September 26, 2007: Geostationary satellites
 

http://cellar.org/2007/nso_geosats.jpg

This was an Earth Science Pic of the Day a few days ago.

This is 8 and a half hours of an open shutter pointed at the sky. Now,
that makes clear what the trails are - stars, captured as they move
across the sky while the earth rotates. But then, the dots that don't
have any trail are geostationary satellites, in geostationary orbit.

They don't have any trail because they move along with the rotation
of the Earth. They orbit at exactly the equator. That means stationary
dishes on Earth can "see" them at all times, which is why there are so
many of them. People don't want to move their dishes!

So if you follow: the camera is stationary on Earth, except that it's not
stationary at all; it's moving with the rotation of the Earth. The
satellites appear to be stationary in the picture, but that's only
because they are moving in exact harmony with the motion of the
camera. And the things that appear to move completely across the
image are stars, entirely stationary.

Well, except that they probably aren't -- but with our short span of
attention, our 70 years, we can't sit around long enough to notice
that motion... we can't perceive it.

So why does XM Radio have three satellites while Sirius appears to
have none? Sirius' satellites use a different type of orbit, a Tundra orbit.
This allows two of their three satellites to be visible to all of North
America at any given time.

We need more Directv satellites.

Now I know why XM radio is always playing ZZ Tops LaGrange.

This is too complicated and 'boy' looking for me to know or care what it is. It's some kind of "graph" that employs the ugliest green color in the world so it is not worth my attention.

How come there are no GIRL-focused IotD stuff like shoes or diamond rings or self-tanning products on the Cellar? Ever ask yourself that, UT?

Actually, Brianna, that's a close-up of the skidmarks you left when you dragged your butt across the carpet.

The labels pinpoint different things you've had for dinner recently.

Oh! Thanks, Flint! I knew it was something you'd know about!

Did you just volunteer for IotD-er of the month duty? Cause we're looking for one.

Has anyone noticed several of the star tracks suddenly winked out? Is the sky falling?

End of the Star
 

That's just where the star happened to be when the exposure started or stopped.

Help
 

Where do you put suggestions for IotD?

Send as links or attachments with all relevant info to undertoad @ cellar dot org.

Thanks

Damn...there are still women who play that "I'm too dumb to understand because I'm a girl..." game? I truly hope that was sarcasm...

um...what do you mean by that?

Where are the GPS satellites?

Not geostationary, so not visible in the picture.

They are not geosyc!

Nah, they are just specs of dust on the camera's sensor! Space objects? Whatever next! :p

Cool beans.

Geosycamore?

neither are they geodesic.

Orbits
 

GPS Satellites operate in a Mid-Earth Orbit, approximately 1/2 of the height of the satellites shown in UT's pic. This type of orbit allows for better GPS service near the polar regions of the Earth.

<-- doesn't play the "dumb" game :D

8.5 hours; the photographer must have steady hands.

Undertoad, I didn't mention this before, but this IotD is a great one. Good job!

It has slowly grown on me over the last couple days. I was mulling over the possibility of taking a similar image myself. I wonder what sort of equipment you need? The link says it was taken at Kitt Peak, but not which instrument was used. I wonder if it was one of the big telescopes there, or just a camera on a tripod with a long exposure? The satellites are +10 to +14 magnitude in brightness, but I don't know exactly what that means in camera exposure speak. Eight hours is a long exposure.

Looking at the link again, it says the view spans about 10% of the arc. That's roughly like a 50mm lens. You should be able to reproduce this shot in your back yard with a 35 mm camera on a tripod! (assuming a clear night.)

Cool.

Wouldn't you get too much light pollution there in Arlington?

Yeah, way too much here. I can see the planets and the moon though.

But you know, when you travel to someplace nice and have a clear night, you can do this.