Answered by Dr. Brian Tonks, Astronomy Professor, BYU-Idaho
On 21 August, 2017, Southeastern Idaho and many other places in the United States are in for a rare treat. We will experience a total Solar eclipse. In Rexburg, the total phase of the Solar eclipse will begin at about 11:33:14 a.m. and last for 2 minutes, 14 seconds. In Idaho Falls, totality start at about 11:33:01 a.m. will last about 1 minutes 48 seconds. Because our skies are typically clear in August, we have had many inquiries about the possibility of coming to Rexburg and Idaho Falls to witness the eclipse. We have groups coming from MIT and UCLA and we are involved in a research project with scientists from Montana State University to make sky measurements during the eclipse.
Outside of the path of totality, the Moon will not cover the Sun’s entire surface, so these observers will see a partial solar eclipse. The sky may darken (depending on the extent of the eclipse) but will not become completely dark and you would not see the Sun’s corona. Those just outside the path of totality will see the sky darken. I was a student at Ricks College in 1979 when the US experienced a solar eclipse. The path of totality passed north of us; we experienced about a 90% eclipse here. I distinctly remember the sky growing darker but we could not see the Sun’s corona. Even so, it was an impressive event. The farther away you are from the path of totality, the less of the Sun will be eclipsed and those observers will not notice anything different about the day (I had that experience when we lived in Tucson Arizona. I saw the eclipse through a small telescope my parents-in-law had given me, which showed about ½ of the Sun covered, but the sky looked completely normal.).
Make sure to prepare for the eclipse by obtaining a pair of eclipse glasses. They are not very expensive. It is extremely dangerous to look at the eclipse, except during the total phase, without them. The Sun’s intense light, even if only a tiny sliver, remains uncovered and can cause severe eye damage or blindness. Check to make sure that there are no tiny cuts or pinpricks in the protective material. After making the preparations, plan to stay at home and enjoy the spectacle. Travel will probably be difficult. Although it is hard to know how many people we will expect in our area, it will likely be at least as crowded as the Melaleuca fireworks on the 4th of July!!
Total Solar Eclipse
The Aug. 21, 2017, total solar eclipse is the first in the continental United States since 1979. During a total eclipse of the Sun, the Moon covers the entire disk of the Sun and casts a shadow on Earth. Because the apparent size of the Moon is so much less than that of the Sun, this shadow will only be seen in a small area of Earth. To understand this phenomenon, let’s do a solar eclipse experiment.
Materials: Grape (Moon), orange (Earth), toothpick, small piece of Styrofoam, flashlight, ruler
- Take the Styrofoam and stick the toothpick through it. Place the grape on top of the toothpick so it is about two inches high.
- Place the orange about three inches behind the grape on a table.
- Shine the flashlight (Sun) directly at the Moon and Earth from about one foot away.
Look at the Earth. You should see a shadow that is darker in the middle and lighter on the outside.
The darker part of the shadow represents the umbra, the shadow of the Moon from which total solar eclipses can be seen. The lighter part of the shadow represents the penumbra from which only partial solar eclipses are seen.