[Chaos-l] Nice Animated GIF Of Comet Lulin

[Jim Scarborough]

I imagine they were satellites, but they probably weren't geosynchronous.
Geosynchronous satellites are in orbit over the equator at the distance that
keeps them over the same longitude all the time, so they seem to rotate
roughly the same speed as the sun.  These satellites were in lower, faster
orbits, probably between 200 and 500 miles up.  Things in this orbit are
GPS, spy, earth observation, Iridium phone, and similar satellites - oh, and
the International Space Station :-)

GPS and Iridium are low because they need to communicate with tiny devices
that do not have dishes.  Earth observation and some spy satellites are in
low orbits (often polar orbits) to cover the surface of the planet fairly
often.  Geosynchronous satellites are usually communication satellites -
with TV, phone, and internet types of communication, but they have fallen
out of favor for phone/internet because of their distance, about 0.2
light-seconds from Earth.

If that was interesting, there's more here:
http://en.wikipedia.org/wiki/Geosynchronous_orbit

Jim

On Thu, Feb 26, 2009 at 9:17 AM, Joe Pedit <pedit at email.unc.edu> wrote:

> It is easier to see that the majority of streaks in the video are probably
> geosynchronous satellites if you composite the individual frames.
> http://www.unc.edu/~pedit/lulin.jpg<http://www.unc.edu/%7Epedit/lulin.jpg>
> The field of view is roughly four degrees across with the long axis skewed
> slightly counterclockwise from an east-west orientation. It takes about ten
> frames for the streaks to cross the field, which would suggest 1.6 minutes
> between starts of individual frames (which is a bit shorter than 61 frames
> in two hours).
>
> By coincidence, I imaged a few geosynchronous satellites last Friday from
> Jordan Lake. They appear as dots in a fixed tripod image.
> http://www.unc.edu/~pedit/geo_sat_7517.jpg<http://www.unc.edu/%7Epedit/geo_sat_7517.jpg>
>
> An animation of the comet over a 90 minute period taken last Friday from
> Jordan Lake is at
> http://www.unc.edu/~pedit/Lulin0221.html<http://www.unc.edu/%7Epedit/Lulin0221.html>
>
> Joe
>
>  I think those streaks that kept appearing were satellites rather than
>> meteors.  I did "mispeak" about the stars "slewing" past, though.  Let me
>> clarify my hypothesis...
>>
>> Meteors probably would have been to brief to appear at in the time-lapse
>> movie and even if they did show up, they would have passed through the field
>> way too fast to be appear like for so long in that movie.  Each image of the
>> "movie" showed a steak about an "inch" long in the frame.  Orbiting
>> satellites would also have moved too quickly to appear as short streaks in
>> each exposure.  If they were geosynchronous satellites, the apparent motion
>> (which showed up a the short streak in each image) would be due not to the
>> relative motion of the satellites, but to the slewing of the telescope to
>> counter the rotation of the Earth (and make the stars appear stationary).
>>  It seems to me that the telescope slewing speed would be the only motion
>> slow enough to keep those lights in the frame for so long (since even a
>> split second in that film would have to represent a minute or more in real
>> time).  Furthermore, the position of the meteor at that time had to be near
>> the ecliptic (since it was near Saturn) which is where you would expect to
>> see geosynchronous satellites.
>>
>> I had some similar pair of apparitions appear in some webcam images I made
>> a few years back, and this was the explanation given to me by someone on a
>> listserve.   I was hoping they were invading alien ships, but I must admit
>> that the satellite explanation seems more likely.  The guy even looked up
>> some satellites and told me which ones they probably were.  Now that might
>> be interesting to figure out--which satellites they could have been if
>> that's indeed what they were....
>>
>> Chris Breivogel
>> CHAOS member wanna-be
>>
>
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