How to see the August 2017 solar eclipse
A guide to watching the total eclipse of the Sun on August 21 2017.
The last total solar eclipse visible from the United States occurred 38 years ago in 1979. The next is due to occur on Monday August 21, 2017. If you miss this one, there won’t be another chance in the continental US until 2024.
What is a total solar eclipse?
A total solar eclipse occurs when the Moon, passing between the Sun and the Earth, fully blocks the Sun, leaving just the star’s upper atmosphere, its corona, visible as a halo.
This is only possible due to a happy coincidence of size and distance: while the radius of the Sun is approximately 400 times that of the Moon, the Sun’s distance from Earth is also about 400 times the Moon’s. This means that both Sun and Moon appear about the same size to the eye of a ground-based observer.
The effect of a perfect total eclipse depends on the closeness of the Moon to the Earth. When the Moon happens to come between the Earth and the Sun while it is at the furthest distance of its elliptical orbit around our planet, it would appear slightly smaller than the Sun from our vantage point on the ground, resulting in an ‘annular’ – or ring-shaped – eclipse, with the rim of the Sun remaining visible.
When and where will this eclipse be visible?
While a partial eclipse can take place over several hours, a total eclipse lasts just a few minutes. It can only be seen by those in the “path of totality”, while people in a much larger area will be able to see the partial eclipse.
In this case the path of totality is about 112 kilometres (70 miles) wide and extends from the northwest to the southeast of the US. The eclipse will begin in Oregon at 9:06:43 PDT and will proceed through Idaho, Montana, Wyoming, Nebraska, Kansas, Iowa, Missouri, Illinois, Kentucky, Tennessee, North Carolina, Georgia, and South Carolina – where it will end at 2.48pm EDT.
The best locations to see an optimum total eclipse will be in southern Illinois and western Kentucky. In Hopkinsville, Kentucky, which will experience the eclipse at its longest duration – 2 minutes, 41 seconds – the population of 33,000 is expected to swell by more than 200,000 visitors.
A partial eclipse will be visible across North America, as well as in parts of South America, Africa and Europe. But everyone anywhere in the world can join in the full experience by watching the event courtesy of NASA’s 4.5-hour webcast. Beginning at 11:45 am EDT (3:45 pm UTC), the webcast from Southern Illinois University in Carbondale, Illinois, will track the eclipse from Oregon to South Carolina.
How do I watch the eclipse directly?
There are important safety precautions to be taken when observing the eclipse. Outside the phase of ‘totality’, looking straight at the Sun or through an optical device can cause great damage to your eyes. NASA advises that even when 99% of the Sun’s surface is obscured during the partial phases of a solar eclipse, the light from the remaining crescent is still intense enough to cause a retinal burn.
Specialised solar filters known as ‘eclipse glasses’ should be worn directly and used with equipment such as binoculars and cameras. The American Astronomical Society has this useful list of reputable manufacturers and authorized dealers of solar filters and viewers.
The only time the filters can be removed is during the total eclipse, as the moon will be completely blocking the sun.