Hi Suzy & All,
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Originally Posted by Suzy
Have a go at the technique I use... 
Starting from Hadar, I join up to the next bright star which is Epsillon.
I use Zeta & Epsillon to form a triangle using Omega Centauri; it forms an easily discernible triangle.
Omega Cent. is 4 deg. (that's nearly the width of three fingers out stretched closing one eye) from the mid point of Z & E Cent. to make the triangle with Omega.
Stare at the space for a tiny bit and it will pop out.
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Okay, I find it just as easy to draw a line from Beta Centauri through Epsilon Centauri and extend it once in the same direction. Beta and Epsilon "point" at Omega, as does a line from Delta through Gamma Crucis (and no one, not one of you will flippantly ask ... "oh do you mean Garcrux?" -- be warned ... grrrrr
Quote:
Originally Posted by Suzy
P.S. Les will be proud of the correct genitive usage here.   |
... he is indeed!
Quote:
Originally Posted by Suzy
Regarding what Les said...
I am soooo going back there to find those three blue stars. I'm trying to decipher blue & white stars thru my scope at the moment, so thanks Les for the info.
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You should also bear in mind that we all see colours a little differently, so what I say on colour may not be in complete agreement with your view -- there's no right or wrong here, it just the way we see it. (ie your mileage may vary).
It interests me (I like experimenting on people) when I'm at work at the obs and I show people Spica in the night sky and ask them what colour it is? About half the people will say "white" instantly, about 1/3 will say "light blue" and of the rest, there are a few that say "mid-blue" and significant residual will answer "greenish". We all see colour at least a little differently -- it is a combination of the eye's age, the brightness of the star (more light means better sampling by our eye's cone cells) and our genes I think. Kids always dominate the group that tend toward blue, probably (I'd guess) because their cornea is more transparent to shorter wavelengths that those of us with a decade or few under our belts. To me, Spica appears "sky-blue" naked-eye.
But, when I show Beta Centauri, almost everyone seems to agree it is blue -- because it is sitting next to yellowish Alpha Centauri of course (there will be one or two who will still answer "white"). Contrast always helps (but in some cases can be deceptive). Same thing with Gamma Crucis, next to Alpha and Beta Crucis it appears decidedly more warm-toned than when looked at in isolation. Take a look at a few of the colour-contrasting pairs like h 3945 in Canis Major or Dunlop 94 in Carina etc etc. Describe the colour of the "bluer" star and then look up its spectral type. While the "blue" star in Albireo is genuinely blue (B0) The other two blue components aren't really that blue at all. In the case of Dunlop 94 it is a B9 star (that should appear white or perhaps cold white) and in h 3945 the "blue" star is an F0 star that has the same colour temprature as Canopus, but looks a strong sky blue in moderate apertures -- because of contrast.
Stars with a B-V figure around the -1.3 mark and higher (ie higher negative number) are about as blue as the human eye will normally perceive. There are stars with higher B-V figures (up to around -2.5 in fact) but that usually translates into more ultra-violet light that your eyes can't see at all. "O" type stars aren't more "blue" to the eye -- they're just putting their energy out at wavelengths we don't see well or at all. Naos (Zeta Puppis) is an excellent example of this. Of the bright naked eye stars, Zeta Puppis has the highest spectral type (O5) but looks perfectly white to me -- because its peak output is well into the ultra-violet we can't see. If we could see U.V and our atmosphere didn't scatter it so strongly, Naos would be a brilliant beacon as bright as Jupiter.
The spectral types B1-B3 are
normally as blue as you can see in a star. Optical aid (because it gathers more light which in turn switches on your cone cells more readily) accentuates the colour.
Hope this helps.
Best,
Les D