On February 20, 2008, a full lunar eclipse graced the skies of most of the Americas, Europe, and parts of Asia and the Middle East. The Earth passed between the moon and sun in such a way that the shadow of the Earth fell upon the moon, darkening its surface to a blood-red color.
A lunar eclipse is an example of an event for which we are required to perform Namaz-e-Ayaat, the Prayer of Signs. The exact events which make this prayer necessary vary slightly depending on your Marja, but Ayatollah Sayyid Ali Sistani mentions in his code of practice that it should be performed for lunar eclipses and solar eclipses (whether full or partial), earthquakes, frightening thunder or lightening, frightening wind storms like hurricanes or tornados, receding sea water and tsunamis, landslides, and similar phenomena.
Islam teaches its followers to remember Allah at all times, and when one witnesses such events occurring, they should serve as a reminder of God's power and might. Hence, the Prayer of Signs is mandated.
If you observe any of these events, you should perform the prayer at that time or as soon as possible. In some cases, if you do not perform the prayer but learn about the event later, even if you did not observe it yourself, you will need to perform the Qadha, or make-up prayer.
In the case of the lunar eclipse on February 20, since it was a full eclipse, if it occurred in your area, the Qadha of the prayer is required if you did not perform it that evening. People normally exempted from prayer on that evening, such as women in menses or children who have not reached the age of majority, are also exempted from Namaz-e-Ayaat.
There are a few methods of the prayer, but here is the simple standard:
Namaz-e-Ayaat consists of two Rak'ats, and there are five Ruku' in each. After making intention of offering the prayers, one should say Takbir (Allahu Akbar) and recite Surah al-Hamd and the other Surah, and then perform Ruku. Thereafter, he should stand and recite Surah al-Hamd and a Surah and then perform another Ruku. He should repeat this action five times. When he stands after the fifth Ruku, he should perform two Sajdah, and then stand up to perform the second Rak'at in the same manner as he has done in the first. Then he should recite Tashahud and Salam.