The climactic moment of the Ten Plagues was the final one, the killing of the firstborns at midnight. Last year I posted about the star Sirius' connection to this event. This year I would like to add one more point to that post.
An entire lunar cycle (from our perspective) takes approximately 29 days, 12 hours, 44 minutes and 3 1/3 seconds. Since this tenth plague occurred on the 15th of the lunar month, that means that the moon was full.
Many notice that the moon is sometimes visible in the daytime and at other times at night. The basic overview of its rise and set times is that in the beginning of the lunar month it is visible in the afternoon and sets just after sunset. Every subsequent day it appears a little later in the day and sets a little later in the evening. In the middle of the month it rises at sunset and sets at sunrise and it then begins to rise after sunset and set in the morning until the cycle begins again.
When putting all this together, one can see that at midnight,the moment of the plague, the moon was full and at its peak. The sun, on the other, has its peak at midday and is at its lowest at midnight. The other nations of the world are compared to the sun (see Maharsha Yoma 20) and Klal Yisrael to the moon (see Midrash Tehillim 22). This was finally the moment when Klal Yisrael was shining and at its peak and their oppressors were at their lowest.