Annular Solar Eclipse on Sunday, May 20th


An Annular Solar Eclipse will occur in our area late Sunday, May 20th.  For this area encompassing southeast South Dakota, southwest Minnesota, northwest Iowa and extreme northeast Nebraska, the eclipse will begin about 7:20 pm Sunday evening, with the maximum eclipse occurring an hour later near 8:22 pm.  This is only about a half hour before sunset.  In this area, the duration of maximum eclipse will be a minute and a half with about 63% of the sun obscured.  The path of the maximum annular solar eclipse will begin in southern China shortly after 5 pm CDT, then move across the north Pacific.  The path of maximum annular eclipse will encompass parts of the western and southwest United States in the early evening!  In the path of maximum eclipse, nearly 95% of the sun will be blocked by the Moon's shadow.

Click this link from NASA gives details on the exact path.  This link from NASA shows the path of the maximum portion of the solar eclipse in the United States.  (The area outlined in red shows the maximum part of the annular eclipse.)

A solar eclipse occurs when the Moon passes between the Sun and Earth, casting the Moon's shadow on Earth. A solar eclipse can only happen during a New Moon. The Moon's orbit is titled 5 degrees to Earth's orbit around the Sun. Therefore a solar eclipse is a relatively rare phenomena and a Total or Annular eclipse even more rare.

To understand the difference between a Total and Annular eclipse of the Sun, we must state that the Moon has an elliptical orbit around Earth. In fact, the Moon's distance from Earth varies from a minimum of 221,000 to a maximum of 252,000 miles. Therefore the Moon's apparent size in our sky will vary by 13%. When the Moon's orbit is toward its minimum distance from Earth, the Moon will appear visually as a larger disk than the Sun. If an eclipse occurs during this time, it will be a Total solar eclipse because the Moon has totally obscured the Sun's disk, producing the beautiful solar corona ejecting outward from the Sun. One important element to remember though is that the Moon's shadow will obviously become narrower as it is cast from the Moon to Earth (in a shape of a cone with the wide end being at the Moon and the narrow end on Earth). Therefore the path of totality on Earth is narrow. It is also very short-lived as the Moon is moving quickly away from its perfect location of being situated between the Sun and Earth.

An Annular solar eclipse is different than Totality in that it occurs when the Moon is closer to its maximum distance from Earth in its orbit. If an eclipse happens during this situation, the Moon will appear visually smaller than the Sun and its shadow cast will not be long enough to reach Earth. What reaches Earth is the antumbral or "negative" shadow. If you are within the antumbral shadow, you will see a solar eclipse where a thin ring or annulus of bright sunlight surrounds the Moon. Therefore Annular solar eclipses are still spectacular in that they are almost Total, but the solar corona is not seen due to the brightness of the annulus. Like a Total eclipse, the Annular solar eclipse will have a narrow path on Earth with short duration, most often less than 10 minutes.

DO NOT observe a solar eclipse with the naked eye. Serious eye damage can result. Use approved solar filters (camera film negatives do not count) or cut a pin hole in a shoe box and watch the Sun's light cast through the pin hole onto a smooth surface such as cardboard.


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