The Goldendale Sentinel - Headlines & History since 1879

By Troy J Carpenter
For The Sentinel 

Eclipses (or when things get in front of other things)



ECLIPSES ON OTHER PLANETS: This picture was taken in March at the Goldendale Observatory with the new C14 imaging telescope and shows Jupiter and its moon Io in the middle of a "shadow transit." From Jupiter's perspective, Io is eclipsing the sun. Such transits can be witnessed regularly, even in small telescopes. The next evening, Io was rendered invisible by Jupiter's shadow for a number of minutes, creating the equivalent of a lunar eclipse.

A little before 10 p.m. PDT on Monday, April 14, the moon's orbit will begin carrying it through a great shadow cast by planet Earth-the first lunar eclipse of 2014.

Instead of discussing this event as it would appear from our vantage point, let us temporarily imagine the experience from the perspective of a person (or robot) gazing up from the lunar surface: the sun will appear to slowly retreat behind our home world, becoming completely obscured by the earthly disk after roughly two hours of gradual motion, thus beginning a period called totality just after midnight. The sun will remain hidden for more than an hour, but all will not be darkness, for, from any viewpoint on the moon, the night side of Earth will be transformed into an enormous red and golden ring of light, the culmination of every sunrise and sunset seen by anyone, anywhere.

Back on Earth, this planetary sunset will manifest as a darkened and blood-tinted moon, the same atmospheric mechanisms responsible for the colorful skies of dawn and nightfall now selectively scattering crimson sunlight across the lunar orb. Our moon will remain entirely reddened and dimmed until about 1:30 a.m. PDT, at which point its orbit will begin a return to direct sunlight. By 3:40 a.m. PDT, the moon will have completely escaped the shadow of Earth, and the eclipse will be over.

So to summarize, Earth will be positioned between the moon and sun for a period of approximately five and a half hours, an alignment beginning the evening of April 14 and ending the early morning of April 15. Big deal, right? This is what happens during every full moon. Why, then, are lunar eclipses so rare?

It must be remembered that the moon is a relatively small target for Earth's shadow to strike, an object one quarter the diameter of our planet, orbiting at an average distance of 240,000 miles. To visualize such size disparity and physical separation, one should compare a baseball to a common 12-inch classroom Earth globe. One must then stand approximately 30 feet away from said globe to properly simulate the Earth-moon relationship. Now consider the additional reality of our moon's elliptical orbit, far from exactingly circular, and imperfectly parallel with the plane of Earth's orbit around the sun. Given all these variables, it is not surprising that lunar eclipses do not happen very often. It is furthermore unsurprising that solar eclipses happen even less frequently, given the precise alignments required for our tiny moon to block the light of a sun that appears roughly its equal in angular diameter from our perspective on Earth.

The April 14 eclipse kicks off a "lunar tetrad," a series of four successive total lunar eclipses occurring at six month intervals. There will be only eight tetrads during the 21st century, so don't miss this one! 2014 in particular is a special year for eclipse viewing opportunities in North America: after the April 14 event, there will be another fully visible total lunar eclipse on Oct. 8 and a partial solar eclipse on Oct. 23! Special viewing hours have been arranged for each event at Goldendale Observatory; check out our website for details.

Of course, if three eclipses in a single year still aren't enough, you can always move to mighty Jupiter (if you can find a place to stand on a ball of gas). Thanks to his huge size and 67+ moons, the King of the Planets experiences both lunar and solar eclipses on a daily basis!

Troy Carpenter is Interpretive Specialist at the Goldendale Observatory State Park.


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