Visual double stars: colour & aperture

[badhex]

16 hours ago, Mircea said:

Related to the topic : StelleDoppie , a mirror of WDS, is stating 52 Ori consisting of A5V stars. Other A stars are Vega and Fomalhaut.

Well, maybe it is something wrong with me but always - this include the observation of last night - I saw 52 Ori as a deep yellow or light orange. Definitely not a sister of Vega.

How do you see this wonderful double star ?

Definitely haven't observed this before but will add it to my list of doubles to check out and report back! 

[glafnazur]

17 hours ago, Mircea said:

However, last night I was able to split Rigel / STF 668. The main star is of blueish white color , no doubt.

But what is the color of the companion ? How do you see it ?

Last night the seeing was bad, I was able just to confirm the existance of a companion, flooded by the intense, pulsating light of the primary star.

But in the past, in my 200mm Dobsonian, with a steady image, I saw the color of the companion as indigo.

Mircea

I would have said purple, but as I am notoriously terrible identifying colours and shades of colours, I googled indigo and I'd say you are spot on with that.

[bomberbaz]

On 23/11/2023 at 10:26, John said:

I must try one someday !

I get on OK with binoculars so it might be what I'm looking for.

 

On 23/11/2023 at 07:19, The60mmKid said:

Have you ever used a binocular telescope? It's a different beast. I have a friend who detests binoviewers but is head over heels for his Kowa Highlander. A binocular telescope can be a brilliant stargazing tool, including for doubles. Possibly worth trying.

You should try the observatory at Todmorden. @Peter Drew has made them up to 300mm but of interest in particular here with regards double is I think a telescope binocular of 120mm using two sw evostar 120 fracs.

I am not sure if there is an ED glass version, perhaps Peter will drop in an advise!

 

[lunator]

I thought I would look at Albireo and Almach in the ST80 tonight. I just used the 25 and 5mm orthoscopic eyepieces. I had started the session with the Moon and Jupiter. The ST gave a very warm hue to Jupiter. I looked at Albireo next at x25 mag. The secondary appeared pale blue (similar to my other scopes but the primary appeared yellow orange rather than yellow that I see in my othe scopes. I moved onto Almach and at x80 magnification the secondary was blue ( I thought I might see a greenish tint.)the primary was again a yellow but had an orange tint as well. 

Not this proves or disproves anything but certainly the apparent colours in the ST80 are different to the OMC250 and the Newt. 

Cheers

Ian

[Mircea]

badhex

I hope my suggestion in the document attached will be not seen as a lack of modesty.

I suggest to see all the six stars in what I call ''Lockyer's List''.

52 Ori is the most difficult as separation. But there are also plenty of dim companions there at Sig Ori, Lam Ori, Zet Ori.

On topic : Lockyer mention the color of Alnitak stated by Struve as being ''olivaceasubrubicunda'' !!!  😍

 

glafnazur

Thank you for confirming I used the correct word. My mother tongue is Romanian which belong to Romance languages this is why I used ''indigo''.

 

Clear sky, Mircea 

Lockyer's List.pdf

[badhex]

On 24/11/2023 at 22:44, Mircea said:

badhex

I hope my suggestion in the document attached will be not seen as a lack of modesty.

I suggest to see all the six stars in what I call ''Lockyer's List''.

52 Ori is the most difficult as separation. But there are also plenty of dim companions there at Sig Ori, Lam Ori, Zet Ori.

On topic : Lockyer mention the color of Alnitak stated by Struve as being ''olivaceasubrubicunda'' !!!  😍

 

glafnazur

Thank you for confirming I used the correct word. My mother tongue is Romanian which belong to Romance languages this is why I used ''indigo''.

 

Clear sky, Mircea 

Lockyer's List.pdf 373.45 kB · 1 download

This is excellent, thank you - a fun challenge I will most definitely take up! I enjoyed your additional notes at the bottom.

According to my past observing notes, I have observed and split the first five in the list but not 52 Ori, and not in the same night, so this is something I will aim for. Tomorrow I'm going to compile what I wrote for each previous observation. 

I was not aware of Struve's wonderful description of Alnitak as olivaceasubrubicunda, though I had read something regarding his liberal yet specific use of language to describe various shades of colour in stars! I think the best I have managed are descriptions like "eggshell blue" etc. 

Edited November 26, 2023 by badhex

[Sunshine]

Interesting observation and i am inclined to agree with the article, have observed some of my favourite doubles using my 8" starsense and my 102 side by side. In almost every case I find the 102 provides a better differentiation between coloured doubles whereas in the 8" I seem to notice they are brighter and colours are a little more washed out, if this makes any sense. Also, when it comes to producing pinpoint beautiful stars at high powers the 8" is trounced by the 102.

Edited November 25, 2023 by Sunshine

[The60mmKid]

One of the merits of Sissy Haas's double star book is that it clearly demonstrates that how different observers perceive color is highly subjective. In the book, side-by-side notes from various observers often report different colors. I think there are a few variables at play.

1. The inherent subjectivity of color perception (see https://www.britannica.com/science/color/The-perception-of-colour)

2. Telescopes that are either truly apochromatic (e.g., reflectors) or that exhibit varying degrees of chromatic aberration

3. Atmospheric conditions

4. Aperture

Number 4, aperture, is what concerns us here, so it's helpful to account for the other variables. If we are only considering aperture, then I think photography provides a useful example/parallel. Camera lenses have built-in diaphragms that control the aperture (i.e., "stopped down" to the minimum aperture, "wide open" to the maximum aperture, and all of the "stops" in between). One of the main considerations when selecting an lens stop is that you don't want to let too much light in since that would result in a loss of detail, including color. You "blow out" the details when too much light enters the lens... The vividness and nuance of color is lost because everything is washed out in the overexposure.

I'm not sure whether this is an oversimplification, but to me this seems to carry over to astronomy. On bright, colorful, high contrast targets, larger apertures can overwhelm the eye's/brain's ability to interpret color. So stopping down (i.e., using a smaller aperture scope) can make it easier for the eye-brain to interpret color. This isn't to say that all stars display color more manageably in smaller scopes. I predict it depends on their brightness, and I think there's probably a correlation between 1) brightness of the star, 2) size of scope, and 3) perceived vividness of star color. In other words, I predict that some of the brightest "showcase" doubles display their colors more vividly through smaller scopes, but that the color of fainter stars/pairs benefits from increasing aperture in proportion to their faintness.

[Mircea]

3 hours ago, The60mmKid said:

One of the merits of Sissy Haas's double star book is that it clearly demonstrates that how different observers perceive color is highly subjective.

.........................................................................................................................................................................................................................................................................................................

In other words, I predict that some of the brightest "showcase" doubles display their colors more vividly through smaller scopes, but that the color of fainter stars/pairs benefits from increasing aperture in proportion to their faintness.

The60mmKid

Very good points.

I highlighted the last one because I can provide some examples.

I already mentioned the companion of Rigel. The main star is very bright compared to the companion, this is the main difficulty with this double star.

We had an action on the Romanian ''astronomy.ro'' forum regarding the visibility of the companion of Rigel. Our action confirmed the statement made by William Kitchiner that Rigel can be splitted with a telescope as small as 1 3/4 inch or 45mm.

My colleague Iulian saw the companion of Rigel with a 45mm refractor on February 1, 2018 while I succeeded on February 5. 

Iulian used a genuine 45mm refractor, I stopped down my 60mm refractor.

It was really interesting, the best image of splitted Rigel was provided in my telescope by the 92x magnification obtained with a Galilean eyepiece of -9mm focus.

The color of Rigel's companion reported by me was coppery reddish.

The report of Iulian can be seen at link below on page 2, my report is on page 3:

https://www.astronomy.ro/forum/viewtopic.php?t=17374&postdays=0&postorder=asc&start=15

The indigo color of Rigel's companion was observed by me on February5, 2019 , with my 200mm Dobsonian, at 205x and 308x.

 

badhex

I'm very curious to read your notes about those doubles in the Lockyer's List, you will have a reader here for sure.

 

Mircea

Edited November 25, 2023 by Mircea

[lunator]

4 hours ago, Mircea said:

The60mmKid

Very good points.

I highlighted the last one because I can provide some examples.

I already mentioned the companion of Rigel. The main star is very bright compared to the companion, this is the main difficulty with this double star.

We had an action on the Romanian ''astronomy.ro'' forum regarding the visibility of the companion of Rigel. Our action confirmed the statement made by William Kitchiner that Rigel can be splitted with a telescope as small as 1 3/4 inch or 45mm.

My colleague Iulian saw the companion of Rigel with a 45mm refractor on February 1, 2018 while I succeeded on February 5. 

Iulian used a genuine 45mm refractor, I stopped down my 60mm refractor.

It was really interesting, the best image of splitted Rigel was provided in my telescope by the 92x magnification obtained with a Galilean eyepiece of -9mm focus.

 

Mircea

Hi Mircea

Interesting result on Rigel 😁.

It does fit with the limit of resolution for a telescope. 

Paul Couteau said to resolve tight doubles you need to working at 2x the aperture so for your 45mm scope x92 fits well.

If you combine this with Bruce MacEvoy concept of the resolution ratio where you divide the separation by (116/aperture)  to calculate what difference in magnitude will still be visible. 

I like to substitute magnification for the aperture in the equation as a "how low can you go game"

From experience the equation that shows the limits of resolution is

2.5+5(log)((Separation)/(116/magnification)

Using this equation 

2.5+5(log)(9.42)/(116/92) = 6.87

The Delta M for the pair is 6.5 which is below the limit so it should be resolvable.

Cheers

Ian

[Mircea]

lunator

 

Thank you for your comment and for the formula which is new to me.

I will do the calculations for the other telescopes I have, I'm very curious.

 

Mircea

[lunator]

1 hour ago, Mircea said:

lunator

 

Thank you for your comment and for the formula which is new to me.

I will do the calculations for the other telescopes I have, I'm very curious.

 

Mircea

Hi Mircea

I have the equation in my book but it is something I have calculated from all my observations over the last 20 years 😁

Cheers

Ian

[badhex]

@Mircea I found my notes, scant though they are, but avoid going too far off topic I'll create a new post, and give you a shoutout of course since it's your list!

[tico]

[tico]

[JeremyS]

The S&T article I posted at the top cites this book as a good source of colour descriptions of double stars, so i ordered a copy. 
in my next post I insert the relevant tables - hope they are legible 

[JeremyS]

[Zermelo]

1 hour ago, JeremyS said:

It's interesting that quite a few of these stars are described as being green, and previous discussions have also mentioned green stars. As has been observed above, there is a degree of observer subjectivity in such assessments, and I expect that, with doubles, colour complementarity has an effect too. I've seen green myself, but very rarely.

And yet, there are good arguments for saying that green stars do not exist:

https://stargazerslounge.com/topic/375783-ep44-sunday-18th-april-2021-730pm-bst-why-there-are-no-green-stars-by-paul-money/#comment-4072939

[badhex]

12 hours ago, Zermelo said:

It's interesting that quite a few of these stars are described as being green, and previous discussions have also mentioned green stars. As has been observed above, there is a degree of observer subjectivity in such assessments, and I expect that, with doubles, colour complementarity has an effect too. I've seen green myself, but very rarely.

And yet, there are good arguments for saying that green stars do not exist:

https://stargazerslounge.com/topic/375783-ep44-sunday-18th-april-2021-730pm-bst-why-there-are-no-green-stars-by-paul-money/#comment-4072939

I feel like I've probably also seen something that qualifies as greenish too, but I'm going to guess that I've never seen a star that I'd describe as green on its own in the eyepiece - i.e. only ever as a consequence of colour contrast as you mentioned. I haven't seen the talk but would like to track it down, I think there's a YouTube channel with past talks on somewhere. 

From my astro studies last year, my admittedly basic understanding is that a black body spectrum sits on the planckian locus in the colour space, which does not pass through green. Any black body in space emitting green light also emits lots of red and blue light, and we would perceive this as white. It is similar, although not the same as why an iron bar does not pass through green when being heated (though an iron bar is not truly a black body, it's a close real world example). 

[DirkSteele]

One of the first articles I wrote for my website back in 2013 was "Prettest Colour contrasted double stars."  I had been on a bit of a double star kick that year and in particular the ones that show different colours so I collated my top 35.  Table of that list is on the link.

http://alpha-lyrae.co.uk/2013/11/13/prettiest-colour-contrasted-double-stars/

 

Makes me want to go back over the list as I have not visited a great many of those in many years.

[badhex]

1 minute ago, DirkSteele said:

One of the first articles I wrote for my website back in 2013 was "Prettest Colour contrasted double stars."  I had been on a bit of a double star kick that year and in particular the ones that show different colours so I collated my top 35.  Table of that list is on the link.

http://alpha-lyrae.co.uk/2013/11/13/prettiest-colour-contrasted-double-stars/

 

Makes me want to go back over the list as I have not visited a great many of those in many years.

I have perused this list several times! Definitely going to have to go through the all at some point 😊

[Mircea]

Regarding green stars : last time when observed , I saw Beta Lib / Zubeneschamali as blueish with binoculars.

But when I first searched for it, I used my 60mm refractor and the 125mm reflector and I saw it greenish.

But the green color of Bet Lib  was best seen with my 15mm F/22 singlet refractor, having a magnification of 9x, specially built for reenactment observations.

In that tiny aperture, Zubeneschamali was quite green. I don't think the color  has to do with the lens being non-achromatic. Please see the extract below.

( The French astronomer Nicolas Louis de Lacaille used a 15mm singlet refractor to chart the Southern sky from Cape of Good Hope.  Actually his 15mm singlet refractor was the finder of his bigger telescope so I guess his was made of brass not cardboard like mine. 😄)

Just as a curiosity, you can see my smallest telescope in the attachments together with an extract from my observation log regarding Bet Lib.

 

I just learned Zubeneschamali is the double star RBR 7 but the informations on StelleDoppie are a bit confusing to me. The primary star is quoted as magnitude 7.5. But how can this be when Bet Lib is of magnitude 2.6  !?

Anyway, the companion of magnitude 16.5 cannot be reached by the 250mm Dobsonian - my light bucket.

 

tico

Thank you for the picture of S.W. Burnham !

This name, shortened as ''Bu''  is giving me goosebumps when met on CDSA maps.

It is like being again a kid and the most famous bully of our neighborhood is crossing my way. Probably he will beat me again but maybe this time I will trick him, give him a good slap and than run away.

To be honest, I succeeded twenty, maybe thirty times to snatch the laurel wreath but most of the time not. What's disturbing is that at each such encounter, I feel an uncontrollable urge to try my luck.

Bu 385 was one of those rare moments of glory and is related to the topic. The primary  A is a beautiful azure , B is bone white with a very slight yellow  patina while C and D are neutral white.

Mircea

 

 

 

 

 

[lunator]

1 hour ago, Mircea said:

I just learned Zubeneschamali is the double star RBR 7 but the informations on StelleDoppie are a bit confusing to me. The primary star is quoted as magnitude 7.5. But how can this be when Bet Lib is of magnitude 2.6 !?

 

Anyway, the companion of magnitude 16.5 cannot be reached by the 250mm Dobsonian - my light bucket

Hi Mircea RBR7 is listed as a 'dubious double' (note X) in the WDS. This probably means it doesn't exist.

I'll have a look through the WDS to see if I can make sense of everything.

Cheers

Ian

[lunator]

This is the WDS info. Only one observation in 2002. 

15170-0923RBR 7 2002 2002 1 194 194 2.1 2.1 7.5 16.3 B8V+M2V -096-021 -08 3935 X 151700.41-092258.5

I will have a rummage through GAIA to see if anything fits.

Cheers

Ian

[JeremyS]

Not sure if this was posted before, but Daniel Mounsey on CN explains where small apertures can win in double star observing (including on colours): https://www.cloudynights.com/topic/633339-put-your-stars-on-a-diet/?p=8833872

I must get my Tak FOA 60Q out…