Planetarium Pet Peeves

Last modified: 31 September 2007

For some time, I’ve intended to organize my ludicrous gripes and complaints about the planetarium field (both traditional and fulldome), so I’m in the process of sorting through old emails and various rants, in order to collect them on a single web page. No need to go seeking through my old DOME-L posts to uncover my true vitriol! It’s right here—or if not, it will be soon. Right now, the effort remains very much a work in progress, but I’m not bothering to hide the page while I’m tweaking it. Feel free to email me if you find any typos or other errors.

Let me hasten to add that I don’t intend the comments to malign any of my colleagues in the planetarium field. I deeply admire the energy and commitment with which most planetarians apply themselves to their work, and my fifteen years of experience pale in comparison to the decades that many have invested. As far as I can tell, we all want fundamentally the same thing: to educate, inform, and engage fellow humans with the science of astronomy. Most of us spend our day-to-day existence under darkened domes, trying to figure out how to use the tools (technological, fiscal, and otherwise) at our disposal to do so as effectively as possible. We often disagree on some of the details, however, and the following “pet peeves” evolved out of my expressing opinions about some such disagreements.

N.B. that some of the following language is intentionally inflammatory. It’s on a page entitled “pet peeves,” for pity’s sake.

The topics I have addressed so far:

It should go without saying, but I’ve been burned before, so… The opinions on this page represent my thoughts on various topics and not the views of my employer (let alone my former employer). Don’t get all bent out of shape.

“Planetariums” Not “Planetaria”

I’ll start my pet peeves with a relatively trivial item, namely the use of the snooty “planetaria” in lieu of the more reasonable “planetariums.” You can almost hear the British accent embedded in the former word: “I rather fancy those shows offered by planetaria. Positively brilliant. What say we toddle over to the Rose Center, old chap?” (My apologies to colleagues from across the Pond.)

Also, if you go down the latter route, where do you stop? Would you start to pluralize “museum” as “musea”? And more than one “aquarium” as “aquaria”? Not for me! I happily attend planetariums, museums, and even (occasionally) aquariums. And I’m in good company, too: consult quotes in the Oxford English Dictionary, for a citation of Sagan’s use of the word “planetariums.”

In my not-at-all-humble opinion, planetarians who take pride in their medium pluralize it as any decent English speaker would, with respect to the word’s origins in the 20th Century (well, the 18th Century if you include references to non-domed machinery): “planetariums” pridefully pronounced. On the other hand, apologists for the medium seek greater cachet by latinizing the word for the plural: “planetaria” pompously prevaricated. I have news for you: “planetarium” ain’t Latin. It’s derived from the classical language, sure, but it’s a recent addition.

Other words, of course, should properly use the Latin plural endings. Who would run around saying that scientists collects “datums,” after all? The distinction I typically make is that “datum” and “vacuum” are actual Latin words, so “data” and “vacua” work just fine for me. “Aquarium” and “planetarium” are latinate, constructed from Latin at a later date (“planetarium” even betrays its later coinage with its Greek stem, although “planet” had wiggled into a Latin reference or two), so I favor adding a trailing “s.” Then things get complicated… “Museum” is an actual Latin word, too, but its extensive usage has anglified the plural.

A colleague of mine once said, “I’ll start writing ‘planetaria’ when people start writing ‘musea.’” (In fact, if anyone wants to step forward and attribute this quote, I’d be happy to know who said it—it was ’way back, a decade or so, when I saw it on DOME-L, as I recall.) That simple observation actually sets a very straightforward precedent.

Replacing the Night Sky

I’m surprised how often I hear it suggested that planetariums can somehow provide a replacement for the night sky. The idea usually comes up in terms of providing constellation-deprived moderners an opportunity to “experience” the heavens above. Although it seems reasonable to think that our domes could play a role in advocating protection of the night sky as an important natural resource, imagining the planetarium dome as a replacement for the sky strikes me as absurd. Stated in those terms, most planetarians would probably agree with me, but I nonetheless get the impression that many people’s opinions veer startlingly close to that extreme.

A version of the argument goes like this: given how light pollution has degraded the starry sky, our ersatz starfields must approach perfection in their reproduction of a clear, dark, starry night. Rationalizations can then take you to hyper-real skies filled with tens of thousands of stars or super-bright optical-fiber pinpoints. For example, set at full brightness, the Zeiss Mark IX in the Hayden Planetarium projects an overzealously high-contrast sky, with its brightest stars blazingly bright on the dome, but the sky isn’t realistic: to get a natural-looking sky, I prefer to turn the star brightness down to about 50% and the Milky Way to about 35% (Carter Emmart also recently sat down with Matt Dougherty to tune the Messier objects to appropriate relative brightnesses as well). As Spider-Man’s Uncle Ben told him, “With great power comes great responsibility,” so users of these systems should take care to adjust them properly. With all that work under our belts, the sky looks about as good as any planetarium sky I’ve seen, but not nearly as good as the real thing. I’d be hard pressed to specify the exact problem, but it has to do with the utter richness of the night sky, the faint stars that lay at our beyond the edge of perception yet yield an ineffable subtlety to the actual sky.

Perhaps because I started my planetarium career in a digital planetarium (an original Digstar at at the Houston Museum of Natural Science’s Burke Baker Planetarium) or perhaps because I grew up in Arizona with a relatively pristine view of the sky, I have always seen the planetarium sky as a caricature of the real thing. Some of us who work in large cities can’t expect our audiences to get away from light-polluted skies to see what a dark sky can offer, but other localities may have more options. In either case, I find it difficult to consider the “preservation” of the night sky the main priority of a modern planetarium—at least not planetariums in general. There’s too much else to teach!

Fulldome versus Opto-Mechanical

I forget when I first learned the phrase “false dichotomy,” but I wish it didn’t come in so handy. I don’t understand how we as a profession can get so caught up in our starry-eyed myopia that we can’t realize that, although a planetarium is fantastic for recreating the night sky, it might possibly serve other purposes equally well—if not better. The two (or three or four) competing applications are not mutually exclusive. To borrow a concept from biology, I’d say that the planetarium medium has speciated, and whether fulldome video eventually constitutes a cladistic dead-end or a flourishing new evolutionary niche, only time will tell. Rather than referencing dinosaurs in this analogy, I would prefer to emphasize the more contemporary concept of biodiversity: differing technology does not mean that only the most pixellated will survive, but rather that specialization and variety can thrive. And more like Lamarck than Darwin, we can develop skills to survive and prosper in our changing field…

I would hope that we as a community can begin to see the transformation of technology more like an opportunity than a dilemma. Immersive video is “new” (although I wonder how appropriate the term is as the technology enters its second decade), but so were planetariums in the 1920s. New technology simply expands our palette, and we should use our domes to provide what’s right for our audiences: live star shows, pre-recorded fulldome blockbusters, real-time tours of the Universe, classroom-style interactive pieces, combinations of any or all of these, or ideas that didn’t make it into that list. Why limit ourselves?

I just want to run down a list of complaints that still dog fulldome video in the planetarium community. One still hears that fulldome costs too much, it turns planetariums into playback-only venues, it tries to compete with Hollywood, and it produces a lousy starfield. I’d counter each of those as follows…

Fulldome video is increasingly affordable. Small, single-projector versions of the technology are rapidly becoming available, and although they lack the resolution and (typically) functionality of the larger systems, they nonetheless offer a remarkable alternative for the small- and portable-dome community. Moreover, the cost of these systems continues to drop, and spending a few tens of kilodollars will get you in business.

Fulldome video doesn’t confine a planetarium to pre-recorded “blockbusters.” When I ran planetariums in Phoenix and Albuquerque, live presentation was at the core of my production philosophy. Now, at the Rose Center, my focus is on producing the oft-maligned “blockbusters” and creating content that was impossible to attempt with earlier technologies. But I also get to give star talks and presentations using the Zeiss star projector! Furthermore, I have the opportunity to speak to audiences about the Museum’s Digital Universe—a 3-D model of the Universe that we can display on small flat screens or in the dome, which allows us to talk about some of the astrophysical advances we’ve made since the opto-mechanical star projector was invented eighty years ago. The content base has expanded tremendously from the traditional star show to the new-fangled 3-D tour of the Universe.

Fulldome video doesn’t need to compete with Hollywood. Competition, indeed, would be unwise. But why shouldn’t we use the same (increasingly affordable) tools to produce content that simply cannot be addressed with a plain look at the night sky? When I fly an audience through the Hipparcos data set and outside the Milky Way, when I demonstrate how open clusters and globular clusters have a different distribution (not just in the night sky, but within the 3-D structure of the galaxy), when I display models of the large-scale structure of the Universe,… I’m using technology (in a live performance setting) that allows me to illustrate concepts in an exceedingly accurate, cohesive, and visceral way.

Fulldome video starfields are, well, getting better… No, they cannot yet compete with opto-mechanical projectors, but the highest-resolution systems now produce a starfield that represents the night sky respectably well. In the latest AMNH production, Cosmic Collisions, we created a background starfield that incorporated numerous tweaks to the settings that we’ve adopted over time in the software we use to present live programs—namely, Virtual Director and Uniview. Every time I watch the show, I’m impressed by the appearance of the constellations. (AMNH stars are typically optimized for spaceflight: larger halos make for better depth-cuing, but they rather diminish the fidelity of the night sky.) As my previous peeve indicates, I don’t see the ersatz planetarium sky as a replacement for the real thing, so I believe that video technology now offers a reasonable alternative in many cases.

In short, planetarians should choose the tools that allow them to present the science topics they want to address. Fulldome video is part of the palette of options we now have available to us, and I hope people can understand that I sing its praises while still valuing the star shows that audiences appreciate and enjoy—and, yes, deserve! Those are mighty fine apples. But the plump, ripening oranges that have appeared on the market recently shouldn’t be criticized for their tough rinds and un-crispy flesh. And oranges aren’t the only fruit… (Couldn’t resist a Jeanette Winterson reference. My apologies.)

Pointer Pointers

I’ve noticed a tendency on the part of many planetarium presenters to get (as Jim Beaber wrote on DOME-L) “herky-jerky” with a pointer, especially a laser pointer. It flits around the dome too quickly for the eye to follow, and because domes tend to have a fair bit of real estate, even a seasoned planetarian can have a hard time tracking a pointer’s position. I know I do it, too: getting wrapped up in presenting, one often forgets to consider all the needs of one’s audience. But planetarians should keep pointer etiquette in mind when presenting.

Also, the color of many laser pointers causes problems for some color-blind people, which is another reason to take things slowly. Although an article on “User-Friendly Presentations for those with Limited Color Vision” mentions lasers and color blindness only at the very end of the page, it’s worth reading for other information, including things such as links to tables of safe web colors for color-deficient viewers.

Of course, this is only a serious concern for those of us newbies who tend to use those lightweight laser pointers (and particularly for me, given my caffeine intake). There’ s nothin’ like an old-fashioned, twenty-pound “green arrow” pointer to slow you down! In fact, my earliest presentations relied on the Spitz pointer at the Houston Museum of Natural Science’s Burke Baker Planetarium, and I do believe they benefitted from the heft and (quite frankly) ticklishness of the aged device. A nice slow fade-up followed by a gentle arc across the dome… It was impossible to move it too quickly, at least not without hurting oneself, and who can deny the inestimable pleaure of rotating the arrow to match its direction of motion? If nothing else, it seems that a pointer with more heft could help dampen the caffeine- and nervousness-related oscillations that some experience.

No Lightning (or Rain) on Venus

I know the special effect looks spiffy up on the dome. I know the roiling thick clouds call out for bright cracks of lightning to split the sky. But there’s no justification for depicting Venusian lightning—at least not of the cloud-to-ground variety that we see during storms on Earth. Thus, lightning as it is almost universally illustrated in planetarium visuals—i.e., as big wonkin’ bolts—would not be seen on Venus.

To begin with, no decent evidence for lightning on Venus exists, and the Cassini spacecraft’s observations should have put the last nail in this coffin (basically, if Venus had terrestrial-like lightning, Cassini would have detected it, and it didn’t). Aside from the lack of evidence, Venus doesn’t possess a magnetosphere like Earth, and the atmospheric circuitry that causes terrestrial lightning doesn’t exist on Venus—i.e., there’s no reason to think that Venus would even have lightning! That plus the absence of reasonable evidence should have kept us from putting lightning bolts over our Venus panoramas years ago, but now there’s no excuse.

That said, cloud-to-cloud lightning seems much more easy to rationalize, so if you want to depict a nice, rumbly brightening of the cloud layer, that’s probably okay. Just remember that the altitude of the cloud layer on Venus is a little greater than on Earth—about 30 miles up as opposed to only a miles or so (or much less under overcast conditions).

When I posted a version of this tirade to the Fulldome Mailing List a few years ago, Laurent Pellerin noted that one wouldn’t see terrestrial-like rain on the surface of Venus, either. The infamous sulfuric acid rain evaporates some ten miles up. Another special effect down the drain… Um, as it were.

Venus Doesn’t Look like Dante’s Inferno

While we’re on the topic of Venus, I’d like to grouse about the all-too-frequent depiction of Venus with what appears to be a molten lava surface. Of course, this is just a rendition of radar data from NASA’s Magellan Mission with “simulated hues… based on color images recorded by the Soviet Venera 13 and 14 spacecraft,” but that doesn’t forgive stripping the planet of its cloud layer (which is usually of greater didactic importance that its surface features, after all) without explanation.

Use of the image particularly annoys me when it appears in context with other planets as observed in visible light. One can even detect this phenomenon on the gateway to JPL’s Planetary Photojournal. No, no, no, no, no! Unacceptable. As if the public doesn’t have enough confusions about the planets, we have to obfuscate the issues just to use relatively recent NASA data.

My main issue with the Magellan radar image is simply context—when placed next to optical-wavelength images or when presented without any explanation as to what we’re seeing. If we’re showing a collection of all the planets, they should all appear as they would in visible light. As far as showing Venus solo, my concerns would be allayed by starting with an image of Venus’s cloud-tops, then cross-fading to a view of the radar-imaged surface. At the very least, the Magellan image requires explanation (probably igmored or missed by many visitors) that it shows the appearance of a planetary surface otherwise completely obscured by clouds.

In case it’s not clear from the above, I certainly can’t claim to like images that use a different color scheme, either. It’s not the color choice; it’s the lack of maintaining a distinct parallel with other imagery.

Exaggerated Terrain

Who doesn’t love a flyover? Swooping over a planet’s terrain, over mountains, craters, valleys, rilles, what have you,… We did them with single-projector video, we did them with Digistar I, and particularly as fulldome video borrows more and more stylistically from large-format film, we can expect to see more. But there’s a darker side to the fun, and that’s the exagerrated terrain. Peaks are more peak-y, canyons more canyon-y, cliffs more cliff-y, but it’s not real! Almost every flyover (fulldome or otherwise) does this trick, usually with no disclaimer, and the practice must stop.

As Chris Anderson puts it, “When we fly audiences over a vertically exaggerated landscape, we poison their intuition about the way these worlds would actually appear.” Or, as my colleague Carter Emmart has been known to observe, “even Iowa looks mountainous when you exaggerate its terrain by a factor of ten.”

“Gas” Giants

We have two kinds of planets in our solar system: terrestrial and jovian, call ’em rocky and giant, if you prefer. But please don’t call the big ones “gas giants.” I mean, yeah, there’s a lot of gas in them-there giants, but we mislead our audiences when we refer to them as such. Quoting Chris Anderson again, “it makes about as much sense as referring to Earth as a ‘liquid planet’ because of the oceans.” The bulk of Jupiter almost certainly consists of liquid metallic hydrogen, so in fact, it deserves the ‘liquid planet’ moniker!

My issue here is the impression people (particularly kids) get when we refer to “gas” planets. I fear they may end up thinking such a world consists of gas like Earth’s atmosphere… Perhaps you could fly your rocket straight through such a planet, stirring up puffs of nebulosity in much the way presented in the title sequence from Star Trek: Voyager. So even if most of the planet consists of what could technically be considered a gas, it nonetheless misleads people.

Pluto Dogma

When I initially wrote up my pet peeves, the International Astronomical Union (IAU) called Pluto a planet. But their infamous vote in August 2006 finally defined the term “planet” and, as a consequence, recategorized Pluto as a “dwarf planet.” (Previously, the IAU hadn’t defined the term “planet” but simply called specific objects planets, so their recent vote is very much a step in the right direction.) My pet peeve, however, is not so much about Pluto’s definitional status but rather about the dogmatic fashion in which it is often argued.

For example, one planetarian (who shall remain nameless) stated on DOME-L, “The fact is, that Pluto is a planet… If I start teaching that 2 plus 2 equals 5 because that is my opinion, than I am wrong.” What scares me about such statements is that there are facts and there are facts. A definition is a far cry from a demonstrable principle. If I try to do science by assuming that the sum of two and two is anything other than four, I get garbage results (thank Bertrand Russell for demonstrating that, to the degree that he could). If I do science assuming that Pluto’s not a planet, than who cares? All I’ve done is change the wording.

That’s an extreme example, but I’m still surprised how unthinkingly (and unscientifically) people will defend Pluto’s planethood. It verges on the dogmatic. My peevishness arises from my belief that it’s irresponsible to teach science dogmatically, and the attitude copped by various educators on this topic scares me. (At the same time, results from Rachel Connolly’s recent survey make me think that at least the majority of educators are not so inclined.)

The fact of the matter is that there are good reasons to revoke Pluto’s planetary status: its orbit doesn’t resemble the other planets’, its composition differs significantly from both the giants and the terrestrials—and most importantly, it has numerous companions out there. The analogy to asteroids should give Pluto supporters pause… Astronomers discovered Ceres in 1801 and dubbed it a planet, but as more and more objects were discovered between the orbits of Mars and Jupiter, it became apparent there was a class of objects that could not reasonably be considered planets. Ceres, Pallas, and other asteroids enjoyed the moniker “planet” for nearly 40 years, so Pluto just happened to have a longer run of it (and got a cartoon character named after it to boot).

I heartily recommend Steve Soter’s article, “What Is a Planet?” Among other things, he defines a quantity μ to be the ratio of the mass of the object to the aggregate mass of all the other bodies that share its orbital zone. (For you sticklers out there, “two bodies share an orbital zone if their orbits cross a common radial distance from the primary, and their non-resonant periods differ by less than an order of magnitude.”) What’s nice about μ is that solar system objects neatly divide into “planets” (with values of mu between 5,000 and 2,000,000) and “dwarf planets” (with values less than one). Pretty spiffy. I present a slightly more detailed redux of his article on a separate web page.

Soter writes: “Planets, defined in this way, are few in number because the solar system provides insufficient dynamical room for many. Perturbations by the outer planets destabilize the potential orbits between them on time scales much shorter than the age of the solar system.”

Indeed, I think an aspect of the new definition is “I know it when I see it,” as well as the sense that planets should be few and far between. Personally, I have the sense that we should, by now, have identified all the planets—not dwarf planets, mind you, but just plain, gotta-memorize-their-names planets. The problem with the initially-proposed definition, which would have yielded a dozen planets for now, is that it offered a future of constantly-changing textbooks, outdated web pages, and unending headaches.

With the current IAU definition, we can say with pride that there are eight planets in our solar system; furthermore, they divide neatly in half as terrestrials and giants. In addition, there’s a host of other interesting stuff—comets, asteroids, icy dwarf planets in the outer reaches of the planetary realm—but regarding planets, we speak of eight. That allows us to spend more time describing the structure of our solar system and less time explaining that, well, the new “planet” we discovered might or might not be a planet ’cuz its diameter as determined by albedo measurements suggests that it could be larger than our arbitrary benchmark of Pluto but in fact it might be smaller, so we don’t know whether to name it after a Roman god, a centaur, or a dead astrophysicist. Whatever! That’s not the kind of definition I want.

I applaud the IAU’s decision to agree on a definition that also doesn’t result in an unwieldy number of planets because, as conversations that took place immediately after the IAU announcement on various astro-ed mailing lists, the mnemonics will persist. “My Very Energetic Mother Just Served Us Noodles?” Sounds good enough to me. Better eight words than increasingly long nonsense about a servile matriarch.

Science changes and evolves. The natural selection of theories and definitions is what allows science to proceed toward a more refined description of the natural world. It seems well worth our while to expose that process to our visitors.

Spectral Squiggle

Here I stray into exhibition design, I do believe, but in case this shows up in a planetarium show somewhere…

The image in question is the “spectral squiggle” that shows a sine wave of varying wavelength (e.g., going from long to short from left to right) as a stand in for the various wavelengths of light (e.g., from radio to gamma rays in the aforementioned parenthetical). Two examples appear on the “Digital Age” page of the online Explore the Universe site presented by the Smithsonian National Air and Space Museum: one under the heading “Electromagnetic Spectrum in Stained Glass,” the other (somewhat inexplicably) under “Museum Road Show.” For somebody familiar with the iconography, the cartoon is a succinct graphical statement; however, I fear that it introduces significant comprehension challenges for a general audience.

The caption for the first image mentioned above reads, “The light rays are arranged by wavelength (symbolized by the wavy white band) from long to short.” Okay. What we’re trying to talk abut here are many different light rays, but of course, we’re only seeing one—one that goes continuously from long to short wavelengths. But the text goes on to refer to various kinds of light, from radio through microwave and infrared, visible, ultraviolet and x-rays, all the way to gamma rays. In one light wave? Or what? It’s a lot of information condensed into an image that’s asked to do too much in service of the content.

Compare this to the gorgeous “Electromagnetic Spectrum” poster distributed by NASA (no picture available, alas) that shows M51 with multiple light waves (of different wavelengths) emanating from it, a clearly labelled spectrum from radio through gamma rays, and objects included for scale. The NASA design strikes me as a much more informative and clear. In co-operation with NASA’s graphic designers, AMNH made a similar image using the Sun instead, produced as part of the Cosmic Collisions Educators Guide.

By the way, the squiggle appears in the Rose Center exhibits—and on some NASA propaganda, too—so please don’t think I’m picking on the Smithsonian!

Gravity Well

Now I’ve definitely entered the realm of exhibit design, but it relates to an exhibit that shows up in many planetariums…

We’ve all seen the gravity well (a.k.a. “vortex”) exhibit, and although I enjoy rolling coins around it as much as the next person (and I recognize how welcome those coins are to institutions with tight purse strings), I also have problems with its didactic qualities. However much the vortex impresses, what does it actually teach? At AMNH, we looked at including a similar design for our “Discover the Universe” Moveable Museum (a gutted Winnebago filled with astronomy- and physics-oriented exhibits), but we kept running into a problem: kids didn’t seem to leave the exhibit with any clearer concept of how gravity behaves. So how do we create the connection? Especially in an exhibit that relies on gravity to work, but using a gravitational force perpendicular to the conceptual, centrally-directed “force” in the exhibit!

The problem as I see it is that the exhibit operates by analogy. Because it uses the downward-directed force of gravity (combined with the shape of the vortex) to create curvilinear motion, it introduces potential confusion between actual gravity and the centrally-directed “force” that stands in for, say, the Sun’s gravitational pull on the planets.

And it gets worse… Because of the curved shape of the exhibit, it creates confusion with a relativistic view of gravity, too. In certain ways, the analogy works all right, but given the confusions associated with plain ol’ Newtonian gravity, it seems risky to push visitors in an even more difficult direction.

It seems to me that the vortex exhibit works well (uh, so to speak) as a stand-alone with virtually no explanation (roll the balls, coins, or whatever, and enjoy watching them get pulled inexorably downward) or as a mediated exhibit with an interpreter describing the analogy carefully. I think its interpretation is a tricky task, best left to people and not to exhibit text. For example, many versions attach the title “Gravity Well” to the exhibit along with some accompanying text that jumps too quickly to the punchline about planets revolving around the Sun. The connection seems sensible to those of us steeped in the background material, but I don’t think most people can step up to the exhibit and draw the appropriate analogy. As one exhibit developer wrote, “we cannot create understanding by starting with the answer.”

I greatly fear that the gravity well exhibit, however memorable and spectacular, may do more harm than good in helping people conceptualize the behavior of gravity. My sense of this is gleaned through anecdotal and subjective experience, however, and not through any systematic study. No one has pointed me to any academic work on the topic, however. I’d love to know if any such work exists.

More to Come

As my increaasingly curmudgeonly attitude should demonstrate, I have only begun to kvetch! I’m sure I’ll find much more to complain about in the coming years, and as I do, I’ll do my best to keep this page updated…

Email Ryan if you have any questions, comments, concerns, or gripes about this page.

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