The Night Sky Script April 2014 April’s Lunar Eclipse
Hello, stargazers, I’m Darrell Heath with the UALR College of Science. Welcome to The Night Sky.
An eclipse is one of nature is most dramatic and startling celestial events. In ancient times, long before science explained the phenomena , eclipses often induced more terror than awe and folks tried to explain them in terms of angry gods or giant, ravenous dragons. Of course we now know that an eclipse is nothing more than a chance alignment of two celestial bodies as seen from the perspective of a third.
From our earthly perspective it is the chance alignment of the Sun, Moon, and our own home planet that offers up the best shows.
Several times each year at least a portion of the planet gets a chance to witness an eclipse of some kind.
A solar eclipse occurs when a new moon lies between our line of sight to the Sun and eclipses the solar disc. In astronomy lingo the moon “occults” the solar disc which just means that it hides the sun from view. Few would argue that a total eclipse of the Sun is one the most spectacular sights in all astronomy.
A lunar eclipse occurs when the Moon is at full phase and the Earth is positioned between the Sun and the Moon so that the Earth casts a giant shadow upon the lunar surface. If you were standing on the Moon during this time, from your perspective you would be witnessing a solar eclipse since the Earth would be blocking your view of the Sun.
But wait a minute, we have a new and full moon every month so how come we don’t see eclipses every single month? Well, the reason is that the Moon does not orbit within the same plane as the Earth’s orbit around the Sun. The Moon’s orbit around the Earth is tilted by about five degrees. Picture it this way: imagine placing the Sun and Earth onto a flat table top. The table top represents the Earth’s orbital plane. If we place the Moon into the picture with it’s slightly tilted orbit then we would sometimes see the Moon floating above the table’s surface and at other times below it.. In order for us to get an eclipse out of this model we have to have the Sun, Earth, and Moon all aligned together within the table’s surface. So an eclipse can only occur when the Sun, Earth, and Moon are all properly aligned on our imaginary table top solar system.
During the early morning hours of April 15th the alignment conditions necessary for a total lunar eclipse will occur and you are invited to see the show. While it will require that you stay up very late on the night of April 14th (or at least set your alarm) this will be worth losing a little sleep over.
To see it just step outside a bit after midnight of April 14/15 and look to the southwest.
The eclipse will be visible from just about all of North and South America and the show gets underway at 12:20 AM Central Time. Early on things won’t look all that exciting as the faint, outer edge of the Earth’s shadow (known as the penumbra) begins to cover the Moon’s leading edge. At 12:58 AM the show gets more dramatic when the Moon’s leading edge begins to enter into the umbra, the darker, inner portion of the Earth’s shadow. At this point you will start to see a reddish-looking shadow slowly gliding over the Moon’s surface. Totality, where the Moon is now enveloped by the Earth’s umbra, begins at 2:07 AM and is a stunning sight. Now the Moon is engulfed by a red or orange shadow. This red color is due to sunlight coming in from the opposite side of the Earth and passing through our atmosphere. As it does so the atmosphere scatters and bends the sun’s light, scattering out the bluer portions of the light and allowing more of the red to enter into the umbra’s shadow. Particulates within the atmosphere can also determine exactly how dark and how red the Moon will appear.
I’m not ashamed to admit that even though I understand the basic mechanics that explain all I am seeing I still find the appearance of the Moon during totality a bit creepy. At such times I can well imagine the feelings of terror a sight like this must have had on people in the past who had no such knowledge. Superstition may be born out of ignorance but it can still be hard to shake off certain primal feelings even when you are armed with the facts. Totality ends by 3:25 AM as the Moon begins to leave the Earth’s shadow and the Moon will fully leave the umbra shortly after 5:00 AM.
A couple of other things to look out for during the eclipse: the Moon on this night will be in the constellation of Virgo and if you look just a few degrees to the southwestern edge of the Moon during totality you will see the constellation’s brightest star, Spica, shining a brilliant blue in contrast to the Moon’s eerie red-orange.
Almost ten degrees from the Moon’s northwestern edge you will see the red planet Mars. The short answer as to why Mars looks red is rust. The planet’s surface is covered in rocks rich in iron oxides and in the past, when Mars had more water on its surface, these compounds literally rusted out and now get spread all around Mars’ globe and through its atmosphere via monstrous dust storms. The result is that Mars reflects a lot of red light out into space.
You won’t need any special equipment to view a lunar eclipse, but it is still fun to use a pair of binoculars to check out the slight changes in color detail as the eclipse progresses over time.
If for whatever reason you miss out on seeing this particular eclipse don’t worry, there will be three more coming soon to a sky near you. The next one will be on October 8th of this year and the remaining two will follow in 6 lunar month intervals on April 4th and September 27th of 2015. Such intervals of four total lunar eclipses are known as tetrads and are kind of rare, happening every few centuries. Remarkably these particular eclipses happen to fall on certain religious holidays on the Jewish calendar and I am already hearing stories on the internet that these are fulfillment of a biblical prophecy for the end times. Granted that these are remarkable coincidences they do happen and we shouldn’t take such prophecies of gloom and doom seriously. After all, in doing a little homework for this episode I learned that a total of 8 such lunar eclipses coinciding with important Jewish holidays have occurred over the past 21 centuries and we are all still here. In the end we can explain such rarities as these by using geometry and celestial mechanics rather than something otherworldly.
Until next time I encourage you to get outside, look up, and wonder,