Re: Night Sky 101

In article <1188044445.578325.80010@xxxxxxxxxxxxxxxxxxxxxxxxxxx>,
"wm.king@xxxxxxxxxxxx" <wm.king@xxxxxxxxxxxx> wrote:

A few very basic questions; I am quite clumsy with this sort of thing
and would be very grateful for nutshell answers:

1. Are the constellations unchanging? I.e., are those we see from a
given time and place (allowing for environmental conditions) the same
(or not perceptively different) than they would have been in 1984 or
1892?

Yes, if you're only considering decades. Over several millennia some
constellations will be noticeably different (and accordingly, the
ancient ones are a little different now than they were when first
delineated); in a few million years they all will become unrecognizable.
Many nearby stars can be seen to move over shorter time-scales, but
almost all of them are too faint to be included in any patterns of
naked-eye stars. An exception is Sirius, the brightest star in the sky
(only about eleven light-years away, and somewhat larger and therefore
intrinsicaly more luminious than our Sun): its motion against the
background stars was noticed in classical times by comparing
contemporary observations with ancient records.

2. Is there a website or reference book that will show you the night
sky from a gfiven time and place and identify the constellations?

Yes, many, including some websites from which you can download software
to run locally. For books there's the caveat that "proper motion" is
rarely shown in printed maps -- if that's at all relevant to your
purposes: see above -- but star-catalogues will often provide that
information in their tables.

3. How much effect do the stars (excluding the moon (which I know is
not a star anyway, and again leaving aside environmental conditions)
have on how light it is at night?

Compared to city lights: almost none, excepting supernovae in our own
galaxy, of which we haven't had any for several centuries. From remote
sites under clear skies: almost all, but with several bright planets up
at once, a fairly rare occurrence, I suppose the stars' contribution
could be as low as 90%. (Excuse the flippancy, but I'm not sure what
you're asking.)

--
Odysseus
.

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