Sacramento Valley Astronomical Society

Let’s build a large Lightweight Dobsonion Telescope

Part 1 of 4      by Lonnie Robinson      LonRobie@surewest.net

INTRODUCTION

 John Dobson really started something with his Dobsonian “DOB” telescope design.  He enabled the average Amateur Telescope Maker “ATM” to create a very large and very stable telescope with common workshop tools.  Since then DOB’s have evolved from a boxy heavy structure to elegant lightweight designs with truly excellent optics.  The DOB design performs best with the wide fields of lower magnifications, where nudging the scope for tracking is negligible.  This design is very stable for high power viewing, but it requires a lot of nudging and motorized tracking, like Servo Cat, would be a great help.  Building your own scope offers the opportunity to continually upgrade and customize over time.  If there is one “must read” and “must own” book on building a DOB, it’s The Dobsonian Telescope by David Kriege & Richard Berry.  This book will expertly guide you through every step of design, construction, and mirror making.  I would like to share my personal thought process and my DOB building adventure with you, hopefully adding some additional fresh ideas to help inspire your new DOB telescope project.

  WHAT SIZE IS BEST?

 Let’s begin with what size DOB fits your needs.  If you enjoy quickly setting up your scope at home for a short viewing session, then a six to ten inch size is very portable and is usually built with a one piece tube or trusses that can be left assembled for storage.  Viewing conditions under city light pollution limits the effectiveness of larger scopes anyway.  As you progress to higher and clearer viewing locations, the range of twelve to twenty four inches is doable.  Bigger is better.  My personal requirements involved the largest scope I could afford, one I could lift out of my car by myself, and one with a reasonable eyepiece height.  It’s a lot of work to build your own scope, so I suggest choosing one large enough that will cure your aperture fever for many years.  The DOB book says “my observing friends and I agree that we could live the rest of our lives observing with a 16” without the slightest regret”.  For me 16” f5 was the maximum comfortable, usable, and affordable size.   

  DRAW YOUR DESIGN

 Now that the issue of size is decided, let’s consider some basic design issues and make a rough pencil drawing of your new DOB.  I spent a lot of time on the web looking at scope design.  The ultra-light trend, in my opinion, borders being too fragile and too open to keep the optics properly aligned and protected.  The heaver box-like designs seem too large for storage, transport, and easy setup.  I really liked the style and graceful lines of the large altitude bearing ultra-lights, so I decided to design a middle weight with the best of both worlds.  Some designs use only six trusses instead of the usual eight, but trusses should probably remain at eight with a medium weight cage and the longer length required for a light-weight design.  Besides, six trusses make for a difficult mounting sequence at the base.  My friend, George, asked a question, after I had pretty much finished roughing out my scope, “Will those longer poles fit in the trunk of your car?”  I hadn’t considered that, and in a mild panic I was immediately motivated to check the fit.  Yes, they fit!  My upper cage design is only as tall as necessary, with enough area to block most stray light and protect the optics.  Big altitude bearings add style and grace, allowing one to design a very short and strong mirror box and rocker box that are easy to carry and store.  Large diameter altitude bearings have a higher surface speed, which enhances the Teflon’s buttery smoothness and speed regulation qualities.  Stiction, resistance to initial movement, is nearly zero after applying silicone car wax.  Designing the altitude and azimuth bearings nearly the same size equalizes the force required to move the scope in either direction.  Larger bearing spacing and low to the ground rocker box make the scope exceptionally stable and a lot stronger.  The bottom of the altitude bearing should not extend below the collimation bolts, preventing their use as feet.  Don’t worry too much about designing in balance since it can easily be achieved later by changing the radius of the altitude bearings.  Truss tube placement and truss connector styles are very difficult choices.  Kriege & Berry like the trusses mounted on the outside of the mirror box for added stability, but that interferes with clean lines and the design possibilities.  I’ll discuss the truss connectors in detail a bit later.  I have a book on router techniques, and in it they described how to make decorative spindles with longitudinal decorative groves.  This inspired my idea for the wooden hourglass shaped cage struts, handles, altitude bearing support, and the telescope name.  To me, hourglass implies looking back in time with a glass optic.  I carried the theme throughout the best I could.  You can do the same with so many available wood turning design ideas.  Here is my first rough drawing.  I would be pleased if you should decide to copy it.  Have fun and let yourself go with the design of your choice.

 
WHERE TO START

 First, acquire all the optical parts: Main mirror, focuser, eyepieces, secondary mirror, and last the secondary spider.  You will need them to establish focal length, fit, and balance.  However, you could use dummy weights until the parts arrive.

 Let’s talk about choosing the main mirror.  Since we are building a large DOB you probably want brighter images for deep space objects, with low power wide field views.  Image brightness is a sole function of aperture size and magnification.  After choosing the biggest mirror you and your budget can handle, the first part of the image brightness equation is locked in.  The second part, magnification, allows you to control how the available light is spread out.  Higher magnification spreads the light over a larger area resulting in a dimmer image.  Because the mirror size is now fixed, different focal lengths (F) change the magnification range and the resulting focal ratio (f).  The focal length and f ratio can now directly relate to each other regarding magnification and image brightness.  Focal ratio is usually used to describe your mirror, and lower f ratios provide shorter focal lengths, resulting in a lower usable magnification range, wider fields, and brighter images.  Eyepiece height is a real issue and if the objective is very large (18” and up), a very low f ratio may be necessary to keep the viewing ladder short.  Field of view is a basic function of magnification, but the eyepiece diameter, field stop, and field of view ultimately determine the actual true field of your telescope.

 For all purpose viewing, f5 to f6 seems the best compromise.  I decided on a 16” f5 for the best all around viewing without using coma correctors, great high power planetary views, low power wide field performance, and reasonable eyepiece height.

 Planetary high power viewing is best accomplished with a smaller mirror (6” to 10”) with a long focal length.   High f ratios of f6 to f15 and over, provide higher magnifications, long in-focus travel, narrower field of view, require a smaller secondary for less obstruction, and provide clear high contrast images.  Longer-focal-length eyepieces can be used with their increased eye relief. 

 Should you decide to make your own mirror, f5 and higher presents the best chance of making a really good mirror.  Between f4 and f5 the in-focus range is extra sensitive, and the steeply angled light cone requires highly accurate figuring.  Coma is two times worse in f4 than f5!  The higher the f ratio, the easier it is to figure.  Polish and figure your mirror first so you can measure the final focal length to set the truss length, assemble the scope, and star test on Polaris before aluminizing.  Polaris works because it moves very little, and the optical tube assembly can be propped up on the ground in a fixed position.  You can get some really great views of bright objects without the aluminum!  The total uncoated light grasp is about 4%, making an uncoated 16” about equal to an aluminized 3.2” (20% of diameter) but with a 16”s resolution.  My 16” showed amazing detail on the moon without a filter, and Saturn was tack sharp.  The DOB book divides mirror makers and telescope makers, saying it is difficult to do both.  They even indicate if you make mirrors you may never observe again.  I did both, and even though it took a lot of time, the reward has been awesome.  Looking at a celestial object with your own mirror is very satisfying, and in many cases you can make a better mirror than a professional simply by spending more time to perfect it.  However, there are many great commercial mirrors available and used by DOB telescope companies.

 The focuser is a fun choice.  I really like the 2” Feather Touch and Moonlight crayford units, with a nod to the Feather Touch.  Moonlight offers some great colors.  Feather Touch has taken the crayford design to the next level.  They use dovetail like stainless steel rails to run the upper ball bearings on, resulting in a very durable, smooth, and tight system.  They both have an excellent gear reduction knob for fine focus, and cant adjustment screws in the base for optically aligning the focuser.  They both have motorized focus available.  I highly recommend compression rings for holding eyepieces and equipment.  The ring holds securely, centers, and doesn’t mar your eyepieces.  They really help when using heavy eyepieces, bino viewers, cameras, and aligning with laser collimators.  There is a complaint that the new recessed security groves on newer eyepieces catches on the compression ring, but I haven’t experienced a problem with it.  Be sure and choose a fairly low profile focuser with at lease a 2” range of focus.  If it is too tall, it will change the secondary mirror requirements.  Focusers have come a long way in recent years relating to smoothness, accuracy, and toughness.

 Secondary mirror size is a difficult choice.  What you want overall is the smallest secondary you can get away with to catch all the available light from the m­­­­­­ain mirror, with a minimum obstruction, and adequate eyepiece illumination.  The size and focal length of the eyepieces you want to use, and their field of view, will affect the required secondary size.  Your largest, widest field, and lowest power eyepiece requires the largest illumination area, so use that eyepiece as a basis to decide the secondary size.  High power 1-3/4” eyepieces can use a slightly smaller secondary.  Eyepieces with very large fields of view, like 80 deg Naglers, require a slightly larger secondary mirror.  Check out the DOB book for details on eyepiece illumination, but it should be between ½” and ¾”.  Try to keep the secondary mirrors maximum obstruction to 19% or less on a linear basis.  Lower than 19% achieves very little visual improvement, and higher gradually degrades the image resolution and contrast.  Cassegrain obstruction can approach 34% linear, so you can see how much wiggle room there is!  My experience is that smaller is not necessarily better, since a little extra obstruction is pretty much undetectable visually.  There is a series of standard sizes available.  I found my exact choice to be in-between standard sizes, so I simply opted for the next larger size making sure not to waste any precious light from the primary mirror.  The larger size fully illuminates a 3/4” field for my favorite, 65 deg, 2”, low power, wide field Tele Vue eyepiece.  Planetary views at 300X are amazing even with a 19% obstruction!

 I have come to really appreciate the secondary spider from Proto Star.  It has a nylon center mount bolt that stretches, applying constant spring like pressure on the collimation screws as you adjust the mirror.  This allows each collimation screw to be adjusted independently, without affecting the other two adjustment screws.  It also keeps things snugly locked in place after adjusting.  I made my own version of Bob’s Knobs from three stainless steel 10-24 bolts with small knobs and loctite.  Optical alignment literally takes seconds with a laser collimator, Proto Star spider, and these knobs.  It couldn’t be easier!  Well perhaps having the significant other set it up for you would help.

 OK, we have completed Part 1 with our drawing and have acquired all the optical components.

Next we will discuss:

Part 2- Mirror Cell & Mirror Box – Upper Cage

Part 3- Truss Poles & Truss Connectors – Optical Tube Balance – Rocker Box – Ground Board &

Pivot Bolt – Powered Ground Board – Encoders              

Part 4- Altitude Bearing Design & Installation – Wood Finishing – Final Assembly, Collimation &

Star Testing

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By Patrick L. Barry and Dr. Tony Phillips

       About 900 light years from here is a rocky planet not much bigger than Earth. It goes around its star once every hundred days, a trifle fast, but not too different from a standard Earth-year. At least two and possibly three other planets circle the same star, forming a complete solar system.
       Interested? Don’t be. Going there would be the last thing you ever do.

       The star is a pulsar, PSR 1257+12, the seething-hot core of a supernova that exploded millions of years ago. Its planets are bathed not in gentle, life-giving sunshine but instead a blistering torrent of X-rays and high-energy particles.
       “It would be like trying to live next to Chernobyl,” says Charles Beichman, a scientist at JPL and director of the Michelson Science Center at Caltech.

      Our own Sun emits small amounts of pulsar-like X-rays and high energy particles, but the amount of such radiation coming from a pulsar is “orders of magnitude more,” he says. Even for a planet orbiting as far out as the Earth, this radiation could blow away the planet’s atmosphere, and even vaporize sand right off the planet’s surface.

       Astronomer Alex Wolszczan discovered planets around PSR 1257+12 in the 1990s using Puerto Rico’s giant Arecibo radio telescope. At first, no one believed worlds could form around pulsars—it was too bizarre. Supernovas were supposed to destroy planets, not create them. Where did these worlds come from?

       NASA’s Spitzer Space Telescope may have found the solution. In 2005, a group of astronomers led by Deepto Chakrabarty of

MIT pointed the infrared telescope toward pulsar 4U 0142+61. Data revealed a disk of gas and dust surrounding the central star, probably wreckage from the supernova. It was just the sort of disk that could coalesce to form planets!

       As deadly as pulsar planets are, they might also be hauntingly beautiful. The vaporized matter rising from the planets’ surfaces could be ionized by the incoming radiation, creating colorful auroras across the sky. And though the pulsar would only appear as a tiny dot in the sky (the pulsar itself is only 20-40 km across), it would be enshrouded in a hazy glow of light emitted by radiation particles as they curve in the pulsar’s strong magnetic field.
       Wasted beauty? Maybe. Beichman points out the positive: “It’s an awful place to try and form planets, but if you can do it there, you can do it anywhere.”

Find more news and images from Spitzer at http://www.spitzer.caltech.edu/ . In addition, The Space Place Web site features several games related to Spitzer and infrared astronomy, as well as a storybook about a girl who dreamed of finding another Earth. Go to http://tiny.cc/lucy208

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Editor’s Note: This article is reprinted with permission of the author from his website www.thecomethunter.com  Please visit Don’s website for updates. To see this article with photos, view the Classic Observer or visit Don’s website.

Some comets are meant to be discovered. They are bright and easy to see. They hang in the sky for months at a time, and some even reach naked eye visibility.

Some comets are nearly impossible to catch. They brighten as they enter the inner solar system, but travel though areas difficult for the comet hunter to reach. Some move quickly, some remain faint, some do both. This is the story about one of those comets. It not only had to be discovered, but had to be found again before it could be verified.

I first got interested in astronomy at the age of 8. From there I graduated to my first telescope, a 2” refractor, on my thirteenth birthday. I used that to view the moon, planets, and stars for the next three years. On Christmas, in my 16th year, I bought a 6” reflector telescope, getting much use out of that for many years. I still use it today for public star parties and found my tenth comet with it.

It was in late 1974, after learning the sky, doing some astrophotography, and getting out of the military after thee years of service that I decided to take my hobby of astronomy to the next level. Of the options open to me I chose comet hunting. Very few amateur astronomers were searching for comets, I enjoyed the view of the night sky through the telescope and it cost nothing to start. So on January 1, 1975 I started a systematic search for comets.

1978

It was nearly 4 years and 1,700 search hours before I found my first comet, in September 1978 from Loma Prieta, CA, in the Santa Cruz Mountains. My second took 6 more years, I found that one in May 1985 from Big Bear, CA, on the last day of an astronomy conference. My next find came less than a year later, my first periodic comet, now known as P/96. It is one of the most unusual comets ever discovered, appears to be the brightest periodic comet on a regular basis, and returns every 5.2 years. In August 1988 I found my fourth comet. Like my second comet it disintegrated as it neared the sun.

We then moved to Colfax, California, where I found two comets in 1992, three in 1994 and one in 2004. For the past 15 years I’ve been doing about 100 hours of searching per year, most of it from my homemade observatory.

So I got up at 4:15 on the morning of Tuesday, March 23, 2010 for comet hunting. Over the previous week I had scanned, or swept, much of the eastern sky, mostly near the equator and south of it. Today I will cover an area in the northeastern sky.

The telescope I used is an 18.5-inch (0.46m) reflector, f/4.8, with an eyepiece yielding 77 magnification and a field of view of 0.8 degrees. I bought it second-hand from a fellow amateur astronomer in May, 2006. I’ve never been one to have “aperture fever”, the desire to have a larger and larger telescope. I have always believed that how faint one sees depends upon the eyes, skies and telescope, and probably in that order. When I got my 10” reflector telescope in late 1975, I had one of the largest telescopes being used for comet hunting. Since then other comet hunters have gotten larger scopes, with 16” being typical since the late 1980s. I used the 10” faithfully for comet hunting until I got the 18” in 2006. Along the way, in 1983, I built 6” binoculars, with which I discovered four comets.

When I began using the 18” telescope for comet hunting I realized that I was picking up nebulous objects as faint as magnitude 13, or about five times fainter than I did with my 10” reflector. But there was a trade-off for this increase in depth; my field of view was about 35% of what I had with the 10” scope. With a smaller field of view, it took me much longer to cover a given area of sky. This is one of the decisions that a comet hunter has to make, to cover a wide portion of the sky and not see very faint, or to cover a smaller area and see many faint objects.

On March 23, after suiting up (the temperature outside was 42 degrees F), my yellow lab dog Roxy and I went out to the observatory to start another session of comet hunting. I began at 4:35 AM, covering a rectangular area between 45 and 30 degrees north declination. After each sweep, I returned to the starting point, and did another sweep. Since the earth is rotating and the stars are rising in that part of the sky, I was now sweeping through new territory.

To visually discover a comet, the comet hunter looks through the eyepiece of the telescope while slowly scanning (sweeping) across the sky. What he is looking for is a fuzzy patch of light. When a comet is discovered, it typically has no tail, and it moves very slowly, covering perhaps one degree (two moon widths) per day. In the course of this sweeping process, many fuzzy objects are picked up, but more than 99% of the time they are galaxies, clusters, nebulae, or small groups of faint stars. These are plotted on star atlases and in computer databases. Occasionally a comet hunter will pick up a previously discovered comet; those are on printouts from Internet web sites. I have such a printout with me when I’m searching for comets. I have also equipped my telescope with an electronic setting circle device; it determines where the telescope is pointed and provides a readout for me. It sorts through its database and tells me if a known galaxy or cluster is in the field of view.

I picked up several objects during this sweep. All were galaxies: NGCs 7217, 7331 and 7426. After an hour of sweeping I realized that I had about 15 more minutes before the approaching twilight would end my session.

At 5:37 AM I picked up another fuzzy object. It was faint, similar to the galaxy 7217 that I had seen earlier. But this was not that galaxy. Nor did I know offhand of any object in this area. I looked up at my setting circles device. It said “Searching Data”. This means that there is nothing in its database in that area. I looked again just to make sure it was fuzzy, and not a tiny group of stars. It was fuzzy, diffuse..

Two more checks needed to be made. First, I had to make sure it was not a known comet. I memorized the position that the setting circles were giving me (RA 22h 53m, +31.3 degrees) and checked against the coordinates of all known comets bright enough to be visible through my telescope. None were known to be in the area. This took a couple of minutes, so I had to find the object again. So now I was fairly certain that it was a comet, and that it was undiscovered.

The second check is to see if it is moving. A comet should show motion against the background stars in a half-hour or so. I made a drawing on my log sheet, showing the stars and placing an “x” where the comet was. It was 11 minutes since I first saw the comet. In the background my radio was playing, Rob Arnie and Dawn were on, and Arnie was talking about exploding whales. It was humorous, but I had to keep to the task at hand.

The sky was brightening, and the comet was becoming harder to see. I switched eyepieces to higher power and made another drawing. I also plotted it in my atlas; this helped to confirm the coordinates of the object. Upon switching back to lower power, I found the comet was now disappearing into the background. I had not detected motion. I closed up the telescope and came back onto the house.

A potential comet discovery is reported to the Smithsonian Astrophysical Observatory, actually, a portion of it known as the Central Bureau for Astronomical Telegrams (CBAT). They are the clearinghouse. They confirm the comet’s existence, if they can, and determine the orbit and place the name on the comet. They then release the announcement about the comet. However, in order to get follow-up observations, they prefer to have some motion detected so other observers down the line would know where to point their telescopes.

Back at my desk, I turned on my computer and entered the world of the Internet. I checked the CBAT’s web site (the “CMTChecker”) to see if any known comets were at the position of this object. None were. I then looked at another web site and downloaded a photo, taken years ago, of the area. No faint galaxies or group of stars were in the area.

So I had a decision to make: should I tell the CBAT about this comet, or wait until the next day and check it on the second night? I woke up my wife and told her what I had found, then decided the best choice would be to notify the CBAT today. I typed up an e-mail, explaining that I did not detect motion, while giving the position, brightness (magnitude 11), and the date and time I saw it. I also said that the sky was supposed to be clear the next morning, so I should be able to get a second position then.

Typically this would be no problem. I had a busy day, but it did not go by fast. As a real estate appraiser I had research, analysis and two inspections to do. In the second half of the day, there were some high clouds coming in from the west.

I did not sleep well that night, checking the weather several times before finally getting up at 3:50 AM, before the comet even rose over the horizon. I got out to the observatory, uncovered the telescope, and looked at some star clusters while waiting for the comet to rise. The weather was not good, with high cirrus clouds hiding some of the stars. As the area rose above the local horizon at 4:30, I put the telescope on it and watched. The stars were fading in and out due to the clouds. My clearest view was at about 5:15, and then the clouds thickened again. I did not see the comet, but also saw nothing at the location that it was at the morning before. I came back into the house and notified the CBAT. I suggested that they put it on the Confirmation Page (for others to try to confirm), or notify other observers and get them to try it. They said they would do the latter.

The weather forecast for Colfax was for rain the next morning. So after checking the weather forecasts for other parts of the US, I notified amateur astronomer Alan Hale, New Mexico, and asked him to confirm it. Alan is co-discoverer of Comet Hale-Bopp, has confirmed my comets in the past, and is fully capable of seeing this object. He said that he would give it a try.

Wednesday was another long day. My car would not start and needed to have its battery replaced. Then I drove to Nevada County to walk 6 miles to inspect a 40-acre land-locked property.

It rained in Colfax early the next morning. I received a phone call from Alan Hale. Did he see the comet? No, he did not, and he searched two to three degrees from the earlier location. The only reason he would have missed it is if was on top of a bright star.

The CBAT indicated that no one had reported seeing it.

I now had two more mornings with no moon in the sky in order to find this comet. The question was; where did it go? With moonset at 4:44 AM on Friday the 26th, I would have only about an hour of dark sky to search. The next morning I would have even less time. But I also have learned that some comets, in this part of the sky, are headed toward the sun. That would favor the area below the comet’s original position. So I mapped out an area to sweep, outlining a rectangle at least seven degrees from the comet’s original position. I had two short mornings to catch this comet, or it would probably be lost forever. My plan was to begin at 4:15 AM.

That day I cleaned my telescope mirror and re-aligned the optics. It rained that day, and into the night, but the storm was fast-moving, and the sky was predicted to be clear by 3 AM. I got up just before 4 AM, and the sky was clear. I began sweeping at 4:20, and for the next 58 minutes I picked up only a galaxy, but no comet. Finally, at 5:19 I picked up a faint fuzzy object, my first and only thought was that this was the comet. There was no galaxy in that part of the sky, so I plotted it on my atlas and made a drawing to see for sure if it was moving in the proper direction. I went into the house and woke my wife and youngest son Mark, but Matt was too difficult to awaken. Mark came out and saw it, but my wife was unable to see it though the telescope.

The comet had been moving two degrees per day, a fast rate for a comet.

I came in and reported it to the CBAT. An hour later I talked to Dr. Marsden of the CBAT. He was thinking of holding off on the announcement until they had a preliminary orbit, and that would require getting more accurate positions from astronomers with electronic cameras. It was placed on the Near Earth Object (NEO) Confirmation page and observations came pouring in. As it turned out, the announcement was made later that day, Friday, March 26. The comet will remain faint, and more difficult to see as it nears the solar vicinity.

This was my 11th named comet discovery, coming 607 hours since my previous find in August 2004. I had swept for a total of 7,654.25 hours since January 1, 1975. This is the first visual comet discovery since October 2006. With the automated search programs finding objects much fainter than the visual comet hunter, it is expected that the number of visual comet discoveries will continue to decrease.

As with each of my comet discoveries, it is both a blessing and a humbling experience to find one of these objects.

This comet had to be found twice.

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Forrest Lockhart

In the first Meridian article last month, I described the observing plan and the scopes to be used for ferreting out interesting objects appearing at or near the meridian that month. There was only one E-mail response to my request for celestial targets for April, but it turned out to be a good choice. The member asked what, if anything, I could see of the open star cluster, Messier 44 under suburban skies. The question brought back memories of the old Messier Group, for I had not observed the cluster since then.

Since I was to be working at the Cameron Park Community Observatory in a few days, and I could make use of the 4” refractor there instead of using my own, I decided to take another look at M44.

Messier 44, commonly known as the Beehive Cluster, was born 400 million years ago from the collapse of a large cloud of gas and dust about 500 light years away. The result was the creation of a cluster of approximately 200 stars spanning about 11 light years. The calculated combined magnitude is 3.1, which should make it stand out well against suburban sky glow, but that isn’t necessarily so. According to astronomy author Stephan James O’Meara, the brightness of the individual cluster stars range from 6^th to 14^th magnitude. So what was my experience with M44?

On a clear observing night with a thin crescent Moon and a limiting visual magnitude of about 4.5, we hosted a group of college students on a field trip to the observatory. I took them outside and, using a laser pointer, gave them a general area to observe with the unaided eye. While a few knew what they were looking for, most did not. They were only told to look at the area and report what, if anything, they could make out. Since the host constellation of Cancer is so faint, M44 is the brightest object in the area. Of 16 students, 15 reported a misty, cloudlike ellipse about the size of a full moon.

Back in the observatory, I directed the 14” SCT scope with the attached 4” refractor to M44. Magnification on the 14” was 125x, while the refractor was set to 27x. Due to the angular diameter of M44, the view through the 14” scope was truly disappointing. Too little of the cluster could be observed in the limited field of view. However, in the 4” scope with its FoV of nearly 3 degrees, the view was scintillating, with at least 70 stars glinting like diamonds on a dark background.  The students were impressed with the view, and I felt that I had re-discovered an old favorite.

Upon my return home that evening, I grabbed my 80 mm Stellarvue, placed it across a convenient tree limb in the front yard and took another squint at M44. While I do not recommend a tree limb as a substitute for a sturdy mount, I was again quite mesmerized by the impact of a low-power view of M44 at the meridian.

If you have a favorite object that will be in the vicinity of the meridian in May, please E-mail me at <forrest.lockhart@sbcglobal.net> with your observations. I’ll try to give it a good look and report back in the May SVAS Observer.

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“Urban Astronomy”: A Great Night for DSOs

Margo Schulter

["Urban Astronomy" is my project to encourage
the observing of Deep Sky Objects (DSO's)
in urban or suburban settings, with a due
acknowledgment that these objects will, of
course, be yet more impressive in darker
skies. Questions or comments by e-mail are
warmly invited.]

Saturday night was a great opportunity for some
DSO watching at Quadrivium Urban Observatory (QUO),
otherwise known as my bedroom, just north of CSUS.

As twilight deepened, Canis Major was a big
attraction, with M41 announcing a delightfully
clear night. I could say, “Good, the less than
ideal viewing earlier this year reflected mist
rather than a sudden increase in light pollution!”

The tour — with my 15×70 binoculars, handheld
with a bit of bracing for the most part, while
reclining — moved to Cr 140, often known to
dark-sky observers who see it with the naked
eye as “The Tuft in the Tail” of Canis Major,
but appearing in binoculars as what I call
Ursa Australis, or “The Southern Bear,” in
my version an asterism including stars in both
Canis Major and neighboring Puppis.

Other open clusters among my urban favorites
are Cr 132 (”Mulberry Cluster”), Cr 135
(Pi Puppis Cluster), and NGC 2451. The latter
two were evidently described by Giovanni
Battista Hodierna in 1654, whose catalogue
of nebulae, like Messier’s, includes some fine
objects for astronomers at all levels of
experience at a latitude like Southern Sicily’s
or Sacramento’s.

One notable event occurred around 1920, when
a satellite (moving mostly north to south)
passed just east of M41. I followed it for
a bit, and then lost the track when I looked
at a red LED clock to check the time. I guess
that I have a strong “hunter’s instinct” to
chase tofu and satellites.

As the evening continued, I was pleased to
locate one of my favorite objects: M93, a good
example of a “faint fuzzy” still clearly visible
with 15×70 binoculars in an urban setting.

At some point, I also did a bit of careful
positioning to get a view of the Sword of Orion:
NGC 1981 and 1977, M42, and NGC 1980. This was
an especially appropriate sight, since this
month marks the 400th anniversary of Galileo’s
_Sidereus Nuncius_, the “Starry Messenger”
(or, perhaps, the “Celestial News”). While it
was his planetary observations which became
the main focus of immediate attention, his
deep sky observations (with M42 and M45, the
Pleiades, as examples of how many more stars
became visible with his primitive telescope)
would inspire Hodierna to make his much more
extensive catalogue and atlas maps.

Gamma Velorum in Vela, “The Sails,” also seemed
in evidence: at a declination of around
-47 degrees, this star marked about the southern
limit of Hodierna’s maps, as was a test of my
ability to see around, or through, some lofty
trees that have apparently been getting a bit
taller in my neighborhood.

A final treat of the evening was the “Alien”
asterism including the bright and reddish
star Lambda Velorum: this asterism looks a
bit like a sidewise view of the head of a
friendly extraterrestrial with what might
be antennae (with east-west as “up-down”).
My warm thanks to Andrie van der Linde, an
amateur astronomer in South Africa whose
newsletter called this charming asterism
to my attention!

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E-Observer by lynda