Satellites can’t ‘hover’ over a particular point except for those in geostationary orbit (at 35,786 km altitude) at the equator. The satellites in the Starlink constellation are in circular orbits at ~550 km altitude and 53° inclination [edit: Group 1 and 4 satellites are at 53.0° and 53.2° respectively; Group 2 is at 70° and Group 3 is at 97.6°]; I assume the locations on the map show the epoch (reference point) for each bird.
Stranger
Are they? I thought they were predominantly deployed in 53 degree inclinations, and then just a smattering at higher inclinations to cover the extreme north/south. If they don’t have any orbiting at inclinations less than 53, then there will be roughly the same number of satellites at every latitude, but latitudes are shorter the further you are from the equator so the actual density of satellites will be higher the further from the equator you get, until you go past 53 degrees. The 53rd latitude is ~60% of the length of the equator, so nearly double the density of satellites.
I did say I found it unbelievable.
Well, which do you disbeleive? That they are hovering, or that they do in fact form that apparent rectangle on that map which is not a globe?
This page Aerospaceweb.org | Ask Us - Orbit Ground Tracks explains pretty well how one orbit looks over the ground and the effect of multiple passes of that orbit in the images farther down the page. Having lots of satellites just makes that web of sine curves into a thicker, more closely spaced web.
So you end up with a spherical globe with a fat band of satellites stretched around it that extends from 50, 60, whatever degrees north to the same 50-60-whatever degrees south.
That they are hovering. It looked at first glance like they weren’t over any ocean. @gnoitall disabused my misinterpretation of the map.
Admittedly that’s a really weird map. About 25% of its east-west extent is duplicated at both ends. It’s not 360 degrees wide; it’s about 460 degrees wide.
If we saw the map without all the satellite icons on top it’d be a lot more obvious just how weird it is.
That’s right. Hence the “fairly”. A 1.7x difference is only a 29% max difference from the average. And I was calculating the typical distance to the nearest satellite, which is an area calculation, which implies another square root, bringing the error down to 14%. For an off-the-cuff calculation like that, I’m not going to worry about 14%. Especially since I was ignoring the sun-synchronous orbits completely.
Zoom in to get a better idea what’s overhead. Obviously they are moving, but in a constellation that guarantees good coverage…
What surprises me is the limited number outside the main coverage range. I guess Scots
and Scandinavians don’t need remote internet? “No true Scotsman would use Starlink!”
I imagine Starlink did the cost/benefit math and determined the higher launch cost for high inclination satellites plus the lower revenue from sparser customer density means they don’t invest heavily in provisioning much above 53° N or S.
There’s a nice 3D map here:
If you angle the globe right, you can get a sense of how sparse they really are at the high latitudes. Despite looking relatively thin, there’s still plenty of coverage. The antenna only needs a satellite at least 35 degrees over the horizon, and there’s always at least one satellite within that field of view.
Another neat feature of the visualization is that satellites in the dark are red. But that’s a surprisingly low fraction of the total, maybe only 1/3. Even their relatively low altitude gets quite a bit more daylight hours.
Note to others that might be confused, to see which satellites are in the dark, you have to go to ‘settings’, then ‘display’ and enable the ‘day/night’ switch.
Huh, didn’t know about the switch. It showed the difference to me by default. I wonder if the default setting changed, but I’d captured it in the on state due to visiting the site before. Anyway, good to know!
I’d never visited that site before so I suspect some default setting changed. I was deeply confused by the the random smattering of red dots until I zoomed in to realize that in my display, those were the ground stations.
What’s the green dot NE of Brazil? And north of Antarctica?
If you zoom in, it’ll tell you (along with presenting more info about the other satellites). The ones shaped like a green head-and-shoulders are the International Space Station and the Chinese space staion.
Also, right at this moment, there’s a long line of them over the Middle East. Those are satellites that just launched, and are still in the process of spreading out and moving to their final orbits. There’s pretty much always one or two of these lines somewhere over the planet these days.
Also, that visualization makes the sky look crowded, but if ou tried to render the satellites to their reall scale, they wouldn’t even be visible on the image. Not even at 100X their real size.
On my screen, Earth is about 1000px in diam and the satellites are 3px across. That 3px is about 38,000 m at that scale. The largest Starlinks are at most 30 m across. So over a 1200x difference linearly, and 1.6Mx in area, and in practice even more since the satellites aren’t squares.
Yeah.
From their ~575km altitude and a 35 degree look angle, they’re still usable ~1150km farther poleward than their own extreme latitude. Which amounts to providing coverage about 10 degrees of latitude farther poleward than the satellites themselves go. There’s not huge bandwidth at those extremes, but there’s also not massive populations there to use that bandwidth.
And, it should be said, that 35 degrees is only for the antenna pointing straight up. It has a 110 degree field of view, which means 35 degrees on each side for the full 180. Which is what you’d want to do in, say, northern Greenland.
But people close to the 53rd parallel will probably want to point their antennas toward it, since the non-polar satellites are very dense there. In principle, they should be visible even 24 degrees away, though the sats will be very close to the horizon then. Even with 10 degrees of margin, that gives you coverage up to the 67th parallel. Most of Alaska (and Europe) is below that.