NGC4755 The Jewel Box in the Southern Cross
I’m lucky to be living at the equator because the northern and southern stars will be mostly visible in my night sky (I can’t see Polaris though…). Every time when I saw the Big Dipper, my first reaction is to turn 180 degrees around and look for Crux – I always enjoy doing that.
I once had an experience on a night plane where my friend woke me up and ask me to look out. After sticking my face to the window and hanging my jacket over my head for some time, I got to see the Big Dipper. Cool… Then I turned and looked at the opposite window, will I see Crux if I looked out there? Fortunately for me there were some empty seats over that side, so I moved over and glued my face to the window again… and WOW… Crux was there! The experience was unforgettable…
I think Crux is the most seen constellation to me. My house is facing south, so every time I go out, I’ll see it* rising above my neighbour rooftop. When I come back, I may see it again setting below the rooftop. My bedroom window is also facing south, so again, every time I look out of my window, I’ll see a cross* hanging in the sky. (*provided the weather is OK and the month is right).
There is a Jewel Box in Crux. This beautiful open cluster is also known as Kappa Crucis Cluster or NGC4755. It got its Jewel Box nickname from an English astronomer John Herschel in the 1830s because the striking colour contrasts of its pale blue and orange stars seen through a telescope reminded Herschel of a piece of exotic jewellery.
The Jewel Box is located near the “left edge” of the cross, near the star Mimosa (beta Crucis). Through a telescope, the brightest stars can be seen forming an “A” lying down on its side.
Let us now take a journey into the cluster through the eye of the great telescopes…
This picture was taken with a 35-mm camera. Here we can clearly see Crux embedded in the Southern Milky Way Band.
Zoom in the region around Mimosa with the Digitized Sky Survey 2. Here we can see the cluster amongst the rich star fields and dust clouds of the Milky Way.
Taken with the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory, this image highlights the Jewel Box cluster and its rich surroundings. Here you can see the “A” lying down on its side.
This was taken by the ESO 8.2-metre Very Large Telescope (VLT) at ESO’s Paranal Observatory. Since we are using such a large telescope (remember, this is called the Very Large Telescope) for such a bright object, few seconds of exposure will be suffice – in this case, it only took about 5 seconds to get the image above.
The final zoom was taken by the Hubble Space Telescope with its old Wide Field Planetary Camera 2. It was created from far ultraviolet to near-infrared images. Here we can see bright blue supergiants, red supergiants as well as many fainter stars.
The Jewel Box is indeed a beautiful cluster and you don’t need world-class telescopes to enjoy it though. Shining at magnitude 4.2, it’s easily visible with just the naked eye. It’s always my first few objects to target if I’m out observing.