Twist and Shout
After I had downloaded the Full Buck Moon I'd photographed early on July 11, I thought I'd compare it with the Full Beaver Moon I'd taken on November 15 last year. To my surprise, the craters and mares seemed to have "moved".
It shouldn't be surprising. I've noticed how crescent moons change their angle as they cross the sky. ("Moon Series (1 and 17)" shows how the angle of the crescent moon can change in just a bit over three hours.) The full moon was doing the same thing.
Last November's Full Beaver Moon, shown on the left, had risen at 5:15 PM (all times here are Eastern Time). I'd photographed it almost 2-3/4 hours later, at 7:57.
The Full Buck Moon (center) had risen at 9:29 PM, but I'd photographed it more than four hours later, at 1:47:38 AM, when it was considerably higher in the sky.
Tonight's moon (right) rose at 10:14 PM. I photographed it almost 3/4 hour later, at 10:57:42, using a 1/80-second exposure at f/8. At that time it was just short of 24 hours past full and 98% of full. This is why Mare Crisium (Sea of Crises) is closer to the edge than in the other two photos (see notes).
I'd photographed all three moons from the same latitude/longitude coordinates (the full moons from just outside my house, tonight's moon from a quarter-mile away).
Other factors for the surface detail "moving" could be a combination of factors:
1. The way the Earth's axis is tilting. Our axis tilts about 23.5 degrees from vertical. For this reason, the Sun appears to take different paths across the sky at different times of the year, along a path called the ecliptic. This means our angle with respect to both the Sun and the Moon changes constantly.
2. The tilt of the Moon's orbit, which can range about 5 degrees to either side of the ecliptic. This also changes constantly.
3. A slight, ongoing oscillation of the Moon, called libration. This might apply especially to the position of Crater Grimaldi, which is considerably closer to the moon's limb (edge) in the leftmost shot from November. In the large view (click the magnifying glass), Crater Riccioli, which is just to the upper left of Grimaldi in the center shot, is almost on the limb in the leftmost shot.
Mainly, though, I think the effect comes from the fact that the Moon travels across the sky not in a straight line, but in an arc.
(For surface detail identification I've used this interactive map of the Moon.)
Twist and Shout
After I had downloaded the Full Buck Moon I'd photographed early on July 11, I thought I'd compare it with the Full Beaver Moon I'd taken on November 15 last year. To my surprise, the craters and mares seemed to have "moved".
It shouldn't be surprising. I've noticed how crescent moons change their angle as they cross the sky. ("Moon Series (1 and 17)" shows how the angle of the crescent moon can change in just a bit over three hours.) The full moon was doing the same thing.
Last November's Full Beaver Moon, shown on the left, had risen at 5:15 PM (all times here are Eastern Time). I'd photographed it almost 2-3/4 hours later, at 7:57.
The Full Buck Moon (center) had risen at 9:29 PM, but I'd photographed it more than four hours later, at 1:47:38 AM, when it was considerably higher in the sky.
Tonight's moon (right) rose at 10:14 PM. I photographed it almost 3/4 hour later, at 10:57:42, using a 1/80-second exposure at f/8. At that time it was just short of 24 hours past full and 98% of full. This is why Mare Crisium (Sea of Crises) is closer to the edge than in the other two photos (see notes).
I'd photographed all three moons from the same latitude/longitude coordinates (the full moons from just outside my house, tonight's moon from a quarter-mile away).
Other factors for the surface detail "moving" could be a combination of factors:
1. The way the Earth's axis is tilting. Our axis tilts about 23.5 degrees from vertical. For this reason, the Sun appears to take different paths across the sky at different times of the year, along a path called the ecliptic. This means our angle with respect to both the Sun and the Moon changes constantly.
2. The tilt of the Moon's orbit, which can range about 5 degrees to either side of the ecliptic. This also changes constantly.
3. A slight, ongoing oscillation of the Moon, called libration. This might apply especially to the position of Crater Grimaldi, which is considerably closer to the moon's limb (edge) in the leftmost shot from November. In the large view (click the magnifying glass), Crater Riccioli, which is just to the upper left of Grimaldi in the center shot, is almost on the limb in the leftmost shot.
Mainly, though, I think the effect comes from the fact that the Moon travels across the sky not in a straight line, but in an arc.
(For surface detail identification I've used this interactive map of the Moon.)