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Q: Naked eye astronomy ( Answered 5 out of 5 stars,   4 Comments )
Subject: Naked eye astronomy
Category: Science > Astronomy
Asked by: petronius-ga
List Price: $10.00
Posted: 20 Dec 2002 07:23 PST
Expires: 19 Jan 2003 07:23 PST
Question ID: 127315
What bright object in the sky December 19 flew over 80degrees
52minutes 30seconds West, and 32degrees 14minutes 30seconds North
(Bluffton, SC), coming from the NW heading SE at between 6:10pm EST
and 6:20? It came right overhead. It was as bright as Jupiter or
Venus, and it moved like a sattelite. We watched it to the SE
horizon. We skywatch a lot, and see a lot of sattelites, but this
seemed different. Can you tell us
what it was?

Request for Question Clarification by seizer-ga on 20 Dec 2002 08:52 PST
Hi there petronius.

I just completed a preliminary scan of the sky over Charleston for
that time, which didn't indicate any madnmade objects particular near
your sighting - although there were 12 satellites flagged as visible.
I now have the lat/long data for Bluffton, so I'm rescanning, which
will take approximately 30 minutes. Would you be interested in the
results of this scan, and the tools to do other scans, even if it did
not show any objects that matched yours?



Request for Question Clarification by kutsavi-ga on 20 Dec 2002 12:39 PST
Hey Petronius, 

Is there anyway what you saw could have been closer to 6:00?  If so,
I've got your answer.
Subject: Re: Naked eye astronomy
Answered By: kutsavi-ga on 20 Dec 2002 21:32 PST
Rated:5 out of 5 stars
Hi there Petronius,

The more I research your question, the more sure I am that what you
saw was the International Space Station.  The station rises and falls
in its orbit due to friction from Earth's gravity, and is boosted
periodically into higher orbits.  It was last boosted on the 1st of
December, and so is now descending slowly.  There is a time
discrepancy between your sighting and the stated time below, but it's
only on the order of 10 minutes.

On the 19th, the International Space Station flew almost directly
overhead  32.2417N, 80.8750W, Bluffton, NC, at an angular altitude
of  77 degrees, from NW to SE:

Magnitude:  -0.4
Local start time:  17:54:45
Altitude (deg):  10
Azimuth:  NW
Local Max Time:  17:57:57
Altitude (deg):  77
Azimuth:  SW
Local End Time:  18:01:10
Altitude, (deg):  10
Azimuth:  SE

Unfortunately, to view this information from Heavens, you
will have to register on their site if you have not already, but it is
simple and they don't ask for more than a log-on name and password. 
The site is of value for anyone who watches the sky:

This pass took about 7 minutes to complete, which is close to your 10
minute estimate.

Here is a visual  representation of the ground track the ISS took on
this particular pass.  Again, you will have to be registered and
logged on to view this page:

Considering the proximity in time and the fairly bright magnitude, the
direction and altitude of the path, I'm sure this is what you saw.

If  I can provide clarification of anything, or add any information,
I'd be happy to.



I went to
where I am a registered user, and input the long. & lat. information
for Petronius' location to function as my observing location.  I then 
searched through the major satellites, including the Hubble Space
Telescope, (HST), visible Irridium Satellite flares, along with the
International Space Station, (ISS) for close and high-angle passes.
petronius-ga rated this answer:5 out of 5 stars and gave an additional tip of: $5.00
Thankyou Kutsavi, I am totally satisfied with your answer. Thankyou
also for the address for heavens-above.

Subject: Re: Naked eye astronomy
From: racecar-ga on 23 Dec 2002 18:01 PST
Friction from Earth's gravity??
Subject: Re: Naked eye astronomy
From: kutsavi-ga on 23 Dec 2002 20:17 PST
Yup, gravity.  "Drag" or "attraction" might have been a better terms. 
Gravity holds the ISS in orbit.  As it draws the ISS toward the Earth,
the ISS' orbit decays.  Call it friction, drag or attraction, the
result is the same; the orbiter comes closer to Earth and needs to be
boosted to a higher orbit periodically.  There is friction on the ISS
from the outer layers of the atmosphere as well.

Subject: Re: Naked eye astronomy
From: racecar-ga on 09 Jan 2003 17:02 PST
I agree that the ISS slows down, and hence moves closer to the earth,
due to friction.  But that friction has nothing to do with gravity. 
It's due to collisions with tiny particles, air molecules, or whatever
else is up there.
Subject: Re: Naked eye astronomy
From: kutsavi-ga on 16 Jan 2003 16:52 PST
Hey Racecar, 

I bow to you.  On researching satelltes in general, I found the

Geostationary orbit requires:

1.  An orbit of significant height to stay there without occasional
boosts; ie, the weight of the spacecraft is balanced to equal the pull
of gravity.  Our moon is representative of this relation.

2.  The satellite's orbital speed matches the speed of Earth's
rotation and as such stays over a particular place on Earth's surface
like the GOES satellites.

Then I found this, verifying your correction, from the very source I
"The height [of the ISS orbit] is averaged over one orbit, and the
gradual decrease is caused by atmospheric drag. As can be seen from
the plot, the rate of descent is not constant and this variation is
caused by changes in the density of the tenuous outer atmosphere due
mainly to solar activity."

Thanks for the information, and as I said, I prostrate myself at your
feet for the gaffe and ensuing comment. ;-)

I am still of the impression that gravity is responsible for the
satellite's orbit, and as such must create a drag/friction, however
having never been in space and not being a physicist, I'm unable to
make a further case for myself.


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