2014-03-24

Globular clusters: ω Centauri vs. 47 Tucanae

Blessed with clear, moonless evening skies, I imaged my two favorite globular clusters last night. They are, not by accident, the brightest and most impressive of them all: Omega (ω) Centauri and 47 Tucanae, a.k.a. NGC 5139 and NGC 104.

Omega Centauri (left) and 47 Tucanae, the most magnificent globular star clusters of the sky. For both images, I used a Canon DSLR camera (600D) at 1600 ASA and a 70mm f/6 refracting telescope. I stacked 11 images each (60sec exposure time) and several dark frames. Tracking was done with an Astrotrac TT320X portable tracking mount. No further image processing except minor color correction with Photoshop. Klick for larger version.

ω Centauri is easily visible with the naked eye under a fairly dark sky, it looks clearly different to a normal star - somewhat fuzzy and diffuse. Point binoculars or a small telescope: ω Centauri is a giant cluster containing millions of stars within a sphere measuring about 150 light years. It represents probably the core of a small galaxy that was devoured by our own milky way millions of years ago. ω Centauri is more than 17000 light years from Earth and more than 12 billion years old (the universe itself is about 13,4 billion years old).

47 Tucanae is the second brightest globular cluster of the night sky, a little fainter than ω Centauri, but still easily visible with the unaided eye. The cluster is more concentrated and smaller than Omega - it looks almost like a star. It contains less stars (about one million) and is also about 17000 light years from our planet.

Both clusters are best viewed from the southern hemisphere, especially 47 Tucanae, which is close to the Small Magellanic Cloud in the constellation Tucana.

Below is a picture of my equipment used to take these pictures. It's pretty simple and light weight. Tracking was done with an Astrotrac TT320X-AG mount on a home made "Vela" travel pier, the optics is a 70mm/420mm ED refracting telescope. The camera used is a Canon 600D DSLR (not shown here, because I used it for this snapshot).

 

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