View Full Version here: : Names of Crux pointers
Am I losing my mind?
I was taught as a young fella in the 70s that the two Crux pointers were named Alpha and Beta Centuri. Not as Starry Night 6 tells me..Rigel Kentaurus and Hadir. I was getting used it in a “something’s not right” kinda way.
I saved some (over 100) old 60s, 70s and 80s high school text books from the bin at work the other day. One of which was entitled “Focus on the Stars” dated 1973.
I started reading and was engrossed by page 2. Turns out it contains lectures given to The Science Foundation for Physics within the University of Sydney in ‘73 by seven speakers including a young Frank Drake and even younger Carl Sagan.
Long story short there is a pic on page 25 taken at Stromlo (a few kms from where I grew up) by A.R Hogg that shows the pointers as Alpha and Beta Centari.
It bought memories flooding back and made me think.
A) Am I mistaken? (be kind)
B) Has there been a change in nomenclature, and if so why.
As Southern Hemisphere Australian observers how do we currently refer to these stars and more importantly why?
Erg - Pete
19-09-2011, 07:49 PM
Hi Pete, I am with you on this, also know them as alpha and beta Centaurus. Till I was recently doing a star alignment with the Losmandy mount and came across Rigel Kentaurus for the first time.
Interested to see what the more learned have to say on this.
Yeah, you'd think in the modern computer age they'd be listed both ways - proper astronomical convention and traditional (Arabic I think?) names. If I was writing software I'd favour astro convention over text names. Grrr.
19-09-2011, 08:02 PM
Hi Pete, quite a few of the bright stars have more than one name.
Alpha, is the first letter of the Greek alphabet which denotes the brightest star in the Constellation,in this case Alph Centouri
The Bayer catalogue uses the Greek Alphabet to denote the brightness of the star, Alpha being the brightest and Omega being the faintest.
As an amateur Astronomer I use mainly Rigil Kent or Alpha Cent when I am talking about this star in the abreviated form I have put here, as you may in the future if you talk to other observers .
Its Arabic name is Rigil Kentaurus which means foot of the Centour.
Same with Hadar,Beta Centauri which also has the name of Agena,but to most is Hadar or Beta Cent.
I hope this helps ?
PS it is Rigil, not Rigel.
19-09-2011, 08:16 PM
Those popular names for stars are mostly derived from the Arabic (Muhlifain), Latin (Capella), Greek and other languages. Not every star has a well-known popular name.
The designations beginning with a letter from the Greek alphabet are called Bayer designations, and are often given in order of apparent magnitude starting with Alpha for the brightest.
However this is confusing because there are about 30 constellations in which Alpha is not the brightest star !
It gets more tangled still when the Greek alphabet runs out of letters in a constellation.
Friend Tony Buckley, who was ASNSW President for a while, loves to recount the story
of when he was present at a public observing night and a little old lady asked him,
"If the stars are so far away, how do we know what their names are?"
19-09-2011, 08:41 PM
That is just so beautiful!
19-09-2011, 08:45 PM
Good one Gary,:lol:
I wonder what Funny questions I will be asking when I am an Old Man:question: :rolleyes: :lol:
19-09-2011, 09:46 PM
For example we have Orion where Betelgeuse is Alpha Orionis and Rigel is Beta Orionis and is about 0.5 magnitudes brighter. Sometimes this has happened because one star has dimmed or another brightened, or they were just measured incorrectly in the first place.
Then there are the ones that have been renamed. For instance Acamar used to be called Achenar. After the time of the Greeks with people observing more southerly stars, Eridanus was extended further south and the name was moved to the new "end of the river".
When it comes to names stars tend to have lots of them:
NAME ACAMAR * tet01 Eri CCDM J02583-4018A
CD-40 771A CPC 0 1403 CPD-40 253A
CSI-40 253 42 CSI-40 771 22 FK5 106
GC 3584 GCRV 1661 HD 18622
HR 897 IDS 02545-4042 A N30 613
PLX 624 PPM 307195 ROT 404
SACS 63 SAO 216113 SKY# 4464
NAME ACHERNAR * alf Eri ALS 16724
CD-57 316 CPC 20 447 CPD-57 334
EM* CDS 176 FK5 54 GC 1979
GCRV 916 GEN# +1.00010144 GSC 08478-01395
HD 10144 HIC 7588 HIP 7588
HR 472 IRAS 01358-5729 JP11 517
2MASS J01374284-5714119 N30 335 NSV 15353
PLX 344.00 PLX 344 PPM 331199
ROT 233 SAO 232481 SKY# 2444
TD1 938 UBV 1700 UBV M 8330
uvby98 100010144 2XMM J013742.5-571413 [JE82] 39A name for every occasion.
19-09-2011, 11:55 PM
They are both valid ways of referring to those particular stars. Alpha Centauri is the Bayer system and Rigil Kentaurus is its Proper Name, which it would have been give in ancient times.
Just stop and think about that for a bit - the Greeks knew the Centaur with two front feet, yet they can't see them from Greece today...a little example of the effect of precession for you. :thumbsup:
Cool - thanks for that Jacquie :)
Same as per Blue Skies.
When I was in 8°N and I had to explain the stars under a starry night to the peoples, I referred to the Southern Pointers as Alpha and Beta Centauri, and only after the explaination I would say "they have also a proper name...". This is because their proper names, Rigil Kentaurus and Hadar, are a bit less known than their Bayer designation. I checked it on many books and atlases. On the other hand, many bright stars like Sirius, Canopus, Achernar, Antares, Vega, Capella, and so on, are best known with their proper name, and rarely (only on certain academic publications) I saw them called Alpha Canis Majoris, Alpha Carinae, Alpha Eridani, Alpha Scorpii, Alpha Lyrae, Alpha Aurigae, and so on.
Concluding, both the names are correct, it is only your discretion using one instead of the other.
PS: about the precession. Here in Sardinia we have an ancient megalithic monument aligned with the Southern Pointers. 3000 years ago, they were visible from my island; now these two stars are at least 10° below the horizon. ;)
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