February: Prime Time Lunar Eclipse

February 2008

Prime Time Lunar Eclipse

By Calvin L. Chrisman

Celestial events tend to happen very late at night when many prefer to be in bed asleep. This is not true for February. On the evening of the 20th, we will have a prime-time full lunar eclipse. If the weather is clear, it will be a beautiful sight. Plan to take a look.

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 7:34 pm Eastern time on Wednesday the 20th. Its effect is a subtle dimming and is easily missed. The Umbra will first touch the Moon at 8:43 and will totally eclipse the moon at exactly 10:00. Totality will last for 52 minutes and then the process will reverse itself.

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.

Another target to observe during the eclipse is the planet Saturn. Saturn, which is always a favorite sight for astronomers, will be a short distance behind the Moon and, at first, will be overshadowed by the bright full moon. As the Moon is eclipsed, Saturn will become more and more prominent. It’s rings are still tilted to the planet, and so are observable, but will shortly be entering a period where they will be edge-on to the Earth and thus difficult to observe. Don’t miss this chance.

As a reminder: weather permitting, on the early morning of January 31st or February 1st, bundle up warmly, get a cup of coffee and go out before dawn. Look to the southeast and you will see Venus and Jupiter (the first and second brightest planets and the third and fourth brightest celestial objects) very close to each other. It should be a spectacular sight.

Clear Skies!


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