[Chaos-l] Nice Animated GIF Of Comet Lulin

Thu Feb 26 10:39:18 EST 2009

Jim et al,

According to those numbers, those streaks were moving at the speed that
the earth rotates (or the speed the sun and stars cross the sky),
meaning they almost had to be geosynchronous satellites.  Each streak
took crossed about 1/10 of the 4 degree frame in each image which was
about 1.6 minutes of exposure.  That's about 0.4 degrees each 1.6
minutes or 0.25 degrees/minute, which is the rotation speed of the earth
(360 degrees in 1 day or 1440 minutes, which is 0.25 degrees/min).

Satellites that we can see moving across the sky (like the ISS) move
from horizon to horizon in only a few minutes (when directly overhead
maybe 5 minutes) or on the order of 10's of degrees per minute (I get
about 36 degrees/minute for an overhead pass).  One of those would have
crossed the entire 4 degree frame of the image in seconds (in the
neighborhood of 8 seconds), while the exposures were more like 1.6
minutes long.

I would guess that they were the geosynchronous type of satellites like
the communication satellites you mentioned.  This seems especially
likely since the image was taken in the region of the sky near the
ecliptic or directly above the equator where these satellites would be
found.

Chris 

________________________________

From: chaos-l-bounces at rtpnet.org [mailto:chaos-l-bounces at rtpnet.org] On
Behalf Of Jim Scarborough
Sent: Thursday, February 26, 2009 9:58 AM
To: chaos-l at rtpnet.org
Subject: Re: [Chaos-l] Nice Animated GIF Of Comet Lulin

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

_______________________________________________
Chaos-l mailing list
Chaos-l at rtpnet.org
http://rtpnet.org/mailman/listinfo/chaos-l

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://rtpnet.org/pipermail/chaos-l/attachments/20090226/08a9528d/attachment.htm>