The Lake County Astronomical Society

Observing the Moon: A Different View

Jack Kramer

Forget about seeing the Moon as shown below. This is an image of the north polar region as obtained by NASA's Galileo mission when the spacecraft passed by the Moon at a distance of 75,000 miles. The north pole is to the lower right of the image. The view in the upper left is toward the horizon across the volcanic lava plains of Mare Imbrium. Note the combination of smooth plains, cratered terrain and impact ejecta deposits in this region of the Moon.

In the center of the picture is the large, very old crater John Herschel with a diameter of 105 miles. From our perspective on the Earth, it appears long and narrow due to being so close to the northern limb of the Moon. The central section of the crater is rough and somewhat convex, so when the angle of sunlight is very low, the bases of the walls will be in shadow while the central area of the floor appears as an illuminated island floating amid the darker surroundings. Immediately to the south of Herschel ("up" in the image) is Sinus Roris -- the Bay of Dews. At the terminator with two prominent central peaks showing (to the right and slightly up from Herschel) is the large crater Pythagoras. Having once identified these craters, it's interesting to compare how they appear under different libration conditions as the north pole of the Moon is tilted toward or away from us.