Archive for April 6, 2014

Tax Day Eclipse – April 15, 2014

April 6, 2014 3 comments

From the April  2014 Stellar Sentinel, the newsletter of the Grand Traverse Astronomical Society

If you stay up April 14th or get up early on April 15th to watch the total lunar eclipse that morning, make sure your taxes are done, because you might not be good for much of anything during the day on the 15th.
That being said,  let’s take a look at the what and where of the eclipse.  Lunar eclipses only occur at full moon.  The Sun, Earth and Moon have to line up so the the Earth casts its shadow on the Moon.  This occurs in about one in six full moons.  Below is the Moon and the earth’s shadow at the March full moon.

Eclipse miss

On March 16, 2014 the full Moon missed the Earth’s shadow, so no eclipse was seen. Created using Cartes duCiel.

In the illustration above the “bulls-eye” is the Earth’s shadow as it would appear at the Moon’s distance.  The outer gray circle represents the Earth’s penumbra, where the sun’s light is increasingly blocked by the earth.  The umbra (in red for emailed PDF versions of this newsletter) is the Earth’s inner shadow where no direct sunlight enters. When the Moon enters the umbra the partial phase of the eclipse begins.  When the Moon is entirely within the umbra the Moon will be totally eclipsed.  The Moon back on March 16th missed the earth’s shadow by passing several degrees south of it. When the moon is in the umbra it is still dimly lit indirectly to some degree by the combined rays of the sun that are refracted through Earth’s from all the accumulated sunrises and sunsets occurring around the Earth at that time.  Back in 1967 the robotic lunar soft lander Surveyor 3 was able to take some images of the earth during a lunar eclipse.  For Surveyor this was a solar eclipse and illustrated the light being refracted around the earth.

Surveyor3 solar eclipse

Solar eclipse by the Earth as viewed by Surveyor 3, April 24, 1967. Credit: NASA

The current Chinese Chang’e 3, should it survive one more lunar night, has a chance to take a better quality photograph of the eclipsed Sun this April 15th if its camera can tilt far up enough.
The light that illuminates the Moon in the Earth’s umbra is generally red in color, though the edge of the umbra generally has a gray cast to it.  The light level is so low in the umbra, that, to the naked eye, it appears that the Moon is indeed being eaten by something invisible as the ingress partial phase progresses.  About three quarters the way in the color of the umbra can be perceived even to the naked eye.
There are exceptions.  Two notable lunar eclipse of this person’s memory occurred in 1982.  On July 6, 1982 the early morning eclipse when the Moon passed centrally through the umbra the Moon was unevenly lit.  The top or northern half was much darker than the southern half.  In late March and early April that year the El Chichón volcano erupted in southern Mexico sending 20 million metric tons of ash high into the stratosphere.  Apparently it masked the light from the northern hemisphere making it into the earth’s shadow.  That year’s December 30th lunar eclipse was exceptionally dark.  In fact during totality one had to hunt to find the Moon at all with the naked eye.

The events of the April 15th eclipse

Eclipse Diagram

The Moon travels through the Earth’s shadow from right to left. What are seen are points of contact with the shadow and mid-eclipse. From Five Millennium Canon of Lunar Eclipses (Espenak & Meeus) NASA.

Contact times are labeled P1, U1, U2, U3, U4, and P4.  P2 and P3 are omitted because they are synonymous with U2 and U3 respectively:
P1 – 12:53:37 a.m. Enter the penumbra (unseen).  By about 1:30 the duskiness on the left edge of the Moon will start to be pronounced.
U1 – 1:58:19 a.m. Enter the umbra (partial eclipse begins).
U2 – 3:06:47 a.m. Totality begins.
Mid eclipse 3:49:40 a.m.
U3 – 4:24:35 a.m. Totality ends, egress partial phase begins.
U4 – 5:33:04 a.m. Partial phase ends.  The Moon’s upper right edge should appear dusky for the next half hour or so.
P4 – 6:37:37 a.m.  Penumbral phase ends (unseen).
Note:  The duskiness of the penumbral phase of the eclipse can be enhanced by viewing through sunglasses.
Weather permitting there will be two Grand Traverse Astronomical Society venues to view this eclipse.  The first will be the NMC Rogers Observatory.  The second will be at the Sleeping Bear Dunes National Lakeshore in the Dune Climb parking lot on M109.  Both start at 1:30 a.m. if it’s clear.

Note:  All times are Eastern Daylight Time.  For locations other than Northwestern Lower Michigan, check with your local astronomy club.  However this is a perfect event to be viewed from one’s back yard.  No optical aid is required.

Correction:  The U2 timing was incorrectly stated in the original post.


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