Celestia Forums

I'm running the latest version on WinXP w/ ATI card, but this is not a hardware bug, it's a conceptual bug (maybe between my ears, maybe a problem with Celestia).

When I turn on the constellation borders (background purple sphere) and put my back to the sun, looking at earth, and accelerate time like 10000x, I get a very rapidly spinning earth (expected) but no drift against the backdrop of the constellations (very unexpected). If I look at the sun, at the same time rate, the drift is very obvious. Seems to me the background layer when looking at Earth in accelerated time, is improperly motionless.

Kirby

Not a problem with Celestia, I think. In Celestia, when you select a body, you can 'follow' it (press 'f'). That means you keep a constant relative offset position to it. When you set up Celestia to look at the Earth, you're actually following Earth around the Sun, but you still hang there in the same place relative to Earth. The constellations are so far away, you don't notice them moving (very small 'parallax'). When you turn to look at the Sun, you're still following Earth as it speeds around the Sun in its orbit, and you see the Sun move through the constellations.

To see what you want to see, go to the Sun (press 'h' (home), 'g' (goto)), select Earth (press 'return', type 'earth', press 'return' again) and then press 't' for track (track the Earth). Zoom in on Earth and speed up time. The constellation lines are very spread out, but you should see some whizz by.

Spiff.

Yes, you've given me the view I'm after.

I also find that if I boot up Celestia and immediately press : (colon) I "lock" and get 'Lock Earth -> Sol' printed on the lower right. Then if I speed up time to 100000x, the constellation borders start drifting by.

I'm still a bit confused what point of view gives me no background change even with time moving at a very high speed. But if I think about it more, it'll probably come to me eventually. Thanks for your help. Great program.

Next I need to find out if there's a way to lie on my back at any particular longitude/latitude and look out from Earth in a direction perpendicular to my local horizon (azimuth) i.e. towards my zenith.

Again, there is a way to do this. Under the Navigation menu there is a "Goto Object ..." option with dialogue box, in which you can select Earth, and add your latitude, longitude and altitude (distance). Put 1km for the altitude, because at lower altitudes, there a bug that causes the atmosphere to go funny. Anyway, since all planets are still smooth orbs, the horizon looks just the same at 1m, 1km or 10 km. When you click OK, you'll zip along there. When you get there, make sure you select 'sync orbit' (press 'y'), otherwise the Earth will rotate underneath you and you want to stay fixed at the same lat-long (which is what 'sync orbit' does). Then use the keys of the 'num pad' (far right on your keyboard) to look up and down (pitch), or turn left and right (yaw). Use the left and right cursor keys to 'roll' left or right. You can advance or reverse time as you like until day or night, whatever.

You might find that looking around is not easy. First, Celestia's not optimised yet for real 'pitch and yaw' looking near the surface of a world, and second, the fact that Celestia appears only in your monitor covering maybe just 30?° in front of you means you get no peripheral vision. If you find you keep swinging, press '5' on that num pad to brake.

Check out Stellarium for ground based observing at http://stellarium.free.fr.

Spiff.