Iridium flare?

Looking towards the dawn this morning (taking a look at Venus) at 06:35 I
caught a bright white light a little above and to the left of where the sun
will rise. It was very bright, easily rivalling Venus. It quickly faded to
zero. It was already very bright as I stuck my head out of the door so I
only saw the last few seconds.

Was this my first Iridium flare? Either that or something too high to be
seen against the brightening sky had a damn intense spotlight. No aircraft
to be seen once the light faded...

Les
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Les Hemmings a.a #2251 SA

Wasn't it Les Hemmings who wrote:

Looking towards the dawn this morning (taking a look at Venus) at 06:35 I
caught a bright white light a little above and to the left of where the sun
will rise. It was very bright, easily rivalling Venus. It quickly faded to
zero. It was already very bright as I stuck my head out of the door so I
only saw the last few seconds.

Was this my first Iridium flare? Either that or something too high to be
seen against the brightening sky had a damn intense spotlight. No aircraft
to be seen once the light faded...

It certainly sounds like a flare. To check if it was an Iridium flare,
go to http://www.heavens-above.com/ and check if there was one for your
location at that time.

Many other satellites can flare, some of them more brightly than
Iridiums. The Iridium flares are famous because the orientation of the
Iridium panels can be forecasted precisely and therefore the flare
visibility can be predicted. This is not the case for other satellites.
A difference of 1 degree in the orientation of the panels can make a
difference of 10 miles or more in the ground location.

--
Mike Williams
Gentleman of Leisure

In message , Mike Williams
writes


Many other satellites can flare, some of them more brightly than
Iridiums. The Iridium flares are famous because the orientation of the
Iridium panels can be forecasted precisely and therefore the flare
visibility can be predicted. This is not the case for other satellites.
A difference of 1 degree in the orientation of the panels can make a
difference of 10 miles or more in the ground location.


See the Spaceweather news item "WEIRD ORIONIDS--NOT!" (Updated: Oct. 19)
for photographs of recently recorded flares from geostationary
satellite.

http://www.spaceweather.com/

It seems that this is a favourable time of year for flares from
geostationary satellites - I assume because we are close to the equinox?
--
David Entwistle

Wasn't it David Entwistle who wrote:
In message , Mike Williams
writes


Many other satellites can flare, some of them more brightly than
Iridiums. The Iridium flares are famous because the orientation of the
Iridium panels can be forecasted precisely and therefore the flare
visibility can be predicted. This is not the case for other satellites.
A difference of 1 degree in the orientation of the panels can make a
difference of 10 miles or more in the ground location.


See the Spaceweather news item "WEIRD ORIONIDS--NOT!" (Updated: Oct. 19)
for photographs of recently recorded flares from geostationary
satellite.

http://www.spaceweather.com/

It seems that this is a favourable time of year for flares from
geostationary satellites - I assume because we are close to the equinox?

Yes.

Note, however, that geostationary satellites are up to 100 times further
away than satellites in Low Earth Orbit, so the flare will tend to
appear something like 10000 times dimmer (10 magnitudes) than a similar
satellite in LEO. Also, the GEO flares will be a lot slower. An LEO
flare lasts a few seconds, so the brightening is obvious. A GEO flare
takes several minutes so you may well not notice the brightness changing
with the naked eye, but only on a long exposure photograph.

--
Mike Williams
Gentleman of Leisure

I could be wrong,ut I don't think the inverse square law applies to a
specular reflection. It will be smaller, certainly, but not a great deal
fainter.
"Mike Williams" wrote in message
...
Wasn't it David Entwistle who wrote:
In message , Mike Williams
writes


Many other satellites can flare, some of them more brightly than
Iridiums. The Iridium flares are famous because the orientation of the
Iridium panels can be forecasted precisely and therefore the flare
visibility can be predicted. This is not the case for other satellites.
A difference of 1 degree in the orientation of the panels can make a
difference of 10 miles or more in the ground location.


See the Spaceweather news item "WEIRD ORIONIDS--NOT!" (Updated: Oct. 19)
for photographs of recently recorded flares from geostationary
satellite.

http://www.spaceweather.com/

It seems that this is a favourable time of year for flares from
geostationary satellites - I assume because we are close to the equinox?

Yes.

Note, however, that geostationary satellites are up to 100 times further
away than satellites in Low Earth Orbit, so the flare will tend to
appear something like 10000 times dimmer (10 magnitudes) than a similar
satellite in LEO. Also, the GEO flares will be a lot slower. An LEO
flare lasts a few seconds, so the brightening is obvious. A GEO flare
takes several minutes so you may well not notice the brightness changing
with the naked eye, but only on a long exposure photograph.

--
Mike Williams
Gentleman of Leisure

"Mark Dunn" wrote in message
...
I could be wrong,ut I don't think the inverse square law applies to a
specular reflection. It will be smaller, certainly, but not a great deal
fainter.

The specular reflection is of the Sun's disk, which fills 0.5 deg. If the
plane mirror's angular size is smaller than that, then the apparent
brightness will indeed follow the inverse square law. And obviously the
satellites are very small in angular terms.

You are probably thinking about a specular reflection of an unresolved star.

A specular reflection **from a plane surface** will have essentially the
same angular size as the original (very distant) object. A reflection will
be smaller in angular size if the surface is convex, e.g., specular solar
reflections from the Earth's oceans seen by orbiting spacecraft.

"Mike Williams" wrote in message
...
Wasn't it David Entwistle who wrote:
In message , Mike Williams
writes


Many other satellites can flare, some of them more brightly than
Iridiums. The Iridium flares are famous because the orientation of the
Iridium panels can be forecasted precisely and therefore the flare
visibility can be predicted. This is not the case for other satellites.
A difference of 1 degree in the orientation of the panels can make a
difference of 10 miles or more in the ground location.


See the Spaceweather news item "WEIRD ORIONIDS--NOT!" (Updated: Oct. 19)
for photographs of recently recorded flares from geostationary
satellite.

http://www.spaceweather.com/

It seems that this is a favourable time of year for flares from
geostationary satellites - I assume because we are close to the equinox?

Yes.

Note, however, that geostationary satellites are up to 100 times further
away than satellites in Low Earth Orbit, so the flare will tend to
appear something like 10000 times dimmer (10 magnitudes) than a similar
satellite in LEO. Also, the GEO flares will be a lot slower. An LEO
flare lasts a few seconds, so the brightening is obvious. A GEO flare
takes several minutes so you may well not notice the brightness changing
with the naked eye, but only on a long exposure photograph.

--
Mike Williams
Gentleman of Leisure




--
Mike Dworetsky

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