Solar eclipse questions and answers

How fast will the shadow move?

The umbra (shadow) will cover almost 2,500 miles, from Oregon to South Carolina, in 94 minutes. That works out to 27 miles per minute, or about 1,600 mph — about three times faster than a commercial jetliner. But it moves faster at each end and slower in the middle of the U.S. Totality will move through Oregon at more than 2,000 mph.

Why is it unsafe to look at the sun when only a small part of it is visible?

The sun’s surface is so bright that if you stare at any portion of it, no matter how small, it produces enough light to damage individual retinal cells. It takes a few seconds for this to happen, but afterwards you will see a spot as big as the solar surface you glimpsed. Depending on how long you gazed at the sun and how badly the retinal cells were damaged, this spot will either fade away or be permanent. Never assume that you can look away quickly enough to avoid eye damage.

Is bright light the only danger when viewing the sun?

While filters and glasses do safely block intense sunlight that damages retinas, the infrared “heat” from the sun can also make viewing uncomfortable as it literally warms the eye. Staring at the sun for minutes at a time even with proper filters can still over-heat the tissues and fluids in the eye, which can be dangerous. Look away frequently.

 What are the earliest recorded and predicted total solar eclipses?

Historians and astronomers believe that the earliest was recorded in China on Oct. 22, 2134 B.C. An eclipse on May 3, 1375 B.C. in Babylonia was the first successfully predicted eclipse in the western world.

 Can I photograph the eclipse with my smartphone?

The short answer is yes, but most won’t look very good because of issues with magnification, focus, exposure and vibration. (And be careful about glimpsing the bright sun with your eyes without the benefit of a proper filter.)

Guidelines for taking successful smartphone images are at: eclipse2017.nasa.gov/sites/default/files/Photographing_the_Eclipse_with_ your_Smartphone.pdf.

 When was the last total solar eclipse seen from the contiguous United States, and when is the next one?

The last total solar eclipse viewed from the contiguous U.S. was on Feb. 26, 1979; the path passed through Washington, Oregon, Idaho, Montana and North Dakota, and Saskatchewan, Manitoba, Ontario and Quebec in Canada. The next total solar eclipse on April 8, 2024 will be visible from Texas to Maine.

 Is there any current scientific value for studying eclipses?

In 1919, a total solar eclipse was used to test Einstein’s theory of general relativity. Currently, there have been attempts to detect interplanetary dust falling into the sun by searching for its faint infrared light beyond the corona. Scientists also are studying the solar transition region when totality provides glimpses of it.

Can I use eclipse glasses after Aug. 21?

Yes, you can view the sun any time. You may occasionally see tiny dark spots on it: These are sunspots — cooler areas on the sun’s surface that look darker to us. But make sure there are no cracks or other damage to the glasses, and you should discard them after three years.

 How long will we continue to see total eclipses of the sun?

Because of tidal friction, the orbit of the moon is increasing by 1 1/2 inches per year. When the moon’s mean distance from Earth has increased an additional 14,600 miles, it will be too far away to completely cover the sun; that will occur in a bit less than 600 million years.

— Sources include eclipse2017.nasa.gov, eclipse2017.org