Annular solar eclipse on October 2: What is it?

What is a solar eclipse?

A solar eclipse takes place when the Moon moves in the middle of the Earth and the Sun. The Moon blocks the light of the Sun, either fully or partially, which casts a huge shadow on some parts of the world.

There are four different types of solar eclipses, including total solar eclipse, annular solar eclipse, partial solar eclipse, and hybrid solar eclipse.

When the Moon blocks the Sun entirely, the areas in the centre of the Moon’s shadow at the time witness a total solar eclipse. The sky darkens and people who are in the path of a total solar eclipse can get a glimpse of the Sun’s corona — the outer atmosphere — which is usually not visible due to the bright face of the Sun.

When the Moon passes in front of the Sun but is at or near the farthest point from Earth, an annular solar eclipse occurs. In this scenario, the Moon covers the Sun in such a way that only the periphery of the Sun remains visible — looking like a ring of fire.

A partial solar eclipse takes place when the Moon blocks just a part of the Sun, giving it a crescent shape. During both partial and annular eclipses, the regions outside the area covered by the Moon’s umbra — the middle and the darkest part of the lunar shadow — will see a partial solar eclipse. Partial solar eclipse is the most common type of solar eclipse.

A hybrid solar eclipse — the rarest type of solar eclipse — is witnessed when an eclipse shifts between annular and total as the shadow of the Moon moves across the globe. In this case, some parts of the world see a total solar eclipse, while others observe an annular solar eclipse.

How often does a solar eclipse take place?

A solar eclipse is witnessed only during the new moon — when the Moon and Sun are aligned on the same side of Earth. A new moon occurs about 29.5 days because that is how long it takes the Moon to orbit Earth. This, however, does not mean that a solar eclipse happens every month. It takes place only between two to five times annually. But why?

It is because the Moon does not orbit Earth in the same plane as the Earth orbits the Sun. In fact, the Moon is tilted by about five degrees with respect to Earth. As a result, most of the time when the Moon is in between the Sun and Earth, its shadow is either too high or too low to fall on the Earth.

“If you think of the Earth’s orbit around the Sun as a disk and the Moon’s orbit around the Earth as another disk, there is a 5-degree angle between the two disks. However, any time you have two circles that intersect each other as the two disks do, there will be two points at which the intersection occurs… These two points on the Moon’s orbit (where the Moon lies in the same plane as the Earth’s orbit) are called nodes, and the line connecting these two points is called the line of nodes,” according to a report by Pennsylvania State University. Whenever the new moon crosses one of these nodes, there is an opportunity for solar eclipses.