Look up!

See the Sun plunge into total darkness

A guide to this awe-inspiring cosmic phenomenon.

by Kate S. Petersen
Originally Published: 

On August 21, 2017 215 million Americans watched in awe as the Sun briefly went dark in a total solar eclipse. The sheer number of people who gathered to witness this cosmic phenomenon eclipsed the turnout for the 2020 presidential vote — a testament to how the universe can move us even when our terrestrial concerns cannot.

On December 14, there will be another chance to marvel at the Sun, as this bright, fiery orb becomes obscured once more. To prepare you for the big day, here's everything you need to know about solar eclipses, how to see them in action, and when you need to look up.

What is a solar eclipse?

As the Moon orbits the Earth, it sometimes ends up positioned between the Earth and the Sun. In this position, it blocks the Sun’s light, resulting in a solar eclipse. While rare, these moments of cosmic alignment are fleeting, typically only last for a few minutes, according to NASA.

Schematic of a total solar eclipse


There are three different kinds of solar eclipse, each dependent on the relative position of the Moon, Earth, and Sun.

  • Total solar eclipse: The Earth, Sun, and Moon are in direct alignment, and the Moon fully obscures the Sun.
  • Partial solar eclipse: The Moon passes in between the Sun and the Earth, but the three are not perfectly lined up. The Moon obscures only part of the Sun.
  • Annular eclipse: The Earth, Sun, and Moon are perfectly aligned, but the Moon is far enough from Earth in its orbit so as to only obscure the central portion of the Sun.

What makes a total solar eclipse unique?

Of the three types of solar eclipses, the total eclipse is most dramatic. For it to occur, the Earth, Moon, and Sun have to be in direct alignment, and it can only be seen from a small band across Earth called the 'path of totality.'

Similar to a lunar eclipse, the Moon casts two shadows onto the Earth. One is called the umbra and the other the penumbra. The umbra refers to the darker, inner shadow and it is only from a perspective inside the umbra that the Sun will appear fully obscured during a total eclipse. From the penumbra, you can still see the eclipse, but it will look more like a partial eclipse.

Partial solar eclipse during Australian brushfires in 2002

Manfred Gottschalk / Getty Images

What does a total solar eclipse look like?

As the Moon moves into place between the Earth and our star, it looks like an ever-increasing bite has been taken out of the Sun. The darkness grows as the eclipse progresses. Eventually, the Sun becomes completely obscured. From our vantage point, it looks as if the Sun has turned black and is surrounded by a halo of pulsing light.

During a total solar eclipse, the interaction between the Sun and Moon is only a part of this visual feast. Because the light of the Sun is blocked, it creates some pretty weird effects on Earth.

The sky grows dark as though the Sun is setting. Shadow bands — thin, wavy lines caused by light distortions from the Earth’s atmosphere — appear on surfaces. A particularly strange effect are crescent shadows, which look like moons early in their cycle of waxing and waning. Once the sky is fully darkened, the horizon may glow red, similar to a sunset.

Crescent shaped shadows as seen through a colander during solar eclipse in 2006

Andrew Holt / Getty Images

How often do solar eclipses occur?

Solar eclipses are relatively common phenomena. Most years, there are two solar eclipses of any kind, but just a third of these — some 27 percent — will be total eclipses, according to NASA.

Do other planets experience solar eclipses?

Yes! NASA’s Curiosity rover captured images of an annular eclipse on Mars caused by the moon Phobos on March 26, 2019. Curiosity also got some shots of another Martian moon, Deimos, crossing in front of the Sun, but since the moon is so small, NASA dubbed the event a “transit” rather than an eclipse, according to NASA.

This series of images shows the Martian moon Phobos as it crossed in front of the Sun.


Can a total solar eclipse happen at night?

Technically, yes, because it is always night somewhere during a solar eclipse, and the eclipse itself will simulate nightfall. The Sun has to be visible to for you to observe a solar eclipse in action, however.

When is the next solar eclipse?

The next total solar eclipse will happen on December 14, 2020 at 11:15 a.m. Eastern.

The eclipse will be visible from the Pacific, South America, and Antarctica. The path of totality runs through the South Pacific, Chile, Argentina, and the South Atlantic.

The next total solar eclipse will occur in December 2021, and be most visible from Antarctica, according to NASA.

Unfortunately, we in the United States will miss these cosmic events. But mark your calendars: A total solar eclipse predicted for April 8, 2024, will be fully visible from North America.

There is also an annular solar eclipse supposed to take place on October 14, 2023 which will also be visible to people in the United States.

Annular solar eclipse in Qatar in 2019

Sorin Furcoi / Getty Images

What is the best way to view a solar eclipse?

A total solar eclipse is relatively uncommon phenomenon, and when they do happen, they will only ever be visible from certain parts of the Earth.

To safely view an eclipse, wear appropriate eye protection such “eclipse glasses” that meet the ISO 12312-2 international standard. Looking directly at the Sun without protection will damage your eyes.

Use eclipse glasses to safely view a solar eclipse

LeoPatrizi / Getty Images

Solar eclipse calendar for North America, 2020 - 2025:

All times are in Eastern.

  • June, 10 2021: Annular eclipse occurring at 5:41 a.m., most visible over Northern Canada
  • October 14, 2023: Annular eclipse occurring at 1:00 p.m., most visible over the Western United States
  • April 8, 2024: Total eclipse occurring at 1:18 p.m., most visible over the United States and Eastern Canada.

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