New Year Eclipse Gifts

New Year Eclipse Gifts

By Dr N T Jiwaji

Email: ntjiwaji at yahoo dot com

A New Year gift in the form of a partial Lunar Eclipse awaits us on New Year’s Eve. In the early night of Thursday 31^st December when the Moon is in Full phase, a small portion of the Moon, about eight percent, will be hidden from view during the partial eclipse of the Moon.

Lunar eclipses are completely safe to watch since we are only seeing reflected light when we observe the Moon.

Just before 10 pm, at 9:53 pm the Moon will in the north east, about half way up the sky, when the edge of the Moon will slowly begin to be covered from the upper right by the edge of the Earth’s dark shadow. Note that a light (penumbral) shadow had already started to cover the Moon since 8:17 pm but this is not all noticeable to watchers.

By around 10:24 pm, about 8% of the Moon will be covered with the dark shadow. After that, during the next half hour or so, the Earth’s dark shadow will slowly move away and will leave the Moon from the top at 10:53 pm.

The light penumbral shadow will continue to cover the Moon until past midnight and the Moon will be completely clear by 00:29 am of 1^st January 2009. This is indeed a New Year gift, delivered at the right time!!

During a Lunar Eclipse, the Earth comes directly between the Sun and the Moon. One might think that this should happen once every month since the Moon moves around the Earth once a month. But there is a slight tilt in the orbit of the Moon so the Earth’s shadow misses the Moon most of the time.

Lunar Eclipse Geometry

Note that in a Solar Eclipse, the situation changes, so that the Moon will be exactly between the Sun and the Earth. This too is a rare occurrence that we will experience after two weeks on 15^th January 2010 when an annular eclipse occurs between 7 am and 11 am that morning and in Tanzania more than three quarters (around 80%) of the Sun will be covered by the Earth causing a very alarming decrease in the morning brightness even when there are no clouds covering the Sun. Remember that during solar eclipses you should never look directly at the Sun even if the Sun’s brightness is very low since dangerous invisible radiation continues to enter and will damage the eyes.

Eclipse times are very good for catching people's interest but for this partial lunar eclipse we should be prepared not to expect that the Moon will become completely dark. Even during a total Lunar Eclipses, the Moon never becomes completely black dark although it is completely covered by the huge shadow of the Earth. There is always some light from the Sun that manages to sneak into the dark shadow because of refraction of sunlight by the Earth’s atmosphere. The light that passes through our atmosphere emerges red because blue light is refracted (bent) away leaving mainly red light to pass on and strike the Moon.

During this partial lunar eclipse, when only a small part (at most eight percent) of the edge of the Moon will be covered up, hence only keen observers can expect to see just slight noticeable darkening of the Moon's face at mid-eclipse around 10:30 pm. Only by carefully following the brightness of the Full Moon before and after the eclipse time will the eclipse effect will be visible, especially if the sky is cloudy.

Expected shadow on the Moon during the partial Lunar Eclipse

This link gives a very good animation of this lunar eclipse as well as that of the next partial (annular) solar eclipse on 15th January and of the retrograde movement of Mars. http://www.shadowandsubstance.com/

For more details and for other interesting astronomy information see http://sites.google.com/site/astronomyintanzania/

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