NGC4755 珠寶盒星團

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平價旅行團可在澳洲天文之都庫納巴拉布蘭攝星, 並可以拍一些在香港、陰那山、雲南都不易拍到的天體, 例如這個Dec=–60°的南天珠寶盒。這個拍了兩次, 第一次用彩色機拍, 但太短焦, 分不出星團的星的色彩, 第二次用較長焦拍, 因為吝嗇, 所以只拍顏色通道, 也試驗這種拍攝方法。

珠寶盒星團(NGC4755、Caldwell94)是位於南十字座的一個疏散星團, 離我們約6400光年, 珠寶盒的名稱來自19世紀天文學家赫歇爾(John Herschel), 他稱這個星團的星是彩色的, 好像有特色的珠寶。當中很光的南十字座κ星(Kappa Crucis)是橙紅色的, 因它雖然年紀應和星團的其他成員相若, 但己快耗盡本身的"燃料", 進入了紅巨星階段。

彩色機版本:
Takahashi Sky90 FL500mm f/5.6, SBIG ST2000XMC, Paramount ME autoguided @Siding Spring, Australia
3mins X 6, DSS, PS, Denoise5, Detail2

單色機長焦版本
RCOS 12.5” Ritchey-Chrétien f/9 FL2857, SBIG STL-11000M, Paramount ME, autoguided @Siding Spring, Australia
R&B 2mins X 4, G 2mins X 3, PixInsight, PS

[davidc129]

真係好似珠寶。

[Chanlunlun]

真係好似珠寶。

The Jewel Box is an open cluster more suitable to be viewed visually rather than photographed. It consists of 4 main stars in green (a visual green star is very very rare ), blue, yellow and red in color. The assortment of stars in this color combination in the same field of view inside an eyepiece looks like gems in sky and that's why this cluster is named.

Shooting this object, especially in CCD, is most likely over-exposed the main stars and the feeling of jewel box is otherwise distorted.

It's still beautiful in picture form, but not in its original sense.

[Wah!!]

Green star? Where does it locate in HR diagram?

[Eddy So]

[bingsze]

mirror god:

are u sure??

[Chanlunlun]

mirror god:

are u sure??

I am absolutely sure because I saw the Jewel Box twice by the 20 incher in Australia - once in east coast and once in west.

We were all astounded by how colorful this open cluster is and thus its name. Chung HL, Chan YP and my wife all saw it. We were all very impressed by the greenish star in middle.

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Green stars are very rare indeed. The most important factor is the colour sensitivity of our three kinds of cone cells in our eye, the green and red sensitivities overlap significantly.



So most stars with mid range temperature appear as yellow or orange by having both green and red cone cells excited.

The source of the above diagram (http://www.astronomycafe.net/qadir/q72.html) has an explanation of the situation.

However, I believe that green stars may be seen in a bright and closely packed cluster, using a large telescope, as there is strong enough light to trigger our colour visions.

I think that the 2nd photo may have originally captured star(s) with a green hue. However, because RGB photos commonly have green noise, I have applied DeepSkyColor HLVG (Hasta La Vista, Green) to remove the green noise, which may have removed the green hue of any star together.

[bingsze]

this is a very interesting topic to discuss,

1st of all, many stars are actully located peak at green region, but bcos they also emit all different wavelength, so when they come into our eyes, they mixed up together and then they look white or so.

But that doesnt means that it is impossible to have stars look green, but it is very unlikely to happen to the knowledge we knew.

I still open to this topic, but I want to ask one question is, if jewel box has a green star, I think they wont exist only a few days or months. There must have many people see this as well, and will be a counted example of green star existing. But I check from theinternet that, no report about this. So, I think may be you acturally saw a green star but by other reason we dont know.
(may be by some reason, the blue and red light were filtered away, then they will look green to our eyes. may be?)

Of course, I love to goto Aussie with you to enjoy such a beautiful skies there and see the strange view of that.

Just science dicussion, dont hit my head! ok

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I may quote

I must admit that with substantial aperatures, like 25inch, some of the stars in ngc4755 do show a green cast...

from: http://www.iceinspace.com.au/forum/arch ... 26916.html

[bingsze]

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.

from the above saying,

the evidence is favourable to MG side now.

Also, if this is true, MG you are really spoilt.

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出幅減低"拉光"程度, 但強化顏色的版本: