Re: Vanguard 1

Leigh Palmer (
Wed, 27 Aug 1997 17:46:06 -0700

>And shortly thereafter, right in the place predicted and just a few
>seconds earlier than expected, just to the top of my field of view
>passed a tiny point of light.  A 39 year old, 15 cm sphere, 1840 km
>away.  Eureka!
>Now, of course I=92m feeling pretty pleased with myself, but before my ego
>gets the best of me, I wonder if any of the more experienced satellite
>watchers out there can comment on whether I really could have seen such
>a small object at such a great distance with such a relatively small
>In other words, is it possible that I just happened to see something
>else and mistook it for Vanguard?

It would help a lot to answer the question "Was the satellite moving
in the predicted direction?" If it was, say ten degrees off (or anything
perceptible for that matter) you could rule it out. If it was moving in
the correct direction, a few seconds (<10) earlier than predicted, at
the spot predicted, you've likely seen it. A 355 mm telescope has a
light gathering power much greater than that of the naked eye*. Roughly
one can expect to be able to see an object of size d through a telescope
of aperture A if one can see an object of size D through one's naked eye
with a pupilary diameter a, in the same illumination and observing
circumstances if

                           d       a
                          ---  >  ---
                           D       A

Solving for your numbers and assuming a pupilary diameter of 3.55 mm
(what a lazy fellow I am!) this means that you could have seen a 15 cm
sphere through the telescope if you could have seen a 15 meter sphere
with your naked eye, and it's likely you could have.

If the direction was the same, then congratulations! I've been mulling
Brian Hunter's suggestion over in my mind and I'm congratulating myself
on having been the first to report an Iridium flare here, even if I
didn't recognize what it was at the time. A similar degree of uncertainty
applies there, but in light of all the confirmations of similar events I
guess I'm convinced.


*about 10,000 times as great, or ten mags, to my tired old eyes. This
is an optimistic number, but it's high precision for astrophysics.
The calculation I have performed here is only valid if you were using
a magnification of 100x or more, by the way. If you had a wider field
of view your light gathering ability was reduced somewhat.