Last updated: 25 April 2002

Subject:	ETX-70AT Globular Clusters
Sent:	Thursday, April 25, 2002 13:11:51
From: (Michael)
I just read Thomas Henry's response to me the ETX 70 site; thanks.  You
are obviously a bit more knowledgeable than I, and I appreciate your
tips.  I have always been interested in astronomy, and took a couple of
college astronomy courses (as electives while working toward my business
degree), but have never owned a telescope of my own until I bought the
ETX 70 last October.

Living in Southern California, my viewing nights at home are few, and
there is always way too much light pollution.  But I drag it out
whenever the skies are clear and it's amazing to me what I can actually
see from my backyard - even with such a bright sky.

We are avid campers, and make several trips each year up to the local
mountains.  Some of the most fun I've had with this thing was camping at
Big Bear Lake in January. This little scope performed great for several
hours, until it reached about 12 degrees (F) outside and we both had to
give up and go sit by the heater in the RV.

Anyway, Albireo was great the other night - I was finally able to see it
at about 1:30, after it came up over the trees.  Thanks also for the
tips on the other doubles, you're right that the Autostar's catalog
leaves a bit to be desired.  Have you or anyone else had any luck seeing
any globular clusters through this scope?

I have seen a few Globular Clusters, such as M13 and M92, through much
larger scopes, and was dazzled.  I'm not sure what to expect with this
little scope, but when I choose most of the ones listed in the Autostar
catalog, I don't see a thing!  I'll double-checked my alignment by
slewing to another known object.  But when I come back to where the
cluster is supposed to be, and nothing!  I would expect to see something
at least as bright as Andromeda, but usually can only make out a faint
smudge, if anything at all.

Can anyone tell me which globular clusters I should be able to see with
the ETX-70AT?

Thanks again,

Mike here: Most Globular Clusters are small. To get a feel for what each looks like, see the SEDS Messier web site (on the Astronomy Links page). They have photos (taken with larger telescopes), magnitudes, and angular sizes.


From: (Thomas Henry)
What might be good globulars to go after with the ETX-70AT?

This is a timely question, since the season of globulars is upon us! 
(The distribution of them is such that most are only well placed in the
heavens for us in North America during summer and fall).

The ETX-70AT is really a richfield instrument and excels on this type of
object. You should be able to see most of the Messier ones.  Several
will be faint and may offer quite a challenge, while many will be quite
bright. In no cases will you be able to resolve the globular to
individual stars (the aperature of the ETX-70AT is just too small). 
However, on a number of them you will be able to see a "form" or
gradations in the light across the extended object.  To add to your fun,
make sketches and keep a log book. And don't ignore the dim ones; I
enjoy the challenge of just finding them.

I pulled out my astro log book and checked which ones I've seen this
month. Here are a few to get you started, with comments straight from my

M13:  spectacular with 9mm, even with bad skyglow
M92:  bright, still one of my favorites, averted vision doubles the size,
good with 6mm
M5:   amazingly good given skyglow; a rival to M13
M3:   fabulous with 6mm; can see gradations
M53:  nice; variations in brightness clearly visible
M68:  very faint; near horizon; had to fight tree limbs, too
M10:  faint, but obvious; near horizon so somewhat washed out
M12:  faint, but obvious

And get ready for M22 in Sagittarius!  I've haven't seen it through my
ETX-70AT yet, but can hardly wait!

One final tip: the Autostar menu tree can be unwieldly at times.  I take
the following approach to minimize keystrokes.  From the OBJECT menu
press [enter], then [down] twice to DEEP SKY, then [up] once to MESSIER.
 Then simply enter the Messier number.  I'm so used to this pattern that
my fingers remember exactly what to do and do it rapidly.

Best wishes,

Thomas Henry
And this:
From: (Thomas Henry)
At 09:18 PM 4/25/02 EDT, Mike wrote:
>Thanks.  Most Globular Clusters are small.  To get a feel for what each 

But if you restrict yourself to the Messier globulars, I have to
respectfully disagree.  They are in fact quite large compared to Jupiter
and Saturn which most people seem to enjoy in their ETX-70AT's.

For example, Jupiter currently has an angular size of 36 arcseconds.  But
M92, not one of the largest globulars by any means, is at a healthy 11
arcminutes---that's some 18 times larger in diameter.  And M13 is a
whopping 38 times larger than Jupiter.

If we're ranking apparent size of deep sky objects within reach of the
ETX-70AT, then I would say that most galaxies (ignore M31 and M33!) are the
troublemakers, not the globulars.  In any event, the Messier globulars are
general pretty bright and usually put on a good show.

Please consider this a courteous and respectful difference of opinion; I
just want to put in a good word for the globular clusters who have given me
hours of entertainment over the years!

Best wishes,

Thomas Henry
Mike here: Good point! That's what I get for a fast reply (trying to get a Site update done).

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