Figure 1. Gibbous moon, 11.8 days old, November 7, 2000, 6:00 PM, PST. Merge of ~15 images with Pictor 416-XTE CCD imager at prime focus of Meade LX-200 Meade Schmidt-Cassegrain telescope, with aperture stopped-down to about 4 inches, with 0.030 second exposure time. Crater Tycho is near the southern end (bottom) of this image, and is the source of an extensicve ray pattern across much of the moon; crater Copernicus dominates the equatorial region in the middle Oceanus Procellarum (the dark mare region on the left side). North of Copernicus is the circular Mare Imbrium, with a "scallop" mare Iridium on its upper-left. To the left of Copernicus is crater Kepler; both craters are the source of ray systems.
Most people assume terminator's location moves so slowly that to see it in a different location you have to wait until the next night's viewing. Not so! I will present a 6-hour sequence for selected locations of the terminator shown in the above figure.
The first region is "Humorum," the sea near the southern end of the terminator. Mare Humorum in the center of the following image.
Figure 2. Mare Humorum, next to the terminator, is 280 miles across. Crater Gassendi, 70 miles in diameter, is on the northern rim of Humorum. The latitude extent of this image is about 560 miles. The small crater near the upper-right corner is Lnsberg, which is close to the equator; the bottom of the picture is at a latitude of about -30 degrees. (You may click this image to see a full resolution version.)
Figure 3. Progression of the terminator, during a 5.5 hour period, from 5:50 PM (left), 9:06 PM (middle) to 11:20 PM (right). The terminator moves an average of 12.2 degrees of lunar longitude per day, which translates to 9.57 miles per hour at the equator. At the latitude of the Gassendi (21 degrees South) the terminator moves 49 miles during a 5.5 hour period (corresponding to the interval between the first and third images, above). The terminator's motion during these 5.5 hours is about 70% the width of Gassendi. (The first image is less sharp than the others because it was taken when the moon was lower in the sky.)
The following sequence is for a region surrounding the famous crater Aristarchus, in the northern hemisphere. The next image shows the Aristachus region.
Figure 4. Overview of Aristarchus region. Aristarchus is the crater with the bright rim on the terminator. Kepler is at the bottom edge (below a row of image defects). Sinus Iridum is the scalloped feature on the edge of the larger Mare Imbrium. From Kepler to Sinus Iridum is about 750 miles. The smallest craters are 2.5 miles in diameter. The "atmospheric seeing" was good when this image was taken; a spectral analysis shows structure corresponding to a resolution of better than 2.2 "arc, which is close to the generally accepted 1 "arc limit for ground-based observing. (For north to be at the top, mentally rotate this image about 30 degrees counter-clockwise. (Click this image to view a full-resolution image, in which each pixel is 1.1 "arc, or 1.27 miles on the moon.)
Figure 5. Sequence of terminator miovement westward beyond crater Aristarchus. These images have been rotated 30 degrees so that north is at the top. The exposures were made at 7:35 PM, 9:10 PM and 11:30 PM, on November 6, 2000. The width of the moon visible in these pictures is about
Figure 6. Detail of crater Aristarchus, which is about
27 miles in diameter (not rotated; therefore, north is 30 degrees clockwise
from the top). The width of the image is about 150 miles. Aristarchus
is thought to be less than 50 million years old, making it one of the youngest
craters known on the moon, and perhaps the brightest one (at full moon).
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This site opened: November 8, 2000. Last Update: November 8, 2000.