Who knows astronomy?

[Careyp74]

But over any particular place on the earth's surface the same satellite should always been seen to be travelling in the same direction, yes?

So, from, say, the US and Canada, any particular russian satellite will, if it is ever seen to be travelling from north-south always be seen to be travelling north-south.

Point taken.

 

[edd]

But over any particular place on the earth's surface the same satellite should always been seen to be travelling in the same direction, yes?

No, I don't think so.

edit: although with a sun-synchronous polar orbit I guess the part visible at night will be the same direction.

 

[godless dave]

But over any particular place on the earth's surface the same satellite should always been seen to be travelling in the same direction, yes?

So, from, say, the US and Canada, any particular russian satellite will, if it is ever seen to be travelling from north-south always be seen to be travelling north-south.

Not necessarily, no.

 

[Roboramma]

Not necessarily, no.

That's interesting. As I was writing that post I started to wonder if it was actually correct, but couldn't figure out how it could not be.

At the very least the satellite's movement as seen from a particular point on the earth's surface would have to transition through an east-west (or west-east) phase before changing from north-south to south-north (over a particular place) wouldn't it?

 

[Roboramma]

No, I don't think so.

edit: although with a sun-synchronous polar orbit I guess the part visible at night will be the same direction.

Okay, I've got this image in my head of an orbit that follows a path through space that doesn't change relative to the surface of the earth. I suppose that's wrong, yes? That the path, relative to the surface of the earth, can be different from one orbit to the next?

I'm just curious how it can go from north-south over, say, Calgary to south-north over Calgary. It's not like the satellite turns around in mid-orbit and comes back.

 

[MG1962]

Oh, ok. Now I get it. I didn't know that most polar orbit satellites are Russian.

It has a lot to do with the initial launch location. The Soviets never had a launch facility near the equator so they needed bigger rockets with smaller payloads to get into an equatorial orbit or even geostationary orbit.

So often it was just easier for them to launch polar orbits.

The Americans had the reverse issue, their most efficient launch direction was east. Thats why their heavy lift flights like the Saturn V and shuttles always launched out over the Atlantic.

When the French got interested in spaceflight they built an extensive facility in French Guiana, which evolved into the ESA facility, and to this day launches a lot of private stuff.

And just to clarify seeing a satellite in polar orbit these days does not mean it is Russian, it just means the probability is higher

 

[MG1962]

Okay, I've got this image in my head of an orbit that follows a path through space that doesn't change relative to the surface of the earth. I suppose that's wrong, yes? That the path, relative to the surface of the earth, can be different from one orbit to the next?

I'm just curious how it can go from north-south over, say, Calgary to south-north over Calgary. It's not like the satellite turns around in mid-orbit and comes back.

You have to include time and the Earth rotation. Not all satellites in polar orbit take 24 hours to go around once, in fact I think it is impossible to do. So if a satellite takes four hours for an orbit, then in theory from Calgary we would see it travelling south twice a day and north twice a day. Make sense?

 

[I Ratant]

How do you figure? Is there something special about Russian satellites, that they take south-to-north trajectories over Calgary?

.
The satellite orbit is fixed in space.
The earth revolves inside it. On any revolution of the satellite in a polar orbit, it will be going south on one side of the earth, and north on the other.
I haven't seen as many as I was used to seeing for some time now.
I did see the Shuttle and the Hubble when the Shuttle released it..
And the ISIS has a regular orbit.

 

[I Ratant]

But over any particular place on the earth's surface the same satellite should always been seen to be travelling in the same direction, yes?

So, from, say, the US and Canada, any particular russian satellite will, if it is ever seen to be travelling from north-south always be seen to be travelling north-south.

.
A satellite launched with a orbital inclination... say 30°, and sent to the east, will always be seen coming from the west to the east in its orbit, which will be at 30° to the equator.
Few if any are launched to the west, as the east launch adds the rotational speed of the earth to the rocket helping it get to the orbit.
The orbit's inclination can an indication of the launch site's latitude.
Go to the ISIS site, it has all the information you might need to locate when and where the ISIS will be visible from your location.

 

[I Ratant]

That's interesting. As I was writing that post I started to wonder if it was actually correct, but couldn't figure out how it could not be.

At the very least the satellite's movement as seen from a particular point on the earth's surface would have to transition through an east-west (or west-east) phase before changing from north-south to south-north (over a particular place) wouldn't it?

.
Changing an orbit to that extent is a mighty energetic situation, and I've never of that being done.

 

[MG1962]

.
The satellite orbit is fixed in space.
The earth revolves inside it. On any revolution of the satellite in a polar orbit, it will be going south on one side of the earth, and north on the other.
I haven't seen as many as I was used to seeing for some time now.
I did see the Shuttle and the Hubble when the Shuttle released it..
And the ISIS has a regular orbit.

I know you are an active observer, did you ever see the formation flying cluster that tripped a few people out back in the day - I just did a Google search and could not find the names of them

 

[CORed]

But over any particular place on the earth's surface the same satellite should always been seen to be travelling in the same direction, yes?

So, from, say, the US and Canada, any particular russian satellite will, if it is ever seen to be travelling from north-south always be seen to be travelling north-south.

Not unless it has an orbital period that's a simple multiple or fraction of a sidereal day. The inclination, apogee and perigee of the orbit will be the same every time (actually will change slowly due to atmospheric drag and perturbation by sun, moon, etc.) but as the earth rotates under it, it will take a different path relative to Earth coordinates on each orbit.

 

[edd]

.
Changing an orbit to that extent is a mighty energetic situation, and I've never of that being done.

Well the ground track of something like a Molniya orbit can loop back on itself.

 

[I Ratant]

It has a lot to do with the initial launch location. The Soviets never had a launch facility near the equator so they needed bigger rockets with smaller payloads to get into an equatorial orbit or even geostationary orbit.

So often it was just easier for them to launch polar orbits.

The Americans had the reverse issue, their most efficient launch direction was east. Thats why their heavy lift flights like the Saturn V and shuttles always launched out over the Atlantic.

When the French got interested in spaceflight they built an extensive facility in French Guiana, which evolved into the ESA facility, and to this day launches a lot of private stuff.

And just to clarify seeing a satellite in polar orbit these days does not mean it is Russian, it just means the probability is higher

.
Vandenburg on the west coast is ideally located for polar orbit launches.. there's no land to the south at all for a damaged rocket to fall onto.
The launches can be seen as far east as Arizona.
I've seen polar launches, and launches to the southwest of ICBMs from here in Palmdale.
And a couple of dual Trident MIRV IRBM launches from the Pacific Ocean just off San Nicolas Island... the launches were to the south, polar orbits.. but I expect the MIRVs were intended to come down just a few thousand miles away.
With binoculars, I could see the buses that contained the MIRV object. The bus would outgas.. and rotate, and a "thing" detach itself and travel with the bus.. which would rotate, outgas...
The ICBM launches can be seen even in the daytime, but they're most spectacular just after sundown, when the exhaust trail is illuminated.
The first is 3 shots of a Cosmos satellite on a Delta rocket going south to a polar orbit from Vandenburg, and the second is the exhaust trail of a Titan ICBM heading to the southwest.. Kwajalein..
Both photos from Palmdale.

 

[I Ratant]

You have to include time and the Earth rotation. Not all satellites in polar orbit take 24 hours to go around once, in fact I think it is impossible to do. So if a satellite takes four hours for an orbit, then in theory from Calgary we would see it travelling south twice a day and north twice a day. Make sense?

.
About the shortest orbital time is 90 minutes... these are Low Earth Orbiters.
Most spy satellites are there.
Then there's some longer periods, up to 6 hours for mapping/communications satellites/GPS.
The 24 hour orbiters have to be over the equator, at about 22,000 miles out.
Their orbital speed matches the rate the earth rotates, so these satellites remain "locked" in position, and the dish antennas need not move with the satellite.
If there's any inclination to the equatorial orbit, the satellite will move up and down relative to the equator, describing an "analemma" type shape to the orbit over the period of a day. Mapping satellites may do this.

 

[Skeptic Ginger]

It's a tradition on our family camping trips to sit and watch for satellites. Given good conditions, there are a lot more that you are able to see than you might expect.

Yes, in good viewing conditions (dark, no city lights nearby) you can almost always see one without too long of a wait.

 

[I Ratant]

You have to include time and the Earth rotation. Not all satellites in polar orbit take 24 hours to go around once, in fact I think it is impossible to do. So if a satellite takes four hours for an orbit, then in theory from Calgary we would see it travelling south twice a day and north twice a day. Make sense?

.
The satellite comes by any one place on the earth, and the next pass will be to the west, displaced by the time of the orbit. LEO satellites can sometimes be seen twice, if the first pass is to the east and the next pass 90 minutes still visible to the west.

 

[I Ratant]

Some ISIS images.. note how the orbits move to the west as time goes by.
And the direction of the pass changes depending on the day. Southeast in the first picture, and northwest in the second.

 

[Archer17]

I know you are an active observer, did you ever see the formation flying cluster that tripped a few people out back in the day - I just did a Google search and could not find the names of them

NOSS Triads

 

[I Ratant]

I know you are an active observer, did you ever see the formation flying cluster that tripped a few people out back in the day - I just did a Google search and could not find the names of them

.
Haven't seen those, nor the Iridium satellites.. My sister worked on those..
I did see a Progress supply ship just ahead.. couple thousand miles... of the ISIS when the Progress was going to reenter.
The last Shuttle/ISIS mission was always in daylight when it came over.
ISIS can be resolved with a 600 mm lens, BTW.