Re: Observing USA 193 - tips for beginners

From: John Locker (
Date: Sat Feb 16 2008 - 07:38:51 UTC

  • Next message: Matt Bartley: "Re: USA 193, ISS, and mystery flasher"

    Thanks for an excellent and timely reminder about basic data collection.
    I spend far to much time with my eye stuck in a viewfinder and tend to 
    neglect the importance of accurate timing , relying instead on the
    laptop clock , which is invariably  a few seconds wrong.
    So I was scratching around to find a stopwatch , when I realised that my 
    portable car GPS has an illuminated clock display , which should be about as 
    accurate as I  could expect...and it swtches to "stealth" mode in if like me anyone else is wondering what to use...this and a 
    notepad to write down the time logged , is a quick fix.
    Transits over the UK start in a couple of days , but , unfortunately it 
    looks like 193 will become missile fodder before the high elevation 
    passes.....unless of course , they miss !
    Assuming the first kill attempt will take place around 1300 GMT on the 21st 
    the UK is well placed for a good sw to se pass just under four orbits later 
    , especially the southern part of the country .
    Will we see it I wonder ???
    ----- Original Message ----- 
    From: "Ted Molczan" <>
    To: <>
    Sent: Friday, February 15, 2008 7:14 PM
    Subject: Observing USA 193 - tips for beginners
    > Allen Thomson wrote:
    >> The apparent divergence between USG estimates and SatEvo persists.
    >> Hopefully enough tracking data will be collected to throw
    >> light on where the difference comes from.
    > Visibility windows for various latitudes are available here:
    > The object has entered a brief period of visibility near 30 N, which will
    > gradually move northward over the coming days.
    > Beginners can useful contribute to the tracking of USA 193, especially 
    > when it
    > has not been tracked for several days, as this case now. It was last 
    > observed
    > with precision on Feb 11, and its orbital elements were updated, but due 
    > to its
    > rapid and uneven rate of decay from orbit, those elements are rapidly 
    > losing
    > accuracy for predictions. Tonight, it could easily be early or late, by at 
    > least
    > 1 minute.
    > In these circumstances, an observation timed to within one or two seconds, 
    > and
    > accurate in position to within one degree or so, would make a valuable
    > contribution to tracking the object, by enabling us to approximately 
    > revise the
    > orbital period and rate of decay.
    > Here is how to make a simple, but reasonably accurate observation.
    > 1. Obtain a Prediction
    > Heavens-Above provides predictions of nearly all satellites, including 
    > star
    > charts showing the time and path. Due to the interest in USA 193, the site 
    > has a
    > special link at the top of the main page.
    > I recommend allowing for at least 60 s prediction time uncertainty, and 2 
    > min to
    > be safe.
    > 2. Observe
    > Go outside at least 10 min before the satellite is due, to give your eyes 
    > time
    > to adapt to the darkness, and to locate the predicted point of arrival of 
    > the
    > satellite shown on the Heavens-Above chart. If you are not all that 
    > familiar
    > with sky, or how to use a star chart, then you may need 30 min or longer.
    > Wait for the satellite to appear, allowing at least 1 or 2 minutes, in 
    > case it
    > is early or late. Beware of imposters! There are many satellites in orbit, 
    > so it
    > is all too easy to follow the wrong one. The one you want will closely 
    > follow
    > the predicted path.
    > When you spot it, observe it as it crosses the sky, and when you see that 
    > it is
    > about to pass close to a star that you can identify, get ready to make 
    > your
    > observation. At the moment of closest approach, note whether the satellite 
    > was
    > above, below, right or left of the star, and the approximate separation. 
    > For
    > example, "one half degree below Procyon". (For reference, the moon's 
    > apparent
    > diameter is 1/2 deg.) The closer the separation the better, but 1 or 2 
    > degrees
    > is acceptable for a rough observation. If you do not know the star by 
    > name, then
    > circle it on the Heavens-Above chart, or other star chart.
    > At the moment of closest approach you must also measure the time.
    > If all you have is a wrist-watch, then turn to read it as quickly as you 
    > can
    > after noting the position of the satellite. You may wish to subtract a 
    > second or
    > two to allow for the delay in taking the reading. The goal is to achieve 1 
    > or 2
    > sec accuracy.
    > You will need to calibrate the watch to a precise time source. Perhaps the
    > simplest method is to phone radio station WWV (303-499-7111), and note how 
    > many
    > minutes and seconds your watch is early or late, and then correct your 
    > observed
    > time accordingly. Or, you may wish to set your watch to synchronize as 
    > closely
    > as possible to WWV. Keep in mind that watches tend to drift, so this 
    > should be
    > repeated each day you observe.
    > If you have a stop watch handy, then that is the preferred timing method. 
    > The
    > usual approach is to hit the start button at the moment of the 
    > observation, then
    > stop it at the start of a minute using WWV. Subtracting the elapsed time 
    > from
    > the WWV time, yields your observed time.
    > 3. Report
    > Your observation report can be as simple as "passed one half degree below
    > Procyon" on 2008 Feb 15 at 7:12:43 PM CST.
    > If you are familiar with Universal Time, aka UTC or GMT, that is 
    > preferred, but
    > local civil time is acceptable, as in the above example. If you know the 
    > time
    > zone, that would help. If you can roughly estimate the accuracy of your 
    > position
    > and time, please include it.
    > Last, but not least, we need to know your location on Earth. Typically, we
    > report latitude and longitude to 0.0001 deg accuracy, and height above sea 
    > level
    > to within a few metres. If you have GPS, use it, else you can use Google 
    > Maps.
    > For low-precision observations, 0.1 deg accuracy should suffice; height 
    > can be
    > within 100 m.
    > Happy Hunting!
    > Ted Molczan
    > -------------------------------------------------------------------------
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