Unifying Concepts and Language

Posted By Pamela on Jul 21, 2008 | 10 comments

Astronomy is filled with ideas that share too many different names. For instance, an Quasar is also a QSO is also an Active Galactic Nuclei. In our solar system, where we once had a bunch of specific objects, we now have terrestrial planets, gaseous planets, asteroids, and icy bodies (and 1 star too). As science starts to understand more and more about our universe, we’re finding that more and more of the things we used to break into many small groups are really different versions of the same object just seen from different vantages or in different environments.

This is scientifically a wonderful thing: Being able to understand what a black hole that is actively feeding looks like as a function of feeding rate and angle of view allows us to say something based on the physics of the system, where as having a bunch of names associated with a bunch of different images is more like leaf collecting without taking DNA samples. Being able to understand how an icy object looks in the solar system both when it is out near Pluto, and when it is making a plunge past the Sun allows us to see how materials get distributed through the solar system. The more we learn, the more we see everything can be broken down into a series of fewer and fewer large boxes.

It is unfortunate, however, that our understanding didn’t come before we had a chance to come up with 40 million names for what we now know are related objects. For instance, all of the following objects are active galactic nuclei: QSOs, Qausars, Seyfert 1s, Seyfert 2s, BL Lac objects, Blazers, and LINERs. Similarly, novae, dwarf novae, classic novae, recurrent novae, Z Cam objects, U Gem objects, and SU Urs objects are all types of cataclysmic variables. The journey to our understanding was a long one, and it came by bringing together many small groups of objects, one at a time, and seeing that at their core they are all the same.

What we are realizing there is a taxonomy of the sky. Just as I am a [mammal, primate, hominid, homo sapiens], a star system might be [binary, cataclysmic variable, U Gem object].

But while we have a clear and agreed upon language for discussing the names of biologicals, such a precise language doesn’t yet exist in astronomy. If I want to find all the latest papers on galaxies with actively feeding supermassive black holes that have observable broad and narrow line absorption regions and tiny little radio jets, I need to search on the terms active galaxy, radio galaxy, Seyfert 1, and active supermassive black hole. This lack of precision in language slows the progress of research. One team may make huge strides, developing their own methods and vocabulary and publishing in one set of journals with one set of keywords, while another group makes parallel and complementary progress, developing different methods and vocabulary while publishing in a different set of journals with another set of keywords. If the teams don’t happen to meet at a conference or have someone point out one another’s work, it could be a couple years into the research before they realize they are doing something that would greatly benefit from collaboration.

As our ideas are unifying we need to take care to unify our language as well. We need to take care to use all appropriate keywords and not be lazy as we check boxes, and we need to take the time to do literature searches on every possible archaic turn of language as well. Even though we now know Andromeda is a galaxy (really, it is), there are those that still call it the Andromeda Nebula. It won’t be easy to change our language habits, but it will be good for the soul (or at least good for those of us doing literature searches) if we can find a way to manage it.


  1. Hmm, shouldn’t that be “a QSO is also an Active Galactic Nucleus”, with “nuclei” being the plural?

    (yes, yes, nit picking etc. etc.)

  2. Interesting. After the recent creation of the Plutoid designation I’d been wondering again about why the IAU felt it had to decide one way or the other back in 2006, and this post makes it clear it was something they couldn’t really avoid.

    Thank you.

  3. FYI these naming conventions and multiple categorizations of objects make if very difficult for beginners to understand anything that is being talked about. We are always extremely overwhelmed.

  4. Heh, you forgot blazar. How that’s different from a BL Lac I still don’t understand…

    Is there a way that searches can include some kind of text-matching like that so that when you put in one term, such as active galaxy, you also get back radio galaxy and supermassive black hole? But then the question is, do you want all active galaxy references when you are just interested in radio galaxies or just in Sy 1s. Sheesh…

    And why do we still say “early and late type” galaxies?!

  5. Thanks for clarifying: I didn’t even know all those Active Galatic Nuclei terms are even related to each other. Maybe the physics community should really start working on a naming system, like chemists do.

    (typos: mamal?, Andremeda?)

  6. Clearly I was blogging while under the influence of not enough coffee.

    About to spell check.

    (And I think it is “A QSO is also an Active Galactic Nucleus” the same way I can say “A cougar is also a cat.” Both are singular.)

  7. Biological names are not always well defined either, particularly in botany. Botanists are now changing the names of many plants and sometimes changing some of them back to their original names. They also seem to loke to change simple 5 letter names e.g. Aster to to hard to remember 14 letter names – Symphyotrichum. And there the splitters and the lumpers. The splitters want to give every little variation in a plant species a variety of form name and the lumpers want to lump those varieties to just the species name. So astronomy is not the only confusing field when it comes to names.

  8. And don’t get me started on “planetary nebula”…nebula used to refer to a whole bunch of different types of objects! And we have waxing and waning Moons but I never hear anyone talk about waxing and waning phases of Venus and Mercury.

  9. To Vagueofgodalming: This is a very informative post, but it does not make clear that the IAU couldn’t avoid the 2006 Pluto decision. That decision made things more complicated, not less. First, it stated that a dwarf planet is not a planet at all–this makes no linguistic sense and is confusing, to say the least. Second, the requirement that an object “clear the neighborhood of its orbit” is so vague that if applied literally, it could disqualify all the planets in our solar system, none of which have fully cleared their orbits of nearby asteroids. The fact that an equal number of astronomers to those who voted immediately rejected the IAU decision speaks volumes about its serious flaws. Then we have the plutoid definition, which the IAU states applies to objects orbiting beyond Neptune. That means Pluto is excluded from the plutoid category when its orbit takes it closer to the sun than Neptune!

    What we have here is a huge mess and all because the IAU couldn’t leave well enough alone and allowed a tiny minority of its membership to push through an unusable definition. It would have been better if they had done nothing and postponed action until we have the data from New Horizons and Dawn.

  10. I think, in part, this apparent confusion arises from forgetting the origin of acronyms. Way back in the early bronze age (the 1960’s) when I was a grad student in astrophysics, a (relatively) new phenomena had been discovered – stars, that looked like stars, but had really strange spectra. These weird things were called “Quasi Stellar Objects”, (shortened to QSO’s) meaning they were “sort of stars but weird”, (Proposals included the idea that they really were stars in our galaxy but were moving away really fast; to account for their redshift). The word “Qausar” was nothing more than a handy way of enunciating QSO or Quasi Stellar, We also knew about Seyfert galaxies (named after some guy called Carl Keenan Seyfert way back in the early 1940’s) but did not yet realize that they were related to QSO’s (so OK some astronomers were hypothesizing that maybe …). Perhaps, in the service of precision and understanding we should learn to be a bit more careful in our use of acronyms, and other shorthands when describing poorly understood phenomena.

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