April’s Lunar Eclipse
By Calvin L. Chrisman
Lunar eclipses occur every year, but it has been a long time since a total lunar eclipse has been visible from Western North Carolina. April brings us the first total lunar eclipse visible in North America since 2011. This one will be late at night (or early in the morning depending on your point of view) with totality beginning at 3:07 a.m. EDT on Tuesday April 15th. It will be visible from beginning to end, weather permitting. The wait for the next total eclipse will be shorter. We will be treated to two others on the morning of October 8, 2014 and the evening of September 27, 2015. The west coast will have another visible on the morning of April 4, 2015.
Eclipses occur when the object that is eclipsed (in this case the Moon) falls in the shadow of another object (in this case, the Earth). Many people do not realize it, but the Earth actually casts two shadows. It has a lighter shadow called the penumbra consisting of light that is only partially blocked by the Earth; and a darker shadow called the umbra which is completely blocked from the Sun. Think of them as concentric circles with the penumbra being the larger outer circle and the umbra being the smaller inner circle. As the Moon passes through the Earth’s shadow, it first enters the penumbra and then the umbra. The penumbral shadow will first touch the Moon at 1:20 a.m. Eastern time on Tuesday morning the 15th. Its effect is a subtle dimming and is easily missed. The umbra will first touch the Moon at 1:58 a.m. and will totally eclipse the moon at 3:07. Totality will last for 1 hour and 18 minutes and then the process will reverse itself ending at 5:33 a.m.
If you have never watched a lunar eclipse, you may be surprised to see that, during totality, the Moon will have a reddish hue instead of being black or dark grey. It is quite striking and is an effect of Earth’s atmosphere. Light that passes through the Earth’s atmosphere is bent as though it had passed through a lens and is deflected into the umbral shadow. The light is bent toward the red end of the spectrum and so gives the umbra and the Moon a reddish tint. If you are observing the eclipse through a telescope or binoculars, you may want to try and time the first appearance of the penumbra and umbra on the Moon. It is also interesting to watch the effect as the umbra touches various mountains and craters on the surface of the Moon.
An additional treat during this eclipse will be the sight of the bright star Spica very near the Moon and red Mars only nine degrees to the Moon’s west. Finally, watch the sky for dim stars that were obscured by the light of the Moon. They will be quite visible during totality.
Visit Calvin Chrisman’s website at: www.DillKnobObservatory.net for links to astronomical sites of interest and past articles.