Everything You Need to Know About the Upcoming Lunar Eclipses
By Gwen Schanker, Journalism, 2017
On April 15, a total lunar eclipse took place and set off a tetrad of eclipses for 2014–2015. Whether you’re an aspiring astronomer or a student who’ll probably be up late anyway, here’s what you may have seen on Tuesday night, and what to expect in the following months.
Wait, what’s happening?
A total lunar eclipse occurs when the Moon passes through Earth’s umbral shadow, turning it a reddish-brown color. There are three different types of lunar eclipses — penumbral, partial, and total — that occur fairly often and in no particular order. A penumbral eclipse occurs when the Moon passes through Earth’s penumbral shadow, which is much paler than the umbral shadow and only stops a portion of sunlight from reaching the Moon. This type of eclipse is rarely visible, even with a telescope. A partial eclipse is more exciting; the moon enters the core of Earth’s shadow, but only part of it, so that a small sector of the moon is darkened. When a total eclipse occurs, the entire moon is shadowed by the Earth, blocking all of the Sun’s rays from hitting the moon and resulting in a change of color due to the refraction of sunlight from the Earth’s atmosphere — the same phenomenon that occurs when the sky changes color at sunrise or sunset. When four total lunar eclipses occur in a row, spaced approximately six months apart, the phenomenon is referred to as a tetrad.
How special is this, exactly?
A lunar eclipse can only occur at full moon, and only if the moon passes through some part of Earth’s shadow. Tetrads themselves are not particularly rare; nine tetrads of lunar eclipses are scheduled to occur during this century. However, this particular tetrad is unique because it will be visible to nearly all of North and South America.
How is this different from a solar eclipse?
A solar eclipse can only occur when the moon is in the new moon phase and passes between the earth and the sun, causing part of the moon’s shadow to cover Earth’s surface and the Moon to eclipse the sun. Total solar eclipses are quite rare — they only occur about once every two years — so generally only part of the sun is eclipsed by the moon. Since the part of the sun that is not covered by the moon is still very bright, observing a solar eclipse requires special filters or homemade equipment.
Unlike solar eclipses, lunar eclipses only occur at full moon and when the moon passes through the shadow of the earth. Lunar eclipses are not at all dangerous to look at, although a telescope can be useful for scientists making observations.
What types of observations can be made during an eclipse?
Using the Danjon Brightness Scale, even novice astronomers can observe the moon’s color and brightness during the phase of totality, and therefore estimate the amount of debris present in earth’s atmosphere during the eclipse. Using a telescope, amateurs can also measure crater timings, or the precise time when each crater of the moon enters and exits the umbral shadow. Crater timings can be used to judge how much the earth’s atmosphere expands during the eclipse.
When do I need to mark my calendar?
The April 15, 2014 eclipse will be followed by an eclipse on October 8, 2014, beginning around 3:15 AM Eastern Time with totality of 59 minutes. This eclipse will be followed by another on April 4, 2015, and then a final eclipse on September 28, 2015.
Since the Moon has to pass through the entirety of Earth’s shadow for totality to occur, every total eclipse begins with a penumbral eclipse followed by a partial eclipse, and concludes with a partial eclipse followed by a penumbral eclipse. The April 15 eclipse began around 2:00a.m. EST. Totality (change in color) began about an hour later and lasted approximately 78 minutes.
Of course, if you don’t have time to catch the eclipses live (or bad weather blocks your view), some websites will stream it while it happens, like Slooh. Enjoy!
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