Rabidoux explains rare solar eclipse

August 18, 2017
Dr. Katie Rabidoux

On Monday, Aug. 21, the United States will fall in the path of a total solar eclipse – a rare event that hasn’t occurred in nearly 40 years. Dr. Katie Rabidoux, an assistant professor of engineering physics at the University of Wisconsin-Platteville breaks down the details of what it is and what to expect.

What is a solar eclipse?

A solar eclipse is when the moon passes between the sun and the earth so that all three objects line up. The moon covers up the sun and the moon’s shadow is cast upon the earth. Anybody who is in the path of that shadow can see the moon covering the sun, which makes the eclipse.

How rare is a total solar eclipse?

Partial, annular or total solar eclipses can happen somewhere on earth about twice a year. A total solar eclipse at your location is a lot rarer than that. You have to be in a very particular spot on earth to see it, because the eclipse’s alignment may not match up with your location. Having the moon’s position in the sky match up with the sun’s position in the sky at your current location is a very rare event.


When was the last total solar eclipse seen from the United States?

The most recent total solar eclipse that passed over part of the continental U.S. was in 1979. The most recent annular solar eclipse that passed over part of the continental U.S. was in 2012. Research shows that the next total solar eclipse visible from the continental U.S. will be in 2024, and the next annular solar eclipse visible from the continental U.S. will be in 2023.

How much of the upcoming eclipse will be visible in Platteville?

At the eclipse maximum, 87 percent of the sun will be blocked as viewed from Platteville. The further south you go toward the eclipse’s path, the higher percentage you’ll see.

What time will the eclipse hit its peak in Platteville?

The eclipse will begin at 11:48 a.m., with its maximum peak hitting at 1:13 p.m. The eclipse will end at 2:36 p.m. Anyone can view their own location on a map at www.timeanddate.com/eclipse/map/2017-august-21?n=4895#.

How do researchers predict solar eclipses?

Astronomers can model the earth’s orbit and the moon’s orbit. They take those calculations and project them out. They can project when the moon will pass between the sun and the earth so that all three objects line up, because that’s all that needs to happen for an eclipse to occur. However, a total eclipse all depends on the particular angle that the moon passes between the sun and the earth, because that tells viewers where that eclipse will happen on earth. In order for a total or annular eclipse to occur, the moon has to pass all of the way in front of the sun’s position in the sky. If the moon is particularly close to the earth when it passes the sun, then people on earth will see a total eclipse instead of an annular eclipse.

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

Even though 80 or 90 percent of the sun is covered, there is still a lot of light that reaches earth. Your eyes are not designed to have that much light hitting them at the same time. It’s not like sunlight is more dangerous than usual during an eclipse, it’s just that there’s a higher chance that people will want to look at the sun during this time.

What is the safest way to view the eclipse?

I can tell you that normal sunglasses won’t be enough. Even if they’re really good sunglasses, they still won’t give enough protection to your eyes. There are eclipse glasses that you can buy, and if you’re going to purchase them, you should look for pairs that are ISO compliant. The specific number that you should look for when purchasing is 12312-2. NASA.gov gives a list of reputable vendors and other safety measures and tactics for those interested in viewing the eclipse.

A message from the UW-Platteville Office of Safety and Risk Management:
The Office of Safety and Risk Management reminds you that the only safe way to look directly at the uneclipsed or partially eclipsed sun is through special-purpose solar filters, such as “eclipse glasses” or hand-held solar viewers.  Homemade filters or ordinary sunglasses, even very dark ones, are not safe for looking at the sun; they transmit thousands of times too much sunlight.  For more information on safe viewing of the eclipse, please view: https://eclipse2017.nasa.gov/safety


Written by: Amanda Bertolozzi, Writer/Editor, Communications, 608-342-7121, bertolozzia@uwplatt.edu

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