Constellation rise times versus hour of darkness .....etc

Alan wrote:

I've been waiting to observe M27 in Cygnus

um...M27 is in Vulpecula :-)

You get some right nit-picky people in here sometimes...

Jim
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"We deal in the moral equivalent of black holes, where the normal
laws of right and wrong break down; beyond those metaphysical
event horizons there exist ... special circumstances" - Use Of Weapons

Alan wrote:

I did hesitate before putting redundant information together without
checking first....... :-) . I suppose I just associate M27 with Cygnus ....

To be honest, so do I - I use stars in Cygnus to find it.

I was only pulling your leg - no insult intended :-)

Jim
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Find me at http://www.ursaminorbeta.co.uk AIM/iChatAV: JCAndrew2
"We deal in the moral equivalent of black holes, where the normal
laws of right and wrong break down; beyond those metaphysical
event horizons there exist ... special circumstances" - Use Of Weapons

I've been waiting to observe M27 in Cygnus, and a thought ocurred to me
recently when I noticed that it is quite high in the sky when it gets dark -
about the same altitude that I remember from last October when it 'got dark'
then (i.e. earlier in the evening). I know that the altitude of Cygus at a
given local time each night will vary roughly linearly with time of year
(day number), but my thought was this: if we were to plot the altitude (or
rise time) of a given object versus the time at which the sky brightness
falls to a given magnitude (i.e. some indicator of the time that 'darkness'
falls), what would it look like? Would there be stationary points, or even
retrogade behaviour? And how would this curve vary with the observer's
lattitude?

Anyone know of websites with relevant equations / graphs? Another topic that
interests me is the relationship between the length of twilight and
latittude / time of year, and also the shape of the curve for rate of change
of day length versus time of year (i.e when does day length change most
quickly etc). Also rate of change of length of twilight........and how is
this defined? .........

Just wondering :-)

Alan

I did hesitate before putting redundant information together without
checking first....... :-) . I suppose I just associate M27 with Cygnus ....

"Jim" wrote in message
...
Alan wrote:

I've been waiting to observe M27 in Cygnus

um...M27 is in Vulpecula :-)

You get some right nit-picky people in here sometimes...

Jim
--
AIM/iSight:JCAndrew2 - Log in and say 'hi'
"We deal in the moral equivalent of black holes, where the normal
laws of right and wrong break down; beyond those metaphysical
event horizons there exist ... special circumstances" - Use Of Weapons

Jim wrote:
Alan wrote:

I did hesitate before putting redundant information together without
checking first....... :-) . I suppose I just associate M27 with
Cygnus ....

To be honest, so do I - I use stars in Cygnus to find it.

I was only pulling your leg - no insult intended :-)

Jim

Umm. Intriguing. I never thought to use Cygnus as a starting point.

I just shift North and west from eta Sge (Sagitta). Actually, its even
easier than that if you have a Telrad. Put Eta Sge at 7 o'clock on the outer
ring. M27 is then at 1 o'clock on the middle ring. Hold that position in
your head and then slew your scope to centre the inner ring on that
position.

Regards,
Chef.

Chef! wrote:

To be honest, so do I - I use stars in Cygnus to find it.

I was only pulling your leg - no insult intended :-)

Jim

Umm. Intriguing. I never thought to use Cygnus as a starting point.

I just shift North and west from eta Sge (Sagitta). Actually, its even
easier than that if you have a Telrad. Put Eta Sge at 7 o'clock on the outer
ring. M27 is then at 1 o'clock on the middle ring. Hold that position in
your head and then slew your scope to centre the inner ring on that
position.

I use Alberio, Sadr and epsilon Cyg. M27 forms the fourth point of a
rectangle, ish.

Jim
--
AIM/iSight:JCAndrew2 - Log in and say 'hi'
"We deal in the moral equivalent of black holes, where the normal
laws of right and wrong break down; beyond those metaphysical
event horizons there exist ... special circumstances" - Use Of Weapons