Hi Rik,
From what I recall, an order of magnitude translates to a factor
of about 5.7x. As a result, if Heavens-Above is off by 1-2 magnitudes,
we are really talking about a factor of 5.7 to 32.5 ... personally I
would consider this a serious error. My experience tonight was at least
a couple of magnitudes off. In fact, I would go further and claim that
it was probably off by about 4 magnitudes (Venus a couple of months ago
at -4.4 had similar magnitude to tonight's pass).
There have been occasions when I have not bothered pursuing photo
opportunities with the ISS and shuttle due to a low predicted magnitude
from Heavens-Above. From now on I will take a more aggressive approach
as I may be foregoing opportunities that I should be pursuing.
Ditto for iridium flares as I have seen differences of the order
of 3 to 4 magnitudes between Rob's program and Heavens-Above.
Anthony.
Rik Hill wrote:
> I too have noticed discrepencies and mentioned them on this list.
> Since I am often doing visual photometry on variable stars on the
> same night I have a pretty good idea what a given magnitude looks
> like. While I would expect variations of 1-2 mag. just due to
> presentation of a satellite, still on several I have noted 4 mags.
>
> With ISS and STS's the variations can get big and the more junk
> they stick on to the ISS the more that will probably increase. Right
> now I've been trying to get video in one of my telescopes of these
> two and have noted some variations from predicted brightnesses, but
> still they were the brightest moving target in the sky!
>
> -Rik
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This archive was generated by hypermail 2b29 : Mon Apr 23 2001 - 11:50:31 PDT