Tag Archives: Messier Objects

CNYO Feature: Going Big

Thinking of going big? Of course you are, and right you should be. Nothing makes up for aperture under dark skies if it’s deep sky objects you’re after. Some may make an argument that refractors show slightly sharper planetary images, but simple physics says the more light you gather (aka, the bigger the mirror), the brighter the image will be. So, how bright and how big is big enough? Let’s take a look at some practical considerations.

Questions to consider before making a final decision on scope size include: What do I most enjoy viewing? Do I observe more at, or away from, my home? How much weight can I comfortably lift? What eyepieces do I currently use? Can I locate deep sky objects by reading a map, or do I depend on computers to point me where I need to go? And finally, do I mind having lines of people waiting to look through my scope, or would I rather observe alone?

The Basics

If you’re a deep sky aficionado, then a big scope will reveal more detail on the faint fuzzies, period. A scope’s light gathering capability is determined by the size of its primary mirror in the case of reflecting telescopes, or its primary lens in the case of refracting telescopes. And you don’t have to double in size to double in light gathering capability. Remember, the area of a circle is π (pi) multiplied by the square of its radius (πr2). With that in mind, here’s a quick reference table of increased light gathering with a number of mirror sizes, each compared to a 4″ telescope:

Mirror Size
Increase in light gathering over a 4″ mirror
Limiting Magnitude*

*Limiting Magnitude – This estimate is based on good seeing, magnitude 6 skies, a 6mm dilated pupil, and 40x per inch of aperture. 40x per inch of aperture requires a well-figured primary mirror. For more information on limiting magnitude, see www.cruxis.com/scope/limitingmagnitude.htm

So, What Does That Mean At The Eyepiece?

The first step is to understand the above table, yet that alone doesn’t tell the whole story. Low contrast objects require not only dark skies and decent transparency, but also aperture. Think about M51, the Whirlpool Galaxy. Under dark skies and pristine conditions, an 8″ telescope will reveal a hint of the spiral arms with averted vision and high scrutiny. Through a 12″ under the same conditions, the arms are easy with direct vision. Through a 16″, knots in the arms can be made out. Through a 20″, the knots are much brighter and M51 begins to look like a black and white photo. Through a 24″, it’s possible to begin to make out faint coloring in the spiral arms, and the core of the galaxy is so bright, one wonders if it’s going to ruin their night vision!

Nebulae, globular clusters and any of the 109 Messier objects are perfect targets for large telescopes. I have found that a 12″ delivers color on the brightest of nebulae, and the color gets easier to see and more vibrant as the telescope size goes up. On globular clusters, an 8″ will resolve M13 and M3, while a 12″ will resolve most of the rest of the Messiers. With a 16″, all of the Messier globs are easily resolved, as well as many of the NGC’s. With a 20+”, you start loosing count of resolved globs!


Who can resist a peak at Saturn or Jupiter? Well, once again, aperture rules.

As a rule, as the primary mirror increases in size, the ability to discern detail increases. To fully recognize the potential of the large scope, a finely figured primary mirror is necessary. A great amount of discussion has occurred regarding smaller refractors and their reputation to outperform larger Newtonians. This mustn’t always be the case, however, and it would be a serious error to believe the superior view through a refractor is constant, impervious to variables in design, optics and weather. Those in the pro-refractor camp often claim their allegiance is due to the inherent design inferiority of a Newtonian. Nothing could be further from the truth.

A large mirror, such as is found in some Newtonians, must not only be properly supported from underneath, but also on its edge as it is being tilted within the telescope. Many a Newtonian builder neglects to provide the appropriate support. A consequence of an improperly designed mirror cell or edge support system will be any of several detail and contrast robbing aberrations, most notably different orders of spherical aberration and astigmatism.

An important aspect of large aperture Dobsonians (Dobs) is that the larger primary mirror requires far more time to cool down than a smaller refractor. Most of the older large Newtonians out there compound this because it was once thought that the mirror had to be relatively thick, otherwise aberrations would be introduced by the mirror cell (we now have finite computer analysis programs that will plot a perfect mirror cell of any size – most specifically David Lewis’ PLOP program). Thanks to the research of Bryan Greer (research article published in the May and June issue of Sky and Telescope) and others, we now have a better understanding of the ways larger optics shed heat. One of the more straightforward discoveries of this research was that the reason larger mirrors take so long to cool is mostly due to their thickness and not overall diameter. So if we choose the thinner mirror for faster cool down, we again shift our attention to the mirror cell. A thin mirror that is not supported properly from underneath will cause a slight deformation in the surface figure, which in turn causes light rays reflecting off the mirror’s surface to not come into focus at a single point. A star test would then readily reveal different orders of spherical aberration, degrading the view at the eyepiece. Now consider the mirror’s edge support. A sling is historically used to support the edge of large primary mirrors, often made out of Kevlar or metal banding. Through the work of Nils Olif Carlin (www.cruxis.com), we now understand that as much care should be given to choosing the proper edge support as goes into the design of the rest of the mirror cell. If this part of the mirror cell is neglected, you once again will experience different optical aberrations at the eyepiece as the telescope is moved from horizon to zenith.

Another point to consider is that bad atmospheric seeing can cause one to believe that a large telescope is performing poorly on the planets. It is true that a larger mirror will seemingly amplify poor seeing conditions, but patience at the eyepiece (waiting for the seeing to settle momentarily and for the planetary image to “pop”) will once again prove the larger mirror to outperform the smaller one.

So, let us review: A big telescope with a thin mirror, excellent mirror cell and edge support, built with an active cooling system (fans to provide air motion within the mirror box) and a night of good seeing – Viola! It’s a recipe for a night of planetary viewing that will leave you and other observers arguing about the spokes in Saturn’s rings!


I often hear of an amateur astronomer selling his scope because it’s just too much of a hassle to get out and observe with. The size and weight limit varies from astronomer to astronomer, so observers must carefully consider for themselves what may be too heavy or too much hassle to result in pleasurable observing.

An 8″ is usually considered the “biggest of the small”, while a 12″ is often referred to as the “smallest of the big.” I agree with this sentiment. An 8″ – 12″ tube-style Dobsonian is a one-person job and both easily fit in a mid-sized sedan, but the 12″ may push the weight limits of some. The 8″ scopes on the market today are around 65 lbs fully assembled, while the 12″ telescopes weigh in around 100 lbs. If you plan to use an equatorial mount, make sure to factor in an additional 30 lbs or so above the overall weight (and prepare to spend an extra 20 minutes or so setting up). Forget about 14″ – 20″ tube-style telescopes – portability is key and unless you have a small observatory, an equatorial mount is probably not feasible due to the sheer size and weight it encompasses.

Truss-style telescope weights vary significantly from vendor to vendor. One telescope I can be sure of knowing the weights of is one that I build, a New Moon Telescope. A fully assembled 16″ NMT is just under 100 lbs, the heaviest component you would lift weighing in at 60 lbs, and the collapsed scope readily fits in the same mid-sized sedan that would cart a smaller tube-style scope around. A 20″ is 134 lbs, the heaviest component weighing slightly over 80 lbs, and this is the size at which to start relying on detachable wheelbarrow handles to maneuver it. A 24″ would weigh roughly 165 lbs and a 27″ almost 200 lbs. When going this big, remember to reflect on what type of SUV, truck, or trailer you might like to own, because car-hauling is doubtful. Any of the scopes through a 20″ can be stored in a bedroom or living area (and the 8″ and 12″ even in a closet), fully assembled, should you choose to showcase them as pieces of furniture. From the 20″ and up, consider utilizing a storage shed, garage, or an observatory (should you be so fortunate!). Keep in mind, telescopes 20″ and larger necessitate a large car in which to travel, or ideally a truck, trailer or SUV, so if you’re an apartment dweller with no access to a storage unit, you’ll want to stick on the small side. Likewise, if you have your own observatory in your backyard, the sky is the limit on the size of scope you could choose, as portability will not be a factor.

Eyepiece Preference

One factor that may be overlooked when considering the purchase of a new telescope is the choice of eyepieces. The longer the overall focal length of the scope, the smaller the field of view (and so the higher the magnification), so the limited field of view of Plossl eyepieces quickly become frustrating when you start using telescopes in the 20″ range. Another factor about your eyepiece collection is the capability of the eyepiece for correcting coma. Coma is an aberration you get with any Newtonian, in which the stars in the eyepiece start looking like tadpoles as they near the edge of the field of view. Everyone seems to have a different tolerance level of coma, but there are ways to correct for it. The easiest – buy all high-end eyepieces. TeleVue, Pentax, Explore Scientific, and a few others are building eyepieces that contain coma-correcting elements (and of course FAR wider fields of view than the typical Plossl) and these usually perform well down to a focal ratio of F4.5. Faster than F4.5, you may need to invest in a specific coma-correcting eyepiece such as TeleVue’s Paracorr (I cannot recommend these enough). All of this being said, you could observe happily for the rest of your life with three high end eyepieces and a barlow lens with as large a telescope as you wish to endeavor (my opinion only of course!).

Further Considerations

Familiarity with the skies will also likely determine the size of the scope to purchase (or build, of course). The obvious determining factor here is cost. If you are brand new to astronomy and can’t tell the difference between Cygnus and Sagittarius, you should probably wait to invest in a $15,000.00 set-up, even if you can afford it now. A modest familiarity of the sky is needed when using any telescope, and wisdom has shown that beginners typically have an easier time with a simple pair of binoculars or a small telescope. In fact, many of the 8″ tube-style telescopes on the market right now are under $400, and perfect for a beginner. Purchasing a telescope like this will give you the time under the stars you need to learn the constellations and familiarize yourself with pointing, moving and using a telescope. If you are a more advanced amateur, however, bigger scopes and better optics start to make more sense. You have probably amassed a few decent eyepieces and know your way around the sky well enough to invest in a larger scope that will open the skies to you exponentially. Even if you aren’t a star hopping pro yet, there are digital encoders available and GOTO capabilities that can be added to even the largest of telescopes. Think of it this way: with a good NGC and IC map (or encoders), you could go to a dark site every night for the next 20 years and upon each visit discover a new deep sky object! And with some of the more obscure objects, you may be one of only a handful of people that have EVER seen said object through a telescope! And remember – the bigger the mirror, the brighter and more picturesque the object is going to look. And of course there’s always that chance of discovering a comet…

Finally, big scopes draw crowds, and crowds are the future of amateur astronomy. If you can point at a few nebulae, open clusters, or galaxies and give a 60 second presentation on what you are looking at, you will quite possibly change the lives and perspectives of countless people. So that’s my final “big scope” pitch: Big scopes change lives!

2013june25_ryangoodson_bioRyan Goodson is the owner of New Moon Telescopes (www.newmoontelescopes.com), manufacturer of custom Dobsonian telescopes. He is a member of several CNY astronomy clubs, hosts observing sessions from his dark skies in West Monroe, NY, and lectures regionally on telescope building. He can be reached at ryan@newmoontelescopes.com.

CNYO Observing Log: Camp Comstock, Ithaca, 1 June 2013


One of the great joys of public observing sessions is introducing non-observers to the immensity of our local sliver of the universe. Hubble imagery and the amazing ground-based astrophotography of the last 25-or-so years is all well and good, but to explain to a new observer that the photons from the Whirlpool Galaxy (M51) currently hitting their retina have been on a 23 million year voyage, or to put all of the Andromeda Galaxy (M31) into the field of view and explain that the photons on one side of the eyepiece have been traveling 150,000 years longer than the photons on the “other” side of the eyepiece, or to aim a Coronado PST at the Sun and point out that the sunspots on the surface are 3 or more Earths across – these are the images that really put the universe, and our place in it, into perspective.

One of the great joys of lecturing on introductory astronomy is being able to describe all of these visuals in greater detail, showing how observation and the rest of the Scientific Method have produced great order in our Nighttime Sky (for, at least, the parts of the sky we can see in the backyard on a clear, dark night). As is true for many of the other physical sciences, a book chapter or wikipedia page alone can be far less informative, and is definitely far less engaging, than a chance to have a conversation with someone who knows the topic well enough to relate complicated concepts by drawing from many additional resources.

And, at a time when we continually fret the state of STEM education in the US, there is nothing better for an academically-inclined scientist (me) than to have someone many years their (my) junior process the information on a slide and ask a question that (1) clearly shows a grasp of the physics involved and (2) they (I) don’t have a good answer to. Lecturing keeps the lecturer just as sharp!

It is with those points in mind that CNYO hosted a Girl Scout lecture on Saturday, June 1 at Camp Comstock in Ithaca, NY as part of their requirements for earning their Night Sky badge. Unfortunately, the mostly cloudy and otherwise unpredictable night before made the Nighttime Sky observing component impossible, compacting the badge requirement section into a combined lecture/solar observing session that went well over allotted time with no (voiced) complaints.

Instead of highlighting lecture points, my goal here is to provide a few pointers for perspective astro-lecturers of kids and young adults (although I suspect the same applies for all generations).

1. Plenty Of Lead Time For Setup

In my case, my leisurely 1 hour drive turned into a compressed 40 minute drive as I waited for a police officer to take my eyewitness statements after a fender-bender on Route 13. Lesson #1 – Don’t text while driving!

2. Short Sections

Based on the Night Sky badge requirements, I had a very good template by which to design seven short lectures that would fit nicely into a 60 minute presentation (that, with questions, then went on for two hours). A full hour on a single topic to a general audience can be way too much for even a focused audience. Make this an audience of young adults and add an un-air conditioned, 85 oF room to the mix just after lunch, and you’ve got a recipe for a very… red-shifted lecture. A very good approach for you and the audience is to pick several topics and try to make a complete mini-lecture out of each. This makes your preparation time more productive (because you can divide-and-conquer as well) and it allows you to give the audience a minute between mini-lectures to digest and freshen up for the next one. In the Night Sky badge case, my seven sections were:

A. The Local Neighborhood

– A “powers of 10” walkabout from Earth out to the Sloan Digital Sky Survey

B. Circumpolar Constellations

– Explaining how the Earth moves (rotation vs. revolution) and why the North Star doesn’t appear to. This part of the lecture was complemented by the CNYO How The Night Sky Moves brochure.

C. Constellations (What & Why) And Stars

– An overview of Western constellations and the stars that define them, including a little discussion of stellar variety (color, age, size)

D. Why Learn The Constellations?

– Stress the historical meaning of the Constellations, then their use for direction (Follow The Drinkin’ Gourd) and use for marking deep sky objects (specifically, the Messiers)

E. Don’t Panic!

– How to learn the constellations, including the circumpolar-first approach, seasonal heavy-hitters, and the Zodiac

F. Solar System Formation

– Two videos I always keep handy in the back of a presentation are “Birth Of Our Solar System” (a nice animation of the formation of the whole Solar System)…

… and “How The Moon Was Born” (a video that shows the history of the Earth-Moon system and the ever-impressive Theia impact).

G. Light and Air Pollution

– Light pollution is bad, but it does help new astronomers find the bright starts in constellations. Air pollution also helps, but at a much higher cost. We should be avoiding both!

3. Ask Lots Of Questions

The biggest lesson I learned from watching professionals present to kids is to ask those kids lots of questions and let them be A driver in the presentation (but not THE driver, as you may never get the wheel back). It keeps the audience engaged, it lets others try to explain a concept in a way that the other-others may benefit from, it breaks up the monotony of the single-presenter approach, and it gives kids a chance to “show off” their scientific knowledge (which some of them love to do).

The best kinds of questions are (1) the very easy ones (how many planets) and (2) the ones that no one there (likely) has the answer to but that all can think about and take a swing at (alien life, what happens at a black hole, how big is the Sun, etc.).

If you’re lecturing to a group of 10 year olds, find a friend with a 10-year-old and see what they (don’t) know. If the kid isn’t astronomically-inclined, assume that their knowledge is similar to that of other 10 year olds in a Regents-guided state. The Girl Scout lecture was to a room of 13 to 17 year olds, and I am pleased to report that I had to move on to the “heavy questions” quite early in the lecture.

4. Preparing For The Power-Less Lecture

The Girl Scout lecture could have been done outdoors with demos or indoors with slides. Being a very visual science, astronomy lends itself better to slides unless you’ve several really good demos planned out beforehand (or brochures to help guide the discussion). There are several demos one can use to help get away from the slide-driven lecture and I hope to eventually get to the point of not needing any power. Simple demos (that will be expanded on in future articles) include:

A. Flashlights to demonstrate optical vs. true binaries (differently-colored flashlights are great for multi-star systems)

B. A tape measure and rubber balls to demonstrate the distances within the Solar System (if you’ve a 15 meter tape measure, you can place the planets at: 14.8 cm (Mercury), 27.3 cm (Venus), 38.0 cm (Earth), 57.0 cm (Mars), 197.7 cm (Jupiter), 360.8 cm (Saturn), 729.1 cm (Uranus), 1143.0 cm (Neptune), and 1500 cm (Pluto)

C. An armillary sphere (or big labeled ball) to demonstrate Earth’s axial tilt and its motion around the Sun (with a laser pointer serving as “Polaris,” a walk around an audience member serving as the Sun works perfectly well to help explain the circumpolar constellations

5. Anticipating The Unexpected Question(s)

When I think about the Sun, the first two questions that come to mind are not (1) Isn’t there a disease where you can’t be in the Sun because your skin breaks apart? and (2) I heard that some people try to live on only sunlight with no food. Isn’t that crazy (answer: yes)?

6. The Daytime Is The Right Time

As CNYO’s Larry Slosberg has determined for his observing sessions, the afternoon sky is a perfectly good substitute for the nighttime sky provided you (1) have a solar filter and (2) plan around the first quarter Moon. In the case of (1), the Sun is an excellent observing target for new observers because they very likely have never looked at it through filters and, as you can stress in your discussion, it is the reason why we’re here.


The Sun on 1 June, 2013. From SOHO/NASA.

As for (2), it is also a reason why we’re here, but the magnified Moon, either against a black or blue afternoon backdrop, never fails to impress. To help lead discussion at subsequent daytime observing sessions, the solar-centric Girl Scout session instigated the CNYO solar observing brochure available for download at: A Guide For Solar Observing.

And A Closing Thought…


Beaver Lake Nature Center Hosts “Stargazing with CNYO” – 8 August 2013 (15 August Weather-Alternate)

CNYO is delighted to schedule another lecture at Beaver Lake Nature Center this coming August for an observing session of the Summer Constellations and all of the Messier Objects visible in the Southern Summer Sky. As with our most recent Beaver Lake session, there will be NO indoor lecture session. We’ll be running the entire discussion from the central yard in front of the main building, starting the lecture near the setting of the Sun and driving the discussion of Constellations and planets as they appear to our dark-adapting eyes.

View Larger Map

We will again be using the CNYO Brochures How The Night Sky Moves and Guide For New Observers to drive discussion (and will have plenty on hand).

Stargazing with CNY Observers & Observing

Thursday, August 8th (Rain Date: Thursday, August 15th), 8:00 p.m.

Age Range: There are no age requirements, but please be aware (and make children aware) that fragile and expensive observing equipment will be present.

Description: CNY Observers (CNYO) hosts an introductory lecture to the Night Sky, focusing on planets and other objects observable during August and September. Part of the lecture will discuss some simple ways to learn the Constellations, while the rest of the lecture will provide details about meteor showers, observing satellites and the ISS, and the ever-expanding description of our own Solar System. If time and weather permits, some early evening views of Venus and Saturn will be had from the Beaver Lake parking lot. Free for members; $2 for nonmembers.


$3 per car • $15 per bus
Free for Friends of Beaver Lake


8477 East Mud Lake Road
Baldwinsville, NY 13027
T: (315) 638-2519

We hope you can join us!