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unlearning the constellations

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#126 drollere

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Posted 08 November 2012 - 02:08 PM

i am certainly intrigued, even fascinated, by the sentiment repeated here that my proposal to look at the sky with fresh, wide eyes is equivalent to trashing the past, burning books, forbidding ideas, purging texts, policing speech or denigrating culture.

as i said, i decline the opportunity to debate those points further. but i appreciate the demonstration of the grip that tradition holds on the mind.

#127 Glen A W

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Posted 08 November 2012 - 02:22 PM

i am certainly intrigued, even fascinated, by the sentiment repeated here that my proposal to look at the sky with fresh, wide eyes is equivalent to trashing the past, burning books, forbidding ideas, purging texts, policing speech or denigrating culture.


I think it's a great idea. And one whose time has come. GW

#128 drollere

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Posted 08 November 2012 - 02:42 PM

the next step, perhaps the most difficult step, is selecting out of the visible sky the features that can orient the observer and mark out the galactic landscape.

since constellations are by and large unsatisfactory as visual guides (as explained in the previous post), and asterisms have no content as structural features (the stars that compose them can be very widely separated in space), the objective seems to lead to a selection of visually bright stars as the solution space.

"bright" is a loose term (professional astronomers would call a magnitude 15 star "bright"), but given the limitation of naked eye orientation a magnitude cutoff of between 2 to 3 seems about right. for example, stars above magnitude 3 are relatively robust against urban light pollution. in cassiopeia, a salient constellation and asterism, four of the five stars in the "W" are above magnitude 3; similarly, in auriga, all five stars in the pentagon are above magnitude 3; in the dipper, six of the seven stars are above magnitude 3. in contrast, in cepheus, an obscure constellation, only alderamin is above magnitude 3; in lyra, another obscure constellation, only vega is above magnitude 3.

what would a list of "bright" stars, however defined, be used for? at least:

* for orientation to the night sky (e.g., season, sidereal time, direction, latitude)
* for orientation to galactic features (e.g., the galactic center, the local arm)
* as a descriptive sample: what kind of star is a typical bright star?
* as a representative sample: what does the population of stars look like?
* as an enumerative sample: what is a visible example of every kind of star?
* as a local sample: which stars are visible local stars (within X parsecs)?
... and so on.

this is a problem i am still working on. a magnitude cutoff between 2 and 3 seems useful, as it limits the number of stars in the list to around 100 or less. a distance cutoff of about 50 parsecs seems useful, as there are about 50 bright stars within that radius. but a preliminary look indicates that many of the late type (K or M) stars in that list are giant stars. and none of the stars within 50 parsecs is an early type (OB) giant star.

so the challenge seems to be this: develop an intuitive and consistent approach to the selection of landmark stars that are both near and far, intrinsically bright and dim, span the entire HR diagram, and point the way to galactic features ... not so easy, it seems.

#129 Dennis_S253

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Posted 08 November 2012 - 03:55 PM

Oh my gosh, the sky is wonderful.

#130 Tony Flanders

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Posted 08 November 2012 - 05:10 PM

i am certainly intrigued, even fascinated, by the sentiment repeated here that my proposal to look at the sky with fresh, wide eyes is equivalent to trashing the past


Sorry, you are the one who said that it's helpful, maybe even necessary, to "unlearn" the constellations -- in other words, to trash the past.

Nobody has objected to your proposal to view the sky with fresh eyes, and many of us have enthusiastically embraced it. But you seem to be the only one here who finds that the old system obstructs the new one. Most of us have no trouble viewing reality simultaneously from multiple perspectives.

I never visualized the constellations as true physical entities, nor do any of the beginners that I speak to at star parties. In fact, one of the first questions I get is usually "Do those stars really belong together, or is that pattern an accident?" To which I reply, "an accident, of course."

#131 Dwight J

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Posted 08 November 2012 - 09:51 PM

"Unlearning" the constellations would essentially be equivalent to unlearning breathing - not possible. Our brain organizes randomness into patterns at an unconscious level. When I look up, I can't stop seeing patterns and shapes defined by the stars. Constellations/star patterns may vary culturally and historically but they occur across all of them. There may be a way to better describe our place in the cosmos but our innate ability to organize randomness cannot be suppressed.

#132 CounterWeight

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Posted 08 November 2012 - 10:12 PM

i am certainly intrigued, even fascinated, by the sentiment repeated here that my proposal to look at the sky with fresh, wide eyes is equivalent to trashing the past, burning books, forbidding ideas, purging texts, policing speech or denigrating culture.

as i said, i decline the opportunity to debate those points further. but i appreciate the demonstration of the grip that tradition holds on the mind.


I think either you missed my point or I muddled it. The past cannot be debated - and not my intention.

My point is what do you intend to retain, if anything at all. This with a mind to not repeating it or simply re-organizing into something purely self suiting.

As I tried to link to... a 3D representaion has ALREADY BEEN DONE. Please convince me you are not re-inventing the wheel.

What are you bringing to the party that others have not already contributed?

It's as though in trying to contribute or even understand... one gets 'dissed' as bound by orthodoxy.

the next step, perhaps the most difficult step, is selecting out of the visible sky the features that can orient the observer and mark out the galactic landscape.


who's galactic landscape? What we do know of and have data for... already done, or am I missing something here? I and at least one other responder linked you to it. This for folks that have no access to the web or star chats/atlas? Living in the city and can't see milky way? And it's to be somehow intuitive? All inclusive?

what would a list of "bright" stars, however defined, be used for? at least:

* for orientation to the night sky (e.g., season, sidereal time, direction, latitude)
* for orientation to galactic features (e.g., the galactic center, the local arm)
* as a descriptive sample: what kind of star is a typical bright star?
* as a representative sample: what does the population of stars look like?
* as an enumerative sample: what is a visible example of every kind of star?
* as a local sample: which stars are visible local stars (within X parsecs)?


At the risk of repeating myself, this too has been done... at least for anyone willing to look for the information. And that takes surprisingly little effort.

Not re-inventing a perfectly useful wheel - fine.

#133 derangedhermit

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Posted 08 November 2012 - 10:31 PM

i am certainly intrigued, even fascinated, by the sentiment repeated here that my proposal to look at the sky with fresh, wide eyes is equivalent to trashing the past, burning books, forbidding ideas, purging texts, policing speech or denigrating culture.

as i said, i decline the opportunity to debate those points further. but i appreciate the demonstration of the grip that tradition holds on the mind.

:roflmao:
Is there an "ignore this user" function in the forum software? I can't find it.

#134 mark8888

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Posted 09 November 2012 - 03:50 AM

Nobody has objected to your proposal to view the sky with fresh eyes, and many of us have enthusiastically embraced it. But you seem to be the only one here who finds that the old system obstructs the new one. Most of us have no trouble viewing reality simultaneously from multiple perspectives.


I agree with this. It's an interesting topic and a great thread, and I certainly agree that it's important to see the sky intuitively, with our place apparent in the galactic landscape, and any effort to make that easier is a good and valuable thing. But it's as if the poster is saying, humans are incapable of "getting" that two birds are flying at different altitudes if we also note that they appear near each other from our perspective, and if that information proves useful in some way. Of course, we can do both. Most people with even a passing interest in astronomy already understand this and see the sky both ways.

#135 bumm

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Posted 09 November 2012 - 03:18 PM

This has been an intriguing thread. I've contributed a couple of posts, but I'm getting a little lost. I may be missing something, but I get the impression that the OP figures that the constellations somehow detract from gaining a broader understanding of the universe. Surely, if someone figures that the constellations are somehow magically arranged as stellar art, or that the visible stars are all at the same distance, this may be the case, but I've never met anyone with a view of the universe this misleading or primitive.
To the vast majority of starhoppers, the constellations serve as an extremely effective and convenient "coordinate system" for finding things in the sky. One could use RA & dec, but the constellations are essentially engraved on the sky, requiring no other equipment to measure and read.
Does this system somehow stand in the way of gaining a broader understanding? Of course not. If anything, having to look at the sky, with it's different star densities in different areas, the proximity or "avoidance" of certain objects to the Milky Way, the visual structure in the Milky Way, and any number of other variations leads to a greater understanding of the solar system, the galaxy, and the universe for anyone who's curious enough to want to know.
In my personal opinion, one would learn much less about the universe by only finding objects by their RA & dec coordinates, or worse yet, letting a GOTO scope find everything without paying any attention to where the scope is pointed.
And no, I'm not arguing against GOTO...
Marty

#136 Tom Polakis

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Posted 09 November 2012 - 03:51 PM

This has been an intriguing thread. I've contributed a couple of posts, but I'm getting a little lost. I may be missing something, but I get the impression that the OP figures that the constellations somehow detract from gaining a broader understanding of the universe.


No, it doesn't sound like you're lost at all. That's a good summary of what the OP is insisting is the case.


To the vast majority of starhoppers, the constellations serve as an extremely effective and convenient "coordinate system" for finding things in the sky. One could use RA & dec, but the constellations are essentially engraved on the sky, requiring no other equipment to measure and read.


Exactly. With all of their flaws, I find that constellations draw associations similar to states in the U.S. Just as I associate Florida with swamps, New England with rolling hills, and Colorado with jagged peaks, the constellations serve the same purpose. They aid rather than hinder my 3-D perspective of the sky. Ophiuchus is that constellation with the globular clusters due to their position in the galaxy's halo. The Supergalactic Plane cuts through Virgo and Ursa Major, hence all those relatively nearby galaxies.

Knowledge of the constellations and a perspective on the structure of the universe are in no way mutually exclusive. If I didn't embrace both as enjoyable pursuits, I'd be inclined to get another hobby.

#137 Crossen

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Posted 09 November 2012 - 05:04 PM

If anything, having to look at the sky, with it's different star densities in different areas, the proximity or "avoidance" of certain objects to the Milky Way, the visual structure in the Milky Way, and any number of other variations leads to a greater understanding of the solar system, the galaxy, and the universe for anyone who's curious enough to want to know.


When I read this, it reminded me of W. W. Morgan's story about how he discovered the Perseus Spiral Arm:

"I used to go to Cleveland for a week or so every few months [to meet with J. J. Nassau to work on the identification of Galactic OB stars], for a number of years. Nassau and I did all the classifying. . . . We had a belt I believe 10 degrees wide, as far south as we could get around the sky, and this [provided] the basic catalogue that we used here [at Yerkes Observatory] for taking slit spectrographs of as many of these stars as possible."

"Anyway, in the fall of 1951 I was walking between the observatory and home, which is only 100 yards away. I was looking up at the northern sky, just looking up in the region of the Double Cluster, and it suddenly occurred to me that the Double Cluster in Perseus and then a number of stars in Cassiopeia and even Cepheus--that along there I was getting distance moduli of between 11 and 12. Well, 11.5 is just 2 kiloparsecs, and so I couldn't wait to get over here and really plot them up. It looked like a concentration. . . . . But the hardest thing is to know what's going on if you're in the middle of something. So when I plotted out the Perseus arm, I then plotted out the other stars, and it turned out through the Sun there was this narrow lane parallel to the other one. So that's the way it happened. It was a burst of realization. It was not a question of a reasoned process of steps." (Page 92 of Owen Gingerich's "The Great Copernicus Chase and Other Adventures in Astronomical History.")

Obviously Morgan's knowledge of the constellations helped him visualize what his astrophysical data meant topographically. It also demonstrates how we ourselves can use the constellations in learning Local Spiral Structure. Moreover, many of the constellations are NOT entirely mere chance alignments of stars: Orion looks the way it does in part because almost all its bright stars are members of the Orion Association. Most of the bright stars in Scorpius, Lupus, Centaurus, and Crux are members of the Scorpio-Centaurus Association. The Big Dipper (anciently known as "The Wagon") stands out because five of its seven stars are the core of the Ursa Major Moving Group. Alpha and Beta Aquarii are members of a decayed association. The face of Taurus and the Hair of Berenice are open clusters. Naturally most of the constellations are indeed chance alignments of stars. But enough of them are not that learning the constellations is a very good first step in getting "Galactic depth perspective."

Craig Crossen

#138 Kfrank

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Posted 10 November 2012 - 03:29 PM

i am certainly intrigued, even fascinated, by the sentiment repeated here that my proposal to look at the sky with fresh, wide eyes is equivalent to trashing the past, burning books, forbidding ideas, purging texts, policing speech or denigrating culture.

as i said, i decline the opportunity to debate those points further. but i appreciate the demonstration of the grip that tradition holds on the mind.

:roflmao:
Is there an "ignore this user" function in the forum software? I can't find it.


I am intrigued and even fascinated by the fact that the OP continues to dismiss those who refuse to jump on his bandwagon as hide bound traditionalists.

Putting forth a controversial proposal, refusing to engage in debate with regard to it and dismissing those who disagree as either simpletons who just don't understand or bound by tradition hardly seems to be the way to get one's point across.

Bruce, I too decline the opportunity to debate this further.

#139 Mxplx2

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Posted 11 November 2012 - 07:37 AM

DANGER!!!

EGOS AT WORK.

ENTER WITH CAUTION!

#140 drollere

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Posted 11 November 2012 - 12:50 PM

a simple place to start the list of anchor or critical stars, the bright stars that orient the observer to the galactic landscape, is with local bright stars -- "companion" stars.

this list depends in part on the magnitude cutoff, in part on the distance cutoff, and in part on an inclusion cutoff ... but i've chosen a magnitude of about 2.0, a distance of 10 about parsecs and an inclusion of 10 stars. this yields the selection below:

Posted Image

stars in red are just outside 10 parsecs, but arcturus is useful to mark the north "window" of the galactic pole.

the selection provides two stars in the winter galaxy, and two stars in the summer galaxy, both very bright and distinctive, and a single bright star near the galactic north and south poles. the diagram, which represents the true distances in relation to equatorial north and the points of solstice, shows a nice distribution.

the 10 parsec sphere is the basis for absolute magnitude, so it is useful to describe the magnitude system, its definition as a logarithmic scale, and the fact that a log scale defines our visual sensitivity and perception of brightness.

it's also useful to characterize the close solar neighborhood, for example as an enumeration of *all* stars within that distance. according to the hipparcos-yale-gliese database (documented and available HERE), the enumeration looks like this (spectral type shown as size and color of icon):

Posted Image

remarkably there are 325 stars in HYG within 10 parsecs, half of them at magnitude 11 or fainter, and over 80% of them too faint to see with the naked eye. most of our "neighbor" stars are invisible to binocular assisted eyes and not part of any constellation asterism.

the reason is that most are K and M type stars (small red icons), cooler and less massive than the sun and also much fainter. (far from being an "average" star, the sun is actually above average, and above median.) in fact the hipparcos and gliese surveys suffer the same "brightness bias" that afflicts every branch of astronomy, because the true number of stellar mass objects within 10 parsecs is higher by an unknown but significant amount.

the james webb telescope, optimized for large aperture infrared astronomy, may indicate by how much. in the meantime, a 10 parsec radius defines a sphere of about 4200 cubic parsecs. given only the stars we see, this implies an average distance between 325 stars of about 3 parsecs.

#141 drollere

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Posted 11 November 2012 - 01:29 PM

As I tried to link to... a 3D representaion has ALREADY BEEN DONE. Please convince me you are not re-inventing the wheel. What are you bringing to the party that others have not already contributed?

i've been as plain as i know how to be: the goal is to identify naked eye markers and asterisms, easily identified in the night sky and easily remembered as indicators of basic facts, facts that represent a basic orientation to our place in the galactic landscape and identify features that are significant examples of galactic process.

i believe i have never challenged the utility of the IAU constellations as tracts in a "two dimensional" celestial area, and i have never made the claim that the past needs to be discarded as useless.

yes, i have said that the tracts are inherently arbitrary, and that the past is fine for those who find it interesting, and specifically that cultural history is irrelevant to organizing and remembering our current understanding of the galaxy.

and yes, i have made the claim that the currently available astronomical literature offers very little support for anyone interested to "see" the galactic landscape apparent to us, and i have made the claim that it is useful to "forget" or "unlearn" the constellations in order to let the eyes (not the learned constellation concepts) do the looking in order to find and piece together the useful asterisms and markers. (see the post above about how the constellations actually appear to the naked eye, if viewed without prejudice as to "what i should see".)

what part of that is unclear or poorly expressed?

who's galactic landscape? What we do know of and have data for... already done, or am I missing something here? I and at least one other responder linked you to it. This for folks that have no access to the web or star chats/atlas? Living in the city and can't see milky way? And it's to be somehow intuitive? All inclusive?

you're throwing a lot of issues at me there. but the nub is this: go to "atlas of the universe", or pick up henbest & couper's "guide to the galaxy", and you have a trove of catalog and graphic information about the galaxy, as imaged from a point far from the earth.

my question to you: what does all that look like as imaged from the earth? if you go out to the sky tonight, in which direction are the significant features?

it's an entirely different cognitive and spatial problem to orient yourself to a map of new york, to orient yourself while standing in times square, and to connect the two as an intuitive understanding of direction and distance. yes, there are lots of maps or three dimensional visualizations of the galaxy. but none of that is helpful to the naked eye or binocular astronomer as an answer to where we are located, what we can see from where we are located, and how what we can see relates to the whole.

that is explicitly stated in the OP: i said i was looking at the sky, and realized that the traditional constellations did not clearly or memorably indicate the major galactic features visible to me.

a simple example is that there is no asterism commonly used by astronomers to identify the center of the galaxy in the same way that there is an asterism (the dipper) commonly used by astronomers to find the pole star. or to identify the local arm. or to identify the galactic pole. and so on ...

in other words, there is no astronomical "lore" delving the galactic landscape as viewed from earth that even begins to rival (much less challenge) the lore about constellations -- their antiquity, their mythology, and their shopping basket contents of interesting and conceptually unrelated things to look at within an arbitrary area of sky.

#142 bumm

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Posted 11 November 2012 - 01:50 PM

Drollere was saying

a simple place to start the list of anchor or critical stars, the bright stars that orient the observer to the galactic landscape, is with local bright stars -- "companion" stars.

But how do we find these more suitable anchor stars? By their position in the constellations? :)
Marty

#143 drollere

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Posted 11 November 2012 - 02:26 PM

we have the companion stars, we know that rigil kent, sirius, procyon, altair, vega, fomalhaut and (approximately) arcturus are all within 10 parsecs. and these bright stars define an area of many unseen companion stars, but most too numerous and faint to identify.

the first asterism is the "summer triangle" of altair, vega and deneb. this is my first galactic asterism.

the elegance of this asterism is that it actually defines a long rectangle receeding into the distance, like a long, straight, road. to anchor the point, i can draw it with a dotted line down the middle:

we have the companion stars, we know that rigil kent, sirius, procyon, altair, vega, fomalhaut and (approximately) arcturus are all within 10 parsecs. and these bright stars define an area of many unseen companion stars, but most too numerous and faint to identify.

the first asterism is the "summer triangle" of altair, vega and deneb. this is my first galactic asterism.

the insight provided by this asterism is that it actually defines a long rectangle receding into the distance, like a long, straight, road. to anchor the point, i can draw it with a dotted line down the middle:

Posted Image

vega and altair, as companion stars, are both quite close to us (about 6.5 parsecs) and to each other (about 4.5 parsecs). in contrast, deneb is very far away -- so far away that its distance is uncertain. i've put it at 990 parsecs, but 1000 parsecs is easy to remember and 100 times farther than our companion stars, if we just say they are 10 parsecs distant and 5 parsecs apart.

now, simple perspective means deneb is the vanishing point, so that the width of the two sides of the triangle common to deneb defines the visual distance between altair and vega at greater distances than 10 parsecs. and this is measured as the distance from deneb to the baseline between vega and altair -- geometrically, the triangle height. located at half height from deneb, the baseline is twice the baseline distance of 10 parsecs, or 20 parsecs away; at 1/4 height, it is 40 parsecs; at 1/10 height, it is 100 parsecs, and so on. the triangle becomes a simple visual guide to judging the effects of distance on apparent size.

the three crossarm stars in cygnus, indicated by their bayer letters, can be distance located along this "road". the location of the 4.5 parsec baseline is shown for delta and epsilon, which are roughly 3 times and 8 times farther from us. the baseline for gamma is not shown because it is half the distance between us and deneb, or 470 parsecs, so its perspective baseline would be located 10/500 the triangle height from deneb.

it's possible to lard this framework with a lot more spatial information, for example as the apparent separation of the 5 parsec interval at different distances, or the apparent magnitude of vega and altair at those distances:

Posted Image

so this asterism -- the summer triangle with the three crossarm stars, forms a visually obvious and intuitive illustration of distance and the effects of distance on visual size and magnitude.

the fact that vega and altair at the distance of del Cyg are both near the naked eye threshold, and at gam Cyg are far below that threshold, gives some context to what distance means to "solar type" magnitudes (both are type A stars, roughly 30 times brighter than the sun). using the inverse square law, we know that vega and altair at twice their distance (near epsilon) will appear 1/4 as bright, and at the distance of deneb will appear 1/10,000th as bright.

the fact that at deneb's distance they would appear separated by only 16 arcminutes puts context around distance and apparent size.

there is also the fact that the vega altair baseline cuts across the visible galaxy at about galactic longitude 60º, which has been found by radio astronomy to be the "tangent line" or outer border of the galactic arm nearest to us toward the galactic nucleus (the carina sagittarius arm, which as we now see extends far beyond sagittarius). so this triangle actually forms a "window" through which we see the interval between this inner arm and our local arm -- we are looking between the two arms, as if looking up a long canyon or valley ... or the way a surfer, riding a large wave, looks back at the curl closing behind him.

it also reveals a significant problem: accuracy is a form of clutter. not a lot is lost by saying deneb is 1000 parsecs rather than 990 parsecs distant. or that vega and altair are separated by 5 parsecs rather than 4.5 parsecs, or that epsilon is 20 rather than 22 parsecs and delta 50 rather than 52 parsecs and gamma 500 rather than 470 parsecs away. the simpler numbers are easier to remember, and easier to manipulate as ratios of triangle height (1/2, 1/5, 1/50).

explaining the galactic landscape to a novice or a young person, simplification is essential. it's only by looking at several galactic asterisms that we can decide how much simplification is necessary as a general principle.

#144 CounterWeight

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Posted 12 November 2012 - 07:57 AM

Not trying to disagree with anything, but am curious if you have read that book "A Skywatchers Year" by Jeff Kanipe? I was looking through for candidate stars and reference... just curious.

#145 drollere

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Posted 13 November 2012 - 11:23 AM

But how do we find these more suitable anchor stars? By their position in the constellations? :)

all i can say is, try the "naive looking" i described in a post above.

i'm pretty sure that you do not locate the constellation canis major in order to find sirius, or piece together the faint stars of lyra to identify vega. you don't first find the constellation of canis minor in order to find procyon ... because procyon is all there is.

bright stars form a whole sky pattern, and that is how you orient to fainter patterns.

indeed, if you study the history of astronomy as crossen advocates, you'll find that bright stars (such as sirius) and a few bright asterisms (dipper, orion, pleiades) are at the root of sky lore. constellations as a general feature of astronomy appear with the rise of astrology, and with the need to identify fainter stars by their position within a standardized figure. this method is fully developed in ptolemy, and persists until william herschel.

#146 drollere

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Posted 13 November 2012 - 12:40 PM

looking outward from the galaxy center, the galaxy band presents a striking contrast from the summer triangle:

1. there are many more bright stars
2. the galaxy band appears less bright, or is not visible

the bright stars form an enormous and complex pattern, as illustrated below.

Posted Image

the important goals are, again, to anchor concepts of distance and scale, and to identify important features. i played around with different groupings, starting with the large hexagon formed by sirius, procyon, pollux, capella, aldebaran and rigel. but i ended up with something more modest: three triangles. i've also added star nomenclature, distances, spectral types and molecular cloud imagery.

Posted Image

1. the distance from pollux to capella is 34º, the same as the distance from vega to altair. it can be used in the same way to evaluate apparent size in relation to distance.

2. the triangle of alhena, capella and aldebaran is centered on alnath, and distances form a 10, 20, 30 and 40 parsec sequence, in alpha beta gamma order. the triangle encloses the auriga gap, and the gem OB1 molecular complex at 2000 parsecs distance.

3. a line extended from capella through alhena defines the north and east edge of the molecular concentrations, which are bounded on the south and west by a line from betelgeuse to sirius: the galactic equator is midway between them. the north line passes near the old and young clusters M46 and M47, at about 1700 and 500 parsecs distance, which therefore are situated above (direction of galactic north) the midplane of the galaxy disk.

4. the triangle of sirius, betelgeuse and rigel encloses the molecular clouds associated with barnard's loop and the orion nebula, a star forming region at around 400 parsecs distance.

5. the stars of the orion asterism are all closer to us than the nebula, by almost half. rigel, saiph and the outer belt stars from a trapezoid at about 250 parsecs; betelgeuse is at roughly half that (130 pc), and bellatrix at roughly half that again (75 pc).

6. the most distant bright star in this area is eta canis majoris, at 980 pc, almost exactly the same distance as deneb. as a visual cue of depth, the triangle of eta with wezen and adhara is, at its distance of ~1000 pc, the same size as the triangle of sirius, betelgeuse and rigel, visualized at rigel's distance of 250 pc. both triangles lie on the inner side of the local arm, and visually describe its recession away from us.

7. stars toward the orion asterism are relatively young and many are intrinsically bright. in fact, they form an orderly sequence in which the absolute magnitude increases with distance: this is why all stars in the asterism are comparably bright.

Posted Image

the sirius triangle region is an excellent illustration of molecular clouds, H-II regions and massive star formation, absolute magnitude and distance, and a good range of "early" or recently formed spectral types.

despite the numerous bright stars, this whole area is relatively barren of distant structures. a "perseus arm" is hypothesized to lie at a distance of 2000 to 3000 parsecs, but the arm is not clearly defined and in fact a considerable extent of the galaxy outward from the sun's location appears turbulent and disrupted. the conventional image of the galaxy is misleading when it shows dense, clearly defined spiral arms in this direction.

#147 drollere

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Posted 13 November 2012 - 12:47 PM

am curious if you have read that book "A Skywatchers Year" by Jeff Kanipe? I was looking through for candidate stars and reference... just curious.

don't know it, but i will look for it. thanks!

i am leaving today to boot up a house in mariposa, california, the possible site of future observing. i'll return to this topic later this week.

#148 CounterWeight

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Posted 14 November 2012 - 02:09 PM

Bruce,

Nice work there!

I think it's still available("A Skywatchers Year" by Jeff Kanipe), but a bit pricy, i think my version is from 1999 - maybe better to find at a used book store if one in your area.

it's a very diferent treatment of the topic, though i think in ways very much along the lines of what you might be after, I am just saying 'along the lines'. it does include some very widefield orientation diagrams and amplifying info about galaxy disk and things like where a meteor shower will come from... it's really an educational read in ways others aren't, part of it by virtue of a weekly indexing.

One useful device I have is the Daivid Levy 16" planisphere. This planisphere includes outline of Milky Way (with center mark near Saggit/Scorp), Ecliptic path of planets, and interestingly the triangle formed by Altair, Deneb, Vega that contains the 4 star structure of Cygnus. Being large it is far easier to use at night than my small ones.

It's impressive how much it can convery in a very short amount of time. yet by virtue of that can also come up quite short without a lot of amplifying information, depending.

I'm not trying to be contrarywise to what you are after at all. Just the curse of being a bookworm is I have many books and more than a few planishpheres.

That's why I am putting all the Q's out to about the idea. Rare ocassions where my daughter has friends over and it's clear and I'm doing visual, I love to hand them the planisphere and show it's usefulness as an orientation tool, then if attention span still there show the 'books'. But for all that, still extremely difficult to convey as you mention our 'neighborhood' and then even more the relationship of this neighborhood to the rest. Of all questions the 'how far away' is most asked. If I'm understanding your intentions there is definately room for something that could easily and quickly convey this, and I suspect it would be quite popular :)

#149 bumm

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Posted 14 November 2012 - 06:19 PM

But how do we find these more suitable anchor stars? By their position in the constellations? :)

all i can say is, try the "naive looking" i described in a post above.

i'm pretty sure that you do not locate the constellation canis major in order to find sirius, or piece together the faint stars of lyra to identify vega. you don't first find the constellation of canis minor in order to find procyon ... because procyon is all there is.

bright stars form a whole sky pattern, and that is how you orient to fainter patterns.

indeed, if you study the history of astronomy as crossen advocates, you'll find that bright stars (such as sirius) and a few bright asterisms (dipper, orion, pleiades) are at the root of sky lore. constellations as a general feature of astronomy appear with the rise of astrology, and with the need to identify fainter stars by their position within a standardized figure. this method is fully developed in ptolemy, and persists until william herschel.


Well, I can't speak for everyone, but I pretty much see the sky as a whole. Often, a bright star in a known location IS easier to pick out than the surrounding constellation. However, I generally confirm the identity of a star by looking at it's position among it's fellows... i.e. the constellations. This is true especially if I happen to be out at an unusual time. The Summer triangle is very conspicuous, and it's easy to identify the individual stars. However, it's not worth much for starhopping. I see Canis Minor as two stars... the brighter one is Procyon. By itself, theres nothing distinctive about Procyon. I'd have to confirm it's identity by the way it relates to Gemini. Sirius isn't much of a problem that way... it's distinctly BRIGHT. However, how many of us don't notice that it's following Orion?
Planispheres have been brought up in this discussion. I happen to collect old planispheres and love the things. (as some here might guess. :)) However, when I look at a military type planisphere showing only navigational stars with no constellations, I can eventually get oriented, but for my needs as an amateur astronomer, something is lost.
Not meaning to pick nits... You've put forth a considerable effort here. But still, I'm having trouble seeing the advantage of ignoring the constellations in favor of certain well picked individual stars.
Marty

#150 bryguy27007

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Posted 22 November 2012 - 12:03 AM

Bruce,

I imagine a planetarium program that could be told to show the naked eye sky from any location in or near the galaxy. It would be like having a virtual spaceship. One would quickly get lost if the program were so sophisticated as to able to put the reference point into light years per second motion.

I wouldn't mind heading out toward the Cone Nebula and tooling around for a while to see what the area looks like from other angles. :grin:

My interest in forming a mental picture of the actual 3D location of common celestial objects within our galaxy took
flight when I learned that the vast majority of what is visible to the naked eye is contained within a relatively small bubble of space with a radius of roughly 1500 parsecs, with us being in the center of the bubble.

Only 7,000 or so of the nearest AND brightest stars are visble to the unaided eye, mostly within that bubble, out of 2 or 3 hundred billion stars in the galaxy. Over half of either total are red dwarfs with only a scant few visible without optical aid, even the relatively near ones.

Looking toward the learned constellation of Saggitarius without optical aid, we can see (with a few exceptions) only about an eighth of the distance to the center of our galaxy. Same story along the galactic plane in the opposite direction towards the outer edge. Then there is the other entire half of the galaxy left to consider.

It's a lot to map, and I have only a very rudimentary knowledge of where the objects I can see actually are on that map so far, but I'm learning.

I too spend most of my time observing the "objects" in a telescope, because I enjoy it so much. But, I do make an effort to mentally place said object within our galaxy where it belongs, as best I can. Knowing what else is also in the locale of that object however, is another question that goes largely unanswered for me most of the time.


You might find this video extremely interesting.
http://www.youtube.c...h?v=8agz9FcDcPk






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