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)

How much more will I see with a bigger telescope?

Many visual observers start small. Maybe a 4, 5, or 6 inch reflector, maybe a 60mm or 80mm refractor. Often the more inexpensive telescopes are smaller and they give a person a chance to try out the hobby to see if maybe somewhere down the line a bigger monetary and size investment would be worth it. Parents have also been known to get a small scope for junior, thinking maybe Dad or Mom might like one themselves, too. A decent first scope can make a nice portable second scope even if you move up to a larger one.

Regardless of type (reflector, refractor, catadioptric), aperture is aperture, and the bigger you have, generally the more you’ll see. Why? Because, all else being equal (quality and telescope design being major points), a larger mirror or lens will capture more light, thereby making dimmer objects look brighter, showing more detail, and allowing for the use of higher powers in good seeing, and therefore a larger image scale before the view gets too dim or blurry.

Downsides of a larger telescope are often cost, size, and weight. I always dreamed of having a big truss-tube dobsonian- say with a 20 or 24 inch mirror. Views through those can be spectacular, especiallly in a dark sky. But reality in terms of money, storage room, and ability to tote it around to dark sites or fit it in the car without buying a bigger car precluded ever getting one.

Still, after about 13 years of using my 4.5” reflector, I had a little more discretionary money and wanted the views I could get with a bigger telescope. So 20 years ago, I bought a Hardin 10” Deep Space Hunter dobsonian telescope for a whopping $490 shipped. It came with a Guan Sheng Optics (GSO - Taiwan) 32mm (39x) two-inch barrel eyepiece and a 9mm 1.25” eyepiece (139x), neither of which were as good quality as the .965” aftermarket eyepieces I had for the 4.5”. Most telescopes come with 1.25” focusers, but many now are 2” with an insert to allow use of 1.25” eyepieces. That is the case with my 10”.

 My Tasco 11TR 4.5" reflector, repainted from the original red and remounted on a homemade dobsonian base.

My Hardin Deep Space Hunter 10" dobsonian with added swivel table for laptop (now using a Chromebook) and homemade dew heaters.

My upgrade was not just going from a 4.5” mirror to a 10” mirror, with the accompanying light gathering ability, but also to the larger barrel 1.25” and 2” eyepieces. That’s a pretty big jump all told, and I’d like to share with you some of my first observations with the 10” to give you an idea of what more aperture will give you, and what it might take away, if you are contemplating a larger telescope.

Aside from a few sessions on our apartment balcony, my first observing trips with the 10” were out to some club observing sites between 30 and 50 miles from downtown Washington, DC, and back in 2004 they were fairly dark- maybe Bortle 3 and 4. Nowadays they are closer to Bortle 5 and 6, but still a good option to partially escape the ever expanding light pollution. One of the first things I noticed right away just from the apartment balcony was how much more color I could see in stars in the larger telescope.

Here are a few verbatim notes I took at the eyepiece on the first couple of nights that shed some light on the difference in views from the smaller to larger telescope. The sky was partly to mostly cloudy with poor seeing. I’ve added explanatory notes in brackets.

Observing notes:

My first view is somewhere in southern Gemini or northern Orion in the 32 mm eyepiece, and my first thought was, "My God, it's full of stars!" Wow, this is going to be a big difference from the 4.5".

My first object is M35 and NGC 2158 [the former a very large, bright open cluster, the latter a smaller dense one nearby]. Very nice in 39x, though the eyepiece leaves a lot of fuzziness around everywhere but the center, which is to be expected in a fast scope (f/5.0) like this [the 4.5” is f/7.9]. A nice wide view. I can't say I'm particularly impressed with the optics of this scope so far. Maybe it's the eyepieces. For example, with NGC 2158 I'm getting quite a bit of resolution on it- it's more half-moon or L-shaped rather than round, but I'm not getting good pinpoints on the stars. Quite a let-down really after seeing everything so sharp in the 4.5”, even on a bad night.

M37 is very nice with lots of stars in 139x. Just not dazzling, though. Little spots instead of little points. Kind of disappointing.

But looking at M51 [the Whirlpool Galaxy in Ursa Major, a bright, face-on spiral with a smaller galaxy next to it connected by a bridge of material]- that's more like it. That's what I got this thing for- deep sky. Real nice view. Definite spiral structure there, particularly one big bright arm that goes out from the main galaxy toward the smaller one, and then a dark lane inside of that, very well-defined in averted vision. Due east of the nucleus at the base of that arm is quite a bright area. On the SW side another bright knot. It's more difficult to see structure in the western side. But I can see structure in the smaller galaxy. The foreground star in the SW quadrant of the main galaxy is very plainly stellar in this scope. I can't quite make out the bridge between the galaxies.

I'll try M81 and M82 [showpiece galaxies in Ursa Major, one somewhat tilted from face on-M81, and the other an edge-on starburst galaxy with more readily visible detail]. M82 in 139x also very nice. What's peculiar is that it's similar to what I see in the 4.5", but a whole lot easier- much brighter. I'm seeing the same features, but they're much more distinct and I can tell the difference between a fuzzy spot and a star, and can see more detail in the bright sections, too. This scope will be nice for galaxies. I hardly recognize M81. Seems like the core is more prominent than in the 4.5". The galaxy shape is not so much an oval in this scope as a glow that diffuses out more slowly, and the extensions out to the north and south are more elongated. The fuzziness extends out further. No hint at all of any structure in there. Almost looks like an elliptical. A really nice view in 39x of the two galaxies- they fit easily in the 2" 39x eyepiece. M81 is just huge. I'm getting to like this scope a little bit more.

M33 [the Pinwheel Galaxy in Triangulum. This is visually a very large galaxy that can be seen easily with binoculars and may be glimpsed with the unaided eye in a reasonably dark sky.] In 39x it is a smooth fuzzball with a brighter core, no real nucleus to it. Couple of stars within it. In 139x there are two stars just NNE of the nucleus, and the nucleus itself isn't stellar. The rest fades out a bit. I was sweeping around the area, and thought I came up with another galaxy, but it's actually the nebula in M33, NGC 604! Looks like what a 10th mag galaxy looks like in my 4.5. It's slightly N of due west of about an 11th (?) mag star. Just a fuzzy patch, brightens a little bit toward the center. Rough edges, not cleanly round. Can see it now in 39x but it's better in higher power. 

As you can see in the above examples, a larger aperture generally gives better views. However, there are situations where I prefer the 4.5”, for example on planets and double stars, mainly because where I am we rarely get really good steady seeing conditions, so most of the time I have to put an aperture mask on the 10” to make it act like a smaller scope to improve the sharpness of bright objects.

Eyepieces also make a huge difference in terms of sharpness, brightness, viewing comfort, apparent field of view (the viewing angle, i.e., like looking down a narrow tube versus wide open “floating in space” views), and true field of view (how much sky in degrees and minutes you can actually see. I have since gotten better eyepieces for the 10” that make the views more pleasing.

Also, it’s easier to move the 4.5”, so if my back or other body parts are acting up, or I’m just feeling lazy, I may choose to bring the smaller scope, or even stick to binoculars. Ditto if space is a premium in the car, although I’ve managed to fit the 10”, all my observing gear, and all my camping gear in some pretty small vehicles. Where there’s a will, there’s a way! At least to some degree.

All this being said, I recommend using your small scope to learn the sky well and learn what objects look like. Push the scope to its limit and see where it excels and where it falls short. See what difference darker skies make (hint: huge). Then consider a larger scope if it fits into your progression in the hobby, lifestyle, and budget. Some people stay with that 3.5” Questar tabletop scope because it fits them well and makes them happy. Bigger isn’t always better when you add the human factor, which is the most important one.