When I see clouds moving in the sky, based on a “fixed” position (i.e. the moon) are they moving at the same relative speed as if they were at ground level?
Or, are clouds that appear to be moving slowly based on the moon, moving at the same mph as they would across a tree in my yard if they were at the same altitude?
I’m struggling with wording this properly, as indicated by the OP.
How about “a cloud is moving at a set speed, would it appear to be moving faster if the cloud were at a 20’ altitude, as opposed to being juxtaposed to the moon which is that much farther up”?
Is earth’s rotation a factor?
Maybe saying “clouds move across states at a relatively quick pace, yet they seem to move very slowly in relation to the moon” best states my basis for my confusion.
If I’ve made this even remotely clear, please help. Right now I’m thinking it’s an angular view sort of thing. I think.
You’re referring to parallax, the amount of angular displacement of a distant object as it moves in relation to an observer (or the observer in relation to the object–all motion is relative). Stand right next to a busy highway and the cars seem to zoom past. Move farther and farther away, and the cars seem to move slower. Their linear speed hasn’t changed, but the angular speed has. Close up, the cars move through a given angle much faster than they do when you’re farther away. Same thing with clouds and anything else that moves.
Think of it this way. When you see an airliner at 40,000 feet it looks like it is moving very slowly. In fact it is going about 520 MPH (give or take)
Now think of what that airliner would look like if it were doing that same 520 MPH at an altitude of 20’
Most clouds move with the speed of the wind at the altitude where they form. This wind often (but not always) increases with altitude, which will complicate calculations of their apparent speed to a ground-based observer.
Certain clouds (e.g. altocumulus standing lenticular) do not move with the wind - they are more or less anchored to the gound.
You could I suppose, though there is a broad range of altitudes for cloud formation so that knowledge won’t necessarily be helpfull. You’d be better off just guestimating the cloud height (not easy, people are not good at judging altitude) and going from there.
Notwithstanding the above good answers I just wanted to add that the moon is a red herring. Judging the speed of clouds against the moon is tantamount to comparing the speed of the clouds against your forefinger held out in front of you.
