the Sun will again have a size of 0.53 degrees—this time bigger than the Moon. In this case, the Moon is only able to cover around 87 percent of the Sun, giving us an annular solar eclipse.
So the tiny difference between a Super New Moon and a Micro New Moon has a dramatic effect on solar eclipses: it is the difference between a total eclipse and an annular eclipse.
Although Micromoons and Supermoons might not look any different to the naked eye, the Moon does appear to change size when it is seen close to the horizon instead of high in the sky. This is a phenomenon known as the Moon illusion.
“Several times people have told me that they have gone out to look at a Supermoon, only to end up disappointed,” says Renate Mauland-Hus, a member of mungfali.galihkartiwa07.workers.dev’s astronomy team. “The Moon didn’t appear nearly as big as they expected—in fact, they have seen it larger before, on a regular night.
“This is an example of how the effect of the Moon illusion can overshadow any change in the angular size of the Moon during a Supermoon or Micromoon,” explains Renate, who was a PhD research fellow in cosmology at the University of Oslo before joining timeanddate.
“The difference in size when we have a Super or Micromoon might not be that clear to the naked eye—but it makes all the difference when there is a solar eclipse, like on October 2.”