While solar eclipses have existed ever since the moon was formed — which scientists say happened several billion years ago — humans’ understanding of the eclipse is more recent.

Below are answers to some common questions about eclipses.

What is a Total Solar Eclipse?

A Total Solar Eclipse is an astronomical phenomena in which the moon passes in between the Sun and Earth unveiling a solar corona as the Moon’s shadow crosses the Earth. This only occurs at a new moon. 

How often does a total eclipse happen?

On average, a total solar eclipse occurs somewhere on Earth every 18 months. The timing for a total eclipse over any specific spot, though, can vary dramatically depending on how the cosmic bodies align. According to Science.com, a ballpark estimate of 400 years is a reasonable average for any given point, but some spots on Earth can take up to 3,600 years between totalities. 

What is the difference in a partial and total eclipse?

A total eclipse occurs when the sun is completely blocked by the moon’s path, revealing the corona that normally cannot be seen with the naked eye. In a partial eclipse, the moon passes the sun off center so that a portion of the sun’s disk is still visible.

What should I look for in a Total Solar Eclipse?

An out of body experience that will be a peak moment in your life. You will look for elements such as the solar corona, Baily’s beads, shadow bands, prominences, diamond ring, the chromosphere, and not to mention the breath-taking twilight around the horizon. With clear skies in the forecast you should be able to see several planets as well.

Will I see a total eclipse?

If you live within the path of totality — a relatively narrow strip from Oregon to South Carolina — you will see a total eclipse on Aug. 21. Otherwise, observers in America will see a partial eclipse.

What is the difference between greatest eclipse and greatest duration?

The greatest eclipse is the moment the Moon’s shadow passes closest to the center of Earth and typically within a millisecond to the greatest duration.

The greatest duration is the longest point of the total solar eclipse, which is 2 minutes 40 second, located in Makanda. These terms are not to be confused with one another.

How long will this eclipse last for?

In total this total solar eclipse will last for 90 minutes from Oregon to South Carolina. This eclipse is expected to last for 2 minutes and 38 seconds in Carbondale, which is slightly north of the greatest duration. The longest eclipses have a duration over 7 minutes. 

Can I watch it online?

Yes. If the skies are cloudy or your job keeps you working at a desk, NASA is planning a two-hour-long live broadcast during the eclipse from the Newseum in Washington, D.C. It can be seen at nasa.gov or on cable television’s NASA Channel.

What time will the eclipse pass over Carbondale?

The exact time of totality is about 1:20 p.m. (CDT). We suggest that you stop what you are doing and make plans to get to a viewing destination by 12:00 p.m.

I need assistance during the weekend. Who can I contact?

There will be an Eclipse Hotline (staffed 24 hours a day from August 19-20, and from 8 a.m. – 5 p.m. on August 21) at 618-967-5220. Resources are also available at www.carbondaleeclipse.com and www.eclipse.siu.edu.