ngc4755 Jewel Box

[Argonavis (William)]

Is the Jewel Box full of jewels?

This is the question posed by David Riddell, a northern hemisphere observer visiting the south.

David writes: ".....One of the most celebrated open clusters in the heavens is NGC 4755 -- the Kappa Crucis cluster commonly referred to as the "Jewel Box."

How did this cluster receive its reputation as being spectacularly colorful?

Obviously, John Herschel's description of NGC 4755 as a "rich piece of jewelry" (in his Outlines of Astronomy) and "a superb piece of fancy jewelery" (Cape Observations) advanced the idea that has been repeated over and over in observer's manuals. Nowhere can I find that Herschel actually used the phrase "jewel box", so this nickname's origin remains obscure.

Later observers disagreed about the intensities of colors. W. C. Russell (1872) thought Herschel's remarks to be fully justified, citing a number of red, yellow, blue, green and blue-green stars visible with a 7 1/4" Merz refractor and an 8 1/2" reflector.

It must be confessed that, with moderate telescopic apertures, it fails to realise the effect of colour implied by Sir John Herschel's comparison..."


Using 25inch and 12 inch telescopes in South Africa, David noted only 3 stars with a particular colour, the numerous other members remained essentially colorless. He notes that the close proximity of relatively bright stars introduces some interesting physiological effects giving the illusion of a variety of colors. He thought the colors of Messier 41 to rival those of NGC 4755.

I tend to agree. For modest aperature telescopes, the jewel box does not to my eye show a wealth of colour. Maybe I am a little insensitive to star colours, but I have always preferred the open clusters ngc2516, ic2602 (southern pleadies) and ngc3532. They are just as colourful and richer.

I must admit that with substantial aperatures, like 25inch, some of the stars in ngc4755 do show a green cast, and it is then and only then that you can appreciate the name jewel box. But with the wealth of rich open clusters in the southern milky way the name "jewel box" could only belong to a former era of long refractors with narrow fields of view. We are spoilt. Our modern era of large reflectors with wide field eyepieces show off the sky like nothing before.

[AJames]

The questions you pose are interesting.

Firstly, you are correct in saying that John Herschel did not name NGC 4755 as the Jewel Box. It seems that its origin of the name was made in some causual quip at one of the London Astronomical Society (Now the Royal Astronomical Society) meetings in the late 1830's.
Like any given name or nickname, the origin of it remains in question, and the person who stated it is often lost in the confusion. It is probably like saying, who was the originator of the joke; "Why did the chicken cross the road?" The person continues to be nameless, even though it is probably quoted as a common joke through the known world.

I also think the Jewel Box does not necessarily mean just coloured stars. Ie.
You can have a Jewel Box just with diamonds you know! (A any decent female would probably desire!) Although perhaps inaccurate, I think it at last portrays the lustre of a small collection of brilliant stars in a small area.

Oh! ... and Merry Christmas to you all!

Andrew

Note: Your timing could not have been better. I have written an extensive article on the Jewel Box, which I was going to post on the 1st January, but due to your post here, I have posted it tonight. This was an article written almost 10 years ago, which I have updated in recent weeks.
In Southern Astronomical Delights Pages, the Jewel Box article, the Index starts at; http://homepage.mac.com/andjames/Page001.htm

The portion written on the historical aspects you describe can be read at;
http://homepage.mac.com/andjames/Page003.htm
and
http://homepage.mac.com/andjames/Page004.htm

Note 2: I have place some drawn colour images of these "colourful" open clusters in another Southern Astronomical Delights page, which highlight your point here; Ie. See
http://homepage.mac.com/andjames/Page03002.htm and
http://homepage.mac.com/andjames/Page03003.htm

Note 3: It was H.C. Russell - not W.C. Russell, which heads the 1872 article.
I have a soon published paper on this reference examining the actual micrometrical measures and the alleged changes in NGC 4755 based on the current positions.

[Zuts]

I don't know. Maybe it was my first scope a 6 inch newt i made myself and it was around 15 years ago but the jewel box was one i always remember because of the different coloured stars.

Doesnt look nearly the same through my 11 inch nexstar but i just got a tv85 and when the clouds clear here's hoping.

That and Albireo are the ones that stick in my mind from that period

Paul

[saberscorpx]

The brightest jewels in the box are of B, A, and early-M spectra, so a nice mix of color is there for the taking.

There are some tricks we can employ to enhance the experience which work well on doublestars and bright clusters.

Lower powers: Increasing power generally spreads, dims, and dilutes color.

Bino-vision: Two incoming color signals are better than one.

Suburban skies: Our cones (color receptors) work best under higher illuminations. Dark adaptation puts our rods in the driver's seat. Some of my most vivid color observations have been enjoyed under the light of a Fat Moon.

More atmosphere: This is cheating, but perusing our prey within 20 degrees of the horizon almost always guarantees a splendid lightshow.


Happy holidays,
SJS

[rwong]

I am no expert in observing. But I remember the best view of Jewel Box I got was from my 4" refractor.... yellow, blue, white stars. It definitely deserves the name "Jewel box".

There is never enough light from the Jewel Box to wear high power and the images deteriorates as the power goes up.

Cheers

[erick (Eric)]

Stephen, Thanks for these suggestions. I'll try them out. Some are completely counter to normal observing tips! Eg. under moonlight and low elevation!! I've already learnt to stare directly at an object for some time, if it's colour you want to see - Eg. Hind's Crimson Star which I tracked down last night for the first time.

Eric

Originally Posted by saberscorpx

The brightest jewels in the box are of B, A, and early-M spectra, so a nice mix of color is there for the taking.

There are some tricks we can employ to enhance the experience which work well on doublestars and bright clusters.

Lower powers: Increasing power generally spreads, dims, and dilutes color.

Bino-vision: Two incoming color signals are better than one.

Suburban skies: Our cones (color receptors) work best under higher illuminations. Dark adaptation puts our rods in the driver's seat. Some of my most vivid color observations have been enjoyed under the light of a Fat Moon.

More atmosphere: This is cheating, but perusing our prey within 20 degrees of the horizon almost always guarantees a splendid lightshow.


Happy holidays,
SJS

[Gargoyle_Steve (Steve)]

You can also try defocusing just slightly Eric too, letting the colour from each star spread over a slightly broader "blob". I've done this a number fo times on the Jewel Box, but this might not work so well in smaller apertures, I do this with my 12" dob.

[saberscorpx]

re: I've already learnt to stare directly at an object for some time, if it's colour you want to see...

Hi Eric,

This is another tactic that at first seems counter-intuitive as our eyes do not store color. Yet the continually reinforced memory of color does an amazing job of simulating a longer 'exposure'.

I haven't visited Hind's for awhile. Thanks for the reminder.
Just waiting for the sky to stop snowing on me.


SJS