I know I sound very dumb asking this but I am still confused at how the moon moves across the sky at night. I just don’t understand how it works, is it perception? The way the sun reflects light off the moon? I know the moon orbits around the earth every 28 days but it makes no sense to me. Many thanks.
In: Physics
The moon moves across the sky primary for the same reason the sun and the stars move across the sky. Earth is rotating around its axis.
Only something directly above the north or south pole is stationary. So Polaris that is very close to that point is almost stationary.
Stuff in any other direction will move circles. The size of the circle depends on where relative to the earth axis and the moon is close to directly over the equator.
The orbit of the moon around the earth will have an effect so the moon moves at a sight different rate than the stars.
If the moon orbited the earth once per day it would be stationary.
You can compare it to you sitting on a chair that can spin around. Sit on it and spin at a constant rate and the room around you will move like the start. Have a friend walk around you in a circle once for 28 rotations of the char. That will be the motion of the moon.
IF you then look it is quite clear that most of the motion each day is because you spin but some is because of the moment of the moon.
The moon moves around earth one per 27.322 days relative to the star so an angular movement of 360/27.322= 13.17 degrees per day. The moon’s actual size is 0.5 degrees so it will move 13.17/0.5=26.35 times its own per day. That is its own width in 54 minutes.
It crosses the sky at close to the same speed the sun does for the same reason: the earth is spinning way faster than it’s moving. It’s orbital speed is why it rises & sets at slightly different times each day (at a different rate from the changes in sunrise/sunset times) and changes phase. I.e., as it’s orbiting around the earth, it’s position relative to earth and sun changes. That doesn’t happen fast enough to observe in one look, but you can see a minor change night by night.
The moon is indeed orbiting the Earth, but that’s not what explains that it moves across the sky. This is due to the rotation of Earth, just in the same way as the sun moving across the sky is the consequence of the rotation of Earth.
The moon is orbiting the earth and the earth is rotating itself so that is why the moon and sun move across the sky.
The earth is spinning, the same reason the sun shows up and goes down daily, and why constellations shift across the night sky.
Day and night are simply the earth spinning in approximately 24 hours.
The fact that the moon rises and sets at different times is because the moon is going in a circle around the earth. Sometimes it’s between the earth and sun (new moon). Sometimes it’s directly behind the earth from the sun (full moon) each day in its 28-day orbit it moves a little bit. When it’s beside the earth relative to the sun and earth, you get a quarter moon.
So the rising and setting at night is the earth spinning. The moon‘s changing appearance and how early/late it rises/sets is the moon moving around the earth
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