Solar Eclipse Definition: What Is a Total Vs. Partial Eclipse of the Sun?

On August 21, millions of Americans who live in the path of totality will experience the first total solar eclipse visible over the U.S. since 1979. But if you don’t live in that path, you will actually see a “partial solar eclipse.” In both cases, the moon’s shadow falls on the earth, with the moon right between the earth and the sun.

NASAA diagram of why eclipses happen from NASA. AS you can see, it happens exactly when the three objects – sun, moon and earth – are lined-up.

What’s the difference between the two? Here’s a look at the different types of solar eclipses.

Total Solar Eclipse

NASAThe path of totality is the dark line through the U.S. in the above NASA map.

First, here is the basic explanation of what causes and eclipse, via NASA:

Solar Eclipses Happen when the moon moves between Earth and the sun. You might think that this should happen every month since the moon’s orbit, depending on how it is defined is between about 27 and 29 days long. But our moon’s orbit is tilted with respect to Earth’s orbit around the sun by about five degrees. Not much, you say? Yes, but the moon, itself, is only about ½ degree in width in the sky, about ½ the width of your pinky finger held at arm’s length. So, sometimes the moon misses too high and sometimes too low to cause a solar eclipse. Only when the sun, moon, and Earth line up close to the “line of nodes”, the imaginary line that represents the intersection of the orbital planes of the moon and Earth, can you have an eclipse.

As NASA explains, a total solar eclipse occurs when the moon comes between Earth and the sun, blocking our view of the sun. The sun’s corona, its upper atmosphere, will still be visible, creating a “halo” effect. The event can take up to three hours from beginning to end, while the exact moment that the moon covers the sun lasts around two minutes and 40 seconds.

Those who live in the 14 states – or who are visiting them to get a great view – will see a total eclipse. The path cuts diagonally south from Oregon to South Carolina. People along the path of totality will experience almost complete darkness at totality. This means you’ll be able to see planets and stars in the middle of the day when you typically only see them at night. Those standing in the path of totality will be within the umbral shadow of the moon.

The last time a total solar eclipse happened over the contiguous U.S. was in February 1979. That total eclipse was only visible for residents in the Northwest. So the 2017 total eclipse is the first time since 1918 that a path of totality will run completely from one coast to the other.

The total eclipse begins in Oregon at around 9:06 a.m. PDT, NASA notes. Totality will start at 10:19 and end at 10:21. The eclipse will be over at 11:41.

On the east coast, Columbia, South Carolina residents will see the eclipse begin at 1:13 p.m. EDT and end at 4:06 p.m. EDT. Totality starts at 2:41 and ends at 2:44.

The states in the path of totality are (from west to east) Oregon, Montana, Idaho, Wyoming, Nebraska, Iowa, Kansas, Missouri, Illinois, Kentucky, Tennessee, Georgia, North Carolina and South Carolina.

Partial Solar Eclipse

GettyA partial solar eclipse visible in France in 2011.

Even if you live far from the path of totality, especially in the Northeast and Southwest, you will still see a Partial Solar Eclipse. The partial solar eclipse happens when the moon never completely covers the sun. If you live in Southern California, you’ll see at least 75 percent of the sun covered by the moon. If you live in New York and other northeast cities, you’ll see around 70 percent of the sun covered.

That won’t be enough to experience complete darkness in the middle of the day, but you still need safe, specially made eclipse glasses to view the partial eclipse. You can cause permanent damage to your eyes if you star directly at a total or partial eclipse.

Those who see a partial solar eclipse are standing in the penumbral shadow of the moon. It’s a much larger shadow than the umbra, which is seen by those standing in the path of totality.

2 Other Kinds of Solar Eclipses

GettyAn annular solar eclipse viewed from Japan in 2012.

As NASA explains, there are two other types of solar eclipses. The first is the “Annular Eclipse,” in which the moon appears in the center of the sun, but it doesn’t completely cover it. This happens because the moon’s orbit of the earth is elliptical – meaning it is sometimes closer or further from Earth. It creates a “ring of fire” around the moon.

The fourth kind of eclipse is a “hybrid eclipse,” which happens when a total eclipse becomes an annual eclipse, or vice versa. All total eclipses are considered a “hybrid eclipse,” but not all annual eclipses are total eclipses. For example, the August 21, 2017 eclipse is both a total eclipse and a hybrid eclipse. The May 20, 2012 solar eclipse, which was the last annual eclipse visible to anyone in the U.S. (its path of totality ended in the Northwest), was an annular eclipse.

The next annual eclipse is on December 26, 2019, but this will be visible only to those in Southeast Asia and Australia. The next total/hybrid eclipse takes place on July 2, 2019 and will only be visible to those living in the Southern Hemisphere. The only countries its path of totality crosses through are Chile and Argentina.

The October 14, 2023 eclipse is the next annular eclipse visible in the U.S. The next total eclipse visible in the U.S. is the April 8, 2024 eclipse, although it won’t be anything like this week’s coast-to-coast eclipse. The August 12, 2045 total eclipse will have a path of totality that goes from coast-to-coast.

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