Solar Eclipse: The Science Behind the Shadow

by Yuvi K - January 7, 2024

Solar Eclipse: The Science Behind the Shadow

A solar eclipse is a spectacular celestial event that occurs when the Moon passes between the Earth and the Sun, blocking out a portion of the Sun’s light. It is the Earth’s best-known natural phenomenon, and one of nature’s great wonders.[1]

The Moon’s orbit is elliptical, so its distance from the Earth changes throughout the month. As the Moon passes in front of the Sun, its shadow casts a dark silhouette over the Earth’s surface. When and where this shadow passes can vary, depending on the Moon’s position relative to the Earth. This shadow is known as the umbra.[2]

This article will explore what causes eclipses and how the shadow of the Moon passes over the Earth.

Causes of Eclipses

Unlike a lunar eclipse, a solar eclipse does not occur every month. It happens only when the Moon is in just the right position to align with both the Sun and the Earth, a phenomenon called syzygy. Such alignments occur at least twice a year in some parts of the world.[3]

To understand how this works, it is important to consider the size and orbits of both the Earth and Moon. From the Earth’s surface, the Moon appears to be roughly the same size as the Sun. This is because the Moon’s orbit around Earth is about 400 times closer than the Sun’s. So in a syzygy alignment, the Moon’s shadow covers the Sun’s disk.[4]

The angle that this shadow sweeps across Earth is determined by the Moon’s position in its orbit. If the Moon is near its closest point (perigee) to Earth, its shadow will be larger. If the Moon is farther away (apogee), the shadow will be smaller.[5]

Types of Solar Eclipse

There are three types of solar eclipses: total, partial, and annular. During a total eclipse, the sun is completely covered. This type of eclipse is often referred to as “totality” and usually lasts for only a few minutes. A partial eclipse happens when only part of the Sun is obscured. An annular eclipse happens when the Moon is at its farthest point from the Earth, so its shadow is too small to completely obscure the Sun. Instead, a bright ring (or annulus) of sunlight surrounds the Moon’s silhouette.[6]

Eclipse Duration

The length of an eclipse is determined by its type and where it happens on Earth. For example, a total eclipse can last for up to 7 minutes and 41 seconds while an annular eclipse may last up to 12 minutes and 10 seconds. A partial eclipse can last anywhere from a few seconds to a few hours, depending on the position of the Moon and Sun. [7]

The Path of the Moon’s Shadow

As the Moon moves in its orbit, its shadow passes through different parts of the world, from east to west. A total eclipse can pass over millions of people at the same time and may even span multiple countries. The path of the umbra usually follows a narrow band around 70 miles (110km) wide. This band is known as the path of totality.[8]

The speed of the umbra’s movement also varies depending on the Moon’s position. When the Moon is near its perigee, the umbra moves faster. When the Moon is near its apogee, the umbra moves slower. The umbra usually moves across Earth’s surface at an average speed of 1,400 miles (2,300 km) per hour.[9]

Conclusion

A solar eclipse is a spectacular phenomenon that occurs when the Moon lines up just right to pass in front of the Sun and cast its shadow over the Earth. During a total eclipse, the Sun is completely covered, and the path of the umbra may pass over millions of people at the same time. It can last for up to seven minutes, depending on the Moon’s distance from the Earth. Annular and partial eclipses are also possible, depending on the positioning of the Moon.

Eclipses are awe-inspiring events, but they can also teach us a lot about the science of space, as well as the ways in which the Moon affects the Earth. Next time we are fortunate enough to witness one, let’s take a moment to appreciate its beauty and reflect on the many mysterious processes which make it possible.

References

[1] National Geographic: What Is a Solar Eclipse?

[2] National Solar Observatory: The Formation of Solar Eclipses

[3] Space.com: Solar Eclipses: What They Are and Why They Happen

[4] National Solar Observatory: Maximum Solar Eclipses

[5] Sky & Telescope: The Cycle of Solar Eclipses

[6] National Aeronautics & Space Administration: Solar Eclipse

[7] Great American Eclipse: Eclipse Facts

[8] National Geographic: Earth’s Shadow

[9] National Geographic: Eclipse Paths