Astronomy Picture of the Day

While I am an incurable fan of looking at my own personal set of photons given off by deep sky objects, I can also be attracted to beautiful photographs of the same sky objects. I grew up with black and white versions of long photographic exposure time pictures that showed much more than I can see with my eye. These days, color photos and false color photos are all the rage. They are beautiful.

Sometime last fall, I decided to take an online course offered free by Robert Nemiroff (Michigan Technical University) from the upper peninsula of the state. It was an online collection of the lectures used for a college course. They were offered completely free as long as no college credit was needed. Dr Nemiroff is one of the editors of the Astronomy Picture of the Day (APOD). This is a NASA hosted site where one photograph or piece of art is featured each day. In the course, the students were responsible for knowing something about each one of the APODs for their testes.

I started taking a closer look at the descriptions under the pretty pictures. It turns out that the writing about the photographs is as well done as the photography. Here is a recent example:

“Why take a picture of just the Badlands when you can take one that also shows the spectacular sky above it? Just such a picture, actually a digital stitched panorama of four images, was taken in late June near midnight, looking southwest. In the foreground, the unusual buttes of the Badlands Wall, part of the Badlands National Park in South Dakota, USA, were momentarily illuminated by flashlight during a long duration exposure of the background night sky. The mountain-like buttes visible are composed of soft rock that show sharp erosion features from wind and water. The South Dakota Badlands also contain ancient beds rich with easy-to-find fossils. Some fossils are over 25 million years old and hold clues to the evolutionary origins of the horse and the saber-toothed tiger. Bright Jupiter dominates the sky on the left just above the buttes, while the spectacular Milky Way Galaxy runs down the image right.”

When I take a careful look at this prose, it is as illuminating as the photograph it described. Here is another recent description from the APOD site:

“Sprawling across hundreds of light-years, emission nebula IC 1396, visible on the upper right, mixes glowing cosmic gas and dark dust clouds. Stars are forming in this area, only about 3,000 light-years from Earth. This wide angle view also captures surrounding emission and absorption nebula. The red glow in IC 1396 and across the image is created by cosmic hydrogen gas recapturing electrons knocked away by energetic starlight. The dark dust clouds are dense groups of smoke-like particles common in the disks of spiral galaxies. Among the intriguing dark shapes within IC 1396, the winding Elephant's Trunk nebula lies just right of the nebula's center. IC 1396 lies in the high and far off constellation of Cepheus.”

I like the idea of the nebula sprawling across the heavens instead of many more prosaic ways of saying the same thing. I might have written something like “IC1396 I several hundred light years in diameter.”

I got into the habit of looking at the APOD each day while I was taking the course last fall. I keep a link to the APOD on my blog site. It is one of the great internet archives of both beautiful photographs and instructive descriptions of deep sky objects. There is a lot of cosmology to be learned just by reading the descriptions from a month’s worth of the APOD library. Enjoy them.

The daily APOD can be found at

http://apod.nasa.gov/apod/

Risk Management in Astronomy

One of my nicknames is Risk. Hence, “Risk’s Wildly Successful” series of helpful insights. The way I came across that nickname was my function in an Air Force laboratory as the champion for Risk Management.

Life would be pretty boring if risk was always eliminated or minimized. My goal has never been to eliminate risk, but to control it – and to never let risk control me. I enjoy the heart pounding experience of pushing my limits on a mountain bike, teeth chattering as I descend a rocky trail. I enjoy the experience of standing in front of 300 people with a brand new talk, knowing that a few of those people may know more about the subject than I do. I enjoy reading people’s faces and knowing whether I am talking over their heads, or whether I am being dreadfully boring. These sorts of things are the spice of life.

Something happened this weekend which brought back to my mind the necessity of practicing Risk Management in Astronomy. We were on the way back from Hill Country State Natural Area. My son was in the pick-up with me and his fiancée was in our Corolla with Diane. It was about midnight.

Somewhere on Bandera Highway, Diane fell asleep for a moment. She was driving the car and drifted left of the yellow line. Ashley was sleepy but awake enough to know that Diane was not playing a joke on her. She quickly woke Diane and both of them drove the rest of the way home with a fresh pile of adrenaline in their veins!

Its not that our family is unaware of the dangers of driving sleepy. I personally think it is now more of a problem than “driving drunk” for our society. Driving drunk may have been more of a problem in the past, but most people now know the severe penalties for driving drunk and avoid doing so.

That brought to mind the kinds of risks that we astronomers need to control in our sport. We all know the risk of looking at the sun with a telescope. It will instantly and permanently ruin eyesight to look at the sun with aided optics. But how many of us are very careful when moving a scope around during the daytime? I remember one time this summer when I happened to glance down the tube of a reflector to see how much dust was on the mirror. The sun’s reflection hit me hard in one eye! Stupid, stupid, stupid! It took 5 minutes before I was convinced that my eye was not damaged.

Driving around at night, we not only run the risk of falling asleep, but we have to stay on the alert for large animals in the roadway. Here in Texas, that means deer and pigs. Driving back from Hill Country, Diane and I have counted up to 17 deer next to the highway.

We have to be careful about heavy scopes hurting our backs, tripping over tent stakes, and letting large scopes crush fingers and hands. These are not idle threats. As I have written, the reason I got a nice camping spot at the Texas Star Party this year was that a fellow tripped over a tent stake going to a restroom and broke his leg.

We need to be careful about being alone in lonely places. The only people who have bothered me while observing at the side of the road have been policemen. But other observers have not been quite as lucky. We need to be ready to defend ourselves while in lonely places. We also need to make sure that we have permission to be observing. One significant form of my risk management is developing friendships of folks that are willing to allow me to observe from their property instead of stopping along lonely roads like I used to do.

But learning to only drive while awake remains the most important risk management technique. There are two means of controlling this problem. The first is to learn how to stay out all night. This takes some equipment and experience. The second control mechanism is to learn to stop driving whenever I get sleepy – before getting so sleepy that I nod off. It does not matter if I am 10 miles from home or 1 mile from home. There is ALWAYS someplace where I can pull off the road and take a short nap. Even a 10 minute nap will give me many more minutes of awake time. It is always OK to stop to sleep. Dad is not at home looking at his watch. Go to sleep after the wheels stop rolling. Really. Please.

Satellite Observing

Sometimes it is a challenge to find something to do after the scope is set up at a remote location and before the sky turns inky black. One thing that an observer can do while waiting for regular observing is to look for low earth orbit satellites. The activity can be done alone or with groups. Diane and I find it especially nice to work together. We share the tasks: reading a list of times and azimuths for satellites that will come over, and recording times when the satellite passes celestial landmarks. We also compete with each other to be the first to see a satellite.

There are several tools available for finding satellites. All of the tools I use involve computers and internet resources.

One easy source for finding out what bright satellites can be seen is Heavens-Above (http://www.heavens-above.com). You tell the site where you are and it will tell you what bright satellites will be visible in the coming evening and morning. Heavens-Above lists both the satellites that are on the publicly available lists and other satellites which are not published. Most of these are the so called “spy satellites” put up by our country and others. They are often big bright satellites, the size of the Hubble Space Telescope, but aimed at earth instead of at the stars.

I have an Ipod Touch. One day I will have an Iphone if I am good and have enough patience. These devices have a couple “apps” that are handy for satellite observing. I downloaded the free ISSLite program from VosWorx. It downloads orbital information from the web and helps folks that want to watch the International Space Station and any Progress spacecraft or Space Shuttle passes. The program lists the passes that will be visible for a location for the next week and it gives two views of the orbital movement of the spacecraft. One view is the traditional view seen at Houston mission control – the sinusoidal wave of the space craft position. The other view is a 3-D rendering of the earth (and the earth can be spun around) which makes for a pretty good tool to explain the traditional view.

Having up-to-date information on satellites is important. Their orbits change over time, and sometimes the change is rapid. Orbits are defined by a series of numbers – there are several that are important to plug into equations to allow calculation of the satellite’s position in space and the viewing angle from an observer’s location. Fortunately, the computer programs that I am writing about here know how to import the numbers – officially called orbital elements or Keplarian orbital elements – and work the advanced math necessary to calculate where a satellite may be visible. As an observer, I need to tell a program where I am on the surface of the earth, and I need to download a current version of the “keps” which are also sometimes called the NORAD Database or the “els”.

There is an advanced version of the ISSLite program that will follow a much larger group of satellites – amateur radio sats, and bright visual sats among the group. That program is also distributed by VosWorx and is called ProSat. It cost about $10 to download. It is worth every penny IMHO.

There are also programs available for laptop computers. One that I have been using recently is Earth Orbiting Objects or EOO. This program, written by Steve Boucher, allows download of recent keps, allows one to store multiple observing locations and does everything that the ProSat program does. It goes one step further. It allows me to see a view of the sky with the simulated satellite going past the starry background. That is, it contains a planetarium program which shows the movement of a satellite across the sky. It can be set up so that it will show in near-real time where a satellite is. That is really good for both finding a dim satellite and for replaying a satellite passage to remember the pass with greater accuracy.

One activity involving satellites and telescope has been a real challenge for me. It is an activity for the nimble observer. On a space station passage, try following the station with a telescope at about 120-150X magnification. For me, it took using a Telrad, a finder scope, and quick reflexes. I was rewarded with a series of views of the station with enough resolution that I could see a distinct rectangular shape and a different color for the station’s wings than for its central occupied core.

A second activity can be done either at dusk/dawn or sometimes in bright sunlight. That is the observation of Iridium flares. The Iridium satellites (used by the global telephone system of the same name) have very bright mirror like sides and they can “flash” an observer with surprisingly bright flares of light. At a maximum they may reach -8 magnitude – much brighter than Venus. The best source of information about Iridium flares for me has been the Heavens-Above site mentioned at the top of this piece.

So, next time you see me with my scope all set up and the sky not yet dark, if no one has engaged me in an interesting conversation and you wonder what I might be doing with all those pieces of paper, my iPod, and a voice recorder… well now you know the rest of the story.

Observing Chair/Step Stool

When I get sawdust and plane curls going in one project, it often leads to another.

Having just finished the base for Looking Glass, I decided to solve the problem that Diane had looking at M13 the other night. Hercules is nearly at the zenith in the evening this time of year, and My first mate was not quite tall enough to see through the vertical scope and that led to contortions as she tried to keep her toes on the rungs of my observing stool, holding onto my shoulders to not fall over.

I remembered a chair that I had taken at the Texas Star Party, made by StarMaster. My neighbor at the TSP had a used one for sale and I thought the idea was clever.

I thought about that design and decided that I could make a similar device for about 5 dollars in materials. I made the two "ladders" from 2x2s. The total lumber was four of these inexpensive boards. I had a scrap of 3/4 inch plywood from the scope project, and that made a good platform.

The step can be moved to any of the "rungs" on the seat. That allows Diane to stand on a low step for a quick observation. The same usefulness will probably be enjoyed by kids at public star parties. The four foot height of the rails may give them something to hold onto instead of the scope too. But the design is also an observing stool with multiple levels.

My thanks to the folks at StarMaster who built the version that I saw. I recommend their design as a great way to show people wonders and for the observer to sit down and enjoy an object.

HyperLightbridge Base

Last week, my Meade Lightbridge (aka Looking Glass) arrived in Helotes, TX. I had ordered it with the plan to rebuild it, and this weekend I had the chance to do so. I had previously practiced building some of the design features on the Resurrection scope – large diameter altitude bearing and a small base. So, on my way home from work on Friday I picked up a 4x8 sheet of birch plywood ¾ of an inch thick with great expectations for construction.

I had drawn up a sketch of my idea and a cut plan for the sheet of plywood:

Sketch

Cut Plan

On Saturday evening, the first thing I did was to cut out the two three-foot-diameter semi-circles with a router and a circle cutting jig. This jig was a piece of Masonite cut and drilled to fit the base of my router with an arm that extended out toward the operator. (I got the idea for this by searching the Internet for “router circle cutting jig”.) I measured from the inside edge of a straight router bit to a spot 18 inches down that arm and drilled a hole that would be the center of my 3 foot half circle altitude bearing. I screwed the jig ¼ inch from the edge of the plywood and 18 inches from one end. I then cut through the plywood about a quarter inch at a time around the arc.

After cutting these two half circles, I cut a strip of bumpy fiber reinforced plastic (FRP) ¾ of an inch wide and as long as the half circumference. That was about 57 inches (pi*18). I coated the back surface of the FRP and the round surface of the altitude bearings with two coats of contact cement. After about 10 minutes of dry time, I began at one end of the strip and pressed the strip on the edge. After getting the whole strip on, I used the floor to press the strip on very securely by rolling the semi-circle against the garage floor. Then it was time for a night’s sleep.

The next morning, I used a plane to trim the width of the FRP to the width of the plywood, which is actually 1/16 of an inch under ¾ of an inch.

Then I set about cutting the box pieces to hold the sides of the light bucket. I unscrewed the mirror cell from the bucket walls and lifted the top of the bucket off the mirror cell. I put the mirror cell in the house, away from saw dust. (I also took this opportunity to adjust the mirror holding brackets so that they do not press too firmly on the edges of the mirror.) I measured the diameter of the bucket several places and decided that it was very close to 19 inches. I added the width of my plywood to that and came up just below 19-3/4 inches. I knew that I wanted four identical pieces of plywood 12x19-3/4. I also needed a base and a ground board.

I very carefully measured and drew cutting lines on the plywood. First, I cut the plywood with a circular saw so that I had a 48x48 inch piece. I then divided that into two 24x48 inch pieces and then two more cuts gave me four 24x24 inch pieces. Two of those pieces I cut to 19-3/4 inches long, and then each of them was divided to one foot widths. I put the two remaining 2x2 foot pieces to the side until I discovered exactly what size the base would need to be.

I routed the long edges of each of the box sides, top and bottom, with a round off router bit. Then I drilled and countersunk three screw holes on one end of each of the box pieces. I assembled the box, making sure to drill a pilot hole for each of the 1-1/4 inch drywall screws.
I removed the aluminum altitude bearings from the light bucket. Then I slipped the box over the bucket and secured it to the bucket with a ¾ inch wood screw through two of the holes which had held the aluminum altitude bearings.

My plan was to have the center of my 3 foot diameter altitude bearing at the center of the upper edge of the box. I knew, from the collected wisdom of many owners that the scope was bottom heavy. I confirmed this on my scope when I attached a radian eyepiece, a Telrad finder, and a finder scope to the secondary housing. When my Looking Glass approached level, it wanted to nose dive. I also knew from the collected wisdom of the group that moving the center of the altitude bearing an inch up would make a world of difference. That was where I attached the box – with its upper edge an inch and a quarter above the center of the factory bearing. I also attached a third screw to the topside (opposite the seam in the bucket) to reduce rotary movement of the scope in the box.

I attached the half-round altitude bearings to the box with home made knobs and tee-nuts. I made the knobs by threading three 1-1/4 inch diameter ¼ inch fender washers over a 2 inch long 1/4x20 hex bolt and tightening them down with a nylon insert nut. I drilled ¼ inch holes through the bearing and the box in locations which spread the load and which gave me room to work between the bucket and the box. Then I drilled the box holes to accept a 1/4x20 Tee-nut and drew that Tee into the wood with a hex bolt and a washer. This makes it easy to remove the two altitude bearings from the light bucket without tools. A minute or two is all it takes to install or remove the large bearings. Of course, the bearings were oriented so that they allow both vertical and horizontal use of the scope.

I measured the width between the outer edges of the altitude bearings to make sure that they were parallel. They were just a little under 22 inches from side to side at three locations – ends and middle. That was very good news. All my careful cutting had paid off. Now I was able to build the base.

The width of the base would be the same as the width of the altitude bearings. I cut both the remaining 2x2 foot boards to 21-7/8 inch squares. I rounded off the corners of the ground board by using a varnish can to trace ¼ circles at each corner.

Next I needed to know how high the base needed to be at the center. I measured how far the corner of the light bucket extended outside the altitude bearing. It was about 2 inches. Allowing room for the center screw on which the telescope would rotate, I decided to make the center 3 inches tall. I marked that height at the 11 inch center of a 22 inch piece I was drawing on the part of the plywood from which I had cut the two three foot circles. I used an altitude bearing to draw a curved upper edge so that the bottom center was 3 inches tall and the sides were even. It ended up being about 6-1/2 inches on each side.

At this point, a bunch of routing was done to round off edges. The bottom edge of the rotating base board was routed. The outside corners of the two supports (with the concave rounded edges) and most of their round surface was rounded. Both top and bottom of the ground board were routed. The full edges inside and out of the altitude bearings including the FRP was rounded – the FRP only slightly.

A 5/16 inch hole was cut in the center of the base and ground boards. (To do this easily, place a straight edge from corner to corner and draw an X in the center. A 5/16 Tee nut was placed in the bottom surface of the ground board after that hole was drilled one size larger.

The side supports were screwed to the base from below with countersunk drywall screws. A brace was cut for both the front and the back of the base, adding strength to the support sides. The front was cut to length from one of the 4-1/2 inch wide pieces left over from the cutting of the box sides. The rear brace needs to be a little shorter to allow the swing of the telescope. 3 or 3-1/2 inches tall works pretty well. These braces are screwed to the sides of the supports and to the base. All holes are countersunk.

Only a little bit of work remained. I used the lazy susan azimuth bearing from the stock base, except that I also placed three felt furniture pads just outside the circumference of that bearing. I cut about half the thickness of the pads off so that the azimuth bearing is smooth, but does not turn in the wind. I attached square furniture glides on the upper rails of the supports. (I left small areas which were not routed so that the full width of the rail would support the furniture glide.) I also attached pieces of 1” aluminum bar, cut 2 inches long and drilled to be attached to the outside edges of the supports.

I cut triangular braces for the box, one for each corner, 4-1/2 inches wide. This is to strengthen the box so that a handle can be attached. The handles make it much easier to carry the light bucket. They also allow two people (I’m not strong enough to do it by myself) to lift the scope from the base after it is assembled.

I put a handle on one of the braces for the base, and it can easily be carried on one hand while carrying the bearings or the secondary housing in the other hand.

I really like the feel of the scope now. It is much easier to move around. The light bucket with mirror attached is still a heavy item. My only recourse if I had to move the scope a long way by myself would be to use a hand truck or to remove the mirror cell from the light bucket. That is not too hard, but it would still be a bit of a pain.

Resurrection Scope

A month ago, there was an announcement on our local astronomy group’s web page about a telescope that had been found in the garbage. Was anyone interested in seeing if it could be rescued? I responded right away because I had in mind a project that required an optical tube.

I made a call and got directions to come pick up the relic. The scope was rescued from the trash by a friendly fellow. He got a bike that he wanted and he knew someone in the SAAA and found out how to post a notice that he had this “partial telescope”.

When I went to collect the scope, I learned from the neighbor that the scope had been in a lady's garage since 1985. She had recently died and her extended family had thrown out several things that were considered useless by them. The home was off Ingram Rd just inside 410 in San Antonio.

The scope was originally put together by her son, I learned. He was 16 years old when he went to China on a youth missionary trip in 1985. He contracted an infectious disease and died there. His family was unable to even bring his body back to the US because of fears of the infection. I was told they eventually got him buried in Hawaii. If anyone ends up knowing anything about this unfortunate telescope builder, drop me a line and I will update the entry here.

The scope was about a dirty as could be expected from sitting unprotected in a garage for 25 years. It was the optical tube from a reflector telescope. There was a 1.5 inch sighting scope screwed into the tube next to a broken down focuser. The secondary hung by a wire from the focuser and bounced back and forth like a scared kitten. The mirror was labeled on the back as American Optical and had a focal length of about 67 inches.

I disassembled the finder scope and cleaned the lenses. It was usable, though the mount was not of the modern type that fits into a base. The tube had a strange collection of nuts all strung out on an unreinforced two inch long 3/16 inch bolt at about the balance point. Maybe it had once been attached to a tripod by that bolt.

I removed the mirror cell and then the mirror. I submerged the mirror in a tub of water with a little detergent. After soaking, I gently removed the accumulated crud on the mirror with a series of surgical cotton balls. I used each one for a very short cleaning stroke. After cleaning the mirror in this way, I rinsed it with water out of my Culligan filter and then touched the corner of a paper towel to each water drop that did not run off the mirror surface when it was hung vertically. There was one small flaw in the mirror coating about an eighth of an inch in diameter and my work did not seem to have introduced any scratches in the coating.

I reassembled the mirror cell with double sided sticky tape and checked out the optics. Even though the focuser was very difficult to use, and the secondary holder bobbed around, I was able to see that it would focus and give me a decent image.

So I set about doing what I had intended from the beginning. I started building a large diameter altitude bearing dobsonian mount.

I designed the altitude bearing to be two feet in diameter and wrapped the tube in a box a foot long. I made the altitude bearing half moons to be removable with knobs made from bolts and washers. I built the base from two round circles 20 inches in diameter. All these were made from ½ inch hardwood plywood, with the altitude half circles made in double thickness, an inch thick.

I made the bearing surface of each axis from fiber reinforced plastic with sliders made from pieces I cut out from a kitchen cutting board.

I designed a saw blade spring secondary spider to replace the original bouncy secondary holder. The new one is rock solid. I also bought an inexpensive ($40) 1-1/4 inch focuser from Orion.

The project cost about $45 in wood, $45 in hardware, and $40 for the focuser. It ended up being a reasonable deal for a pretty nice 8 inch scope. It also helped me to explore several technologies I needed to understand for my project intended to replace the stock base of a Meade 16 inch Lightbridge.

The photograph shows all the pieces. I had taken them apart to varnish all the surfaces. It was a good photo opportunity. All edges were routed to make them approximate a half round. The bearing surface of the half circles was also routed but not as deeply.

First Light – Looking Glass

I enjoy the tradition of celebrating the first time that a telescope is pointed to the sky. Yesterday I had the privilege of assembling my new Meade 16 inch Lightbridge telescope and (miracle that it was) the sky was clear during the evening hours.

The scope went together easily. The directions were clear enough and no pieces were missing. It took me a few minutes to discover a way to easily mount the focuser/secondary ring. But once I learned that a case wedged between the base and the light bucket holds the bucket at a 15 degree angle, putting the top ring on was much easier. I replaced the screws in the secondary with a set of Bob’s Knobs.

I made the scope a little welcome home gift while I was waiting for the sky to turn dark. I made a shroud to cover its bare midriff from 1-1/8 yards of black bathing suit liner. The stretchy material was on sale at Hancock Fabrics, so the shroud cost less than $10 and fits better than a shroud sold by the manufacturer – for ten times the price. It took about 10 minutes at the sewing machine to complete the project and thread a couple bungee cords in the hem at each end of the shroud. (Thanks to the Starmaster folks for this idea on the construction of a shroud.)

I discovered that the oversize reflective cover that I bought for my 10” Texas scope at the Texas Star Party fits this larger scope just about perfectly.

Then, finally, it was dark enough to begin to look around the sky. The moon was near full and I was in my semi-dark Helotes (Texas) neighborhood, so it was not a night for deep sky observing. First object was Vega. I wanted to adjust the Telrad and finder scope for this scope. I did not hear any strains Contact or Jodi Foster's voice as I was collecting those 20 year old photons. Next up was Mizar, the visual/telescopic double in UMA.

As it grew a little darker (and several satellites later) I went back to Vega and took a left turn to look at epsilon Lyrae, the double-double. I ran through my eyepieces, including the supplied 2” 26 mm that came with the scope. It was easy to split each of the pairs with all my usual eyepieces except the 36mm Plossel, as expected. I pushed right and found the Lyrae pair at the end of the constellation. I set the cross hairs of the finder scope to the position of the Ring Nebula. Despite the washed out sky, the Ring was quite pretty. With my 10mm Radian eyepiece, it appeared to have some color. In a dark sky this may be a very pretty sight.

Luna finally rose above my neighbor’s roof top and I experimented with a moon filter. At 180X, my view of a number of mountain peaks along the terminator was pretty good. Not great, as the San Antonio heat was still warming the air near the roofs and the view was not steady. After looking around at high power, I put the 2 inch lens in and looked at the whole moon. It looked so pretty that I decided to get my simple digital camera and take some pictures with it, up next to the eyepiece. The photo at the top of this column is one of those pictures.

At 11 PM, Jupiter was above the housetops and the Great Red Spot was turning the bend toward the west. I looked in vain for evidence of the recent comet impact with Jupiter. I went to bed for a while and woke about 1 AM just to go outside and take a look at Jupiter again. Still no sighting of the comet impact. (Well… without taking a look at my computer and seeing when that impact spot would be visible, one can’t expect miracles.)

It was a great evening with a new scope. I woke this morning just a little tired from the loss of an hour of sleep. It was worth it. As I thought about a name for this scope while I was taking my shower, several names came to mind. Big Bertha seemed apt, because I am overwhelmed by the size of the mirror. But I have seen other scopes that REALLY are big. This one is just handy-large. I thought that Big Momma, my name for UMA could be right – after all, the second object I looked at was Mizar. Big Ben or Gentle Ben were good names. But then I thought about why I had ordered this scope – to better see the dim Hershel list objects. It was about this time that “Looking Glass” came to mind. Along with that name came Alice and her Wonderland. Those happy thoughts persuaded me. “Looking Glass” it is.

Building a Telescope

The hardest part of building a telescope is beginning.

Fortunately, I had a good reason and a good example late last winter to take on this project. There was a competition fostered by one of the forums on the CloudyNights website to build a telescope that cost less than a hundred dollars. Matt, my San Antonio astronomy friend, posted the details on our local Yahoo group. He mentioned that he had found a place to buy a 4 inch mirror and a diagonal for $40 including shipping.

On a whim, I ordered the mirror and started thinking about how to build a scope. I decided that my goal was not only to design an inexpensive scope, but one that would be easy to build too. Maybe a family or a school science club would take up plan and build one of their own.

After the mirror had been sitting in my hobby room for a month or more, I began thinking of actual plans for building a scope. It seemed like I needed to divide the project into several areas: Optics, Furniture, and Mechanics.

For the Furniture portion, I thought of different ways that I could build a simple Dobsonian scope with as little use of wood working equipment as possible. I knew that a base could be constructed much like the base of my XT10. I needed to think about a way to build an optical tube. After scouring the local hardware store, I came up short on tubes that would fit the mirror, without being way too big. I decided that the easiest way to create the tube was to make a long box with open ends using standard lumber.

Next, I started working out the optics. On a clear night with a bright moon that shone nearly overhead, I put the mirror on my driveway, just in front of my garage door. My garage faces south, so I was able to find the moon’s reflection from the concave mirror on a piece of paper that I held along the door frame. I moved the paper up and down until the image was in focus on the paper. When it was, I made a small mark on the door frame and then measured the distance from the surface of the mirror to the mark. It was 36 inches, and I knew that the optical length from the mirror to the underside of the eyepiece needed to be very close to that distance.

The mechanical distance needed to be the distance from the eyepiece to the center of the secondary mirror plus the distance from the center of the secondary to the surface of the mirror itself. Knowing that distance, I knew that the optics needed three pieces of machinery. I had to find a way to hold the secondary mirror, a way to move the eyepiece in and out to focus, and a way to columnate the secondary mirror.

For focusing, I decided that I would use the oldest and cheapest focus trick: I would have a friction fit between the optical tube and the eyepiece so that I could move the eyepiece in and out for fine focus. How would I achieve such a fine tolerance? By applying just the right number of layers of duct tape to the inside of a hole cut with a 1-1/4 inch hole saw.

For the secondary mirror, I borrowed an idea from the web: using hack saw blades to spring fit a spider into the optical tube. However, with a four sided tube as I envisioned, I would need to have a spider with four legs, each leg resting in a corner of the tube. To make the spider, I slotted a piece of PVC to receive two crossing hack saw blades. I measured the distance from corner to corner and cut each hack saw blade an inch short of that measurement. I fit a piece of dowel into the PVC pipe with a 45 degree angle cut at its end. I used some clear silicon bathtub calk to attach the secondary mirror to the angle cut on the dowel. That gave me a platform that I could move around in the tube to have the secondary under the eyepiece, and in which I could rotate the secondary to correctly reflect the primary into the eyepiece.

For the eyepiece holder, I elected to make the eyepiece hole in one corner of the optical tube box. I used a hole saw to make the hole, making sure that it was pointed straight at the far corner when I was cutting the hole. After measuring twice, I cut the hole about 2-1/4 inches from the open end of the optical tube.

I jumped past the primary mirror cell construction in my description, though it was actually the first thing I made. I cut two pieces of 2x6. One was square and one was just a little longer, so that it could be attached to the sides of the “tube” made with 1x8 standard lumber.

For the cell, I suspended the square by counter sinking 1-1/2 inch bolts in the floating square, and then placing a spring between the floating square and the cell frame. I used wing nuts to adjust the floating mirror holding square from the bottom of the scope. For the springs, I obtained a screen door spring and pulled the spring until it came a little “unsprung”. I cut the spring at three coils for each of the adjusting bolts.

The tube itself was four 1x8 pieces of lumber 3 feet long.

The base was created from several pieces of 1x12. The two rotating base boards are 11” square. I originally used an old record as my turning device, and later found that it worked even better to use three furnature glides on the bottom board turning against the record. There are two vertical pieces to the base, braced by a piece of 1x6 on the forward end.

The tube turns in altitude on two 4 inch PVC pipe caps.

A piece of pipe can be used to aim the scope, or perhaps a red dot finder can be added to the set-up.

That is a building history for the wood box scope. Since I came up with the idea in Helotes, Texas, I began calling the design the Helotescope.

My friend Matt did mostly the same design. He added a used focuser instead of my friction device. That works very well too! The picture at the beginning of this blog shows our two scopes at a meeting of the San Antonio Astronomical Association this last winter.

I have taken this scope to several public star parties. It never fails to attract some young men that look carefully at the scope. I can see the wheels turning in their minds. However, I have not yet seen the third Helotescope.