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Antares

double star reflector refractor SCT
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15 replies to this topic

#1 ed_turco

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Posted 24 February 2020 - 11:34 AM

Before I became an "official"  ATM, I was an observer of double stars.  As time went by, I started using doubles as a test for the resolution of my increasing menagerie of telescopes.  Using my 6" reflector, I attempted to resolve Antares, among others.   I cannot remember whether a 6" was capable of doing this at 200 power. 

 
No resolution at all.   Or so it seemed.  But at my highest magnification, I noticed a greenish spot of light at the very edge of a out-of-focus image.   This wasn't an artifact due to bad optics as it showed on repeated nights and different magnifications.  

 

It was a no-go for my telescope  At some time later, I learned that the light from Antares' partner was reported as green.  Had I stumbled upon an incipient artifact of resolution?  I've thought about this many times since.

 

Has anyone else seen this sort of thing?  I look forward to answers from the experts who do doubles as a major part of their hobby.


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#2 gfeulner

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Posted 24 February 2020 - 02:10 PM

The few times I've seen it in my 6" refractor it was definitely green.
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#3 flt158

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Posted 24 February 2020 - 02:28 PM

I would love to see a green star through my William Optics 158 mm apochromatic refractor. 

But as my scope "kills" false colours I don't think I will ever see any. bawling.gif

In astronomy we have such things as spectral classes. 

And I'm sorry to say there is no spectral class which covers green stars. 

A while ago I had the experience of observing Alpha Herculis (Rasalgethi) through an achromatic refractor. 

And there it was: a green companion!

However the B star is blue in my scope. 

 

We can always wish, Ed Turco!

 

But you are very welcome to share with any of us some of your findings throughout 2020. 

 

Kind regards to you and Gerry. 

 

Aubrey.  


Edited by flt158, 24 February 2020 - 02:29 PM.


#4 Bonco2

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Posted 24 February 2020 - 04:45 PM

I've mostly view the companion with reflectors and it always appears green. Observations with 4 inch refractor same thing.
Bill

#5 Bigzmey

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Posted 24 February 2020 - 04:45 PM

It is certainly doable with 6". I split it with 5" APO triplet at 357x.  

 

@flt158. Yes, there are spectral classes and there are no green or pink stars in nature. However, colors are subjective and what we see (and interpret) is function of optical chain (with EP and scope coatings) and observer eye and brain. Also, don't forget color contrast effect.

 

So, if the star looks green or purple to me, I report in my log what I see, not what it suppose to be. :) I find inspiration in Sissy Haas book with delicious star colors like lilac or turquoise. 

 

In this particular case Antares B looked white to me.


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#6 ssmith

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Posted 24 February 2020 - 06:15 PM

I have photographed the secondary as ranging from turquoise to an incredible royal blue .  When one speaks of aberrations I think that atmospheric considerations account for much in regards to the colors reported by northern observers since Antares is relatively close to the horizon.

 

Here is a link to a previous thread.

 

Here is a Video I took of Antares with my Tak TSA120.  You can see flashes of green and turquoise.  The secondary is not resolved.


Edited by ssmith, 24 February 2020 - 09:11 PM.

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#7 ed_turco

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Posted 25 February 2020 - 11:11 AM

Thanks to those who have tried to resolve this quandry of mine.  Please remember that my comments are from anera 65 years ago.   I know about nature abhoring green stars but one observer, during an occultation saw the companion masking the primary to reveal a green seconday -- alone for a tiny amount of time.

 

He stated that it was "as green as a traffic light."  So opposite the rules of Nature.  Go figure!


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#8 Bonco2

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Posted 25 February 2020 - 05:00 PM

Interesting subject. I think we can agree on a few things:
1) It is frequently observed as being green but not by ALL observers.
2) Doesn't matter if it's viewed with an APO refractor or a reflector, many see it as green
3) We all know there are no green stars.
4) At least on this thread there has not been a definitive explanation.

I disagree with the assumption its cause by atmospherics. From Florida it rides fairly high in the sky. When I have observed it is a steady green color, not flashing like you see when the air is turbulent. I personally think it's how our eyes and brains interpret the color contrast next to a very red star. In any case when viewed it's perhaps one of the most colorful doubles.
Cheers, Bill
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#9 Bigzmey

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Posted 25 February 2020 - 05:15 PM

4) At least on this thread there has not been a definitive explanation.

Wikipedia provides two possible explanation on the subject of green stars:

 

1) Color contrast. If you have two bright colored dots side by side human eye/brain tend to exaggerate the difference. As a result white star next to yellow will appears bluish and next to orange greenish.

 

2) Star light mixing. Bright glow from main tints secondary color.  

 

I would also add EP coatings. Some have warmer and some colder tones. 


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#10 tchandler

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Posted 27 February 2020 - 09:31 AM

Antares B is one of those holy grail targets that I’ve long sought after but never seen. After several attempts I have no definite sightings of the secondary. There were a few “I think I see something”s, but that’s it. Antares only gets to an altitude of 20 degrees in my sky.
 

The secondary appears to range from 3.1” to 2.5” of arc from the primary, and is presently near minimum separation, according to Sky Safari.

 

In contrast, Sirius B is presently near its maximum separation of about 11” from Sirius. However Sirius B is about 3 magnitudes fainter than Antares B. I should note, I have seen Sirius B but from an observing site in Florida on a spectacularly steady night. 
 

I suspect that Antares B closeness to its primary makes it a more challenging double than Sirius these days. Maybe I need to visit Florida in the summer?


Edited by tchandler, 27 February 2020 - 09:32 AM.

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#11 Dave Mitsky

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Posted 28 February 2020 - 01:18 AM

The times that I've observed Antares B it looked green to me.

 

I've read that Antares B still appears to be green when Antares A has been occulted by the Moon.

 

https://www.star-facts.com/antares/

 

https://nineplanets....es-a-α-scorpii/



#12 ed_turco

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Posted 03 March 2020 - 11:47 AM

I have photographed the secondary as ranging from turquoise to an incredible royal blue .  When one speaks of aberrations I think that atmospheric considerations account for much in regards to the colors reported by northern observers since Antares is relatively close to the horizon.

 

Here is a link to a previous thread.

 

Here is a Video I took of Antares with my Tak TSA120.  You can see flashes of green and turquoise.  The secondary is not resolved.

I came back here and paying attention (this time) I saw the video.  This is what I saw in 1959 or so.    Now I'm glad I asked!


Edited by ed_turco, 03 March 2020 - 11:48 AM.


#13 leonard

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Posted 03 March 2020 - 07:53 PM

      As bonco2 said , Antaries is quite doable with a 4 inch refractor . In the only 4 inch refractor I ever owned , in 

Pickering 7 seeing , b was sitting on the first diffraction ring of it’s primary . Don’t remember the separation , this was in

 1992 or 93 about 2 sec. ? Color of secondary was green . Very cool .


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#14 fred1871

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Posted 03 March 2020 - 09:28 PM

 

The secondary appears to range from 3.1” to 2.5” of arc from the primary, and is presently near minimum separation, according to Sky Safari.

Measures of the separation of Antares A and B have quite a scatter over time. In recent decades, the separation, currently given around 3.2", has not changed enough to be outside the measuring errors/uncertainties. Estimates of the orbital period range from 800+ years to thousands. The problem is that the PA has changed very little, and the measures show a lot of scatter within each era, so orbital estimates (they're no better than that) are very uncertain, based too much on the stars' masses and separation as projected in the line of sight, but without significant measured changes. That doesn't allow for even a good ball-park guess, beyond suggesting the period is very long. So one should read the Sky Safari numbers as indicating uncertainty because you don't get enough information to assess the pair's changing pattern, which, as mentioned, is uncertain.

 

Current best estimates suggest the separation is slowly decreasing. But one could make out a case for little change, or slight widening, or .....? My feeling is that Antares needs some high quality measures perhaps once each decade to better assess what's happening. 

 

Regarding observation, with around 4.5 magnitudes brightness difference and the glare factor, it's notoriously seeing dependent. I've occasionally seen it double, though I've often seen only flare and glare from the primary without th companion. My best observation was in the late 90s with a 7-inch apo refractor, at only 100x - the secondary was obvious as a small green point of light, in very good seeing. I've always considered the colour I saw as a contrast effect with the orange/red primary.

 

To confuse the issue further, EJ Hartung (Astronomical Objects for Southern Telescopes, 1968) mentions that the noted double star observer WR Dawes in 1856 saw Antares B "emerge from behind the dark limb of the moon before Antares itself and noted the colour as green...".


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#15 John Fitzgerald

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Posted 03 March 2020 - 09:35 PM

I've only clearly seen the companion a couple of times.  Once, with a 6 inch f/15 refractor, and once with a 10" f/5 Newtonian.  The seeing must be very good.


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#16 Tyson M

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Posted 05 March 2020 - 12:14 AM

I ave only split Antares with a TSA102S, and it is beautiful and definitely green. 




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