| |
Main
Date: 18 Jul 2007 07:44:44
From: Margo Schulter
Subject: Surfing to M25: An inside story
|
Hello, everyone.
What a pleasure it is to report that this last Sunday I surfed with my
new Sky-Watcher 20cm f/6 Dobsonian to a beautiful open cluster, which
proved to be M25/IC4725, my first identified DSO with this telescope.
This viewing was done from a very basic window observatory located in
my third-floor apartment in the urban setting of Sacramento,
California, USA. The portal for this observatory is a bedroom window
opened with the screen left in place, so that the telescope remains
completely within the building, and a bit of "built-in apodizing"
takes place.
Knowing that Tony Flanders and others have had discussions here about
"windowsill astronomy" and in-home observatories, I'm delighted to say
that for me this has so far proven a happy solution in practice as
well as theory. As the adage says, "That telescope is best which is
most used."
Why observe from indoors? For me, the first reason is that I can't
drive and get to a dark-sky site by myself. The second is that the
building has no elevator, and routinely getting my Dob down and later
up two flights of stairs is not such an appealing proposition. The
third is that in my older years, I feel a bit more cautious about
personal safety when alone outside at night.
After I ordered the Dob in April, my Mom in her intuitive wisdom urged
me to consider using it indoors. At first I quoted the usual advice in
the manual (which I had downloaded from the Web) about the
disadvantages of viewing through a closed or open window: "Astronomy
is an outdoor activity."
Then my taste for the unconventional allied itself with my common
sense: as my Mom suggested, window viewing _would_ be a neat solution
for evening-to-evening observing. I searched with Google and quickly
found some attractive precedents for this style of urban observing.
Rapidly I was convinced that storing and using the telescope in the
same place would be a logical solution -- in other words, an
observatory!
-----------------------------------------
Weeks of preparation: A binocular prelude
-----------------------------------------
During my weeks of waiting for the new telescope to arrive, I spent
many pleasant hours observing with 7X50 binoculars through the
unscreened portion of my closed bedroom window, which has a southerly
exposure not too far from the local meridian. Getting acquainted with
some stars and asterisms in Scorpio and Sagittarius, the latter of
which I affectionately call in Yiddish the _chaynik_ or "tea kettle,"
was an absorbing and often contemplative experience. I was excited
quite confidently to locate M7, Ptolemy's Cluster, and likely also the
bright cluster in M8. Other DSO's like M4 and M25 were fun to look
for, but more problematic with binoculars under urban light pollution
conditions (limiting magnitude around 3.2-3.5, I might guess).
During those weeks, I also got a chance to make a trip with a couple
of Dob-owning friends to a dark-sky site called Cronan Ranch. Taking
my 7X50 binoculars and looking in the place so familiar from my urban
observing, I quickly found M4 -- and learned how reducing light
pollution can make a difference! Each location has its own charms and
challenges.
--------------------------------------------
The telescope arrives: an open window policy
--------------------------------------------
When my Dob arrived and had been set up and collimated with invaluable
help from some mentors who are members of the Sacramento Valley
Astronomical Society, which I joined in April, one distinction between
binoculars and the telescope with its much greater aperture quickly
became clear. Observing through a closed window had been fine with the
binoculars, but as predicted by one mentor caused very dramatic
distortions with the Dob. Opening the window solved the problem. Since
I was not ready to take the risks of trying to remove and replace the
screen in an apartment where even experienced people could find this
process a bit finicky, I gracefully accepted a bit of apodizing as
something coming with the territory.
-----------------------
Sidereal surfing to M25
-----------------------
This last weekend, with a towel duly placed on my head to alleviate
local light trespass and glare, I was ready for a proper inauguration
of my Newtonian sweeper on a Dobsonian mount in its observatory
setting. Using a 25mm Super Plossl eyepiece at 48X. I was impressed
with the richness of the starfields and the spacious region of the sky
accessible through my modest domestic portal.
Using a towel which might have been larger, and not yet equipped with
a convenient chair (I am ordering a Cosmo Comfort), I resorted to what
might be called "surfing" -- in contrast to the purposefulness implied
by starhopping or sweeping. While trying now and then to use the
finder scope for orientation, I often abandoned myself simply to
moving around with the 48X eyepiece, and seeing if I could come upon
something interesting.
Since I knew that I was in or near the constellation of Sagittarius
(my beloved Chaynik), a region rich with the Milky Way and DSO's, this
strategy wasn't quite totally random -- and serendipitously I arrived
at what appeared a beautiful open cluster.
The richness and the geometry drew me in, and I attempted a sketch.
Near the visual "south" of the field (taking "west" as the direction
in which things were being moved by the Earth's rotation) were three
bright stars below the cluster plus a fourth near the middle star of
this group, a distinctive landmark. My eye at once delighted in the
central cluster and tried to organize its features: a "diamond" of
stars in the lower part of this central area, and a "W" pattern near
its middle that captivated my eyes. In a small trapezoid of sorts near
the heart of this "W" was a small region of what I might describe as
luminous nebulosity. Later, looking at charts, I saw that this was
readily explainable as the light of unresolved fainter stars -- the
same basic explanation which Dante and some other medieval observers
correctly offered for the Milky Way. Above the "W" was another line or
region where four or so stars stood out.
While most of this was evident with direct vision, I remembered some
good advice to try averted vision also in order to see more and
better. Trying a range of angles can help, and I often visualize using
the portion of my eye near my nose. New views appeared, and stars
sometimes seemed to come and go in and out of the view.
When people speak of "immersive" views, they are thinking of something
with a wider angle than a Super Plossl at 52deg AFOV, but I found the
perspective on M25 quite immersive and encompassing. The field at
slightly more than 1deg was very pleasant. Of course, I look forward to
trying some ultra-wide 2" eyepieces I have, and also some higher
magnifications on the central region of M25, for example. However, I'd
consider the view and framing of it with the Super Plossl as a very
nice place to start.
As I finished my sketch, I knew that I had a likely open cluster, and
a beautiful one, with a radius of something like 30' -- very possibly
a Messier, but I wasn't sure which one. Hopefully my sketch would help
in finding out.
The next day -- or actually the same one, since my observing had gone
on a bit after midnight -- I used two fine resources freely available
on the Web to solve this puzzle.
First, I checked my printouts of _Taki's 8.5 Magnitude Star Atlas_,
<http://www.asahi-net.or.jp/~zs3t-tk/atlas_85/atlas_85.htm >. This is a
wonderful atlas by Taki Toshimi which I had already gotten to know
well in my binocular observing. The main complication is that the pdf
files for this publication are quite reasonably formatted for the
standard international A4 paper size, while in the USA the 8.5"x11"
letter size is more prevalent. At least on my Linux system, this isn't
a problem for viewing on screen. For printing, I converted the pdf
files to PostScript, and edited the PostScript code to rescale and
reposition the pages for letter-size output.
Unfortunately, while Taki's 8.5 magnitude atlas is ideal for lots of
purposes, identifying my "mystery object" seemed to require a higher
level of detail.
Then I remembered a Linux program I have, fchart by Michiel Brentjens,
available at <http://www.astro.rug.nl/~brentjen/fchart.html >. This can
generate finder charts in Encapsulated PostScript (.eps) or pdf format
for objects in the Messier and NGC/IC catalogues, and also some others
such as the Palomar globular clusters. The default field of view is
7.0deg, and can be customized to fit a given eyepiece or finder, with
some other parameters such as the faintest magnitude at which to show
DSO's and stars also adjustable by the user.
One my first guesses was M25 -- and seeing that more detailed chart
with the cluster's "W" pattern and that nearby grouping of four stars
left me without a doubt that this was what I had observed. Duly I
noted that my visual impression of those four stars as "south" of the
cluster translated to an actual direction of north on the chart -- as
would be expected with a Newtonian reflector.
That afternoon I looked at some images of M25 available on the Web.
Curiously, while some of the color photographs were very striking, I
much liked a black and white image that looked like a somewhat richer
version of what I had seen through the sweeper. Also, I have
downloaded some articles about this open cluster, and am fascinated to
reflect on its distance of somewhere around 2000 light years, or
possibly a bit more.
The full name for my sweeper, by the way, is the "Margaret Flamsteed
20cm Optical Sky Survey Telescope." Around 1700, Margaret Flamsteed
served as an asssistant astronomer to her husband John Flamsteed, the
first Astronomer Royal, and also wrote on the mathematical topic of
Newton's fluxions, also known as the differential calculus. A fine
point is that the "20cm" of this name refers to aperture rather than
wavelength; at a frequency of 1.5GHz, the mirror could claim 1/18-wave
accuracy <grin >. If the name serves as a playful reminder that
astronomy uses many wavelengths, each placing the others in better
perspective, then it will have served its purpose.
At to the practical domestic economy of my apartment observatory, I
might conclude by noting that a 20cm f/6 Newtonian sweeper would
traditionally be known by its focal length as a "four-feet telescope."
In addition to affording a rich-field view, this rather compact focal
length conveniently reduces the amount of clearance space required
when the telescope is in use and moving about in a room already
populated with other items and furnishings. While the balance between
aperture and portability is often discussed, maneuverability in close
quarters is not to be disdained.
Most appreciatively,
Margo Schulter
mschulter@calweb.com
|
|
| |
Date: 18 Jul 2007 18:16:07
From: Marty
Subject: Re: Surfing to M25: An inside story
|
Margo Schulter wrote
>What a pleasure it is to report that this
> last Sunday I surfed with my new
> Sky-Watcher 20cm f/6 Dobsonian to a
> beautiful open cluster, which proved to
> be M25/IC4725, my first identified DSO
> with this telescope.
And what a pleasure it is to read your report! Always nice to read of
someone simply and unpretentiously enjoying the night sky, along with an
appreciation for the history of those that went before! Lucky for us
all that the turn of the seasons and the architecture of your building
put the visual playground of Sagittarius outside your apartment window.
Your infectious enthusiasm almost leaves me envious of your far less
than perfect conditions!
Marty
|
| | |
Date: 22 Jul 2007 06:01:46
From: Margo Schulter
Subject: Re: Surfing to M25: An inside story
|
Marty <movac5@webtv.net > wrote:
> Margo Schulter wrote
>>What a pleasure it is to report that this
>> last Sunday I surfed with my new
>> Sky-Watcher 20cm f/6 Dobsonian to a
>> beautiful open cluster, which proved to
>> be M25/IC4725, my first identified DSO
>> with this telescope.
>
> And what a pleasure it is to read your report! Always nice to read of
> someone simply and unpretentiously enjoying the night sky, along with an
> appreciation for the history of those that went before! Lucky for us
> all that the turn of the seasons and the architecture of your building
> put the visual playground of Sagittarius outside your apartment window.
> Your infectious enthusiasm almost leaves me envious of your far less
> than perfect conditions!
> Marty
>
Thank you for your encouragement, and your description in your Comet
LINEAR report of Sagittarius as a "Disneyland" is very apt.
Last Wednesday evening I made my first "official" and purposeful
starhop -- or maybe sweep, if the two are distinct. Early in the
session, I ran into what looked like a _big_ open cluster, possibly
M24, which Messier considered a kind of open cluster but was later
recognized to be actually a region of the galaxy revealed through
a break in the dust veiling the central regions, the Small
Sagittarius Star Cloud.
Anyway, the size was impressive -- over a degree. I took some time
to make a sketch of the geometry, and then moved on to other objects,
unsure where I was.
Then, sometime later, I found a familiar friend -- M25! Now I realized
that a right ascension sweep of about 4 or 5 degrees West would get me
to M24. In my 1.25" 25mm Super Plossl (48X) that would be four fields
or so -- so I tried to take it smoothly and estimate the fields.
Lo and behold, there was -- the object I had visited and sketched
earlier, and now was more confident was indeed M24. A comparison of
my sketched geometry with a chart of M24 from the fchart program for
Linux the next day quickly confirmed this.
I apologize for my delay in responding, but deeply appreciate the
encouragement -- and also the enthusiasm in that report from Mount
Lassen what we both enjoyed. It's fascinating how worthwhile and
delightful observing can happen from so many different sites and
situations.
With many thanks,
Margo Schulter
mschulter@calweb.com
|
| | | |
Date: 22 Jul 2007 09:36:57
From: Marty
Subject: Re: Surfing to M25: An inside story
|
OH... and SAVE YOUR NOTES AND SKETCHES, no matter how crude or seemingly
unimportant. Even things like spotting a nice planetary grouping while
driving home from getting groceries. I glue mine into a very informal
"observing log." Yes, there are books and such that will have more
authoritative descriptions and info, but in years to come, it's fun to
look back on your own observations! I only started doing that with any
regularity back in 1990, but I wish I'd started much earlier. I only
have a few random sketches and notes I made over the years before that,
and I wish now I'd written so much more down. Who came by, what animals
happened along, what "went wrong," etc. and, of course, what you saw in
the sky.
Marty
|
| | | |
Date: 22 Jul 2007 09:22:27
From: Marty
Subject: Re: Surfing to M25: An inside story
|
Hi Margo,
While the "teapot" of Sagittarius is drifting past your window,
there are a few other things you might try for. Light pollution can be
very frustrating and it can be hard to tell how nebulous objects will
show... they tend to suffer worse than star clusters, which are groups
of point sources of light. You've already found the cluster with M8,
the Lagoon Nebula... M8 floats like a puff of steam just above the spout
of the teapot, and is a good starting point to look for other things.
On a good night, you may pick up some of the nebulosity. Just above M8
is M20, the famous Trifid Nebula, but despite it's fame, you probably
won't see much through your light pollution... really kinda dim, but
nice if you can get to a darker site. Look for M22, a bright globular
star cluster a little closer to the top of the teapot than your M25...
It's just "behind the top of the lid." You also have a decent chance of
picking up M16 and 17 a bit above M25. You've already mentioned M7...
You might want to try for M11, the "Wild Duck Cluster" up in Scutum,
just off the tail of Aquila... I'm not sure how high you can get
through that window.
This is one of the best general interest groups for amateur
astronomers on the net. No moderation though, so any sicko jerk can
post here, and they often do, so if somebody gets nasty with you, ignore
them. Dark sky sites have gnats and mosquitos, USENET has trolls.
Shortly before Starlord had his stroke, some cretin was hounding him
mercilessly through an anonymous remailer. Beats me what they get out
of it. Anyway, enjoy the group and the sky. Amateur astronomy can be
as much of a lifestyle as a hobby. :)
Marty
|
| | | | |
Date: 24 Jul 2007 09:23:29
From: Margo Schulter
Subject: Re: Surfing to M25: An inside story
|
> OH... and SAVE YOUR NOTES AND SKETCHES, no matter how crude or
> seemingly unimportant. Even things like spotting a nice planetary
> grouping while driving home from getting groceries. I glue mine
> into a very informal "observing log." Yes, there are books and such
> that will have more authoritative descriptions and info, but in
> years to come, it's fun to look back on your own observations! I
> only started doing that with any regularity back in 1990, but I wish
> I'd started much earlier. I only have a few random sketches and
> notes I made over the years before that, and I wish now I'd written
> so much more down. Who came by, what animals happened along, what
> "went wrong," etc. and, of course, what you saw in the sky.
> Marty
Hi, Marty, and already I've seen that this is wise advice. Generally I
use a spiral notebook, and it _is_ fun to look back.
Last Wednesday-Thursday, for example, I spent lots of times sketching
curious asterisms which _might_ be open clusters, although later I
found that there are lots of picturesque asterisms around Sagittarius
that occur between rather than within recognized clusters. For
example, I wrote down something more or less like this (20cm Dob, f/6,
25mm Super Plossl at 48X, a tad more than 1deg FOV):
.
.
. .
.
. .
. . .
. .
In my notes I dub this asterism a "Drinking Cup," with a date and
time of "~0001 July 19." ASCII asterisks might be more readable than
dots, but I want to suggest the vagueness and impreciseness of my
attempt to sketch the vivid shape that I saw. The next day, or later
Thursday, that is, I guessed that I may have seen this in or near
M22, although if so, I wonder if the globular cluster wouldn't have
made some impression even with the light pollution.
The best solution might be to look for this pattern again and locate
it in relation to other known objects, hopefully including some
Messiers or other DSO's I'll be finding in that session!
Anyway, I'll happily follow your advice about saving those notes and
sketches.
Most appreciatively,
Margo Schulter
mschulter@calweb.com
Lat. 38.566 Long. -121.430
|
| | | | |
Date: 24 Jul 2007 09:21:35
From: Margo Schulter
Subject: Re: Surfing to M25: An inside story
|
> Hi Margo, While the "teapot" of Sagittarius is drifting past your
> window, there are a few other things you might try for. Light
> pollution can be very frustrating and it can be hard to tell how
> nebulous objects will show... they tend to suffer worse than star
> clusters, which are groups of point sources of light.
Hi, Marty, and thank you for this encouragement and the nice summary
that follows. It's just what I need to energize me a bit. After the
session last Wednesday-Thursday when I hopped from M25 to M24, I took
a break because while three hours of enthusiastic observing was lots
of fun, it might not have been so wise for my back without a chair.
Now I've ordered one, and it's a fine time to plan for more
observing.
Possibly I can manage in the meantime to use a chair on hand in a
reasonably ergonomic manner -- and, if so, I might try before the
StarDust arrives. Either way, you've put together a fine itinerary for
me. What I may do is prepare a log with the objects you've mentioned,
so that I can easily follow the sequence with my red LED flashlight
and fill in my observations.
> You've already found the cluster with M8, the Lagoon Nebula... M8
> floats like a puff of steam just above the spout of the teapot, and
> is a good starting point to look for other things. On a good night,
> you may pick up some of the nebulosity.
Yes, this could be a great object for a first light for my Lumicon UHC
filter and a couple of 2" ultrawide eyepieces at 30mm and 20mm.
Actually I got the filter used, but at least it would be a first light
for it from my apartment observatory. Tony Flanders found a Lumicon
UHC helpful for M8 with a 178mm Dob in an urban setting
<http://mysite.verizon.net/vze55p46/id20.html >
and people have reported that either a UHC or OIII type of filter can
bring out different aspects of an object like M8 or M20.
> Just above M8 is M20, the famous Trifid Nebula, but despite it's
> fame, you probably won't see much through your light
> pollution... really kinda dim, but nice if you can get to a darker
> site.
I'd agree that this isn't such a likely urban prospect, even with the
Lumicon UHC, at least as far as seeing the nebulosity. What I might do
is try for Webb's Cross and the general area around M20 and M21,
experimenting with the filter and averted vision. However, under urban
conditions, even an observer as experienced as Tony wasn't sure if he
actually saw a small area of nebulosity or imagined that he saw it.
> Look for M22, a bright globular star cluster a little closer to the
> top of the teapot than your M25... It's just "behind the top of the
> lid." You also have a decent chance of picking up M16 and 17 a bit
> above M25.
M22 is one of my top priorities, and maybe an opportunity to
experiment with higher magnification when I've found it. So far I've
been using a usual 25mm 1.25" Super Plossl at 48X, but this globular
might stand some magnification, which could also make the background
seem darker.
As to M16 and M17, I'll definitely try for those also.
> You've already mentioned M7... You might want to try
> for M11, the "Wild Duck Cluster" up in Scutum, just off the tail of
> Aquila... I'm not sure how high you can get through that window.
That's a good question about the window, and trying for M11 and also
M26 might help to answer it.
> This is one of the best general interest groups for amateur
> astronomers on the net. No moderation though, so any sicko jerk can
> post here, and they often do, so if somebody gets nasty with you,
> ignore them. Dark sky sites have gnats and mosquitos, USENET has
> trolls. Shortly before Starlord had his stroke, some cretin was
> hounding him mercilessly through an anonymous remailer. Beats me
> what they get out of it. Anyway, enjoy the group and the sky.
> Amateur astronomy can be as much of a lifestyle as a hobby. :)
Thanks for this wise advice: as I might put it, the way to raise the
signal-to-noise ratio is to contribute more signal. I'll lend some
more encouragement to our friend Starlord also. As I'm learning,
your "as much of a lifestyle as a hobby" is a neat way to put it.
Most appreciatively,
Margo Schulter
mschulter@calweb.com
Lat. 38.566 Long. -121.430
|
|
