Terminator in Motion
It's not necessarily obvious that the moon is actually rotating as it orbits the earth, because it completes exactly one rotation per orbit. But it is, and these two frames, taken an hour and a half apart, show the motion of the terminator as it approaches the west edge of the Sea of Crisis. Several interesting features are seen here. The very eastern edge of Cleomedes is visible in the earlier picture, and has disappeared in the later one. The shadows of the western peaks at the edge of Crisis have lengthened considerably, and the terminator itself has nearly engulfed Pierce and Picard, the two prominent craters in the basin of Crisis.
Veteran moon observers know that there are a large number of features on the moon's surface that can only be seen for a few minutes as the terminator crosses them. Low-rising hillocks, for example, only cast visible shadows just as the terminator crosses them. Some of these features are only visible at particular libration angles, as well! All in all, for those of us who enjoy the moon, it presents us with an unfathomable variety of things to look at in wonder.
Terminator in Motion
It's not necessarily obvious that the moon is actually rotating as it orbits the earth, because it completes exactly one rotation per orbit. But it is, and these two frames, taken an hour and a half apart, show the motion of the terminator as it approaches the west edge of the Sea of Crisis. Several interesting features are seen here. The very eastern edge of Cleomedes is visible in the earlier picture, and has disappeared in the later one. The shadows of the western peaks at the edge of Crisis have lengthened considerably, and the terminator itself has nearly engulfed Pierce and Picard, the two prominent craters in the basin of Crisis.
Veteran moon observers know that there are a large number of features on the moon's surface that can only be seen for a few minutes as the terminator crosses them. Low-rising hillocks, for example, only cast visible shadows just as the terminator crosses them. Some of these features are only visible at particular libration angles, as well! All in all, for those of us who enjoy the moon, it presents us with an unfathomable variety of things to look at in wonder.