BROOKINGS – On Monday, the moon will pass between the Earth and the sun with the moon’s shadow crossing the continental United States in what is called a total solar eclipse. The total eclipse will be visible within a 70-mile wide path from the west coast of Oregon to the east coast of South Carolina.

The last total solar eclipse to cover this much of the U.S. was on June 8, 1918. While other types of eclipses have been visible across the United States since then, the last total solar eclipse visible on U.S. soil was in 1979, and the path of totality (darkest part of the moon’s shadow cast onto Earth) was only visible over the northwestern part of the country.

The path of totality will pass through Nebraska so observers in South Dakota will see a partial eclipse with 80-95 percent of the sun’s disk appearing covered by the moon, depending on your location in the state. The Brookings area should see about 90 percent coverage of the sun, weather permitting. In this area the eclipse will start at 11:37 a.m., reach maximum coverage at 1 p.m. and end at 2:24 p.m. An animation of the eclipse, as viewed from Brookings, can be found at https://www.timeanddate.com/eclipse/in/usa/brookings.

It is not safe to look directly at the sun during a partial solar eclipse, even with sunglasses. The safest and most direct method of viewing is with eclipse glasses or solar viewers which have specially designed filters to block out 99.99 percent of the sunlight. Fortunately, these glasses are available in the Brookings community.

A limited supply of free eclipse glasses are now available from the Yorkshire Eye Clinic. They are also available for purchase at the Children’s Museum of South Dakota gift shop, Wal-Mart and Casey’s. The SDSU Society of Physics Students will be hosting a campus viewing session near the west entrance to the Student Union and will have free eclipse glasses available at that location starting the morning of the event.

When purchasing eclipse glasses, be certain ISO 12312-2 (or EN1836) is printed somewhere on them. This certification is used to indicate they are safe for viewing the sun. Some people have used welder’s glass to view an eclipse but, according to NASA, it must be No. 14 welder’s glass to be safe. In case of inclement weather, the eclipse can be viewed online through NASA at https://eclipse2017.nasa.gov/eclipse-live-stream.

You can also indirectly view the eclipse using pinhole projection. Simply make a round pinhole in a stiff material like an index card or paper plate. Allow the sunlight to pass through the hole and project onto another white stiff material. A small image of the eclipse should be visible.

If you look on the ground under a tree, you might see many images of the eclipse as the overlapping leaves act as a natural pinhole projector.

To commemorate the Great American Eclipse, the U.S. Post Office has released a specially designed eclipse stamp. The Total Eclipse of the Sun stamp was made with thermochromic ink which reacts to heat and changes the moon’s disk from new moon to full moon phase. The back of a sheet of stamps shows the path of the total solar eclipse.

What if you miss this eclipse?

Solar eclipses are actually not rare events as there are typically two to three each year, but they are not always total eclipses and are only visible over a small area of the planet which differs with each eclipse.

The next total solar eclipse is July 2, 2019, but will only be visible in Chile and Argentina. The next total solar eclipse visible in the U.S. (partial eclipse in South Dakota) will be April 8, 2024, and will be visible from Texas to Maine.