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My Friends the Naked-Eye Stars

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#1 Tony Flanders

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Posted 03 February 2024 - 06:54 AM

Claudius Ptolemy's Almagest, the foundational textbook of Western astronomy, includes a catalog of more than 1,000 stars visible from Alexandria, Egypt, around 150 AD, when the book was published. Ptolemy divides the stars into six classes, from first class for the very brighest stars down to sixth class for the faintest stars visible with the unaided eye.
 
Somewhat shockingly, this magnitude system, as Ptolemy called it, is still in use today. It's now defined in terms of rigorous brightness measurements, but the scale was carefully adjusted to make the scientifically measured magnitudes match Ptolemy's seat-of-the-pants estimates as well as possible. And the scale still runs "backward," with the brightness stars having the lowest magnitudes, just as it did in the Almagest.

First-magnitude stars are now defined as those with visual magnitudes less than 1.5. Unlike all other classes, this one is usually considered to be open-ended on the bright side; there is no zeroth class for Vega at magnitude 0.03, nor a minus-first class for Sirius, the sky's brightest star at magnitude -1.46.

 

There are just 21 first-class stars. From brightest to faintest they are Sirius, Canopus, Alpha Centauri (Rigil Kentaurus), Arcturus, Vega, Capella, Rigel, Procyon, Achernar (Alpha Eridani), Betelgeuse, Beta Centauri (Hadar), Acrux (Alpha Crucis), Altair, Arcturus, Antares, Spica, Pollux, Fomalhaut, Becrux (Beta Crucis), Deneb, and Regulus. The five stars with parenthesized alternate names are too far south to see from mid-northern latitudes, which is why their "common" names never became fully standardized in the Western tradition. In addition, Canopus is invisible from the northern half of the United States and almost all of Europe.

Anybody who spends much time viewing the night sky soon becomes familiar with all the first-magnitude stars visible from their latitude. They're bright enough to stimulate color vision and to dominate their sectors of the sky, so you soon come to recognize them at a glance. Like the planets they shine apparently effortlessly through the worst artificial light pollution; they're even visible shortly after sunset, while the sky is still quite blue.

Second magnitude stars, from 1.5 down to 2.49, are the backbones of the most prominent constellations. They include six of the Big Dipper's seven stars, all three stars of Orion's Belt, all four stars of the Great Square of Pegasus, and so on. Second-magnitude stars are visible in all but the very worst sky conditions, except maybe when they're very close to the horizon. I'm not sure I could tell you the proper name and Greek-letter designation of each one of the 50 or so 2nd-magnitude stars visible from my latitude, but if any one of them were to disappear, I'm sure I would notice its absence almost immediately.

Third-magnitude stars, from 2.5 to 3.49, are also critical to most of the constellation stick figures. They include Megrez, where the Big Dipper's handle joins to the bowl, two of the stars that form Cassiopeia's signature M or W, Albireo at the long end of the Northern Cross, and so on. Unfortunately, third-magnitude stars can be severely injured or even rendered invisible by heavy urban light pollution or bright moonlight, especially when atmospheric conditions are poor.
 
That's doubly true of fourth-magnitude stars, the true litmus test of an urban sky. I can see many fourth-magnitude stars from New York City's Central Park on a good night, but only with considerable effort. Without them the Little Dipper is reduced to three stars, and Cancer and Pisces are completely invisible. Yet under a dark, transparent sky fourth-magnitude stars still seem quite bright.
 
Fifth-magnitude stars are another matter entirely. They're certainly not hard to make out under a dark sky, but they always seem rather faint to me even there. They're hopeless inside the boundaries of most major cities, and often challenging even from the outer suburbs. Yet even fifth-magnitude stars play important roles in many of the constellations. Eta Ursae Minoris, the faintest star of the Little Dipper, shines at magnitude 4.95 according to the Yale Bright Star Catalog. Messier 44, the Beehive Cluster, is enclosed in a box whose westernmost stars shine around magnitude 5.3. The far-southern constellation Mensa has no stars brighter than 5.0.
 
And finally, there's sixth-magnitude stars, which are just plain faint any way you look at it. Yet under dark, transparent skies they outnumber all other stars by a large margin. They're the ones that make stars a proverb for anything too numerous to count, as in the memorable folksong On Top of Old Smokey:
 
They'll hug you and kiss you
And tell you more lies
Than the crossties on the railroad
Or the stars in the sky.
 

How alien that last line must seem to most inhabitants of the industrialized world!


Edited by Tony Flanders, 03 February 2024 - 07:18 AM.

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#2 Javier1978

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Posted 03 February 2024 - 08:50 AM

Thank you, Tony, I enjoyed reading this!

 

Are constellations like Mensa creations of astronomers to fill gaps in the night sky?


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#3 CarolinaBanker

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Posted 03 February 2024 - 09:20 AM

Thank you, Tony, I enjoyed reading this!

Are constellations like Mensa creations of astronomers to fill gaps in the night sky?


They were creations of mostly one guy, Lacaille. Here’s an article that may be of interest: https://www.skyatnig...lations-history
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#4 CarolinaBanker

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Posted 03 February 2024 - 09:21 AM

Tony, an excellent piece for any of us observing under less than pristine skies.

#5 Tony Flanders

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Posted 03 February 2024 - 09:30 AM



Thank you, Tony, I enjoyed reading this!

 

Are constellations like Mensa creations of astronomers to fill gaps in the night sky?


Precisely. My favorite discussion of this subject (and many more relating to stars and constellations) is on Ian Ridpath's website.

 

It's interesting that in ancient times astronomer's didn't feel the need to fill the gaps; the Almagest describes many stars as being near, but not inside, a constellation. Even earlier, the entire idea of dividing the sky up into well-defined constellations seems quite alien to most traditional star lore. And it was only with the IAU reforms of the 1920s and 1930s that the constellation's boundaries became well defined. Before that it was considered perfectly reasonable for a single star to belong to two different constellations, like Alpha Andromedae, formerly also known as Delta Pegasi, at the corner where Andromeda joins the Great Square.


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#6 NinePlanets

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Posted 03 February 2024 - 10:35 AM

... it was considered perfectly reasonable for a single star to belong to two different constellations, like Alpha Andromedae, formerly also known as Delta Pegasi, at the corner where Andromeda joins the Great Square.

In my world it is still perfectly reasonable.  wink.gif

 

I make up my own constellations based upon what I think they look like. Many/most of "my" constellations are the traditional ones, but there are others that just make more sense to my eye/brain. Like The Bikini Bottom of Capricorn, The Harbor Seal of Perseus, The Caltrops of Aquarius, The Lemon of Scutum, The Wine Glass of Serpens/Hercules... It goes on.

 

I figure if these big dob guys can make up names for nebulae, like The Elephant Trunk, I can make up names for constellations. Besides, I have found that when I point out MY constellations to newbies, it's easier for them to see them than to see the classic figures.

 

By the way, Aquila's head is to the south of Altair. Altair is the center of his tail feathers.  (See?)  ;)

 

But that's just me.
 


Edited by NinePlanets, 03 February 2024 - 10:38 AM.

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#7 mikemarotta

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Posted 03 February 2024 - 10:47 AM

Precisely. My favorite discussion of this subject (and many more relating to stars and constellations) is on Ian Ridpath's website.

 

It's interesting that in ancient times astronomer's didn't feel the need to fill the gaps; the Almagest describes many stars as being near, but not inside, a constellation. Even earlier, the entire idea of dividing the sky up into well-defined constellations seems quite alien to most traditional star lore. And it was only with the IAU reforms of the 1920s and 1930s that the constellation's boundaries became well defined. Before that it was considered perfectly reasonable for a single star to belong to two different constellations, like Alpha Andromedae, formerly also known as Delta Pegasi, at the corner where Andromeda joins the Great Square.

 

Thanks, Tony. Ian Ridpath's website (http://www.ianridpath.com) is a great resource.  He is prolific and well respected within both the professional and amateur communities. I have used him as a citation.

 

He is editor of the Oxford Dictionary of Astronomy and Norton's Star Atlas, and author of observing guides such as The Monthly Sky Guide and the Collins Stars and Planets Guide ...  --  https://en.wikipedia...iki/Ian_Ridpath

 

 

 

It is a basic problem in the writing of history to put yourself in another time and place. We accept our cultural context all too easily. As a minor note, long ago we enjoyed a time travel story set in Regency England and the modern guy, being polite, says, "How do you do?" and the woman replies, "How do I do what?" The absolute magitudes of stars has a physical basis explained by consistent theory. Constellations are cultural and as you note, there was never much need to map out the entire sky.

 

Coins are among the incidental artifacts of astronomy. See Astronomical Symbols on Ancient and Medieval Coins by Marshall Faintich; McFarland & Co., 2008, 232 pages. I believe that Dr. Faintich dropped the ball a couple times but his major premise is correct: coins symbolize political power and record celestial events. Among the very earliest of issues of Croesus (Kroisos) near the invention of coinage c. 600-550 BCE, are those with Bulls confronting Lions. With the Scorpion and Orion, you have all you need for farming. In the Odyssey, Calypso tells the hero to steer by the Bear which some men call the Wagon. But at that time of writing -assuming that Homer lived c. 800 BCE and the poem was set in writing circa 500 BCE - there was no North Star. More to the point here the archaic Greeks did not perceive the planets qua planets per se

 

Anyway, thanks again for the summary. I archived it for my own observing notebook and I will link to your post here for some of my astro-friends in our local club.

 

Clear Skies!

Mike M.


Edited by mikemarotta, 03 February 2024 - 10:50 AM.


#8 mountain monk

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Posted 03 February 2024 - 08:57 PM

Great post, Tony. Thanks.

 

Dark skies.

 

Jack



#9 PXR-5

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Posted 03 February 2024 - 09:36 PM

Very enjoyable read Tony, thanks.

#10 star69

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Posted 04 February 2024 - 11:12 AM

Thank you, Tony. Excellent post. I honestly had no idea Ptolemy was the originator of the magnitude system. 

-Kevin



#11 MEE

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Posted 04 February 2024 - 03:02 PM

From a report posted on a meteor observers discussion group, 1998- observer and author was Lew Gramer:

“ So I waited... And then, as the cloudline swept past the bright Winter Milky Way, I noticed something strange: first Sirius, and then the stars of Orion, and finally all the 3rd magnitude stars of Lepus began to EFFERVESCE. Their twinkling became so intense and rapid, I couldn't help but think of fast-blinking lights in a Christmas display…..A few more minutes passed, and I noticed the sky had darkened: already-small light domes from Islamorada to East and the Resorts to West were now nearly invisible…..I was seeing a sky darker than any I've yet measured. Now I began to notice asterisms which were strange to me: Orion's sword now suddenly had four stars - the little open cluster NGC 1981 completing the unaccustomed figure on the north end. Canis Minor was not a simple two-star pattern, but a complex of 6 or 7 stars, tracing a fanciful image of a little dog to my imagination. Monoceros and Camelopardalis had become rich fields, Mon particularly showing whorls within whorls. I still don't know what my true Limiting Magnitude was during that time. I guess now it fell somewhere worse than 8.0 - but not far.”
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#12 dave253

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Posted 04 February 2024 - 06:02 PM

Cheers Tony! We’re tremendously lucky to be living under dark southern skies, and heading into my favourite time of year.
The cool autumn nights are coming, with Crux standing proud in the south.

 

As always, I love reading your words, one of my great joys is going through my 40+ years of S&T back issues and revisiting the great articles you’ve written. 


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#13 dryfly

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Posted 05 February 2024 - 09:35 AM

Thanks, Tony, a Fun read.  Kind of funny how we mad everything fit Ptolemy's estimates.

 

Mike


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#14 Tony Flanders

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Posted 06 February 2024 - 06:00 AM

Thank you, Tony. Excellent post. I honestly had no idea Ptolemy was the originator of the magnitude system.


It's amazing just how much of modern science descends more or less unchanged from the Almagest. Most obviously, all the important constellations north of declination 20S are still almost exactly as Ptolemy described them.

 

But much more profoundly, the degree-minute-second system of measuring angles comes straight from the Almagest. It became obsolete sometime around 800 AD, when Muhammad ibn Musa al-Khwarizmi (Latinized as Algorithm) standardized the decimal system in the "Western" world, which was at that time centered in Baghdad. Yet it's still the standard way to express angles in every technical discipline.


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#15 Urban Uraniborg

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Posted 08 February 2024 - 01:10 PM

Flat earthers, false western astrology, fixed star and earth centric idioms. A lot more than knowledge in books was lost when the library of Alexandria was destroyed. If not for the House of Wisdom in Baghdad and all Arabic astronomers there after, we would have only crawled out of the dark ages recently. The most notable part of the story lost(to the astronomer) was the knowledge of the Precession of Equinox. 
 

I could go on and on…on this topic. However I will leave you with an observation to make of the Precession since Ptolemy. 
In geography we still call them the Tropics of Cancer and Capricorn as they were in Ptolemy’s time. 

Currently in the Precession the 90° and 270°(solstitial points) on the ecliptic are approaching the Houses of Taurus and Scorpio. For the next hundred years or so it’s the Tropics of Gemini and Sagittarius. 
 

 

Eygpt at this time and before made optical primary lenses of glass and crystal said to be inset in the eyes of the large Pharaonic statues. I think it is TIME for a fresh perspective! 

 

-Micah

 


Edited by Urban Uraniborg, 08 February 2024 - 03:55 PM.

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#16 Mike in Rancho

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Posted 09 February 2024 - 08:45 PM

Arcturus bought two first-class tickets.  Somebody got left at the gate!

 

...probably also starts with an A.  wink.gif



#17 Urban Uraniborg

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Posted 10 February 2024 - 06:55 PM

Arcturus definitely made the trip! With a Proper Motion of 2” arc seconds per year it was one of the stars used to discover our Solar Apex and Proper Motion, whence Edmund Halley compared the stars of his sky to those of Ptolemy’s. Halley also calculated the rate of Precession( highest accuracy of the time) with the time passed between the Almagest. 

Had Kepler, Newton and Halley not learned to read and write Arabic to join the conversation with the Ghost of Ptolemy and Hipparchus, would we have reached the Astronomical Unit with one of the few Venus Transits since 1769?

  
 



#18 KBHornblower

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Posted 10 February 2024 - 07:38 PM

Arcturus definitely made the trip! With a Proper Motion of 2” arc seconds per year it was one of the stars used to discover our Solar Apex and Proper Motion, whence Edmund Halley compared the stars of his sky to those of Ptolemy’s. Halley also calculated the rate of Precession( highest accuracy of the time) with the time passed between the Almagest. 

Had Kepler, Newton and Halley not learned to read and write Arabic to join the conversation with the Ghost of Ptolemy and Hipparchus, would we have reached the Astronomical Unit with one of the few Venus Transits since 1769?

  
 

Arcturus is an outlier, in an inclined galactic orbit that gives it a rapid, anomalous motion relative to the Sun.  It is of no use in determining the Sun's apex.  That is determined from statistical analysis of the proper motions of numerous stars appearing to move at moderate rates in roughly the same direction.



#19 Urban Uraniborg

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Posted 10 February 2024 - 07:57 PM

http://leosondra.cz

 

this website has an paper on Edmund Halley’s discovery of Proper Motion and the role Arcturus played. 

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Edited by Urban Uraniborg, 10 February 2024 - 08:00 PM.


#20 Urban Uraniborg

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Posted 10 February 2024 - 08:21 PM

Perhaps Halley only placed a general location for the Solar Apex? 
This article titled “The Solar Apex” says:

“Herschel was the first to prove that our Sun is no exception to this rule. He took as the basis of his calculations such proper motions of stars as were known in his day and available for the purpose.”

 

http://articles.adsabs.harvard.edu

 

Crediting Herschel for doing the calculations to place the Solar Apex. 


Edited by Urban Uraniborg, 10 February 2024 - 08:51 PM.


#21 Mike in Rancho

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Posted 10 February 2024 - 08:51 PM

Well, I really just meant that Arcturus is listed twice in the OP's list of 21.  Which I probably should have just said, instead of trying to be funny.  tongue2.gif

 

And thus, Aldebaran got snubbed?



#22 Urban Uraniborg

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Posted 10 February 2024 - 09:20 PM

I would apologize for spewing on and on, but these replies have brought me to new to me old articles of the subject. So thanks for that!

 

If my links don’t get you straight there, here are the full titles. 

Edmond Halley: Discovery of Proper Motions 

by Edmond Halley

Philosophical Transactions Vol. 30 (1717-1719)

 

The Solar Apex

by Thomas Curran Ryan


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#23 Astroman007

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Posted 10 February 2024 - 10:26 PM

Thanks, Tony, a Fun read.  Kind of funny how we mad everything fit Ptolemy's estimates.

 

Mike

Sometimes the facts must fit the theories.

 

"I know that most men...can seldom accept even the simplest and most obvious truth if it be such as would oblige them to admit the falsity of conclusions which they have delighted in explaining to colleagues, which they have proudly taught to others, and which they have woven, thread by thread, into the fabric of their lives.” ~Leo Tolstoy

 

You run a risk every time you oppose the reigning theories that have by lack of full facts or subterfuge found favor with the Arbiters of Truth of the moment, but history will thank those brave ones who do. Intellectual honesty and loyalty to the scientific method demand it.


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#24 jakabasej8

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Posted 11 February 2024 - 03:42 AM

Precisely. My favorite discussion of this subject (and many more relating to stars and constellations) is on Ian Ridpath's website.

 

It's interesting that in ancient times astronomer's didn't feel the need to fill the gaps; the Almagest describes many stars as being near, but not inside, a constellation. Even earlier, the entire idea of dividing the sky up into well-defined constellations seems quite alien to most traditional star lore. And it was only with the IAU reforms of the 1920s and 1930s that the constellation's boundaries became well defined. Before that it was considered perfectly reasonable for a single star to belong to two different constellations, like Alpha Andromedae, formerly also known as Delta Pegasi, at the corner where Andromeda joins the Great Square.

That's a fascinating observation!



#25 jakabasej8

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Posted 15 February 2024 - 06:09 AM



Well, I really just meant that Arcturus is listed twice in the OP's list of 21. tabletop miniatures Which I probably should have just said, instead of trying to be funny. Sharp Edge Shop  tongue2.gif

 

And thus, Aldebaran got snubbed?

Ah, got it! Thanks for clarifying.




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