30th Anniversary of the Comet Shoemaker-Levy 9 impacts on Jupiter

One of the great things about being an amateur astronomer is that you can take advantage of some really cool things that happen in space every once in a while that can only be seen in a telescope. Such was the case 30 years ago when, starting on July 16, 1994, pieces from Comet Shoemaker-Levy 9 (D/1993 F2), which had broken apart two years earlier, impacted Jupiter over the next week. This could be seen even in small backyard telescopes.

Image of Shoemaker-Levy 9 impacts on Jupiter by Hubble Space Telescope Comet Team and NASA.

You may not have been around or into astronomy when this happened, so here I'm posting my observing log entries from those special nights when black marks appeared in the cloud tops of Jupiter. It was an exciting event and I hope this gives you some sense of that, or brings back memories if you observed it yourself.

Comet Shoemaker-Levy 9 Impacts - Observing log entries

Notes:

• Most observations were made with my Tasco 11TR 4.5 inch reflector from the parking lot of the apartment my brother, Paul, and I were sharing at the time in Bellevue, PA, on the north side of Pittsburgh (Bortle 8); some from our astronomy club's somewhat darker site in Freedom, PA, north of Pittsburgh. 
• I lost the sketches somehow, but if I find them, I'll add them.
• At the time, I was using a scale for seeing (steadiness of the air) and transparency ("clarity") of 1 to 5, 1 being the best.

SEB=South Equatorial Belt

NEB=North Equatorial Belt

STB=South Temperate Belt

NTB=North Temperate Belt

July 16-17, 1994 (Sat. night) Bellevue, PA

(4.5-inch) First day of Comet Shoemaker-Levy 9 colliding with Jupiter. Report on CNN said fragment A hit Jupiter this afternoon. Hubble Telescope imaged a plume and a spot. B scheduled to hit at 10:49 p.m. Observed Jupiter in 180x. Could see NEB, SEB. NEB very turbulent- almost joining the NTB. STB quite dark, but a light spot breaking it up- just about center, moving to the west as it rotates. Area to S of that, where impacts will occur is fairly uniformly medium dark.

Seeing about 3/5 but wavy. Clarity not particularly good- some cirrus, a lot of haze, but Jupiter shining through fine. Quite a large festoon extending S off the NEB into the equatorial zone- one of the largest I've ever seen, just a little past the meridian. NEB is very wide, with the tiniest gap between it and the NTB. Much wider gap between the SEB and the STB. All four moons symmetrically lined up on the east side of Jupiter two by two, dipping down toward the center. 10:42 p.m. Seven minutes until predicted impact of fragment B. Image still undulating like Jello, but not blurring too much. Seeing variable.

10:48 p.m. One minute to predicted impact. Jupiter is about 5 degrees NE of the Moon tonight (a little past first quarter). Quite a bit of thin cloud cover in the area.

Seeing improved to 2/5.

11:11 p.m. Moon hazed over. The white spot on the STB of Jupiter about 4/5 of the way to the western limb now. Looking like this may be an event for big scopes above the atmosphere only. Nothing seen so far. B impact site should be coming around into view. Nothing. Jupiter dimming from clouds.

11:19 p.m. Clouds becoming a problem- very murky. Paul got home at 11:36. Conditions deteriorating. Lights in the parking lot don't help either.

11:48 p.m. Jupiter's image brightening a little, but the seeing is terrible. Gave up at 11:51, no impact effects visible.

July 18-19, 1994 (Mon. night) Bellevue, PA

(4.5-inch) First look at the Comet Shoemaker-Levy 9 impact effects. Incredible! Two dark spots on Jupiter's SW quadrant, very prominent. Some other mottling along the same latitude. Beyond what we expected (Paul and I) to be able to see. We can't believe the spots are this prominent! Easier than the Red Spot's ever been. The two spots were heading for the limb- did a sketch.

9:17 p.m. darkest spot nearing the limb.

Did a second sketch. A third spot is now just past the meridian. Fainter than the other two, but still well defined. However, nowhere near as dark as Ganymede's shadow on the N hemisphere (coming up on the meridian). We both noticed that the N polar area seems quite dark. A couple white spots on the STB, just N and E of the third impact spot.

11:30 p.m. We had moved out to the grocery store parking lot around the corner and had some people stop by to take a look - Tom, Dan, a woman and two little girls. No more impact spots came around the limb. We were hoping the big one, G, would appear, but we're losing Jupiter in the hazy murk now. Packed it in at 11:40 p.m.

July 19-20, 1994 (Tue. night) Bellevue, PA 

(4.5-inch) Jupiter has two very big, very dark spots now in the impact zone. Amazingly large and dark- very prominent- most prominent features on Jupiter right now. We're still in twilight now. Clear but very hazy. Clarity only about 4/5.

Jupiter looks like a coconut with the two round dark spots on one end. Or maybe a bowling ball! The spots are definitely darker than the NEB or any other feature. The spot on the E side has an outer ring that's fainter than the inner area. The spots were so dark we could see them in Paul's little 60mm refractor with my 9mm eyepiece- fantastic! Tonight the spots are as dark as Ganymede's shadow was the other night, without sharply defined edges. Bob, from the astronomy club, is out at the [Freedom, PA] site tonight with some of the other guys (later reported the spots looked like two black eyes on Jupiter this night).

Seeing started out at about 4/5 and improved to 3/5. Jupiter a dark maize color due to the haze.

11:36 p.m. new spot coming around the E limb. First of the two dark spots going round the W limb.

10:55 p.m. packing it in- seeing worsened. The new spot is fainter and more diffuse than the other two big spots.

July 23-24, 1994 (Sat. night) Bellevue, PA

(4.5-inch) The last few nights all clouded up at sunset. Thought tonight might be different. Got a view of a big spot coming around Jupiter's limb- seeing very poor. Looks like there's a sprinkling of smaller spots along the zone, and they appear to be attenuating, forming more into a band. Started viewing at 9:10 p.m. The main spot is quite elongated, about the size of the Red Spot, but flatter and very dark- darker than any other feature on Jupiter. A large amount of activity on the S edge of the NEB, including one really big bump or festoon preceding the large impact spot in longitude. I'm continuing my series of sketches that I've done since the impacts started. A pronounced white spot visible on the STB. A little in front of the second spot visible (which is also elongated). May be my imagination, but there appears to be a dark band forming at the opposite latitude in the N hemisphere.

Clouds have pretty much stayed out of the way tonight.

Now it looks like there are actually two white spots close together on the STB.

Io is in shadow. Watched it reappear at 2203. Seeing improved for a while- best it's been since the comet impacts began. The darkest spot has a lighter center, with perhaps a detached portion more to the S. May even be a third white spot on the STB- smaller than the other two and following them around. The large impact spot now coming up on the meridian. Obviously more elongated now than three nights ago when these same three spots were visible. Almost cigar-shaped now, although a bit fatter. This is the same view as 7/18 (see sketches).

2155- Another spot came round the limb. Three teenage guys came by and took a quick look. I'm happy to report that Jupiter is rad.

Seems like the STB section just north of the darkest spot is correspondingly darker than the rest of the STB. Large festoon on the NEB makes it easy to identify this face of Jupiter. The darkest impact spot is slightly following (E) in longitude by 10 or 20 degrees.

Io reappearance from shadow was remarkably quick. It came up to full brightness in about a minute.

The Red Spot hasn't transited during any of my viewing times, so I don't know what it looks like now. I don't think I've seen it at all this viewing season.

2213- Another big impact spot "coming round the bend."

2251- Jupiter on the edge of a cloud bank. In and out of the clouds. Seeing deteriorated to about a 4 or 5. Call it 4.5. Two major spots still visible.

2315- Paul still not home from his temp job. Not much left to see with the clouds and altitude becoming a factor. Jupiter is only up about 20 degrees now. The second spot is a little larger than the first and not quite as elongated. Hard to see now. These spots are further apart than the ones on Tuesday night. The new one coming around the limb is massive.

2320- Seeing is 5. Jupiter rippling madly like it's in boiling water.

2338- Seeing improved a bit. Paul got home and got a halfway decent view. Another new spot is coming around the limb. Seeing worsened and we went in

July 25-26, 1994 (Mon. night) Bellevue, PA

(4.5-inch) Out looking at Jupiter again. Poor seeing=4. Started at 2225. At 2243 another large spot coming around the limb.

July 28-29, 1994 (Thu. night) Bellevue, PA

(4.5-inch) 2056  Continuing the "Jupiter Watch." Nice big spot approaching the meridian. Dim because the sky is very murky. Can make out the NEB, SEB, and the impact zone as a dark patch. Clarity=4.

2130  Still very dim through clouds. Gave up at 2139.

July 30-31, 1994 (Sat. night) Bellevue, PA

(4.5-inch) Seeing=2.5 to 3. Large sport coming around the limb followed by another fainter one, preceded by some straggly dark features in the impact belt. STB has darker segment past the meridian. A couple of bumps on the S side of the NEB.

Clouds came over Jupiter so I took a look at Albireo.

Jupiter came out again and I recognized the double-lobed spot as being the one from previous observations (7/23-24). Elongated more now, but not much. Hasn't changed much over the last week.

Seeing is very variable. NTB has gotten much less distinct lately- seems almost contiguous with the NEB now. Bright zone between the two doesn't seem to be as definite.

This major spot is the most interesting. Looks almost like there's a bright moon in front of it- a white "eye" in the middle, shifted up a little toward the S edge of the spot.

Packed it in at 2250.

July 31-Aug 1, 1994 (Sun. night) Bellevue, PA

(4.5-inch) Some of the larger spots visible. Possibly same view as on the night of 7/18-19. Spots are the darkest features on the planet, much more elongated now. Two major dark complexes visible now. Seeing=3 but very variable. Clarity=4. Viewed until 2207. Excellent view tonight!

Aug. 5-6, 1994 (Fri. night), Freedom, PA

(4.5-inch) A large elongated spot was just touching the W limb when I viewed it. Looked similar to the one I sketched on 8/1. Two moons were aligned N and S on the eastern side, presenting a nice overall effect.

Aug. 14-15, 1994 (Sun. night), Freedom, PA 

(4.5-inch) Spots from comet impact still surprisingly dark; elongated but not forming a complete belt. Europa reappearing shortly.

Sep. 5-6, 1994 (Mon. night), Bellevue, PA

(4.5-inch) Quite a bit of dark spotting at the impact zone, still darker than the SEB. No individual spots visible due to smearing. Surprising how dark the impact site is, and the south polar cap also appears quite dark. Seeing very poor- scope has only been out in the air about 10 minutes, but Jupiter is setting lower. Looks like impact zone is a dark mottled belt, surprisingly dark- about same darkness as the NEB.

Composite of Hubble images showing the comet fragments approaching Jupiter. Stereogram created with Owl3D and Paint.net.

NASA, ESA, H. Weaver and E. Smith (STScI) and J. Trauger and R. Evans (NASA's Jet Propulsion Laboratory)

Amateur astronomy humor

Amateur astronomy: it's not all just fun and games. Sometimes we get stupid. I've posted my original amateur astronomy cartoons here. 

Eyepiece cheat codes: Averted vision

Getting the most from your visual observations involves using a few "tricks of the trade," or cheat codes, as gamers might view them, at the eyepiece. I've picked up several over the 30 or so years I've been visually observing, but the most useful and well-known is the use of averted vision.

Averted Vision

One of the first things you hear about when you start observing is "averted vision," looking slightly away from a dim object to see it better. This uses the rods in your eyes to best effect. I would posit that there are several variations of averted vision (AV), what I call close, medium, and extreme. 

In all three variations, which are really just part of a continuum, you are usually not keeping your eye fixed on one spot, but moving it around slightly to find the sweet spot where you can get a fleeting glimpse every now and then of the object or detail. When logging my observations, I'll sometimes refer to the percentage of time I can actually get glimpses of an object to indicate how dim it was. For example, I may see a brighter or larger galaxy 50% of the time, but a tiny dim one only 10%, sometimes even less. 

Consciously trying to determine this number is a fun way of determining how difficult the observation is for you and how it compares to others. You might be surprised how infrequently you are getting glimpses of an object, despite being absolutely certain you're seeing it. This gives more meaning to terms such as "bright," "difficult," or "extremely dim."

Medium AV

Medium-sized objects such as some galaxies, globular clusters, more compact open star clusters, and some double stars respond well to what I would call medium averted vision. This is the most common variation I use as an observing "generalist." In medium AV, with the object centered, you are usually looking about 1/5 to 1/3 of the way from the object to the edge of the field of view (FOV) to see it best. Depending on your own eyesight and equipment, you may find looking in one particular location consistently yields the best results, but more often it just pops out randomly as you move your eye around the periphery of the object. Be aware that your eye has a blind spot, but by moving your eye around, you will likely not notice it.

Above: Image of M22 by StudentAstronomyGroupUoC, CC BY 4.0, via Wikimedia Commons. Edited to simulate eyepiece view with annotations.

A good example of using medium AV is observing the line-of-sight "double" star 55 Cygni. This one has a 4.9 magnitude primary component and an 11.1 magnitude secondary, with a separation of 22.7 arc seconds at position angle 174. Close doubles with a big difference in magnitudes are a fun challenge. At first glance it's not easy to spot the secondary in my 6-inch reflector from my light-polluted Redneck Observatory. But it's not particularly hard if I use medium averted vision at around 150x. It pops into view if I look about 1/5 of the way to the edge of the FOV with the pair centered, but blinks out when I look directly at the primary. Give it a try or a similar one that is a good fit for your telescope.

Close AV

Close averted vision is useful for observations of tiny objects like Saturn's dimmer moons or detail in the core of a galaxy. When viewing Saturn, I notice that the brighter moons require a bit more distance (medium AV) and the dimmer moons often require I look right next to them (close AV), sometimes seeing them if I look directly at Saturn itself, which also helps keep my orientation fixed. I recommend a free app called Moons of Jupiter and Saturn. There is also a paid app for iOS called SaturnsMoons, although I have no experience with that. Apps like Sky Safari also will show the positions of planet moons. Just zoom in on the chart.

Above: Image of Saturn and its moons by Kevin M. Gill, CC BY 2.0, via Wikimedia Commons. Edited to simulate eyepiece view with annotations.

Close AV is also useful for seeing more detail in larger or brighter galaxies. For example, the other night I was observing NGC 5907, a striking 10th magnitude edge-on galaxy in Draco about 11 x 2 arcminutes in size. I can pretty easily see the ghostly slash-shaped galaxy in medium powers in my 10-inch in a Bortle 4.5 sky, with a hint that the center is slightly brighter. This core area pops out a little better if I use close AV, looking right next to it. 

Above: Image of NGC 5907 by By Kết Nối, Việt Nam, Public Domain, via Flickr. Edited to simulate eyepiece view with annotations.

M82 in Ursa Major is another good galaxy to practice AV on. It will likely yield more detail in close AV. You might even be able to pull out a brighter core or some mottling in dimmer and smaller galaxies with this technique.

Left: Image of M82 by David Warrington from England, CC BY 2.0, via Wikimedia Commons. Edited to simulate eyepiece view with annotations.

Extreme AV

I call it extreme, because in this case you're really trying not to look directly at anything in the eyepiece. Instead you're trying to take in the whole FOV at once rather than focusing on a particular spot. Just think of relaxing your vision and letting the entire view wash into your brain. Your eye is moving around trying to soak up every photon to make some sense out of the scene. It's almost like you're trying to pull your eye back into your head a bit to get the widest field possible to register.

This is useful for extended objects or dimmer objects such as a dim but rich star cluster. A good example is NGC 6645 in Sagittarius. It's a beautiful and interesting cluster for a darker sky, but often ignored because of all the other flashy stuff nearby (M8, M20, M17, etc.). 

Left: Image of NGC 6645 by Mike Durkin from Forest Hills, NY, derivative work: Winiar, CC BY-SA 2.0, via Wikimedia Commons. Edited to simulate eyepiece view with annotations.

Extreme AV is pretty much essential for most nebulae other than planetaries. Coupled with a nebula filter (I use an NPB narrowband filter), this can often yield great results where you can see the shape of the brighter portions of nebulae. 

Left: Image of NGC 2174, the "Monkey Head Nebula" by Nigel Hoult, CC BY 2.0, via Flickr. Edited to simulate eyepiece view with annotations.

Sometimes even a small object that's extremely faint can benefit from extreme AV when you're trying to get any hint at all that something is slightly brighter than the surrounding sky. You just have to experiment, as everyone's situation can be different.

Make a table for a tabletop telescope

If you or your child are just getting started in visual astronomy, I can recommend a tabletop telescope of 4.5" to 6", such as the Sky-Watcher Heritage 150 Tabletop Dobsonian. This telescope (reviewed here) has good quality optics, is compact and portable, and very comfortable to observe with. But it's missing a table.

Why make one

You would think that a tabletop telescope is designed so that you can use whatever table you may have handy: a picnic table, a foldup table, a stool, or just a small end table. That may have been the intention, or maybe just the marketing, but when you’re looking at objects in powers of 30x, 50x, 100x, or 200x, you need something very stable so the view isn’t all shaky.

Picnic table? Nope. When you sit on it, you’re going to make it shake. It is also unlikely to be in the best spot for observing and you can’t move around the telescope.

Foldup table? Nope. Really shaky unless you get one that’s built like a tank, and that defeats the portability factor that is often the main advantage of the table.

Stool? Maybe, if it’s solid and the right height. You could cut the legs to size, but will it be large enough to fit the telescope? It may also be bulky if you have to transport your telescope to a remote location.

End table? Three legs will be better for leveling on uneven ground, and you have the same problems listed above as a stool.

Well, that’s a bummer. You thought a tabletop scope would be just the thing for portability. Now you’ve got one and no good table to put it on.

Fear not. Some people use a milk crate, build a simple tripod, or buy something at Ikea like this stool.

Or...and you knew this was coming...you could have fun and build your own observing table. It’s not hard (if I can do it!), and you can customize it for your own observing needs. Continue reading to achieve tabletop nirvana.

How to do it

The table I built for my Sky-Watcher Virtuoso GTi 150P, a 6-inch collapsible tabletop telescope, is simply a round piece of 1/2” plywood with holes drilled in it to hold eyepieces and three legs made out of cheap 2x2 lumber that can be unscrewed so the table top lies flat for transport. The legs are cut with about a 10 degree angle so they provide a little more stability than straight legs, although you could make them straight to simplify things even further. Each leg has a 1/4-20 hanger bolt screwed into one end which allows it to be screwed into a t-nut fastened in the tabletop. Easy-peasy, and it takes up very little room in the car if you unscrew the legs.

I started by making a circular cutting jig for my jigsaw since I don’t have a router, the preferable way to cut circles. If you don’t even have a jigsaw, you can buy an edge-glued round piece of wood (I recommend 18”), although some reviewers have said they sometimes come unglued or split.

The base of my scope is about 14" in diameter. I decided on an 18” diameter circle so I would have a couple inches around the outside to drill holes for eyepieces and to put my cell phones and filters down. I used 1/2” plywood to keep the table as light as possible. With the scope feet directly over the table legs, it only needs to be stiff enough to keep the legs in place without bearing the weight of the scope. [9/22/2024 Update: Because the go-to on my scope is unreliable, I added an azimuth circle to the base of the telescope. The circle sticks out about 3/4" all around, so I built a new table, this time using 3/4" plywood and making it 20" in diameter. I like it better, and I recommend you go with those dimensions. It's a little heavier, but not by much. It also makes a great camping side table when you're not observing.]

My mistake in cutting the plywood circle with the jig and jigsaw was I trusted in a YouTube video that showed how easy and neat it was to use a cutting jig. In reality, the saw blade wants to either go inside or outside the circle unless you watch very closely. I had the saw run outside the circle on one part and inside on another, breaking two blades. 

Were I to do it again, I would only cut a couple inches at a time and check to make sure it was still cutting on the circle. Or I would just draw the circle on the wood and cut it freehand with the jigsaw. I’ve done that before and it comes out fine. I just might not do it if I need the precision necessary for an altitude bearing, for example, but for this purpose it’s fine.

Once I had a pseudo-circle cut out, I marked where the three feet of the telescope would go. You can simply place the telescope base in the center and mark where the legs go. To be more precise, you can divide the circle into three sections by drawing a diameter (1), then drawing lines (2 and 3) the length of the radius (9” in this case) from the outer point of the first line (1) to where it intersects the outer edge of the circle on both sides, then drawing the other two lines (4 and 5), as in the diagram.

To make sure I had the scope centered, I partially screwed a wood screw into the top of the circle in the center. Some of these tabletop telescopes have a threaded hole in the center of the base. I just placed that over the screw and marked where the three feet would go.

If you don’t have the center of the circle marked, you can find it by drawing a chord at any point on the circle (line 1) and drawing a second line (line 2) from the midpoint of that line using a carpenter's square or other object that will give you a 90 degree angle. Repeat in a different location (lines 3 and 4) and where lines 2 and 4 cross is the center.

To screw in the table legs you can get angled leg brackets, but I don't like the inserts they use and I wanted a nice flush surface so I could slide the tabletop in between stuff in the car easily. So I put three 1/4-20 t-nuts where the feet would sit. These need to go in from the top of the table so that when you screw in the legs from the bottom, they will be pulled in tighter, rather than pulled out of the wood. Make sure the t-nut barrel is long enough to grab at least a few threads of the hanger bolts in the legs but doesn’t stick out the bottom if it is inset about 1/8” (see below). You want the legs to contact the table when screwed in tightly to give a nice stable grip.

I used a 3/4” Forstner bit in my cordless drill to first inset the holes about 1/8” in the top of the table where the t-nuts would go. I didn’t want to go too deep in 1/2” plywood, but if you use thicker plywood you can go deeper. You just want them inset to give some edge for the telescope feet to catch on so it won’t slide easily.

Then I drilled a hole in the center of each inset with a 9/32” regular drill bit. If you don’t have that size, use a bit that’s just slightly larger than 1/4” because the threaded barrel of the t-nut will be a little larger than 1/4”. Hammer in the t-nuts from the top side until they sit below the surface of the table.

I wanted some eyepiece holders, so I marked off three holes along the outer edge of the table top in each of the three sectors. Test the fit by placing the telescope on the table and your eyepieces where the holes will be. Make sure the telescope clears the eyepieces through its full rotation of 360 degrees. When satisfied it would, I drilled holes with a 1-1/4" hole saw.  I also added a 2" hole to each sector, even though my telescope doesn't have a 2" focuser. I figured I might want to use the table for stuff while using my 10-inch, and I have a couple of 2" eyepieces. It would also lessen the weight further. [8/28/24 update: I may redo the top without the 2" holes. Twice now I've almost dropped an eyepiece through the 2" hole onto the driveway, thinking it was the 1.25" hole. Oops.]

I sanded both sides and the edge of the table top with a random orbital sander and the holes manually with small pieces of sandpaper and a scrap piece of PVC pipe.

As noted above, you can just make the legs straight at whatever height you prefer if you don't want to take the extra steps to angle the legs, although you will sacrifice a little stability. 2x2 lumber is cheap and you can make several sets if you like. I like to use balusters, which are the vertical pieces in a deck railing, because they tend to be straighter than the 8’ lengths of 2x2. Those can be horribly warped and actually cost more per linear foot at my local store.

To make straight legs, drill a hole in the center of one end, as straight as possible, a little deeper than the length of the wood screw part of a 2" 1/4-20 hanger bolt. Use a drill bit a little smaller than 1/4” so the screw will have plenty of wood to bite and hold tight. Screw it in by threading two 1/4-20 nuts and tightening the upper nut with a 7/16” wrench until you get the length sticking out that will work with your t-nuts, roughly 3/8 to 1/2 inch. You can unscrew it if you overdid it by putting the wrench on the lower nut and twisting counterclockwise.

To make angled legs, which will add stability to the whole setup, I found an easy way is to take a typical mitre box and lay the uncut piece of 2x2 diagonally so that one side is up against the top of the box as seen from above and the other against the bottom. Clamp it down. If you cut along the 90 degree slot in the middle you’ll get about a 10 degree angled end. For the first and the last cut, you’ll have to estimate and just clamp the wood down. 

Cut three legs so the ends are all at parallel 10 degree angles, i.e., the piece looks like a parallelogram from the side. I cut my legs 10-5/8” long, which, with the 1/2” plywood top and the 10 degree angle, gives me a table top height of about 11 inches, just right for my adjustable observing chair at the height I like to sit.

Now put each leg in a vise if you have one, so that the angled face is horizontal. Then just drill your hole in the center vertically. Screw in the hanger bolts as described above using two 1/4-20 nuts and a 7/16” wrench. When you screw the leg into the table, the other end will trace a small circle, but it will work. 

I adjusted the depth of each screw so that the leg would screw in tight to a particular t-nut where it points outward, and just marked each pair with painter’s tape on the table and leg so I could easily match the leg to the hole. Later I’ll use a Sharpie once I’m sure everything fits well. You can always readjust the screw depths as things wear.

If you use outdoor plywood, you don’t really need to paint it because you're not going to leave it out in the rain, but I got a spray can of spar varnish and gave the table a few coats. A cheaper option would be paint. I recommend white so it's easy to see at night and you can see where to put your eyepieces. If you use treated wood for the legs, they don't need to be painted but you can paint them. If a few drops of water soak in, they are dry enough to be painted, otherwise wait a week or two for the chemical treatment to dry completely before painting. Use a tack cloth after sanding everything to remove any sawdust and grit.

Lastly, I put a piece of white duct tape on the table top at each point where the legs go to assist setting the scope on the table so the feet are directly over the t-nuts.

That’s it. If you mess up, all the parts are cheap and you can redo any or all of it. You can also make legs of different lengths if needed.

My Sky-Watcher Virtuoso GTi 150P tabletop telescope (same as the recommended scope at the beginning of this article but with an electronic mount) on the table I built for it. It looks happy, doesn't it?

[9/22/2024 Update]: Here's the new table I built to accomodate the addition of an azimuth circle to replace the go-to. I made all the eyepiece holes 1.25" and painted it white. 20" diameter using 3/4" plywood. The scope is even happier now!

Materials:

Piece of Plywood 1/2" to 3/4" thick big enough to cut a suitable sized circle (18" is usually good) or precut wood circle

One or two 2x2" stair balusters

Three 1/4-20 t-nuts, short enough not to stick out from the plywood, depending on the thickness

Three 2" x 1/4-20 hanger bolts

Two 1/4-20 hex nuts

Paint or varnish

Tools:

Mitre box and hand saw

Power drill with 9/32" (for t-nut holes),  1/8" or 3/16" bit (for hanger bolt holes), 3/4" Forstner bit, 1-1/4" hole saw

Jigsaw (unless you are buying a precut wood circle)

7/16" wrench

Sandpaper, sander (or sanding block), and dust mask (I like this one for sanding, painting, and gluing)

Tack cloth

Two bar clamps or C clamps large enough to clamp a 2x2 in your mitre box and to the workbench surface (which could be a piece of plywood laid over two saw horses if necessary).

Bench vise

Hammer (a big, short bolt helps to hammer the t-nuts below level so you don't damage the table surface)

Carpenter's Square or L-Square 

Pencil or X-acto knife (makes more precise measuring marks for cutting)

Ophiuchus and Serpens in 3D

 3D Constellation post index and instructions

OPHIUCHUS, The Serpent Bearer, and SERPENS, The Serpent

The pattern we see.

The 3D version. Click for a larger image (for phones and small screens).

PARALLEL VIEW:

With labels:

CROSS VIEW:

With labels:

Data:

Object                                    Magnitude     Dist. (light yrs.)

67 Oph                                   4.0                 1200
θ Oph                                     3.3                   440
κ Ser                                       4.1                   380
ζ Oph                                      2.6                   370
δ Ser                                       4.1                   228
λ Oph                                      3.9                   173
Yed Prior (δ Oph)                    2.7                   171
μ Ser                                       3.5                   170
β Ser                                       3.7                   155
ν Oph                                      3.3                   151
Yed Posterior (ε Oph)              3.2                   106
ξ Ser                                        3.5                   105
γ Oph                                       3.8                   103
κ Oph                                       3.2                     92
Sabik (η Oph)                          2.4                     88
72 Oph                                     3.7                     87
Cebalrai (β Oph)                      2.8                     82
Unukalhai (ɑ Ser)                     2.6                     74
ε Ser                                         3.7                     70
η Ser                                         3.2                     61
Rasalhague (ɑ Oph)                 2.1                     49
γ Ser                                         3.8                     37
70 Oph                                      4.2                     17

Sagittarius in 3D

3D Constellation post index and instructions

SAGITTARIUS, The Archer

The pattern we see.

The 3D version. Click for a larger image (for phones and small screens).

PARALLEL VIEW:

With labels:

CROSS VIEW:

With labels:

Data:

Object                Magnitude     Dist. (light yrs.)

μ                             3.8                  1000
π                             2.9                    510
ξ²                            3.5                    370
δ                             2.7                    350
φ                             3.2                    239

Nunki (σ)                2.1                    228

η                             3.1                    146

Kaus Australis (ε)   1.8                    143

ο                             3.8                    142

τ                              3.3                    122

γ                              3.6                      97

Ascella (ζ)               2.6                      88

λ                              2.8                      78

Scorpius in 3D

 3D Constellation post index and instructions

SCORPIUS, The Scorpion

The pattern we see.

The 3D version. Click for a larger image (for phones and small screens).

PARALLEL VIEW:

With labels:

CROSS VIEW:

With labels:

Data:

Object                Magnitude     Dist. (light yrs.)

ι                               3.0            1900

Alniyat (σ)               2.9              700

π                             2.9              590

υ                              2.7             580

Shaula (λ)               1.6              570

Antares (α)             1.1               550

μ¹                            3.0              500

Dschubba (δ)          2.3              490

κ                              2.4              480

τ                              2.8              470

μ²                            3.6              470

ρ                             3.9              470

ω¹                           4.0              470

ν                             4.1              470

Graffias (β)             2.6              400

θ                             1.9              300

ω²                           4.3              291

ζ²                            3.6              132

HR6630                  3.2              126

η                             3.3                74

ε                              2.3               64