Thousands of star clus­ters are scat­tered in our skies

Central and North Burnett Times - - NEWS | COLUMNS - Phone 4164 6194 or email mao123@big­ to book a stargaz­ing show at the Kin­garoy Ob­ser­va­tory. JAMES BARCLAY

OUT of the bil­lions of stars, neb­u­lae and so­lar sys­tems that make up our Milky Way gal­axy, two ob­jects amaze the hu­man eye in a tele­scope: open star clus­ters and glob­u­lar star clus­ters.

The first type is made up of thousands of young stars with lots of space be­tween them. Like a black cloth sprin­kled with a few bits of glit­ter, these OCs come in all shapes and forms. Some are dubbed the “jewel box”, “but­ter­fly”, “wild duck”, a “poo­dle with two tails” and the “seven sis­ters”.

This is how they ap­peared to the early tele­scope ob­servers who drew and de­scribed them, since Galileo pointed his lit­tle op­ti­cal tube to the night skies in 1610.

Out of the 250 OCs that we know of, the av­er­age dis­tance is 7000 light years, which is quite close by as­tro­nom­i­cal means – one light year is equal to

9.4 tril­lion kilo­me­tres.

While some of these OCs can be glimpsed with the eye on dark, moon­less nights, binoc­u­lars show more but to re­ally see these pretty OCs in their full bloom, you need a tele­scope at 50X to 100X.

Some OCs have nu­mer­ous coloured stars, with the most fa­mous of all, the “jewel box” open clus­ter lo­cated un­der Mi­mosa (Beta Crux), the se­cond bright­est star in the South­ern Cross. Within are three coloured stars: yel­low, green and red. This is why it’s a favourite to all stargaz­ers with a tele­scope, best seen from March to Septem­ber, peak­ing in June.

It got its name when as­tronomer John Her­schel – the son of fa­mous English as­tronomer Sir Wil­liam Her­schel – first ob­served the clus­ter with a large tele­scope at Cape Town, South Africa, in the early 1800s, when he set about ob­serv­ing, record­ing and sketch­ing the south­ern night skies.

Glob­u­lar clus­ters, on the other hand, are a lot fainter to the eye. They not only con­tain mil­lions of stars but all of them are packed into one gi­gan­tic clus­ter, six to 10 times fur­ther than open clus­ters.

Stars in GCs have lit­tle colour to the hu­man eye but are eas­ily de­tected with spec­tro­graphs, as they can de­ter­mine their age, based on their av­er­age dis­tance of 25,000 light years.

From the spec­tra data col­lected over many decades, it’s now a for­gone con­clu­sion that all GC stars were the first stars formed in our gal­axy, 14.7 bil­lion years ago, while our so­lar sys­tem is only 4.5 bil­lion years old.

In large tele­scopes like we have at the Ob­ser­va­tory, glob­u­lar clus­ters are a wow fac­tor as they ap­pear like a kalei­do­scope of stars. Like a hand­ful of glit­ter­ing small di­a­monds but in binoc­u­lars, they ap­pear as lit­tle fuzzy blobs or smudges.

The largest of all is Omega Cen­tauri, best seen in au­tumn and win­ter.

At a dis­tance of 13,000 light years, this glob­u­lar clus­ter con­tains about eight mil­lion stars, while its smaller cousin, 47 Tu­cana at 48,000 light years’ dis­tance, is best seen in the spring or sum­mer night skies.

❝ Stars in GCs have lit­tle colour to the hu­man eye ...

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