Think I just saw my first Iridum flare

....but I'm not entirely sure!

What I saw was in the right place in the sky according to Heavens
Above, but occurred a good 70s after the predicted time. Does that
sound about right or did I see something else?

Cheers

TopBanana wrote:

...but I'm not entirely sure!

What I saw was in the right place in the sky according to Heavens
Above, but occurred a good 70s after the predicted time. Does that
sound about right or did I see something else?

Maybe your watch was a good 70s ahead...? My experience is that the
predictions are very, very precise.

Originally Posted by Iordani

TopBanana wrote:

...but I'm not entirely sure!

What I saw was in the right place in the sky according to Heavens
Above, but occurred a good 70s after the predicted time. Does that
sound about right or did I see something else?

Maybe your watch was a good 70s ahead...? My experience is that the
predictions are very, very precise.

Agreed ....and if your position [selected town/ suburb] is slightly off.

Nytecam 51N 0.1W
http://home.freeuk.com/m.gavin/iridium.htm

On Fri, 21 Jul 2006 10:15:52 +0100, nytecam
wrote:

Iordani Wrote:
Maybe your watch was a good 70s ahead...? My experience is that the
predictions are very, very precise.

Agreed ....and if your position [selected town/ suburb] is slightly
off.

I synchronised my watch via Manchester Uni's NTP server about 10
minutes beforehand, and I entered my position via handheld GPS. I
suppose it must have been something else I saw. It could have been a
plane emerging from the cloud and going behind it again.

TopBanana wrote in
:

...but I'm not entirely sure!

What I saw was in the right place in the sky according to Heavens
Above, but occurred a good 70s after the predicted time. Does that
sound about right or did I see something else?

It's unlikely something else happened there and (nearly) then.

An Iridium flare IMO builds slowly, shines brightly for a few swconds, and
then dies away - it's not a *flash*

I can generally observe the movement of the satellite against the starfield
in this period,

In some conditions you can see the satellite for quite a time outside the
flare period as an ordinary AS.

Any of this sound right?

mike

mike wrote:

It's unlikely something else happened there and (nearly) then.

An Iridium flare IMO builds slowly, shines brightly for a few swconds, and
then dies away - it's not a *flash*

I can generally observe the movement of the satellite against the
starfield in this period,

In some conditions you can see the satellite for quite a time outside the
flare period as an ordinary AS.

Any of this sound right?

Maybe this has something to do with the OP's observation.
From the FAQ at www.heavens-above.com

Q.While observing one of the predicted flares, I saw another one just a few
seconds before or after the predicted one in almost the same place. Why?

A.Several "double" flares have been reported by observers. They seem to come
from the same satellite, but no-one is completely sure what's causing them.
The most likely reason is a reflection of sunlight off another part of the
satellite structure.

Wasn't it TopBanana who wrote:
On Fri, 21 Jul 2006 10:15:52 +0100, nytecam
wrote:

Iordani Wrote:
Maybe your watch was a good 70s ahead...? My experience is that the
predictions are very, very precise.

Agreed ....and if your position [selected town/ suburb] is slightly
off.

I synchronised my watch via Manchester Uni's NTP server about 10
minutes beforehand, and I entered my position via handheld GPS. I
suppose it must have been something else I saw. It could have been a
plane emerging from the cloud and going behind it again.

Make sure that the numbers displayed by the GPS are in the correct
format.

Most GPS systems work internally in an odd format that uses degrees,
minutes and decimal minutes (DDMM.MM), and they may display the location
as degrees, minutes and seconds (DD MM SS). Heavens Above requires the
location to be entered as degrees and decimals of degrees (DD.DDDD).

If in doubt, use the coordinates you passed to Heavens Above on Google
Maps and see if the position agrees with where you were. Like
http://maps.google.com/maps?q=53.851453,-3.0257753
Google Maps in Sreetmap mode are extremely accurate, but there's
currently a positioning problem with the Satellite mode maps for
Northern England.

--
Mike Williams
Gentleman of Leisure

JRS: In article , dated Fri, 21 Jul
2006 10:15:52 remote, seen in news:uk.sci.astronomy, nytecam nytecam.2b
posted :

Iordani Wrote:
TopBanana wrote:
-
...but I'm not entirely sure!

What I saw was in the right place in the sky according to Heavens
Above, but occurred a good 70s after the predicted time. Does that
sound about right or did I see something else?-

Maybe your watch was a good 70s ahead...? My experience is that the
predictions are very, very precise.

Agreed ....and if your position [selected town/ suburb] is slightly
off.

I don't recall the mean height of Iridium, but they are certainly well
below GSO. Circular speed in GEO is 3 km/s; in LEO is 8 km/s; we cannot
be far out in estimating Iridium at 5 km/s. The motion of the flare
spot along the ground must be at about that speed, increased by a
geometrical factor for the appropriate component of the angles involved.

So 70 s should correspond with a position error no less than about 200
miles, which is more than slightly off.

If it was a secondary flare from the same satellite, then, to judge from
the rather perceptible motion of the satellites during individual
flares, ISTM that it would occur at a perceptibly "wrong" position.


--
© John Stockton, Surrey, UK. Turnpike v4.00 MIME. ©
Web URL:http://www.merlyn.demon.co.uk/ - FAQqish topics, acronyms & links;
Astro stuff via astron-1.htm, gravity0.htm ; quotings.htm, pascal.htm, etc.
No Encoding. Quotes before replies. Snip well. Write clearly. Don't Mail News.

On Sat, 22 Jul 2006 06:43:22 +0100, Mike Williams
wrote:


If in doubt, use the coordinates you passed to Heavens Above on Google
Maps and see if the position agrees with where you were. Like
http://maps.google.com/maps?q=53.851453,-3.0257753
Google Maps in Sreetmap mode are extremely accurate, but there's
currently a positioning problem with the Satellite mode maps for
Northern England.

Thanks for your suggestions Mike. The GPS location was plotted about
two doors down the road. Unfortuantely the houses in my road aren't
big enough for that to cause a significant error

I turns out that Manchester Uni's NTP server was a good 70s out!
What's the point of running a public time server if it isnt
maintained? Tsk.

So it almost certainly was my first Iridum flare!

Cheers

If you think your timing's off, check this out.
http://www.worldtimeserver.com/atomic-clock/

It's kept my computer and all household clocks /watches accurate for the
last 18 months and I have no trouble picking up Iridiums!

Beeb