I usually only see one satellite. It’s mostly white, round and changes shapes over a 28-day period – And that suckers more than a few hundred miles away.
Well, that’s kind of what I was getting at.
I know we can’t see any object without light reflecting off it, but the moon is so big, you could just imagine seeing it at that distance, reflected light or no (I know that makes no sense, but wha ev).
Shit, the moon eclipses the sun.
And, you can see it during the day.
A satellite at 200 miles is so small, it’s invisible. If it passed in front of the sun, you would not notice it.
But, I guess that reflecting sunlight against a dark backdrop gives it a big advantage.
I remember going out to watch Skylab.
Echo 1.
While the sun does emit light in all directions, when viewed from far enough away the rays are basically straight almost parallel.
Even if we accept that approximation*, what’s that got to do with why we can see satellites?
(*The sun’s apparent size is about 1/2 degree, so approximating it as a parallel beam - which implies a point source - is not a good approximation for most applications.)
We are not seeing the satellites, we are seeing the sun(light) reflected off the satellites. Very intense light focused on the satellite in that 1/2 a degree ‘tight beam’, the combo of the 2 means there is enough light in that reflection to see the bird. Which answers the OP.
Not really. Yes, we’re seeing the light reflected off the satellite, but as I explained, most of the time it’s not specular reflection off of a flat surface. It’s random scattering from an irregularly shaped object. So the only thing that matters is the intensity of light hitting the satellite. It doesn’t matter what the light source looks like.
scr4 so is it safe to scale your statement into a experiment we can do on earth? Lets say taking a irregular but reflective object, perhaps a piece of aluminum foil illuminated by either a incondescend source of light (more like a point source) or a equally bright florescent tube and you are claiming that the light reflected by the IC light would not be as concentrated as the florescent tube?
That’s correct.
Assuming you mean wrinkled aluminum foil, which is what most satellites look like (e.g. the hubble). If you had a smooth flat sheet of aluminum foil, things would be a little different - the reflection would be very bright in one direction, and much dimmer in all other directions. The solar panel on a satellite behaves that way, which is why we sometimes see a brief but very bright flash of light from them. That’s what “Iridium flares” are. But the rest of the satellite is, and behaves like, an irregular object - it reflects/scatters light in all directions. It remains visible as it moves across the sky, with very little change in brightness.
Mangetout’s right.
Well, the movement is how you know it’s a satellite. But many satellites are bright enough that you’d see them even if they weren’t moving. They’d just look like ordinary stars.
(Although to be pedantic, the satellites would fall out of the sky if they weren’t moving… Unless they’re in geosynchronous orbit, in which case it would really be too far to see.
This reply is for Phlosphr, ShagNasty, and anyone else who has seen the same thing: What time of day/night are you seeing these? I know I’ve seen these things as late as 1-2am, but the SDopers told me satellites can only be seen shortly before/after sunrise/set, respectively. The SD argues the satellite would be on the ‘dark side’ of the earth by then; yet, what else could it be??? Operation Fail-Safe fighter jets, perhaps?
Forgive me for a slight hijack, but this is sort of related…
I forgot who said it, but “every boring city has a space needle”. So sorry Sydney, auckland, Toronto, Seattle, etc. Anyway, a picture of Sydney’s one is here. If you click on the link, you’ll see the slender stem of the thing is barely thick enough to hold two or three elevator shafts, a fire escape, and a few wires and water pipes. Yet I can see this thing from the middle Blue Mountains, over 60 miles away. Not only can I see it, but I can clearly see it, to the extent that if it were even only half as thick, it’d still be very easy to see. It never fails to make me wonder.
To be additionally pedantic, I’ll note that if geosynchronous satellites were visible, they would definitely move (albeit reasonably slowly) against the starry background. After all, the Moon - quite a bit further than any artificial satellite - does so.
I maybe going out on a limb here, but my satellite dishes stay pointed at them rather well. Or am I confusing geosynchronous and geostationary?
Well, sort of. Geostationary is a subset of geosynchronous.
But, I’ll also add that I don’t understand Xema’s point about the Moon. The reason geostationary satellites are geostationary is because their orbital altitude is such that their orbital period exactly equals the rotational rate of the Earth.
I wanted to add: Geostationary satellites don’t move with respect to the stars, but geosynchronous ones appear to bob up and down with a displacement which depends on the orbit’s tilt with respect to the equator.
So geostationary satellites are above the equator in the Clarke belt.
Oops, I stand corrected.
(A satellite in geostationary orbit appears to stay fixed in the sky, while the stars go around once a day. The satellite has to be outside the solar system for it to stay fixed relative to the stars… )