An Astronomer's Lowdown on the Solar Eclipse

The Aug. 21 total eclipse is the first in the continental U.S. in 38 years
image of a solar eclipse
“Never view an eclipse directly or through binoculars or telescopes that are not equipped with special solar filters,” said Anna Sajina. Photo: Ingimage
August 14, 2017

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The first total solar eclipse to be seen in the continental United States since 1979 will make its way across the country on Aug. 21. The path of totality—the area in which the sun will be completely blocked out by the Moon—travels east from Oregon to South Carolina, starting at 10:18 a.m. Pacific time, and ending at 2:48 p.m. at Charleston.

We asked Anna Sajina, associate professor of astronomy and astrophysics, to tell us more about the eclipse, and what we can expect here in Massachusetts.

Tufts Now: How often do total solar eclipses occur, and is there a regularly occurring pattern?

Anna Sajina: Yes, these are regularly occurring phenomena, as the Moon’s orbit around the Earth and the Earth’s orbit around the Sun are very consistent. The question on how often depends on whether you mean “from anywhere on Earth” or from a specific place on Earth. The first is pretty often, actually; roughly once every 18 months, somewhere on Earth experiences a total solar eclipse.

However, the path of totality—where a total solar eclipse can be seen—is quite narrow, so any given eclipse is visible from a very small portion of the Earth. Any given place on Earth will experience a total solar eclipse only once in about every 360 years, though it varies by location.

A useful guideline to consider is when the last time a total solar eclipse was visible from anywhere within the mainland U.S., which was 1979.

Why is it that we only see a partial eclipse in Massachusetts?

It is because we are outside the path of totality. The eclipse is the result of the Moon completely blocking the Sun, but only if you’re looking at it from the right point of view—basically where your location on Earth, the Moon and the Sun form a straight line. From Massachusetts’ point of view in this eclipse, the Moon only partially covers the Sun. 

What’s the safest way to view the eclipse?

Never view an eclipse directly or through binoculars or telescopes that are not equipped with special solar filters. The easiest and cheapest way is through solar glasses, which are inexpensive and widely available.

Several organizations around Boston have organized viewings, including the Boston Public Library, the Medford Public Library and MIT.

What can scientists learn from eclipses?

The best scientific use of total solar eclipses is that they allow us to study the solar corona, an aura of plasma that surrounds the Sun that is hard to observe otherwise. 

Taylor McNeil can be reached at taylor.mcneil@tufts.edu.