October 23

solar eclipse Photo Credit: Clipart.com

Science Fact

Solar Eclipses

There are four types of solar eclipses: total, partial, penumbral, and hybrid. They occur when the moon passes between the sun and the earth. In order for an eclipse to occur, the three bodies roughly must form a straight line. The moon's shadow is cast back toward earth, causing the sun to be totally or partially blocked from an observer's view. In order to witness a solar eclipse, an observer must be within the area upon which the shadow falls. The observer's location in relation to the moon's shadow over the earth and the moon's location within its orbit of the earth determine the type of eclipse it will be.

Today's solar eclipse is partial and should begin at approximately 5:45 p.m. EDT, although the time will vary by your altitude and latitude. It will last less than two-and-a-half hours, although sunset will cut short the visibility in the Eastern and Central timezones of the United States.

A total solar eclipse occurs when there is a new moon and when the moon's orbit around the earth is at its perigree, or closest. The moon seems to appear at its largest from earth at this time. When the three bodies come into alignment, the moon completely blocks out the sun, causing a total solar eclipse. In order to observe a total solar eclipse, you must be within the area that the innermost and darkest part of the moon's shadow covers when it is cast back on the earth. That portion of shadow is called the "umbra." The next total solar eclipse visible from the U.S. will be Aug. 21, 2017.

A partial solar eclipse can occur at any time during the moon's orbit. The moon only partially blocks the sun, allowing a crescent-shaped piece of it to appear behind the moon's edge. In order to see a partial solar eclipse, you must be within the area traversed by the lighter, outermost part of the moon's shadow called the "penumbra." The next parial solar eclipse visible from the U.S. will be Jan. 14, 2029.

An annular solar eclipse is a type of partial eclipse. It occurs when the moon is further from the earth in its orbit, which means the moon appears smaller than it does during a total solar eclipse. Because of this perceived size difference, the moon does not appear to be the same size as the face of the sun, leaving a ring of sun visible around the edge of the moon. During this time, the moon's shadow visible on earth is called "antumbra," meaning "before the umbra." The next annular solar eclipse visible from the U.S. will be June 10, 2021.

A hybrid solar eclipse, sometimes called an annular/total eclipse, occurs rarely and only when the coverage of the sun shifts during the eclipse from annular to total back to annular over the course of the eclipse. (Even more rarely the eclipse may shift from annular to total or vice versa and not back again.) This change is caused by the curvature of the earth, which raises certain areas of the surface of the planet slightly, bringing it into the umbral shadow of the moon. As the curvature shifts away, the surface of the earth shifts out of the umbral shadow and back into the antumbral shadow. The next hybrid solar eclipse visible from the U.S. will be Dec. 6, 2067.

It is only safe to look directly at a total solar eclipse when the sun's face is completely obscured by the moon, but as the moon is coming into alignment and during all other types of solar eclipses, looking directly at the sun can damage your eyes. Using special equipment is the only safe way to observe most eclipses.

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