Celebrate Spring with an Annular Solar Eclipse

by Rod Kennedy

Some events are so rare they come around only three or four times in a person’s lifetime.  Such an event is coming this May.  This event is an annular solar Eclipse and it  will occur on May 20th, 2012.  Like all solar eclipses, you will have to be in the proper location on the Earth to see it.  However, if you are in the right place it will be a fantastic show.

An annular solar eclipse is one in which the disk of the moon does not completely cover the disk of the sun, as in a total eclipse). The moon will be directly in front of the sun, but there will be a margin of the sun visible around the edge of the moon (see the illustration at right).  This is because the moon’s orbit around the Earth is not a perfect circle, it is an ellipse.  An elliptical orbit means that the Moon is sometimes closer to the Earth and sometimes further away.  When the moon is further away it appears smaller in the sky and therefore cannot completely cover the sun.  This is different from a partial solar eclipse, in which only part of the moon covers part of the sun.

For those of us in Wyoming, we will only see the partial eclipse.  This is because we are a bit too far north to see the annular eclipse.  However, observers in the Southwest U.S. will be able to see the annular eclipse in its entirety.  The eclipse will begin at approximately 6:20 pm, what astronomers refer to as “first contact”.  The height of the eclipse occurs at approximately 7:25.  The eclipse will be ending at sunset, approximately 8:20 pm.  To see the eclipse in its entirety, you will need observe from a place where the horizon is flat and clear of buildings and trees.  The best view of the annular eclipse will be in or near Cedar City Utah, approximately 175 miles northeast of Las Vegas.

Eclipses invariable cause observes to raise the question: “What is the best way to observe the eclipse?”  Obviously you should NEVER look directly at the sun, even welding hoods do not provide sufficient filtering for the light from the sun.  There are solar filters for telescopes and binoculars but these should be purchased only from a reputable telescope dealer.  Telescopes without a solar filter can be used by using the projection method.  This means the image is projected onto the ground or a white board.  However, this method is not recommended for Cassegrain telescopes that have sealed tubes as they can overheat.  The best, and safest method is the “pinhole camera” method.  Use a push pin to punch a small hole in an index card, then focus the light onto another card.  Adjust the distance between the cards until there is a sharp image.  The eclipse will play out clearly on the card.

Eclipses occur during two times each year, known as eclipse seasons.  However, the location at which the eclipse is visible is highly variable.  May 2012 offers observers in the US a chance to experience this rare and wonderful phenomenon first hand.  Best of all this eclipse is just a warm up for another eclipse that will be visible from Wyoming in 2017.

May 2012 Chart

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