Solar Eclipse

Table of contents

What is an Eclipse?

An eclipse (solar eclipse or a lunar eclipse) occurs when one body passes in front of and obscures another body.
In general, an eclipse typically refers to the Sun being blocked by the Moon (a solar eclipse) or the Earth blocking the Sun (a lunar eclipse).
In order for this to occur, the three bodies (Sun, Moon, and Earth) have to be in a nearly perfectly straight line.

A solar eclipse is a celestial event that occurs when the Moon passes between the Earth and the Sun, fully or partially blocking the Sun’s view and casting a shadow on Earth.

Umbra and Penumbra

When the Moon does eclipse the Sun, it casts two types of shadows on Earth: a smaller, darker shadow known as the umbra and a larger shadow known as the penumbra.

What is Path of Totality?

When the moon completely covers the sun, it casts a shadow on Earth, forming a “path of totality.” This path is a relatively narrow band that moves across the surface. People on the path of totality can see the moon completely covering the sun.

Why does a solar eclipse occur only on a new moon day?

For a Solar eclipse to occur, the moon must be between the sun and the Earth, which can happen only on a New Moon Day.

Why a solar eclipse does not occur on every new moon day or every month?

A solar eclipse (two to five a year) does not occur on all new moon days (12 to 13 a year) because the Moon doesn’t orbit in the same plane as the Sun and Earth (the lunar orbital plane does not coincide with the ecliptic plane, i.e., they don’t lie in the same plane).

Why does a solar eclipse occur only during a few new moon days?

For a Solar eclipse to occur, it must be a new moon day, and the sun, the Earth, and the moon must lie in almost the same plane. This is only possible when the moon’s position on a new moon day is close to the ascending and descending nodes — where the lunar orbit (selenocentric orbit) intersects with the ecliptic plane.

Types of Solar Eclipse

Total Solar Eclipse

A total solar eclipse occurs only when the Moon passes exactly between the Sun and Earth, completely blocking the face of the Sun and casting an umbra (the smaller, darker shadow of the Moon) on Earth.
People in a total solar eclipse (path of totality) can see the Sun’s corona. This outer atmosphere is otherwise usually obscured by the Sun’s bright face.

Annular Solar Eclipse

An annular solar eclipse happens when the Moon passes exactly between the Sun and Earth but when it is at or near its farthest point (Apogee) from Earth.

Because the Moon is farther away from Earth, it appears smaller than the Sun and does not completely cover the Sun. As a result, the Moon appears as a dark disk on top of a larger, bright disk, creating what looks like a ring formed by the sun around the Moon (annulus / Ring of Fire).

Partial Solar Eclipse

A partial solar eclipse occurs when the Sun, Moon, and Earth are not perfectly lined up, and the Sun, which is only partially covered by the moon, appears as a crescent.
During a total or annular solar eclipse, people inside the penumbra see a partial solar eclipse.

Hybrid Solar Eclipse

Because of the earth’s curved surface, sometimes an eclipse can shift between annular and total as the Moon’s shadow moves across the globe. This is called a hybrid solar eclipse.

Factors affecting the duration of Total Solar Eclipse

Distance of the Moon from Earth

The closer the Moon is, the larger it will appear in the sky, and the longer it will be able to cover the Sun.
If the Moon is near its farthest point from Earth (apogee), totality is not possible because the Moon is too small to completely cover the Sun.

Distance of the Earth from the Sun

The farther Earth is from the Sun, the smaller it will appear, and the easier it will be for the Moon to cover the solar disk.

Location of the observer in the umbra

If one is near the center of the path of totality, the widest part of the shadow passes over and totality is longer.
If one is near the edge of totality, then there may be only a few seconds of total eclipse.
If one is near where the umbra shadow just comes into contact with the Earth, totality will be very short due to the shadow racing over the curved surface of the planet.

What can be observed during a Solar Eclipse?

Corona

Corona is the outermost layer of the Sun’s atmosphere.
The corona is made up of ionized gas called plasma, with its temperatures upto many millions of degrees.
The corona is visible to the naked eye only during a total solar eclipse.

Solar Chromosphere

The part of the edge of the Moon looks like it is highlighted by a very thin, deep-red crescent.
This glowing red feature is the lower portion of the Sun’s atmosphere, which is known as the chromosphere. Named for its stark colouration, the chromosphere is approximately 10,000 degrees Celsius and is comprised of hydrogen gas emitting its distinctive red colour.

Prominences

Immediately after the diamond ring and during totality, Prominences may be seen.
They appear as pink fiery features extending out from the black disc of the moon, held in place by the Sun’s magnetic field.
They are actually giant gaseous extensions from the Sun.

Bailey’s Beads

Bailey’s Beads are named after English astronomer Francis Baily, who is credited as the first person to describe them after seeing an annular eclipse in 1836.
The beads are due to the irregularities on the Moon’s surface that allow slight portions of the Sun’s surface (the photosphere) to shine through.
The beads are typically most visible along the edge of the path of totality but can sometimes be observed in the few seconds before and after totality.

Diamond Ring

The Diamond Ring effect occurs during the few seconds before and after totality while an extremely small fraction of the Sun’s photosphere is still visible.

FAQs

What happens during a solar eclipse?

The Moon casts two shadows – a lighter, outer shadow known as the penumbra and a darker, inner shadow known as the umbra.
Eclipse viewers located in the larger penumbra shadow will only witness a partial solar eclipse.
The closer to the umbra (the darker, inner shadow of the Moon), the more of the Sun that is obscured and the longer the partial eclipse.

How often does a solar eclipse takes place?

A solar eclipse is witnessed only during the new moon — when the Moon and Sun are aligned on the same side of Earth.
Although a new moon occurs about 29.5 days (the time taken by the Moon to orbit Earth), a solar eclipse takes place only two to five times annually. It is because the Moon does not orbit Earth in the same plane as the Earth orbits the Sun.
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.

Why is a total solar eclipse so rare?

While there can be between two and five solar eclipses every year, total eclipses only happen about once every 18 months or so and a particular spot on Earth witnesses a total solar eclipse only once in 400 years. This is because a total eclipse is only visible if one is standing in the umbra — the other part of the shadow is called the penumbra, which is not as dark as the umbra.
The umbral shadow is very small, covering only a small part of Earth. In fact, the entire path of the umbral shadow during a solar eclipse will only cover less than one per cent of the globe.

Reference: IE | PMF IAS Physical Geography > Motions of The Earth

PMF IAS Pathfinder for Mains – Question 4

Q. Write a note on Solar Eclipse. What are the types of solar eclipses? (150 Words – 10 marks) (250 Words – 15 marks)

Answer Writing Approach

IBC: Introduction-Body-Conclusion (I-B-C) approach is not required as this is a fact-based question.
Diagrams: As the topic has a lot of jargon and is hard to visualise, it’s necessary to provide sketches.
Scoring Brownie Points: Use some jargon and keywords in the brackets. Try to fill up all the important information in fewer words (it comes with practice).