Daylight will dim with Monday’s solar eclipse

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Partial solar eclipse on 20 of March 2015 in Saint-Petersburg, Russia

A solar eclipse will be visible across the entire U.S. on Monday, Aug. 21, but only a 70–mile–wide swath of the country will be treated to the total eclipse.

Weather permitting, North Texans will have to settle for a partial eclipse, unless they want to drive more than 400 miles to Missouri or Kansas.

In Lewisville, the event starts just about 11:40 a.m. Just after 1:09 p.m., the moon will obscure 76.1 percent of the sun before it starts moving out. By 2:39 p.m., the moon will have moved past the sun, which will be at its maximum brightness again.

Because the sun will not be fully covered for local viewers, it is not safe to look at the sun during the event in North Texas without protection.

A solar eclipse occurs when the moon passes directly between the sun and the Earth, casting a shadow on the surface. During a total solar eclipse, the moon completely covers the sun for a few minutes at most.

In portions of Missouri, Illinois, and Kentucky, according to Space.com, the sun will be completely obscured for about two minutes and 40 seconds.

Diagram showing the Earth-sun-moon geometry of a total solar eclipse.
Diagram showing the Earth-sun-moon geometry of a total solar eclipse. (Illustration by NASA)

It’s only in those places, and only during that time of totality, that NASA says it’s safe for people to look without protection at the sun’s corona, visible once the moon obscures the much brighter direct sunlight.

Optometrist Dr. Brad Cooper warned that viewing the sun without protection could damage the retinas.

“Once the retina is damaged the viewer will be permanently blinded,” Cooper said.

“Sunglasses are not enough to protect the eyes from the UV or infrared radiation released from the sun.”

NORTHLAND – NOVEMBER 14: A New Zealander father and son looks trough a welding mask at the partial solar eclipse passes over Northland New Zealand on November 14 2012. (Photo by lucidwaters)

Without protection, the sun’s rays could burn the retina in seconds. Cooper warned that looking at the sun through binoculars or a telescope could burn even more rapidly.

Cooper offered alternatives, such as using number 14 arc welder glasses without scratches or flaws.

All local retailers The Lewisville Texan Journal contacted Friday had sold out of special eclipse viewing glasses.

Cooper said the safest observation is to create a pinhole in a piece of cardboard paper.

“Position the sun behind you, and focus the sun’s rays on a white piece of paper,” said Cooper.

NASA recommends using a pinhole that is 5 millimeters in diameter — about one fifth of an inch — placed about three to four feet above the surface.

CNET has a how-to guide on its website showing how to make a pinhole viewer out of a cereal box, some paper, and aluminum foil.

Taken from Southern Lewisville on 6/5/2012, 7:40 p.m., the last transit of the planet Venus across the sun for 105 years. (Photo by Steve Southwell)

Another technique is to aim a telescope at the sun, but instead of looking through the eyepiece, focus the eyepiece on a piece of white paper several inches away. Do not look through the telescope at the sun, even to aim it.

That was the technique The Lewisville Texan Journal used in 2012 to photograph the sun as Venus transited across.

NASA’s website has information about all aspects of the eclipse and safe viewing. NASA will also provide a live stream of the eclipse online.

“Remember, direct viewing of the sun is likely to create severe and permanent damage to the retina,” Cooper said. “Don’t do it.”

Parents are advised to ensure that their children are aware of the dangers of direct viewing. Pets will probably be fine, according to LiveScience.com, but they say it doesn’t hurt to protect them anyway.

According to NASA, the last total solar eclipse viewed from the contiguous United States was Feb. 26, 1979. For people who miss the chance to see the one on Monday, the next total solar eclipse will be on April 8, 2024. Its path puts Lewisville inside the area of total eclipse.