RASC Calgary Centre - Setting Circles
by: Fr. Lucian J Kemble, OFM - 1990 - Fr. Lucian J. Kemble, OFM - Biographical details
Page last updated: July 21, 2008
Foreword: by John Mirtle
Back in 1990, I published a small quarterly rag for the Observer's Group, called the Stargazer. One of the goals was
to collect a number of observing related articles for a members handbook, with the Stargazer being a mechanism to
get these articles to the membership in hopes on getting some feedback. I asked Fr. Lucian Kemble to write something
on one of his favourite topics - setting circles. Lucian's article follows. At the time he wrote this, digital
setting circles were just hitting the market, and an old debate had come back to light. Was observing with setting
circles really observing, or was it cheating? This was a hot debate, especially with those going for their Messier
certificate or the Herschel 400 lists. Eventually things settled down, and the Messier list observations obtained
with the use of setting circles were deemed 'OK'. Today, the hot topic of debate has moved from setting circles to
GO-TO telescopes. It is interesting to note that Lucian's comments are just as valid today, as they were
over a decade ago.
At star parties or in observing sessions with other amateurs, and in my reading, I often
have entered into a sometimes joking debate over setting circles. This is usually an either/or situation, with
strong arguments of defence or offence. In spite of my preference for the use of setting circles, having used them
for so many years, I am convinced that
ANY method that works is OK. After all, setting circles, sky - hopping, new
electronic gadgetry or any other method are only tools, a means to an end. And we ought never to lose sight of that
end, namely,
OBSERVING. The less time spent in finding an object to observe, the better.
I think we should bear in mind, and it almost goes without saying, that before anything else, the amateur must know
his way around the sky: co-ordinate systems, constellations, seasonal variations, NS/EW orientations in the sky, etc.
This is a prerequisite for any staunch sky - hopper, as well as for those who use setting circles or any other method.
One must know the "workings" and not simply rely on methods that work. An analogy: one can use a calculator to get a
mathematical answer - it "works"; but if the user is ignorant of the basic "how" of even simple arithmetic calculation,
then, deprived of a calculator, he or she cannot even add a column of 3-digit numbers (as can be verified, alas, at
any bank teller's window). For example, if one hasn't got setting circles or other device, one should be able to find
one's way around the sky. There is absolutely no substitute, even electronic gadgets, for this basic knowledge and
required skills. However, using the same analogy as above, once I am knowledgeable in math, I will not hesitate to use
a calculator to get on with a problem and not insist on being a "purist", doing a 5-digit square root long - hand.
Similarly, once I know the basic "how" of the sky, I will not hesitate to use setting circles, with no apologies. But,
deprived of circles, I can surely find my way around the sky.
Having spent years with study, naked-eye and binocular observation, I really got to know the sky and all its workings.
When I got my first scope in 1972, a Celestron 5 with its tiny finder, I used it for two whole productive years "sky
hopping". The best groundwork I've ever done, comparable to my high school math in pre-calculator days. Though I had
become very knowledgeable about wedge, clock drive, setting circles, polar alignment, etc., I was rather intimidated
by their use and simply used the C5 as a sort of Dobson, alt-az, plunking it down somewhere and avidly tracking down
and observing scores of galaxies, clusters, etc.
Then, after this most valuable apprenticeship, which I strongly recommend and consider indispensable for anyone, I
took the plunge and mounted wedge and clock driven C5 on a sturdy tripod, achieved a fairly good polar alignment,
plugged in the scope and I was off flying! Very quickly, using a system devised by Peter Berbusch of Regina Univ. and
me, I began using regularly our method of polar alignment - using setting circles! and in daytime!
When I graduated to a C8 in 1976, and to a C11 on a Byers mount in 1981, I really got into some extensive observing
and drawing, and hardly, if ever, used my finder. How I remember nights at Cochrane lugging out the C8 and tripod,
setting up, polar aligning and working within 15 minutes, relying on setting circles - and almost always finding the
desired object in the eyepiece field. But, I knew all the time what was going on, and learned a lot about the "how"
of the sky. Setting circles have been, for me, a trusted and most powerful tool for OBSERVING. This latter remains
ever the only end or goal. If other observers find and use other tried and trusted tools, then so much the better.
I present the following, then, not as an either/or, but simply as a help and suggestion for those whose telescopes
are already fully and adequately equipped with good setting circles, so that they might not be intimidated, but will
rather welcome them as a valid and wonderful means to better observing. Evidently I am not referring to users of
alt-az mounts, nor to those whose scopes are equipped with fancy but useless circles.
I do not wonder that people are turned off by setting circles. In spite of high - pressure advertising of gadgets that
look impressive, most small telescopes, especially refractors, have small, useless circles whose divisions are the
width of the useless pointer, which itself is mounted so far above the circles that parallactic errors of several
degrees result. Also, some circles are of the old, English type using complicated hour - line markings instead of R.A.
divisions.
But let us talk of most Schmidt - Cassegrain reflectors, of the Celestron or Meade variety, or some Newtonians with
reliable mounts and big circles, having fine divisions, accurate pointers, etc. Some, such as my old C8, even have
vernier scales in R.A. The Byers equatorial mount, which I use, has excellent, practical, very large, finely graduated
circles. I adapted a large vernier scale in Dec. which permits positional accuracy reading of about 15 arc seconds.
The R.A. circle, divided into wide, 5 min. divisions and equipped with a fine pointer; flush with the edge of the
circle, permits positional accuracy readings of about 30 seconds.
PRE-REQUISITES:
- Tube and mount should be accurately aligned to fork or cradle. This is necessary in any case for any good
scope. One or both Dec. circles should be accurately adjusted and fixed in position.
- Telescope should be level and accurately polar-aligned
These procedures are not that complicated and should be routine in any case, whether one uses setting circles or not.
It's just a matter of good practice. These preliminaries will minimize a lot of frustrating, wasted valuable observing
time and, of course, are absolutely required for any kind of decent astrophotography.
DISADVANTAGES: NONE! - if scope and mount are equipped with good circles and are properly set up. To the argument
that they do not permit familiarity with the sky, I reply that that is the fault of the ill-prepared observer
and not of the circles themselves.
ADVANTAGES: Many, many! Here again, assuming good circles and a good set-up.
- SIMPLE OFF-SET METHOD: This was written about in Sky and Telescope, Sept. 1990, p.246. It enables going from a
known star, calculating in advance the correct off-set in R.A. and Dec., and then moving the scope the appropriate
amount. It can be quite an effective use of setting circles, though I rarely use it.
- FINDING BY CO-ORDINATES: A low power eyepiece will usually contain a desired object in the field, even if the
Epoch 1950, 1975 or 2000 catalogue co-ordinates are used. I usually polar align on stars listed with the current
co-ordinates in the R.A.S.C. Handbook or the annual "Astronomical Almanac". With polar alignment achieved (using only
setting circles, remember), either permanent or temporary, I simply point the scope to a bright star, set the R.A.
circle for that position, and I'm away.
- PRECISE POLAR ALIGNMENT: I have my own fool-proof method, day or night. The drift method is also great and
is used by many, especially for astrophotography, but its use is restricted to late twilight or night time. For
example, arriving at Mt. Kobau about 4pm, I had my scope assembled and mounted and, within about 10 minutes I had a
sufficiently adequate polar alignment to find bright stars, Jupiter, Mars and Venus. Only circles permitted me to find
Comet Levy in early twilight. I have made daytime observing a major part of my observing programs, possible only with
setting circles and an accurate polar alignment. Just recently I picked up Mercury only 11 degrees E of the Sun. How
many star hoppers found it at Mount Kobau? On one occasion years ago with the C5 on a windy afternoon, only circles
enabled me to see an occultation of a star by Mars.
- FAINT OBJECT LOCATION: my tiny 10 x 30 finder on the C11 is about as useless as a good pair of binocs for
finding even moderately faint stuff. True, I too have sometimes been tempted by alluring ads, to procure a giant
finder, but why bother when I have circles, and good ones. Thanks to them I have found almost all of my 2800+ drawn
objects, even 14 and 15 mag. galaxies, on a first-shot basis. Rarely, before Uranometria charts, have I had to go
searching for an object. The charts it is true, have been very useful for star-hopping within the low power 24'
field eyepiece I use to locate the very faint stuff, but the object is usually already there somewhere in the field.
- MEASUREMENT: I know the diameter in minutes of arc for each of my eyepieces. It sometimes happens that a
description of a very faint object in the RNGC, Deep Sky magazine or the Observer's Guide will read, e.g. "very faint
galaxy 12" N" (of a given galaxy which one has already located). I simply move the scope precisely 12' with the slow
motion Dec. knob, using my vernier, and there, with a little acute observing, I find the object.
- FAMILIARITY WITH THE SKY: Contrary to current thinking, circles do not hinder, they contribute powerfully to
an understanding of celestial mechanics and familiarity with all aspects of a given constellation, as well as with
constellation motion over a given night, month or year. Intelligent use makes me very conscious of where I am pointing
at any time. It is almost as though I can actually see R.A. lines radiating from the Pole, their angles relative to
the horizon, where equator and ecliptic are, angular distances, and so on. Many times I have used the scope and mount
to demonstrate the celestial sphere, the seasonal position of Sun and Moon, equinoctial and solsticial points, etc.
You want to know what I find ironic? Some observers, purists who scorn such things as setting circles, are being
sucked in by ads for expensive gadgets ($829 US!) such as the one reviewed recently by Alan Dyer in Astronomy magazine,
Nov. 1990, p.63. Imagine! no polar alignment! No levelling! Just push a button or two and point (never mind that
inaccuracy in some cases can amount to as much as 2 or 3 degrees). How much sky knowledge is achieved, I wonder. And
how good are they (or useless) for daytime observing?
- FREEDOM: I figure that, using my setting circles, I can spend at least 5-10 minutes more per object in actual
observing and drawing - time that would otherwise be spent in searching. One little side benefit has been, for example,
locating some interesting stellar planetaries of 12 - 14 mag in a crowded field where I know they lurk. Identifying them
from field stars is then easily achieved with appropriate filter or diffraction grating. This is sometimes a painstaking
or hopeless task simply by star hopping or sweeping.
On another note, using the analogy above-mentioned, just to keep my wits sharpened and my math skills renewed,
I will on occasion work out some complicated math problem, such as a 5-digit square root, or some quadratic equation by
hand. I had a good foundation in math in high school 50 years ago. And it's great fun. Similarly, I will sometimes
forego setting circles and do some sky-hopping. And that, too, is great fun. But then it is back to calculator and
setting circles.
Setting circles, then, are not part of an excluding, either/or debate. But good accurate ones, found on so
many SCT's have distinct advantages. Each observer will find and use his or her own locating tool, system or method.
But I do highly recommend, from long experience, the use of good, R.A. and Dec. circles. In the past I have written an
article for the Calgary Centre's STARSEEKER on "Polar Alignment", Jan. 1987; on "Daytime and Twilight Observation" in
the R.A.S.C. Journal Newsletter, Oct. 1986. Also, at the R.A.S.C. General Assembly in Edmonton, 1985, I presented a
paper on "Daytime Observations of Venus at Inferior Conjunction" (only 8 degrees above the Sun). If anyone is interested
in putting his or her setting circles to good use, please let me know and I can send you a copy, or further detailed
instructions.
Fr. Lucian J. Kemble, OFM - Biographical details
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