What You Need to Know About the Total Solar Eclipse of 2017

Where will you be on August 21, 2017? It may sound like a long way off, but you’ll want to mark your calendar and start planning now. On that date, the 2017 solar eclipse will pass over the continental United States from Oregon to South Carolina in what could be the most exciting celestial event of our lifetimes.

What is a total solar eclipse?

A total solar eclipse is a daytime astronomical event that occurs when the Earth, Moon, and Sun align. It’s all about geometry. All three celestial objects—Moon, Sun, and Earth—must line up perfectly to cause a total solar eclipse. That gets complicated when adding in factors like the tilt of the Earth and the slightly irregular orbits of the objects involved.

What does a total eclipse look like from the ground?

As the Moon casts its shadow over the rotating globe of the Earth, observers on the ground report many unusual and breathtaking phenomena. As the eclipse draws near, the sky darkens near the Sun, but remains light along the horizon, creating a “360-degree sunset.”

Just before totality, some observers can see the “diamond ring.” As the last bit of sunlight penetrates craters and valleys on the Moon’s surface, sunlight forms a bright spot resembling a diamond solitaire while the rest of the Moon’s disk forms a perfect ring.

Once the eclipse reaches totality (when the Moon completely covers the solar disk), the sky darkens to a deep twilight. Stars and planets become visible during the day. It’s during these exciting and fleeting moments that we can observe the Sun’s corona. The word corona means “crown” in Latin, and it refers to the outermost layer of plasma radiating from the surface of the Sun. Within the corona, brighter regions like coronal mass ejections, solar flares, and solar prominences are sometimes seen.

Where can I view the 2017 eclipse in the US?

You must be completely within the path of totality to view the eclipse. A partial eclipse will not provide the same experience of daytime sky darkening. NASA has created a map showing where the eclipse will be visible.

The eclipse makes landfall in Oregon and, traveling at a rate of 1 mile every 2 seconds, passes through 12 states on its journey across the US. Oregon, Idaho, Wyoming, Nebraska, Kansas, Iowa, Missouri, Illinois, Kentucky, Tennessee, North Carolina, and South Carolina will all experience totality.

Notably, the eclipse will pass over several state capitols including Salem, OR, and Lincoln, NE. The point of greatest eclipse is in Hopkinsville, KY, while the point of longest duration is just outside Carbondale, IL, with 2 minutes 41 seconds of totality. The eclipse will pass over half of St. Louis, half of Kansas City, and Grand Teton National Park in Wyoming. The complete city limits of Nashville, TN, and Charleston, SC, also lie within the path.

How rare are total eclipses in the United States?

Even when everything lines up correctly, there’s a high chance that the total eclipse will occur over water or the Moon will be too far away from the Earth, causing an annular eclipse, also known as the “Ring of Fire.” When the Moon’s alignment is slightly off-center, a partial solar eclipse occurs. These are fairly common, usually occurring about once per year somewhere in the world.

The last time a total eclipse was visible in the United States was over the Hawaiian islands in 1991. Unfortunately, bad weather clouded out the skies, putting a damper on things for observers. The last eclipse in the lower 48 was back in 1979. Before that, the last coast-to-coast eclipse occurred 99 years before this one in 1918.