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Re: (IAAC) New



>Hey Gang,
>	Being new to the list I've been encouraged by the postings and
>have had my appetite whetted to do some DS observing.  I've got some
>questions however.
>
>	#1  I only have a 4.5" celestron reflector and it seems that most
>of what you guys see is done on at least 6" scopes.  What can I possibly
>hope to see with my 4.5"er?   Specifically I once saw a globular star
>cluster on somebodyelse's big Dobsonian and wonder if I could locate one
>on my scope.  Where would one be for me living in Philadelphia area, 40
>degrees lat?   I know the Pleides is an open cluster, right?, but I want
>to observe those closed ones.
>
>	#2  I presently have 2 eyepieces that came with the scope that are
>36 and 91 times magnification.  How high can I actually go in
>magnification on my 4.5" scope before I am exceeding it's ability to
>accurately depict DS objects.  The reason i ask is partly because most of
>the postings I read have you guys reporting magnifications of mid 100's to
>200's plus.
>
>		Thanks for your help,
>
>					Bill from Philly
Bill,
I suppose by "closed ones" you mean globular clusters.  Your 4.5" will
"show" you a number of the brighter globulars such as M2, M3, M5, M10, M13,
M15, M22, M28, M30, M92, etc.  You will also be able to observe many open
clusters and a few of the brighter galaxies (M31, M81, M82, etc.) and
nebulae (M8, M17, and M42).  For these and other deep sky fare it is
important to get to as dark a site as possible, however.
The maximum magnification rule of thumb is 50 to 60x per inch of aperture.
This applies to bright objects such as Jupiter and the moon and for
splitting close binaries. Realistically speaking about 200x is the limit
for your aperture.
With a 4.5" deep sky observing should be kept below 100x for the most part.
The image will be too dim otherwise.  Large telescopes gather enough light
to allow high power viewing of DSO's when appropriate.
You might want to consider joining the DVAA (Delaware Valley Amateur
Astronomers - http://www.libertynet.org/dvaa/ ) which meets on the second
Friday of the month at the Schuylkill Center for Environmental Education in
Norristown.
Dave Mitsky
ASH, DVAA
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