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triclon
2008-Oct-08, 05:12 AM
As an astrophysics student, sometimes I come across old terms or concepts that should yield to a more accurate term or simpler concept.

My favorite example is the classification of galaxies. When Hubble first was classifying galaxies by their morphology he called elliptical galaxies "early type" galaxies and spirals "late type" galaxies because elliptical galaxies were once thought to evolve into spiral galaxies over time. Today we know that galaxy evolution does not follow this convention. It is true that these terms have become less and less common but I still hear them now and then. Now they only serve to confuse people who might not be professional astronomers, it conveys an idea of galaxy evolution now commonly held to be false.

Another one is how we measure astronomical distances. The parsec is useful when conveying distances calculated from parallactic angle measurements but I believe it is far too commonly used in place of the simpler to understand lightyear. It takes me only a minute or two to explain to someone what a lightyear means, but takes far longer to explain what a parsec is. When distance is quoted in lightyears, one immediately knows the light travel time from the object to the earth. The unit is even scalable to minutes or seconds when dealing with objects in our own solar system (ie. the sun is about 8 lightminutes away) I must admit that the majority (if not all) professional publications I have read use parsecs, while the lightyear is used for popular astronomy literature, videos, ect. but I still feel the lightyear is the better unit to use in measuring astronomical distances.

Anyone else encounter astronomy terms or concepts that they think should be thrown out in favor of something simpler or more intuitive.

Van Rijn
2008-Oct-08, 06:39 AM
Anyone else encounter astronomy terms or concepts that they think should be thrown out in favor of something simpler or more intuitive.

It's tricky, because you get used to many of them. A couple terms off the top of my head that can cause confusion: planetary nebulae, and the various types of "dwarf" stars.

Ari Jokimaki
2008-Oct-08, 10:58 AM
"Radial velocity" has been used when talking about redshifts of extragalactic objects (even older term for that is "velocity shift").

Dgennero
2008-Oct-08, 02:12 PM
I think main sequence stars should never be called "dwarf" stars - our Sun is not a "yellow dwarf" but among the 10% of the *brightest* stars since real dwarfs (white and red ones) are so much more numerous.

Jupiter should not be called a "failed star" since it is way too small for that, 70 times not enough mass is not just a miss by a narrow margin.

Also, some of the newer illustrated astronomy books still don't show the central bar in our galaxy.

Cougar
2008-Oct-08, 03:20 PM
As an astrophysics student, sometimes I come across old terms or concepts that should yield to a more accurate term or simpler concept.

Hoo, boy! You ain't kidding.


My favorite example is the classification of galaxies. When Hubble first was classifying galaxies by their morphology he called elliptical galaxies "early type" galaxies and spirals "late type" galaxies because elliptical galaxies were once thought to evolve into spiral galaxies over time. Today we know that galaxy evolution does not follow this convention. It is true that these terms have become less and less common but I still hear them now and then. Now they only serve to confuse people who might not be professional astronomers, it conveys an idea of galaxy evolution now commonly held to be false.

dgruss, are you listening? Triclon, you are hitting the nail right on the head. This "tradition" of continuing to use old terminology that has since been shown to be utterly wrong and misleading is outrageous, egregious, deplorable, disgraceful, monstrous, scandalous, preposterous, unreasonable, shocking, unconscionable, and just plain ridiculous.


Another one is how we measure astronomical distances. The parsec is useful when conveying distances calculated from parallactic angle measurements but I believe it is far too commonly used in place of the simpler to understand lightyear.

Dude, you are singing to the choir. Sing it!


Anyone else encounter astronomy terms or concepts that they think should be thrown out in favor of something simpler or more intuitive.

That should bring a lot of responses. Another good question is, what can we do about it? Spread the word that using these old terms is no longer acceptable, and over a generation or two the lexicon is finally transformed to contain terms that actually reflect their meaning? Found the Society for Rational Terminology?

StupendousMan
2008-Oct-08, 03:50 PM
Another one is how we measure astronomical distances. The parsec is useful when conveying distances calculated from parallactic angle measurements but I believe it is far too commonly used in place of the simpler to understand lightyear. It takes me only a minute or two to explain to someone what a lightyear means, but takes far longer to explain what a parsec is. When distance is quoted in lightyears, one immediately knows the light travel time from the object to the earth. The unit is even scalable to minutes or seconds when dealing with objects in our own solar system (ie. the sun is about 8 lightminutes away) I must admit that the majority (if not all) professional publications I have read use parsecs, while the lightyear is used for popular astronomy literature, videos, ect. but I still feel the lightyear is the better unit to use in measuring astronomical distances.


Please feel free to use whatever terms you prefer to discuss concepts with your friends and neighbors.

When you talk to me, or other astronomers, use parsecs. I use parsecs because they are more convenient for some calculations that are common and necessary in the technical literature. I don't care if light-years are easier to explain to your relatives -- I'm not talking to your relatives. I'm talking to other working astronomers.

Imagine going to music school and telling the composers and musicians there, "Hey, I think that you ought to stop using phrases like 'major' and 'minor' -- what do those mean, anyway? Oh, and that business of describing notes with letters, like "A" and "C" and "D-sharp" -- get rid of all those sharps and flats! Let's just use the frequency of a note to describe it. It's more logical and easier for an outsider to understand!"

How successful do you think your campaign would be?

tdvance
2008-Oct-08, 05:42 PM
I don't know of any astronomer confused by "parsec"--I used to be confused, because after all, Han Solo made the Kessel Run in 12 parsecs (which is where I first heard the term), but not anymore. A really simple explanation is: a parsec is about 3.26 light years. If the person wants to know where a parsec came from, then you can explain the parallax bit (which in itself is educational and worthwhile).

On the other hand, I don't recall ever seeing "early type" or "late type" galaxies in a modern textbook (though i've only read about 3).

parejkoj
2008-Oct-08, 06:29 PM
The early/late type confusion goes in my annoyance pile. Not only is it confusing, it's wrong!

And "planetary nebula" isn't very helpful either: so some of them look kinda like a planet. So what? This one had me quite befuddled as an undergraduate...

But parsec, as StupendousMan pointed out, is actually very useful. First of all, it is a unit that is directly measurable for nearby objects (one arcsecond of parallax for a 1AU baseline), unlike the light year which is not. We like being able to discuss things that can be directly measured. And since parallax is the first step of the distance ladder, it makes sense to keep the later steps in the same units. Second of all, things like the Hubble Constant (H0) end up being relatively round numbers when expressed in km/s/Mpc. The parsec will not be fading away any time soon, and with good reason.

Radial velocity is actually a very useful term. It means a velocity measured along the line of sight, as opposed to a transverse velocity which is perpendicular to the line of sight. So the term "radial velocity" when applied to redshifts is correct and explicit. This is particularly important when talking about, say, stars in our galaxy, since they can have both radial (determined through spectroscopy) and transverse (determined through multi-epoch astrometry) velocities. It is perhaps archaic when applied to extragalactic sources, but only vaguely confusing.

The magnitude system is certainly archaic, particularly the fact that it is backwards (negative means brighter), which means I always have to think extra hard about what a color (e.g. B-V) really represents. Also, since it is based on the logarithm, it goes haywire when applied to imaging data that contains non-detections or negative values (which can happen after the background subtraction has been applied). There have been some pushes to replace it with something that is better behaved when discussing upper-limits (SDSS uses the arcsinh function, which is well-behaved near zero, and is asymptotically approaches log for positive fluxes). It may take a while, though: the magnitude system has been around for essentially a couple thousand years...

matt.o
2008-Oct-08, 09:43 PM
I think the worst thing about the magnitude system is the number of different filters!

Oh and I will reiterate parejkoj in saying the parsec is the most "proper" in terms of distance units - light year does not make much sense at cosmological scales either, at least, not in terms of what you're saying (light travel time etc.) and would serve to generate more confusion (think of the different types of distance measurements: comoving, angular diameter, luminosity).

Nereid
2008-Oct-08, 11:50 PM
"metals" anyone?

parejkoj
2008-Oct-09, 12:31 AM
Now, now, Nereid, that one makes a bit of sense. After all, anything more massive than Helium is pretty much irrelevant, right? ;)

BigDon
2008-Oct-09, 01:32 AM
Imagine going to music school and telling the composers and musicians there, "Hey, I think that you ought to stop using phrases like 'major' and 'minor' -- what do those mean, anyway? Oh, and that business of describing notes with letters, like "A" and "C" and "D-sharp" -- get rid of all those sharps and flats! Let's just use the frequency of a note to describe it. It's more logical and easier for an outsider to understand!"

How successful do you think your campaign would be?

It's called "tab" short for "tabulation" written so ignora.. ah non-classically trained rock musicians could compose music for the electric guitar.

Ari Jokimaki
2008-Oct-09, 07:26 AM
Actually, it's a short for "tabulature" (http://en.wikipedia.org/wiki/Tablature), and it shows how to do the fingering. That has some effect on the feel of the playing. That doesn't necessarily say much to the classically trained musicians who are used to thinking notes only in the context of timing, pitch, and duration. In electric guitar, the feel of notes changes when played from different strings, even if the pitch is the same. But yes, it also helps to compose and read the music when one doesn't know the traditional notation.

Another one of the slightly annoying things in astronomy is the habit of giving multitude of different designations to celestial objects.

Ara Pacis
2008-Oct-09, 08:17 AM
When I first saw the title of this thread I wondered to myself. Cosmic-Con or a Star-Geezer Party? [/humor]

timb
2008-Oct-09, 08:31 AM
I think main sequence stars should never be called "dwarf" stars - our Sun is not a "yellow dwarf" but among the 10% of the *brightest* stars since real dwarfs (white and red ones) are so much more numerous.


Red dwarfs are just another main sequence star. White dwarfs are a different kind of object. Referring to the Sun as a "yellow dwarf" is bad on two counts. For one thing the Sun is white, for another it is larger ("dwarf" usually refers to a thing's size rather than its brightness) than about 90% of the objects regarded as stars. A bit like calling anyone under 6'4" a "dwarf". Brown dwarfs are failed stars, and in some ways more like white dwarfs than planets or main sequence stars.

"Early" and "late" are more commonly heard connected with star types than galaxy's. That terminology is based on an incorrect theory too: that main sequence stars evolve into redder main sequence stars as their coal supply runs out.

aurora
2008-Oct-09, 12:57 PM
In reading old books, as well as talking to some older acquaintences who are long retired, I run across the use of the word "nebula" for pretty much any deep sky object. As in the "Andromeda Nebula" when talking about the Andromeda Galaxy.

This usage predates Hubble, but it hung on for quite awhile, and of course paper has a long shelf life.

dgruss23
2008-Oct-10, 04:00 AM
My favorite example is the classification of galaxies. When Hubble first was classifying galaxies by their morphology he called elliptical galaxies "early type" galaxies and spirals "late type" galaxies because elliptical galaxies were once thought to evolve into spiral galaxies over time. Today we know that galaxy evolution does not follow this convention. It is true that these terms have become less and less common but I still hear them now and then. Now they only serve to confuse people who might not be professional astronomers, it conveys an idea of galaxy evolution now commonly held to be false.


dgruss, are you listening? Triclon, you are hitting the nail right on the head. This "tradition" of continuing to use old terminology that has since been shown to be utterly wrong and misleading is outrageous, egregious, deplorable, disgraceful, monstrous, scandalous, preposterous, unreasonable, shocking, unconscionable, and just plain ridiculous.


The early/late type confusion goes in my annoyance pile. Not only is it confusing, it's wrong!

I have to disagree with you guys about this issue of "early" and "late type" spirals. I understand "that" it is confusing, but I don't agree that it "has to be" confusing. Hubble presented his classification scheme in ApJ in 1926 (http://adsabs.harvard.edu/abs/1926ApJ....64..321H). In this paper Hubble discusses his reasoning. The fact is - setting aside peculiar and irregular galaxies, most galaxies fall neatly along a continuous morphological sequence from Elliptical through Lenticular, through Sa, Sb, and Sc spirals.

When astronomers classify them today, they break the spirals down even further - Sa, Sab, Sb, Sbc, Sc, Scd, Sd. There are general changes in characteristics along this sequence. Sa galaxies have tightly wound arms, and larger bulges. They also tend to have older stellar populations and lower gas contents. Sc spirals have negligible bulges, smaller nuclear regions, more loosely wound spiral arms, are more gas rich, and much more likely to have very active star formation and younger stellar populations.

Now this notion of an evolutionary sequence was not Hubble's idea, nor was it used in the development of his classification:


Although a deliberate effort was made to find a descriptive classification that should be entirely independent of theoretical considerations, the results are almost identical to the path of development derived by Jeans from purely theoretical investigations. The agreement is very suggestive in view of the wide field covered by the data, and Jeans theory might have been used both to interpret the observations and to guide research. It should be borne in mind, however, that the basis of the classification is descriptive and entirely independent of any theory.

Hubble further states:


The ends of the sequence are unmistakable, however, and, in a general way it is possible to differentiate a middle group. These three groups are designated by the non-commital letters "a", "b", and "c" attached to the spiral symbols "S", and, with reference to their position in the sequence, are called "early," "intermediate," and "late" types.

Note that Hubble's use of early and late is in reference to their position on his classification sequence. He further states in a footnote:


"Early" and "late" in spite of their temporal connotations, appear to be the most convenient adjectives available for describing relative positions in the sequence. This sequence of structural forms is an observed phenomenon. ...

I would encourage you to read the rest of the footnote. Basically, Hubble was applying the best term he could to describe comparative positions along the morphological sequence and advised to ignore the temporal connotations of "early" and "late" type.

Regarding the theory of Jeans that Hubble mentions, I found this paper (http://adsabs.harvard.edu/abs/1925MNRAS..85..531J) which may be where the theory was explained - although certainly not with any clarity. But again, Hubble's own words are that the sequence he developed was consistent with Jeans idea, but in fact was developed purely through observational criteria. Hubble's initial creation of this classification system was not intended to be a temporal sequence, and early and late type were not intended to imply evolutionary stages.
Sa spirals are "earlier" in Hubble's classification sequence than Sc spirals, hence his decision to call them "early" and "late" type. Note that Sb's were called "intermediate".

dgruss23
2008-Oct-10, 04:15 AM
In reading old books, as well as talking to some older acquaintences who are long retired, I run across the use of the word "nebula" for pretty much any deep sky object. As in the "Andromeda Nebula" when talking about the Andromeda Galaxy.

This usage predates Hubble, but it hung on for quite awhile, and of course paper has a long shelf life.

Yes, Hubble's book about galaxies was called "The realm of the nebula" (1936) and that says it all. I've at times looked through older books seeing if I can identify the first usage of the word "galaxies" to refer to "nebula" outside of our own Milky Way. I don't know if this is the earliest reference, but in the London Popular Science Review (1869) there was a news brief titled "A New Theory of the Universe" which starts off with this:


Mr. Proctor has recently put forward a new theory respecting the arrangement of the stars and nebulae. Instead of looking upon the nebulae as for the most part external galaxies of stars, he considers that they belong to our own sidereal system....

Of course for those that only know the textbook treatment of the story of the "discovery" of galaxies, it might come as a surprise that in 1869 it would have been a new theory that nebulae are part of the Milky Way... thus the old theory was that nebulae were in fact external galaxies.

The correct history is in fact that William Herschel was quite influential and people general believed after his early writings that the nebula were external galaxies. Due certainly in part to Richard Anthony Proctor's efforts ~1869-1872, and the results of new observations, the mainstream opinion shifted away from the idea that the nebula were external galaxies and toward the view that they must be part of the Milky Way. Ironically, Herschel himself had changed his mind about the nebula being external galaxies late in his career (by1817), but his writings were so difficult to follow that people did not notice and his original view carried on until ~1870. The shift in view at that time helped set the stage for the "Great Debate" in 1920.

dgruss23
2008-Oct-10, 09:46 PM
This 1927 (http://adsabs.harvard.edu/abs/1927Obs....50..276H) article again demonstrates that Hubble was not of the view that his sequence was an evolutionary sequence:


The sequence of spirals is subdivided into three sections of approximately equal "length", termed "early", "intermediate", and "late" respectively. This is an arbitrary procedure and is adopted merely because it is possible to distinguish the middle section from the two ends. the nomenclature, it is emphasized, refers to position in the sequence, and temporal connotations are made at one's peril. The entire classification is purely empirical and without prejudice to theories of evolution - ...

Hubble's remaining papers through 1953 really never touched upon the subject of galaxy classification so there is no evidence that Hubble at any point considered his classification of galaxies to be an evolutionary sequence. In general his writings suggest he was very cautious in drawing theoretical conclusions.

dgruss23
2008-Oct-10, 10:00 PM
In taking a look at the most recent article that cited Hubble's 1926 paper it turns out that Baldry (http://arxiv.org/abs/0809.0125) just at the end of August published a paper that says exactly what I've said above - even uses some of the same quotes from Hubble's papers. Too bad I didn't find that paper in the first place, could've saved myself some time. :)

Cougar
2008-Oct-10, 10:35 PM
Basically, Hubble... advised to ignore the temporal connotations of "early" and "late" type.

But, I mean, come on. What comes to mind when you hear someone say, "That's an early-type galaxy"? It's a bit of a mental pain when you have to think, "Lessee, early-type. That means it didn't reach that form in the early universe, but rather much later in the universe's history, i.e., just the opposite of what is said!

Maybe when it is figured out exactly what the evolution of galactic forms IS, we will be presented with a more meaningful nomenclature...

I'll not argue about parsec with you, Stupendous Man , because you made a good argument, mainly that it is "more convenient for some calculations that are common and necessary in the technical literature."

dgruss23
2008-Oct-11, 04:19 AM
But, I mean, come on. What comes to mind when you hear someone say, "That's an early-type galaxy"? It's a bit of a mental pain when you have to think, "Lessee, early-type. That means it didn't reach that form in the early universe, but rather much later in the universe's history, i.e., just the opposite of what is said!

Why do we park on a driveway and drive on a parkway?! Sometimes language is used in ways that may not make sense. Hubble explained his reasoning, and astronomers have stuck with the use of "early" and "late" type galaxies for over 80 years. What comes to mind when I read the words "early type spiral" is an Sa or an Sab spiral because that is what astronomers mean when they say "early type spiral". It is so ingrained in my mind that the issue you're raising is not even an issue for me.

While it is the job of professional scientists to effectively communicate the concepts of their profession to laymen, it is not the job of professionals to modify their use of terminology in professional research just to make things "easier" for the laymen. Once you know what is meant by early and late type, what is so hard about it? Here (http://arxiv.org/abs/0803.1274) and here (http://adsabs.harvard.edu/abs/2008MNRAS.389.1791L) are just two of many papers that use the terminology of "early" and "late" type galaxies. Knowing what those terms mean, you can correctly understand what they're saying in the abstracts - right? It's not that hard to grasp. And if you can understand it, then what is the big deal?

The real problem here is textbooks that don't take the brief time it would take to explain what astronomers mean when they say "early" or "late type".



Maybe when it is figured out exactly what the evolution of galactic forms IS, we will be presented with a more meaningful nomenclature...

I don't think it is meaningless. There are distinct differences along the Hubble sequence. For example, Masters et al (http://adsabs.harvard.edu/abs/2008AJ....135.1738M) identify differences between early and late type spirals in the Tully-Fisher relation. Star formation rate density (http://adsabs.harvard.edu/abs/2008A%26A...482..507J) can be related in the context of early and late type galaxies.

If laymen have that big an issue with the early/late terminology, then perhap they could devote some effort to coming up with an alternate terminology system? Otherwise, learn the terminology used by the professionals and deal with it.

Centaur
2008-Oct-11, 06:06 AM
As an astrophysics student, sometimes I come across old terms or concepts that should yield to a more accurate term or simpler concept.
...

Another one is how we measure astronomical distances. The parsec is useful when conveying distances calculated from parallactic angle measurements but I believe it is far too commonly used in place of the simpler to understand lightyear. It takes me only a minute or two to explain to someone what a lightyear means, but takes far longer to explain what a parsec is. When distance is quoted in lightyears, one immediately knows the light travel time from the object to the earth. The unit is even scalable to minutes or seconds when dealing with objects in our own solar system (ie. the sun is about 8 lightminutes away) I must admit that the majority (if not all) professional publications I have read use parsecs, while the lightyear is used for popular astronomy literature, videos, ect. but I still feel the lightyear is the better unit to use in measuring astronomical distances.

Anyone else encounter astronomy terms or concepts that they think should be thrown out in favor of something simpler or more intuitive.

I totally agree with your comment about light-years and parsecs. The light-year is a marvelous unit relating distance with a natural time period and a fundamental velocity. The parsec is based on an arbitrary number of arcseconds. It’s only half an order of magnitude greater than the older and more intuitive unit, therefore unnecessary. It’s silly to argue that it is easier to determine. How hard is it to divide a result by 3.26156? In all fields of endeavor, professionals seek to separate themselves from laymen through the use of jargon. Parsec seems to be the premier example for astronomers.

Traditionally the term New Moon referred to the slender waxing crescent Moon seen low in the west after sunset a day or two after its conjunction with the Sun. In more modern times it took a second meaning as the moment of conjunction, which in the past was called the Dark Moon or Dark of the Moon or Change of the Moon. Thus there is an ambiguity. I prefer the older usages. I especially love the term The Old Moon in the New Moon’s Arms when referring to earthshine on the dark portion of a waxing crescent Moon.

When the Moon appears in the sky in the form of a disk we refer to it as a Full Moon. When it appears in the form of a half disk people normally refer to it as a Half Moon. But calendars at those times read first or last quarter. Those were originally astrological terms that referred to the Moon’s 90° (quarter circle) elongation from the Sun, and not the Moon’s apparent shape. More precisely they refer to the end of the Moon’s first quarter or the beginning of its last quarter of the four quarters of its orbit beginning with the moment of conjunction with the Sun. It is not correct to refer to a Half Moon as a Quarter Moon, yet many people do so. Such usage just confuses readers or listeners. At the time of a Half Moon it is at the cusp of one of its quarter positions. I prefer the terms Waxing Half Moon and Waning Half Moon, or Evening Half Moon and Morning Half Moon.

dgruss23
2008-Oct-11, 03:00 PM
I totally agree with your comment about light-years and parsecs. The light-year is a marvelous unit relating distance with a natural time period and a fundamental velocity. The parsec is based on an arbitrary number of arcseconds. It’s only half an order of magnitude greater than the older and more intuitive unit, therefore unnecessary. It’s silly to argue that it is easier to determine. How hard is it to divide a result by 3.26156? In all fields of endeavor, professionals seek to separate themselves from laymen through the use of jargon. Parsec seems to be the premier example for astronomers.

This is simply not true. The word "parsec" comes from "parallax in arc seconds". Astronomers don't sit around and say "Hey, when we talk distances we need a word that will make us sound smarter than the laymen."

Nor is it based upon an "arbitrary" number of arcseconds. A parsec is the distance at which a star would have a parallax of 1 arcsec as seen from Earth. That distance is 206,265 astronomical units (AU). The average distance from the Earth to the Sun is 1 AU (~150 million kilometers). The observed parallax of a star can be directly related to the distance of the star.

See the parsec is a distance unit that allows one to directly relate an actual measurement to a distance. If a star has a parallax of 0.1 arcsec, then its distance is 10 parsecs. The formula is very simple:

distance (in parsecs) = 1/parallax (arcsec)

The parsec is a key ingredient in the "distance ladder". The Sandage&Tammann method for obtaining the value of the Hubble parameter (H0) has the following early rungs on the ladder (described in Zelik&Smith's Introductory Astrophysics&Astronomy (1987):

1. Measure the value of the AU using radar reflection from Venus and the distances to nearby stars using parallax measurements.

2. Determine the distance to the Hyades star cluster using the "moving-cluster" method and then compare this distance for consistency with distances found by parallax.

3. Find the distances to Cepheids within our galaxy by comparing their brightness with the brightness of Cepheids in the Hyades cluster

And the rungs go on from there. As you can see, parallax is a very real and fundamental part of the distance scale and the parallax measurement establishes the distance in parsecs - not light years.

And what about using brightness to determine distance?

m = M + 5 log (D/10pc) or D = 10pc x 10^(m-M)/5

Underlying this equation is the inverse-square law of brightness.

The real problem here is the general lack of knowledge that people have regarding astronomy. Most people probably wouldn't be able to find the Andromeda galaxy if you gave them a star chart and 1 hour of time on a crystal clear night. And astronomers are supposed to change the way they do the distance scale just to make things "easier" for the uninformed laymen?

How about this instead - the Cepheid distance modulus to the Andromeda Galaxy was found to be 24.48 by the Hubble Key Project. This converts to a distance of 787 kiloparsecs (kpc). Now why doesn't the layman just take the 787 kpc and multiply that by 3.26 to get 2570 thousand light years? Or if they know their metric system convert that to 2.6 million light years? Is there anything hard about that? Why must professional astronomers re-invent what they've been doing just so that the average layman can blithely continue on uninformed? If they laymen is really that interested, it is not that hard to learn what a parsec is or how to multiply by 3.26.

When I give presentations at the local public observatory, I refer to galaxy distances and diameters throughout my presentation in kpc and Mpc units. I explain to the audience at the beginning that for any of the numbers I give they can just multiply by 3.26 to get the number in thousands or millions of light years.

dgruss23
2008-Oct-11, 03:04 PM
Anyone else encounter astronomy terms or concepts that they think should be thrown out in favor of something simpler or more intuitive.

"Simpler" and "more intuitive" to the layman does not equate to more useful to the professional. But the layman may not see that if the layman does not understand why the professional uses the terms being used.

dgruss23
2008-Oct-11, 03:17 PM
I don't know of any astronomer confused by "parsec"--I used to be confused, because after all, Han Solo made the Kessel Run in 12 parsecs (which is where I first heard the term), but not anymore.

If I remember right, they tried to clean up that "made the Kessel run in 12 parsecs" mistake in the Star Wars books written to continue the story after Return of the Jedi. I think the second trilogy in the series (written by Kevin J. Anderson) had scenes set in the Kessel system of the Star Wars universe. If I remember right getting through the Kessel system was dangerous (of course) and the shorter the distance travelled the more dangerous the route, so it would then be a big deal that Han Solo made the Kessel run in a short distance of under 12 parsecs as opposed to a time unit of under 12 parsecs which was how everyone interpreted it in the original movie.

Of course none of that changes the fact that the scene from which the 12 parsec Kessel run was first mentioned sounded like George Lucas took a bunch of astronomy words he'd heard and jumbled them into a gibberish dialogue hoping it would sound impressive.

Centaur
2008-Oct-11, 03:29 PM
This is simply not true. The word "parsec" comes from "parallax in arc seconds". Astronomers don't sit around and say "Hey, when we talk distances we need a word that will make us sound smarter than the laymen."

Nor is it based upon an "arbitrary" number of arcseconds. A parsec is the distance at which a star would have a parallax of 1 arcsec as seen from Earth. That distance is 206,265 astronomical units (AU). The average distance from the Earth to the Sun is 1 AU (~150 million kilometers). The observed parallax of a star can be directly related to the distance of the star.

See the parsec is a distance unit that allows one to directly relate an actual measurement to a distance. If a star has a parallax of 0.1 arcsec, then its distance is 10 parsecs. The formula is very simple:

distance (in parsecs) = 1/parallax (arcsec)
.....

And astronomers are supposed to change the way they do the distance scale just to make things "easier" for the uninformed laymen?
.....

Why must professional astronomers re-invent what they've been doing just so that the average layman can blithely continue on uninformed? If they laymen is really that interested, it is not that hard to learn what a parsec is or how to multiply by 3.26.

When I give presentations at the local public observatory, I refer to galaxy distances and diameters throughout my presentation in kpc and Mpc units. I explain to the audience at the beginning that for any of the numbers I give they can just multiply by 3.26 to get the number in thousands or millions of light years.

The arbitrariness is due to the convention that there are 360° in a circle, 60 arcminutes in a degree and 60 arcseconds in an arcminute. The length of a year and the speed of light are not arbitrary. The term parsec did not come into use until 1913, long after the term light-year. If professional astronomers have to rely on others of their kind for their incomes, they would be standing in breadlines. Books and articles designed for sale to other pros would not earn very much. When McGraw-Hill asked me to write a book on stock market technical analysis, they insisted it be understood by laymen. We would have been lucky to sell a hundred copies to other technical analysts, but hundreds of thousands have been sold to ordinary investors who have profited from my words. Supposedly astronomers are contributing to the general wealth of knowledge for all of mankind. Using jargon aimed at the “in crowd” of a profession that differs from another term that is at least as good and understood by the masses is particularly pretentious when addressing an audience of laymen.

dgruss23
2008-Oct-11, 05:29 PM
The arbitrariness is due to the convention that there are 360° in a circle, 60 arcminutes in a degree and 60 arcseconds in an arcminute. The length of a year and the speed of light are not arbitrary. The term parsec did not come into use until 1913, long after the term light-year.

If that is your criteria for "arbitrary" then all measurement systems are arbitrary but then the arbitrary state of measurement systems is hardly relevant to the utility of measurement systems.

But the light year distance unit relies upon angular measurement as much as the parsec distance unit does. A sidereal year is the time needed for the Earth to complete exactly one orbit around the Sun relative to the stars. And how do we know when the Earth has done that? Well we look at the positions of the stars on the celestial sphere. And how are those positions defined? Using angular hours (24 hours where 1 hr = 15 degrees), 60 minutes in one degree, and 60 seconds in one angular minute. We must also measure those stellar positions from a position on the Earth - which is again defined by angular units.

In reality the parsec actually has a little less structure underneath it as a measurement unit. Light year requires knowledge of the speed of light which is completely unnecessary to define the parsec distance unit.

Another point - what exactly makes "light year" a more layman friendly term than "parsec"? Neither term means squat to the average person until you put it into a unit that people can relate to. Are you telling me that the average layperson actually has a better grasp of the distances we're talking about if we use light years?

How?

Astronomer: See this big galaxy in the constellation Andromeda... it is 2.6 million light years away. That means that traveling at the speed of light it would take 2.6 million years to cover that distance.

Layman: Wow (google eyes w/jaw drop expression) .... So we're seeing the galaxy as it was 2.6 million years ago? Is it still there?

Astronomer: Well, yes it is still there.

Layman: Well how far does light travel in a year?

Astronomer: You have to multiply the speed of light - which is about 300,000 km/sec by the number of seconds in a year. There are about 31.5 million seconds in a year. So a light year is a distance of ~ 9.5 trillion km.

Layman: But wait, how many miles is that? I don't know what a km is. It's bigger than a mile right? I mean, when I leave the United States and drive up to Canada the speed limits are like 80 km per hour. That's bigger than 60 miles per hour isn't it. So how big is a light year in miles?

Astronomer: Scientists use the metric system ... but there are 1.6 km in a mile so you just divide 9.5 trillion by 1.6 to get the miles.

Layman: Well you astronomers should really learn to use words that are easy to understand. I don't understand why you can't just use miles in the first place. Nobody besides scientists use the metric system. I hated it in school. I always moved the decimal the wrong way. There's a thousands kilometers in a meter - right?

Astronomer: Actually, the United States is about the only nation that still uses the English system of measurement. You see, with the metric system ...

Laymen: So is the Andromeda galaxy the one where Han Solo made the Kessel run in under 12 parsecs?



If professional astronomers have to rely on others of their kind for their incomes, they would be standing in breadlines. Books and articles designed for sale to other pros would not earn very much.

And they don't. Professional astronomers present their results in peer reviewed journals - which the astronomer or their institution must pay a fee to publish. But these articles are not written for the layman. They are written to advance and present scientific results to other researchers.

If a professional astronomer chooses to write a book for layman, they know how to tone down the "jargon" and math so that the layman can follow what is being said.


When McGraw-Hill asked me to write a book on stock market technical analysis, they insisted it be understood by laymen. We would have been lucky to sell a hundred copies to other technical analysts, but hundreds of thousands have been sold to ordinary investors who have profited from my words. Supposedly astronomers are contributing to the general wealth of knowledge for all of mankind. Using jargon aimed at the “in crowd” of a profession that differs from another term that is at least as good and understood by the masses is particularly pretentious when addressing an audience of laymen.

Look when you write something you have to know your audience. In their research, astronomers use parsecs, not light years. When their audience is other astronomers (peer reviewed articles, conference presentations, academic textbooks) they use the language of their research profession.

When they decide to write magazine articles or books for laymen, then they bust out the "for dummies" and "idiots guide" lingo (reference here is to the "Idiots guide to .." and "blah blah for dummes" series of books). And if they choose to include some of the jargon with the idiots guide lingo, they define the jargon in the idiots guide lingo so the layman reader gets both.

I don't see any problem with this and some of you seem to be inventing a problem that doesn't exist.

AndreasJ
2008-Oct-11, 10:54 PM
One that bugs me is "early" and "late" with reference to stellar spectra. "Warm" and "cool" would make more sense.

Also, the whole Pluto debacle made me wish the word "planet" would just go away. I'm not holding my breath ...

Gigabyte
2008-Oct-11, 11:21 PM
Especially since planet means "wandering star".

timb
2008-Oct-11, 11:25 PM
hundreds of thousands have been sold to ordinary investors who have profited from my words

What about the larger number who lost money? Technical analysis is to finance as astrology is to astronomy.

Gigabyte
2008-Oct-11, 11:28 PM
Let's not go off topic here.