Eyepiece cheat codes: Observing Jupiter and Saturn

Jupiter and Saturn, and sometimes Mars, are the planets that will yield the most detail to backyard astronomers. Not only are they bright, but they are large enough for even the smallest telescopes to see them as balls with shading and details. And of course, there are Saturn's rings! Mars generally needs to be at a favorable opposition to see surface details well. 

Jupiter has its four Galilean moons and Saturn has between two and seven moons accessible to typical backyard telescopes. The moons of Mars are generally too close to the planet to spot except when Mars is close to opposition and you have a steady atmosphere with good equipment. 

A night with a steady atmosphere—good "seeing"—will allow you to have much better views than a night where the seeing is soft, turbulent, or mushy. This is probably the single most important factor in how sharp the view will be. Try to observe when the planet is highest above the horizon. Viewing through a lot of "soup" at low altitude will also make for disappointing views, even on a night of good seeing. Heat rising from rooftops, asphalt, and concrete also wreaks havoc with seeing.

If you are observing with a Newtonian reflector, the image will be rotated 180 degrees (generally south is up). In a refractor or Cassegrain with a mirror diagonal the view will be mirror reversed (north up, but mirror reversed). See this explanation of directions in the telescope.

Jupiter

A complete novice can expect to see two main cloud bands on Jupiter and its four Galilean moons. With more practice, not only the South and North Equatorial Belts (SEB and NEB), but temperate belts in each hemisphere may also sometimes come into view, as well as darkened polar areas. 

In addition, features such as festoons, barges, and other spots that represent the turbulent swirls and storms in Jupiter's upper atmosphere become visible with practice and good seeing. 

The Great Red Spot is also sometimes visible when it is rotated towards us, although in recent years it has become rather wimpy in its size and color compared to previous decades. Look at some Jupiter images to see the types of features to look for.

Above: The moon Io and its shadow visible against the cloud tops of Jupiter. Image by Steve Hill, CC by 2.0, via Flickr

Below: The four Galilean moons are aligned on one side of Jupiter in this image by Ivana Peranic, CC by 2.0, via Jeremy Keith/Flickr.

Jupiter's Galilean moons—those that Galileo was able to see in his tiny refractor: Ganymede, Callisto, Io, and Europa—are the only moons, out of the currently identified 95 Jovian moons, that are visible to amateur observers, and can even be spotted in binoculars. Because their orbits are well known, predictions as to transits across the face of the planet and the corresponding shadows, disappearances and reappearances behind the planet or its shadow, and even occasional occultations and eclipses of one moon by another are available. You can plan an observing session to add these to the interesting details you can see in your telescope. 

The easiest are the shadow transits, which show up as dark black dots on the face of Jupiter. The moons themselves are more difficult to see when they pass in front of the planet, and much depends on the level of contrast with the cloud deck below them. I have seen them many times in my 4.5-inch reflector, but have been unable to see them just as many times. The best time to see them is when they are right on Jupiter's limb or just off the limb. Then they show up as tiny disks. Compare the size to the apparent disks of the other moons against the dark sky away from the planet and you'll see how much smaller they actually are.

Averted vision is unnecessary for Jupiter and its moons. In fact, you'll see the most by looking directly at any feature. Bore your vision into the feature, almost as if you are looking through it, to get the most detail to register. Relax your eye and just let the detail burn into your retina. Really stare into it!

Sketching the cloud belts and swirls that you see can really help you focus on the details. You don't always have to sketch what you see, but try it a few times and you'll be surprised at the amount of detail that is actually visible. You may not see it all at the same time, the same with deep sky observing, but you will build up a complete picture with fragmented glimpses. This teaches you to place a detail within the greater context and you'll also see how the features slowly traverse the globe of the planet in an (astronomical) westward direction as Jupiter completes a full rotation in less than 10 hours—the fastest rotating planet in the solar system. For more on observing Jupiter, I recommend How to Observe Jupiter Through a Telescope by BBC Sky At Night Magazine.

Saturn

Of all the sights a beginner can see in the telescope, Saturn is probably the most striking. When I show it to people at public outreach events, most people are thrilled and some even question whether what they are seeing is real.

While Saturn doesn't show nearly the same amount of detail as Jupiter, and it's remarkably smaller in the eyepiece, the sheer beauty and uniqueness of the planet will keep you coming back whenever you can. Something about the rings is precious. Really.

Above: Saturn by John Spade, CC by 2.0, via Flickr

The rings change their tilt over the years, and with Saturn now in the evening sky, the rings are nearly edge-on. This makes it difficult to see the major feature in the rings, the Cassini Division. This thin dark lane is sometimes visible on nights of excellent seeing with the rings tilted towards or away from us at a significant angle. Look for it at the outward ends of the rings, where they become more visible because they begin to curve the other direction and the gap is seen at its fullest width. This gap that appears so tiny to us is actually almost 3,000 miles wide! The next ring plane crossing is in March 2025, when the rings, being an average of only about 30 feet thick, become invisible in our telescopes. The Cassini Division may have to wait.

Above: Saturn's varying ring tilt, image by NASA and the Hubble Heritage Team (STScI/AURA), CC by 2.0, via Flickr. Cassini Division label added.

If you look carefully you will usually see a slightly darker band around Saturn and perhaps some subtle shading elsewhere, especially at the poles. Saturn is much smoother than Jupiter, but it does have very infrequent storms visible in our telescopes, such as the great white spot of 2011.

For Saturn's moons, you'll have to use averted vision for all except the largest, Titan, and Iapetus when it is furthest out on the western side of Saturn and its bright icy side is turned toward Earth. Iapetus strays pretty far from Saturn in its wide orbit and can easily be confused with background stars. The inner moons are dimmer, but with good seeing, patience, and a telescope of around 4 inches or more, you should be able to pick out Rhea, Tethys, Dione, and possibly Enceladus. Mimas is quite difficult, Hyperion requires a larger telescope of 10 inches or so, and you won't have a chance at any of the other moons of Saturn, which currently number 146 and counting [Mar. 2025 update: now 274 and counting!].

Jupiter and Saturn observing resources:

Help! I Can't See Detail on the Planets! (excellent article on the pitfalls of observing the planets)

Cloudy Nights Planet Gallery (more recent images at top)

Cloudy Nights Major and Minor Planetary Imaging thread (latest images)

Online interactive observing tool for Jupiter's Moons (Sky & Telescope)

Great Red Spot transit times (Sky & Telescope) (when it crosses the planet's central meridian)

Online interactive observing tool for Saturn's Moons (Sky & Telescope)

Apps:

Moons of Jupiter and Saturn (Android)

JupitersMoons (iOS)

SaturnsMoons (iOS)

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)

Can we pronounce “Uranus” better?

NASA/ESA and Erich Karkoschka, University of Arizona

Years ago everyone pronounced the seventh planet from the Sun, “Your-ANUS,” emphasis on the “anus.” Okay, it was fun for a while, but then the jokes got really old, so scientists changed it to “URINE-us.” Really? That’s the best they could do- just go from being the “butt” of jokes to the flip side?

I have a suggestion that no one will heed, but I’ll throw it out there anyway. “Oo-RAHN-us, with the emphasis on the middle syllable. This is closer to the ancient Greek pronunciation of roughly “Oo-rahn-OS,” with the emphasis on the last syllable, but it preserves the emphasis that we got used to, while removing the association with excretory bodily functions. He’s an ancient Greek god, for crying out loud. 

Let’s show some respect and bring it at least closer to the original pronunciation. This will get rid of two ugly pronunciations and quell some of the giggling.

I’m going to start calling it that, and I don’t care what people think. Will you join me to promote “Oo-RAHN-us” and make public star parties and science classes a little less awkward (notwithstanding we are a bunch of sometimes socially awkward astro-geeks to begin with)?