A lunar eclipse is different from a solar eclipse in the relative positions of the three celestial bodies namely the earth, moon and the sun. Whereas a solar eclipse is caused by the interruption of the sun’s view from the earth, it is the reverse in the case of a lunar eclipse. During a lunar eclipse the earth is positioned in between the sun and moon along the same line such that the light of the sun is either fully or partially blocked from illuminating the moon. What we are seeing is celestial game of light and shadows since the earth and moon do not
generate light but reflect the suns rays.
Before you can understand the concept of a lunar eclipse, let me explain the two terms: umbra and penumbra. These refer to the shadows produced by celestial bodies when the source of light is another celestial body and hence is not concentrated at a point. This leads to the shadow of the intervening body to be as shown in figure 1 below. The dark coloured region is the umbra while the other is penumbra. There is another region called antumbra but we will not discuss here for sake of simplicity.
Now if you see the above diagram again and imagine that the light source is the sun and the shadow object is the earth. If the moon lies behind the earth on or near an imaginary line connecting the sun and earth it will be in the region of umbra or penumbra shadow. Depending on one's location on earth, the lunar eclipse could either be partial eclipse, total eclipse or penumbral eclipse. It must be remembered that from the standpoint of an average person it is only the first two which are visible, the third should be left for the astronomers to gaze at, because the shadow of the earth in the penumbral region is not strong enough to cause a change in the illumination of the moon, which is easily visible to the naked eye.
After reading about lunar eclipses you might be wondering when the next eclipse is. Well, one eclipse just passed on the 16th of August 2008. There are 3 more eclipses in February, July and August 2009 but unfortuantely they are all penumbral eclipses. The next partial eclipse occurs on the 31st of December 2009, so obviously you would have to choose between enjoying the new year eve or watching the grand celestial event. If you want a detailed list of the dates of lunar eclipses, just click here.
Just because the lunar eclipse occuring on 9th February 2009 is penumbral that does not mean that you should totally ignore it. Try to observe whatever changes you can, in the illumination of the moon and compare it with the partial eclipse later on.
In the meantime you can enjoy a lunar eclipse by viewing the pictures below till the real drama in sky begins. The lunar eclipse of 9th February 2009 will be visible in Eastern Europe, Asia, Australia, Pacific and western North America and you can see the figure 1 below to find out more details regarding that. The various parts of the globe have been differentiated based on colour to describe the regions in terms of the visibility of the eclipse.
The picture (figure 2) after the "Areas of Lunar Eclipse" image shows the time lapse photography of a lunar eclipse which has already occured in the past. That should give you a good idea of how the lunar eclipse looks over a period of time. Just remember that this picture is of total lunar eclipse while the one on the 9th February 2009 is a penumbral eclipse. The picture in figure 3 shows a penumbral eclipse and shows the images of the moon prior to begining of the eclipse and during the eclipse. You can notice that the effect is not very prominent as compared to a partial or total lunar eclipse.