This map of Colorado and its neighboring states shows the path of the Moon's umbral shadow — the path of totality — during the total solar eclipse on August 21, 2017, as well as the percent obscuration (the fraction of the Sun's area covered by the Moon) in places outside the umbral path. The Denver Metro area will have over 90% obscuration. Source: NASA
On Monday, Aug. 21, 2017, a total eclipse will cross the entire country, coast-to-coast, for the first time since 1918. Weather permitting, the entire continent will have the opportunity to view an eclipse as the moon passes in front of the sun, casting a shadow on Earth’s surface. And plans for this once-in-a-lifetime eclipse are underway – scientists are submitting research proposals, NASA is sharing information on safe eclipse viewing with community centers, and citizen science projects are developing.
The total solar eclipse begins near Lincoln City, Oregon, at 10:15 a.m. PDT (1:15 p.m. EDT). Totality ends at 2:48 p.m. EDT near Charleston, South Carolina. The partial eclipse will start earlier and end later, but the total eclipse itself will take about one hour and 40 minutes to cross the country.
Solar eclipses occur when the moon blocks any part of the sun. Total solar eclipses, however, are only possible on Earth because of a cosmic quirk of geometry: The sun’s diameter is 400 times wider than the moon’s, but it is also 400 times farther away. The result is that the sun and the moon appear to be the same size from our perspective. When they line up just right, the moon can obscure the sun’s entire surface, creating a total solar eclipse. This line-up occurs once every 12 to 18 months. Partial solar eclipses, on the other hand, occur when the alignment is such that the moon blocks only part of the sun and these can occur more frequently.
During a total eclipse, we have the rare opportunity to look directly at the sun’s vast, striking outer atmosphere, the corona. The corona appears as pearly white rays and streamers, radiating around the lunar disk. The August 2017 eclipse will present this exciting opportunity to millions across the entire country.
But total solar eclipses are more than simply beautiful to look at. They provide unique opportunities for science – and many kinds of science at that. Indeed, total eclipses throughout history have paved the way for major scientific findings across various disciplines.
It is in the corona that we observe giant solar eruptions like solar flares and coronal mass ejections, and the origin of the solar wind, the continuous flow of charged particles from the sun. All of these constantly shape the very nature of the space around Earth and other planets.
Studying the corona and its role in the interconnected sun-space system is crucial for understanding not only the relationship between Earth and the sun, but also the space environment our satellites and astronauts must travel through for future exploration. Also, different colors provide unique information about the temperature and composition of solar material in the corona.
Of course, the beauty of the August 2017 eclipse is that anyone can view it – no science background or heavy-duty equipment is required. Even during an eclipse, it is not safe to look directly at the sun – except for the brief phase of totality, when the moon fully obscures the sun. The only safe way to look directly at the partially eclipsed sun is through a specialized filter. Eclipse glasses are equipped with the proper filters to minimize ultraviolet, visible and infrared light.
When viewing a partial eclipse, observers must use eye protection at all times. Partial eclipses can be observed indirectly by projection, in which viewers watch the eclipse on a screen. These can be easily constructed at home with few, simple materials – such as a piece of paper and cardboard box.