Finding star cluster worth the effort

Omega Centauri as it appears through one of the telescopes at the University of Canterbury's Mt...
Omega Centauri as it appears through one of the telescopes at the University of Canterbury's Mt John Observatory. GRAPHIC/PHOTO: IAN GRIFFIN
The moon is waning and reaches last quarter on May 4. With moonrise occurring late in the evening, light from our closest celestial companion won’t spoil the early part of the night.

This means the early part of the night is really dark, making it prime time for stargazing, writes Ian Griffin.

Ian Griffin. Photo: Otago Museum
Ian Griffin. Photo: Otago Museum
This week, I’d like to encourage you to take advantage of the hours after sunset to try to find one of the most marvellous objects in the southern sky. Our target is an immense ball of stars located 17,000 light-years from Earth. It is called Omega Centauri.

Known to astronomers as a globular cluster, Omega can easily be seen with the unaided eye from rural locations, provided you know where to look.

To find this spectacular star cluster, you can use the dimmer of the famous pointer stars, Beta Centauri, as a guide. Because Omega Centauri is relatively faint, make sure your eyes are ‘‘dark adapted’’ (give yourself at least five minutes before beginning your celestial search).

Once you have found Beta Centauri, look to the left. The first bright star you come to is Birdun (also known as Epsilon Centauri).

Now draw an imaginary line from Beta Centauri through Birdun, and continue it to a point roughly the same distance as Beta on the other side. Omega Centauri should be visible as a large dim fuzzy patch of light approximately the same size as the full moon.

Through binoculars, or better still a telescope, Omega is a hypnotic object which repays close study. Despite its colossal distance, individual stars can be resolved even through small telescopes.

Astronomers believe there may be as many as 10million stars in the cluster. Weighing in at more than sixmillion times the sun's mass, the cluster is also more than 150 light-years across.

Omega Centauri is the largest of several hundred similar objects which orbit the core of the Milky Way.


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