Timescapes - Digital Timelapse Discussion

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Author:  Drayg0 [ Tue Aug 12, 2008 3:05 pm ]
Post subject:  Analemma

Anyone aware of this phenomena? I find it fascinating.



Author:  flyvholm [ Tue Aug 12, 2008 4:19 pm ]
Post subject:  Re: Analemma

Has become a lot easier with digital cameras/processing, but is still a challenge that requires careful planning. And good weather. :-) I like this one from Turkey including a total eclipse...


Author:  Andrew Curtis [ Tue Aug 12, 2008 6:48 pm ]
Post subject:  Re: Analemma

Ive seen these before, quite the undertaking to capture!

Author:  supernovah [ Thu Aug 28, 2008 5:37 am ]
Post subject:  Re: Analemma

Also while you're staring at the eclipse, don't forget, the sun creates shadows on earth too.




Author:  Antz [ Thu Aug 28, 2008 7:16 pm ]
Post subject:  Re: Analemma

Over a 24 hour period a geostationary satellite effectively does a figure 8 in the sky, as the orbit is never perfectly level with the equator, giving the vertical movement, and it is never a perfect circle (slightly elliptical), meaning it will move left to right twice a day relative to the ground.

Author:  supernovah [ Sat Aug 30, 2008 10:21 pm ]
Post subject:  Re: Analemma

In theory, Geostationary satellites trace the ground perfectly about the equator. Something that traces a Figure 8 wouldn't be about the equator and wouldn't be on the geostationary band (it would collide if it were but not at the equator)

See this link: http://science.nasa.gov/Realtime/jtrack ... ack3d.html

Highlight some geostationary sattelites by clicking on the dots that are in the distinct ring around earth and then go view->ground trace. you'll not see anything because they line up with the equator and are a distinct Dot.

If you however highlight something like Sirius 2 which isn't geostationary, you'll see a figure 8 ground trace. Most other satellites however have far more chaotic ground traces

Author:  Antz [ Sat Aug 30, 2008 11:04 pm ]
Post subject:  Re: Analemma

The newest geostationary ones with plenty of fuel on board to correct their orbits are pretty steady overall, but the older ones typically get progressively worse.
It is not enough to notice on a tv dish etc, but when you are pumping a large signal through them you will still have a constant tracking mechanism making slight adjustments from time to time. On a really stable satellite the tracking will operate about once every half hour to make a minor adjustment, but you can get away with turning the tracking off without it affecting it most the time.
On the really old birds, they can vary a lot. At the South Pole the equatorial orbit plane is below the horizon, so they cannot use a full time link, but there are a couple of old satellites with bad orbits that pop up above the horizon for a few hours each. This is how they do the majority of their data transfer.
From where we are they are only 3 degrees above the northern horizon, so this is about as far south as you can get and still have reliable comms.

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