Explanation: Has your world ever turned upside-down? It would happen every day if you stay fixed to the stars. Most time-lapse videos of the night sky show the stars and sky moving above a steady Earth. Here, however, the camera has been forced to rotate so that the stars remain fixed, and the Earth rotates around them. The movie, with each hour is compressed to a second, dramatically demonstrates the daily rotation of the Earth, called diurnal motion. The video begins by showing an open field in Namibia, Africa, on a clear day, last year. Shadows shift as the Earth turns, the shadow of the Earth rises into the sky, the Belt of Venus momentarily appears, and then day turns into night. The majestic band of our Milky Way Galaxy stretches across the night sky, while sunlight-reflecting, Earth-orbiting satellites zoom by. In the night sky, you can even spot the Large and Small Magellanic Clouds. The video shows a sky visible from Earth's Southern Hemisphere, but a similar video could be made for every middle latitude on our blue planet.
Math idiot that I am, I can't wrap my head around what I'm seeing in the APOD. My mind is telling me that I'm seeing the Earth rotating on its poles, not on its axis.
The Earth looks like a weird version of Uranus rotating like that.
Ann
Re: APOD: Our Rotating Earth (2020 Jul 01)
Posted: Wed Jul 01, 2020 6:31 am
by Chris Peterson
Ann wrote: ↑Wed Jul 01, 2020 5:13 am
Math idiot that I am, I can't wrap my head around what I'm seeing in the APOD. My mind is telling me that I'm seeing the Earth rotating on its poles, not on its axis.
???
Earth's axis passes through its poles. If it's rotating on its axis, it's also rotating on its poles.
Ann wrote: ↑Wed Jul 01, 2020 5:13 am
Math idiot that I am, I can't wrap my head around what I'm seeing in the APOD. My mind is telling me that I'm seeing the Earth rotating on its poles, not on its axis.
???
Earth's axis passes through its poles. If it's rotating on its axis, it's also rotating on its poles.
Click to play embedded YouTube video.
Let's say I think it looks as if the Earth is turning somersaults instead of rotating "sideways".
Ann wrote: ↑Wed Jul 01, 2020 5:13 am
Math idiot that I am, I can't wrap my head around what I'm seeing in the APOD. My mind is telling me that I'm seeing the Earth rotating on its poles, not on its axis.
???
Earth's axis passes through its poles. If it's rotating on its axis, it's also rotating on its poles.
Let's say I think it looks as if the Earth is turning somersaults instead of rotating "sideways".
Don't worry about the math, just try to visualize a couple of special cases. What if you were at the North Pole? Aim your camera at a star near the horizon, and what will happen over the course of a day? The star will stay on the horizon, right? Over 24 hours you'll follow it all the way around the horizon and back to where you started. So the angle of the horizon won't change, just what direction you're looking. Make sense? The movement is completely azimuthal.
Now suppose you're at the equator. Aim at a star on the eastern horizon, and you'll follow it straight up, across the zenith, and back down to the western horizon. For the other 12 hours you'll be aiming through the Earth, until after 24 hours you come back up to the eastern horizon again. Got that? The movement is only in altitude.
For intermediate latitudes, you're going to have a combination of azimuthal movement, and altitudal movement. That's what produces the tumbling effect.
Earth's axis passes through its poles. If it's rotating on its axis, it's also rotating on its poles.
Let's say I think it looks as if the Earth is turning somersaults instead of rotating "sideways".
Don't worry about the math, just try to visualize a couple of special cases. What if you were at the North Pole? Aim your camera at a star near the horizon, and what will happen over the course of a day? The star will stay on the horizon, right? Over 24 hours you'll follow it all the way around the horizon and back to where you started. So the angle of the horizon won't change, just what direction you're looking. Make sense? The movement is completely azimuthal.
Now suppose you're at the equator. Aim at a star on the eastern horizon, and you'll follow it straight up, across the zenith, and back down to the western horizon. For the other 12 hours you'll be aiming through the Earth, until after 24 hours you come back up to the eastern horizon again. Got that? The movement is only in altitude.
For intermediate latitudes, you're going to have a combination of azimuthal movement, and altitudal movement. That's what produces the tumbling effect.
I get it... I think. Thanks for the explanation!
Ann
Re: APOD: Our Rotating Earth (2020 Jul 01)
Posted: Wed Jul 01, 2020 8:28 am
by XgeoX
Watched this on a 50 inch tv, almost hurled!
Wonderful video!
Eric
Re: APOD: Our Rotating Earth (2020 Jul 01)
Posted: Wed Jul 01, 2020 9:38 am
by heehaw
This is why I come to APOD, first thing every day! Occasionally, as today, there is something truly spectacular!
THANK YOU, APOD !
Re: APOD: Our Rotating Earth (2020 Jul 01)
Posted: Wed Jul 01, 2020 10:28 am
by orin stepanek
I don't believe the video is s true representation of the Earth's rotation! JMHO!
Re: APOD: Our Rotating Earth (2020 Jul 01)
Posted: Wed Jul 01, 2020 1:24 pm
by TheZuke!
We live in a topsy-turvy world!
Thanks Chris for the explanation!
Re: APOD: Our Rotating Earth (2020 Jul 01)
Posted: Wed Jul 01, 2020 2:09 pm
by neufer
Click to play embedded YouTube video.
We are riding in a Ferris wheel car at the Prater amusement park.
The Earth is the Ferris wheel itself appearing to rotate around us.
The Universe is the Vienna bobbing around us but not rotating.
Re: APOD: Our Rotating Earth (2020 Jul 01)
Posted: Wed Jul 01, 2020 2:51 pm
by TheOtherBruce
I need to be drunk enough to watch this and appreciate it properly.
Re: APOD: Our Rotating Earth (2020 Jul 01)
Posted: Wed Jul 01, 2020 3:19 pm
by fbivan
Like with the dancing people 2 thumbs down.
Re: APOD: Our Rotating Earth (2020 Jul 01)
Posted: Thu Jul 02, 2020 12:05 am
by Boomer12k
Awesome... interesting how the "flat part" rotates... hmmmmm....
:---[===] *
Re: APOD: Our Rotating Earth (2020 Jul 01)
Posted: Thu Jul 02, 2020 8:50 pm
by heehaw
this is the best APOD ever.
Re: APOD: Our Rotating Earth (2020 Jul 01)
Posted: Sun Jul 05, 2020 9:17 pm
by heehaw
heehaw wrote: ↑Thu Jul 02, 2020 8:50 pmthis is the best APOD ever.
I still feel that way. We humans tend to be self-centered. Yet all this great APOD does is ask you to tie yourself to a telescope pointed generally toward the Magellanic clouds, and look....for days and days on end. Of course the Earth circles around you as it rotates every 24 hours. Now mind you, it is also circling the Sun, and THAT motion has NOT been taken out!
There are other motions too: our solar system is moving with respect to the center of our galaxy, and our galaxy is moving ... you get the picture! But those motions are very very slow on a human time scale; no need to take them out!
This whole APOD gives us a great perspective on our whiligig motion of Earth rotation, and is very educational indeed, even to a jaded professional astronomer. Yay APOD!
heehaw wrote: ↑Sun Jul 05, 2020 9:17 pm
Yet all this great APOD does is ask you to tie yourself to a telescope pointed generally toward the Magellanic clouds, and look....for days and days on end.
To tie yourself telescope pointed generally
toward Sigma Octantis to be more precise.
https://www.etymonline.com/search?q=untoward wrote:
untoward (adj.) 1520s, "not having inclination" (to or for something), also "difficult to manage, unruly," from un- (1) "not" + toward (adj.).
The Taming of the Shrew : Act IV, scene V
HORTENSIO: Well, Petruchio, this has put me in heart.
Have to my widow! and if she be froward,
Then hast thou taught Hortensio to be untoward.
