The earths gravity just outside the earth makes satellites stationary, but farther out makes them travel extremely fast, while even further out, such as the case with the moon, things move but really slowly? Also, how is it the sun passes through the sky at about the same speed as the moon? What are the chances of a moon orbiting a planet at roughly the same pace as the earth spins around the sun? The chances of those two completely random objects going through the sky at roughly the same speed seems astronomical.
Throw a baseball in a path across the sun - it take much less time to see it traverse than an airplane would.
Anyone can objectively realize that the baseball will in no way be thrown at a speed anywhere near how fast a jet travels, yet the observation is that the jet is moving slower.
Starlink satellites seem to be around the 160km orbit. The ISS is about 300km orbit.
Starlink satellites actually travel slower than the ISS. The higher the orbit, the faster the satellite needs to travel. This is due to the bigger circle that a higher orbit satellite travels in.
The actual solvable equations are the gravity equation and the centripetal force equations - orbit makes both of these equal. F=Gm1Me/r^2 and F = m1v^2/r
The pick a velocity and the orbital radius can be found. Set a radius and the velocity to live/orbit there can be found.
The viewing time to travel an arc can be calculated by knowing the radius and the velocity. Closer things appear to move faster. Arclength = Radius angle in radians, distance = velocity * time
Assuming a stationary observer, solve for time. When dealing with geosynchronous satellites, use two different arc lengths - one from the center of the earth to the observer on the surface, with earth rotational speed approximately 1000mph. Solve for time to move an angle on the surface of the earth.
For the geosynchronous satellite, use that time and same angle and then find the radius and speed (or just look up geosynchronous orbits).
Closer objects orbit faster. This is because gravity is stronger when closer, so they have to move faster to avoid simply falling into the planet. The ISS orbits very close at just over 400 km and can pass by in 5 minutes or so. Earth-imaging satellites are at 700-800 km, orbit around 12 times per day and pass by in 10-15 minutes.
Going higher up to a few Mm, some communications satellites can be visible for an hour or two. The visibility intervals keep rising with altitude until around 36 Mm, where the orbit speed matches Earth rotation and the satellite becomes always visible (from one side of Earth of course), which we call geostationary. One orbit equals one day.
Beyond that, the orbits become so slow that your visibility of it depends more on the Earth rotation than on the actual movements. The moon is a few light-seconds up, where one light-second is just under 300 Mm, the distance light moves in 1 second. It orbits around every month, though obviously you see it daily as Earth rotates.
The Sun is around 8 light-minutes away, and Earth is the body doing the 1-year orbiting of course, though the effect is much the same as viewed from the ground. Again, the daily Earth rotation remains the dominant factor in its visibility cycle, as it does for anything further out.
Earth to ISS is 254 mi (90 minutes around the earth) Earth to moon is 238,900 mi (1 month around the earth) Earth to sun is 94,052,000 million mi (takes earth 1 year)
It just seems with these numbers being so different that the moon and sun appearing to pass at the same speed doesn't make a lot of sense. I also don't understand why earth's gravity doesn't make the moon spin but the suns gravity causes the earth to spin, but that's another subject. It just seems like the moon would pass through the sky at a much higher speed than the sun, but watching the moon come up or the sun come up, they both look about the same.
Try to separate the notions of one orbit (around something else) and one self-rotation (own axis). The primary concern of gravity is the former.
The ISS and LEO satellites are so close that gravity makes the orbit dominant; the Earth is also spinning, but not so much that it impacts the duration of one visible pass.
The Moon and Sun are so far that gravity is weak and Earth's rotation is dominant; orbits are still involved, but not so much that impacts the duration of one visible pass.
Effectively, the different distances impact the orbits but not the daily Earth rotation, so the rotation is negligible for close objects and the orbit is negligible for distant objects.
The cross-over point is around 36 Mm (should be around 22500 miles), where the geostationary trick is possible.
How does the moon pass through the sky? It's not a stationary object at the center of the galaxy and it doesn't rotate around since we always see the same side, yet it moves through the sky at roughly the same pace as the sun.
The earths gravity just outside the earth makes satellites stationary, but farther out makes them travel extremely fast
You have it backwards, low orbit satellites travel faster than further out geostationary satellites. Geostationary satellites are still moving, but they revolve around the Earth at the same rate that the Earth spins around its axis. You can see low orbit satellites at night, they look like a star but move across the night sky in a fixed direction at a constant speed.
Aren't the new Elon Musk Starlink satellites low orbit. Wouldn't they have to be mostly stationary in order to work? Also, do any of these mostly stationary satellites ever move slowly in front of the moon, enough that a person could see it?
If starlink was only one satellite, then that satellite would have to "hover" directly over the user to work.
However, Elon is putting hundreds, if not thousands of starlink satellites in orbit - all of them communicating with each other and the ground. The number of satellites makes it possible to be always connected, as there will always be some group of them within line of site.
Direct tv, as an example, would hover over a specific area, and beam back content to the users.
The reason starlinks are so low is because Elon wants the ping time to be very small. A ping time to a direct tv satellite is about 1/4 to 1/3 of a second, and that doesn't work well for internet gaming.
[ + ] SecretHitler
[ - ] SecretHitler 0 points 3.0 yearsMay 19, 2022 01:46:40 ago (+0/-0)
[ + ] 3Whuurs
[ - ] 3Whuurs 1 point 3.0 yearsMay 19, 2022 05:21:27 ago (+1/-0)
[ + ] bosunmoon
[ - ] bosunmoon 0 points 3.0 yearsMay 19, 2022 09:03:51 ago (+0/-0)
[ + ] SecretHitler
[ - ] SecretHitler 0 points 3.0 yearsMay 19, 2022 10:17:15 ago (+0/-0)
[ + ] bosunmoon
[ - ] bosunmoon 0 points 3.0 yearsMay 19, 2022 10:33:34 ago (+0/-0)
[ + ] lord_nougat
[ - ] lord_nougat 0 points 3.0 yearsMay 19, 2022 02:16:06 ago (+0/-0)
[ + ] Her0n
[ - ] Her0n 0 points 3.0 yearsMay 19, 2022 16:07:54 ago (+0/-0)
[ + ] localsal
[ - ] localsal 0 points 3.0 yearsMay 19, 2022 20:35:21 ago (+0/-0)
Closer objects appear to pass quicker.
Throw a baseball in a path across the sun - it take much less time to see it traverse than an airplane would.
Anyone can objectively realize that the baseball will in no way be thrown at a speed anywhere near how fast a jet travels, yet the observation is that the jet is moving slower.
Starlink satellites seem to be around the 160km orbit. The ISS is about 300km orbit.
Starlink satellites actually travel slower than the ISS. The higher the orbit, the faster the satellite needs to travel. This is due to the bigger circle that a higher orbit satellite travels in.
The actual solvable equations are the gravity equation and the centripetal force equations - orbit makes both of these equal. F=Gm1Me/r^2 and F = m1v^2/r
The pick a velocity and the orbital radius can be found. Set a radius and the velocity to live/orbit there can be found.
The viewing time to travel an arc can be calculated by knowing the radius and the velocity. Closer things appear to move faster. Arclength = Radius angle in radians, distance = velocity * time
Assuming a stationary observer, solve for time. When dealing with geosynchronous satellites, use two different arc lengths - one from the center of the earth to the observer on the surface, with earth rotational speed approximately 1000mph. Solve for time to move an angle on the surface of the earth.
For the geosynchronous satellite, use that time and same angle and then find the radius and speed (or just look up geosynchronous orbits).
[ + ] i_scream_trucks
[ - ] i_scream_trucks 1 point 3.0 yearsMay 19, 2022 02:38:28 ago (+1/-0)
[ + ] SithEmpire
[ - ] SithEmpire 1 point 3.0 yearsMay 19, 2022 02:54:28 ago (+1/-0)
Going higher up to a few Mm, some communications satellites can be visible for an hour or two. The visibility intervals keep rising with altitude until around 36 Mm, where the orbit speed matches Earth rotation and the satellite becomes always visible (from one side of Earth of course), which we call geostationary. One orbit equals one day.
Beyond that, the orbits become so slow that your visibility of it depends more on the Earth rotation than on the actual movements. The moon is a few light-seconds up, where one light-second is just under 300 Mm, the distance light moves in 1 second. It orbits around every month, though obviously you see it daily as Earth rotates.
The Sun is around 8 light-minutes away, and Earth is the body doing the 1-year orbiting of course, though the effect is much the same as viewed from the ground. Again, the daily Earth rotation remains the dominant factor in its visibility cycle, as it does for anything further out.
[ + ] Swej_Ehtsag
[ - ] Swej_Ehtsag [op] 0 points 3.0 yearsMay 19, 2022 17:23:55 ago (+0/-0)
Earth to moon is 238,900 mi (1 month around the earth)
Earth to sun is 94,052,000 million mi (takes earth 1 year)
It just seems with these numbers being so different that the moon and sun appearing to pass at the same speed doesn't make a lot of sense. I also don't understand why earth's gravity doesn't make the moon spin but the suns gravity causes the earth to spin, but that's another subject. It just seems like the moon would pass through the sky at a much higher speed than the sun, but watching the moon come up or the sun come up, they both look about the same.
[ + ] SithEmpire
[ - ] SithEmpire 0 points 3.0 yearsMay 20, 2022 03:15:24 ago (+0/-0)*
The ISS and LEO satellites are so close that gravity makes the orbit dominant; the Earth is also spinning, but not so much that it impacts the duration of one visible pass.
The Moon and Sun are so far that gravity is weak and Earth's rotation is dominant; orbits are still involved, but not so much that impacts the duration of one visible pass.
Effectively, the different distances impact the orbits but not the daily Earth rotation, so the rotation is negligible for close objects and the orbit is negligible for distant objects.
The cross-over point is around 36 Mm (should be around 22500 miles), where the geostationary trick is possible.
Edit: I accidentally a unit.
[ + ] 3Whuurs
[ - ] 3Whuurs 1 point 3.0 yearsMay 19, 2022 05:18:30 ago (+1/-0)
[ + ] Swej_Ehtsag
[ - ] Swej_Ehtsag [op] 0 points 3.0 yearsMay 19, 2022 17:12:00 ago (+0/-0)
[ + ] cyclops1771
[ - ] cyclops1771 1 point 3.0 yearsMay 19, 2022 10:50:51 ago (+1/-0)
[ + ] s23erdctfvyg
[ - ] s23erdctfvyg 3 points 3.0 yearsMay 19, 2022 02:23:42 ago (+3/-0)
You have it backwards, low orbit satellites travel faster than further out geostationary satellites. Geostationary satellites are still moving, but they revolve around the Earth at the same rate that the Earth spins around its axis. You can see low orbit satellites at night, they look like a star but move across the night sky in a fixed direction at a constant speed.
[ + ] Swej_Ehtsag
[ - ] Swej_Ehtsag [op] 0 points 3.0 yearsMay 19, 2022 17:08:45 ago (+0/-0)
[ + ] localsal
[ - ] localsal 0 points 3.0 yearsMay 19, 2022 20:39:04 ago (+0/-0)
However, Elon is putting hundreds, if not thousands of starlink satellites in orbit - all of them communicating with each other and the ground. The number of satellites makes it possible to be always connected, as there will always be some group of them within line of site.
Direct tv, as an example, would hover over a specific area, and beam back content to the users.
The reason starlinks are so low is because Elon wants the ping time to be very small. A ping time to a direct tv satellite is about 1/4 to 1/3 of a second, and that doesn't work well for internet gaming.