Understanding Eclipses: Types, Causes, and Scientific Importance

Eclipses

Eclipses are cosmic events that occur when the orbits of Earth, the Moon, and the Sun align, causing shadows to be cast over the Moon or Earth. The Moon's orbit around Earth is tilted relative to Earth's orbit around the Sun, which is why we have occasional eclipses instead of eclipses every month. There are two types of eclipses: lunar and solar.

Lunar Eclipses

Lunar eclipses occur at the full moon phase. During a lunar eclipse, Earth's shadow falls upon the surface of the Moon, dimming it and sometimes turning the lunar surface a striking red over the course of a few hours. Each lunar eclipse is visible from half of Earth.

Types of Lunar Eclipses

Total Lunar Eclipse

Total lunar eclipses occur when the Moon moves into the inner part of Earth's shadow, the umbra. Some of the sunlight passing through Earth's atmosphere reaches the Moon's surface, lighting it dimly. The colors with shorter wavelengths scatter more easily than colors with longer wavelengths, and the longer wavelengths make it through Earth's atmosphere, causing the Moon to appear orangish or reddish during a lunar eclipse.

Partial Lunar Eclipse

An imperfect alignment of Sun, Earth, and Moon results in the Moon passing through only part of Earth's umbra. The shadow grows and then recedes without ever entirely covering the Moon.

Penumbral Eclipse

If you don't know this one is happening, you might miss it. The Moon travels through Earth's penumbra, or the faint outer part of its shadow. The Moon dims so slightly that it can be difficult to notice.

Solar Eclipses

Solar eclipses vary in appearance, but the phenomenon is always stunning.

Total Solar Eclipse 2024

On April 8, 2024, a total solar eclipse will cross North America, passing over Mexico, the United States, and Canada.

The Moon's Tilted Orbit

The Moon's orbit is tilted about 5 degrees compared to the plane of Earth's orbit around the Sun. This tilt prevents us from having monthly solar and lunar eclipses.

Eclipses and Spacecraft

Solar eclipses happen only at the new moon phase, usually about twice a year, when the moon aligns itself in such a way that it eclipses the sun, according to NASA.

Types of Solar Eclipses

There are four different types of solar eclipses depending on how the sun, moon, and Earth are aligned at the time of the event:

Total Solar Eclipse

Total solar eclipses occur when the moon passes between the sun and Earth, completely obscuring the face of the sun.

Partial Solar Eclipse

Partial solar eclipses occur when the moon passes between the sun and Earth when the trio is not perfectly aligned. As a result, only the penumbra (the partial shadow) passes over you, and the sun will be partially obscured.

Annular Solar Eclipse

Annular solar eclipses occur when the moon passes between the sun and Earth when it is near its farthest point from Earth. At this distance, the moon appears smaller than the sun and doesn't cover the entire face of the sun. Instead, a ring of light is created around the moon.

Hybrid Solar Eclipse

Hybrid solar eclipses are rare and occur when the moon's distance from Earth is near its limits for the inner shadow (the umbra) to reach Earth and because the planet is curved. Hybrid solar eclipses are also called annular-total (A-T) eclipses.

Why We Observe Solar Eclipses

Studying the innermost part of the corona, visible only during total solar eclipses, is key to answering fundamental questions about how heat and energy are transferred from the Sun out into the solar wind, the constant stream of particles that the Sun spews into the solar system.

Total solar eclipses provide an opportunity to study Earth's atmosphere under uncommon conditions. The localized blocking of solar energy is useful for studying the Sun's effects on our atmosphere, especially the upper atmosphere, where the Sun's energy creates a layer of charged particles called the ionosphere.

During the 2017 total solar eclipse, NASA funded 11 scientific studies to collect data only available during eclipses.

Recent Solar Eclipse Science

The 2019 eclipse in South America was observed by NASA's Global-scale Observation of Limb and Disk – GOLD – mission, which provided the first measurements of how eclipses affect the layer of Earth's atmosphere called the thermosphere.

In 2021, scientists published findings made with over a decade of eclipse observations.

Discover More Topics From NASA

If you're interested in learning more about eclipses, NASA has a wealth of resources available on their website, including articles on the science behind eclipses, upcoming eclipse events, and how to observe eclipses safely.