The Jewel Box Cluster

April 11, 2009

One of the brightest stars of the storied Southern Cross isn’t a star at all, but splendid cluster of young stars aptly called the “Jewel Box”. This star cluster, one of the treasures of the southern sky, is unforgettable in a small telescope.

** Highly Recommended **

Create your own star charts and custom tours of the night sky. Deep Sky Astronomy Software lets you select from thousands of galaxies, nebulae, and star clusters, as well as real-time information about the Moon and planets. Click here to learn more…

The Basics

• Since they had no telescopes to resolve it, early European navigators classified the Jewel Box as the star kappa Crucis. And that’s exactly how it looks to the unaided eye– stellar– even to a keen observer. It’s almost bright enough to include on the flags of Australia and New Zealand.

• Nicolas de Lacaille, who systematically mapped the southern sky with a tiny half-inch telescope in the mid-18th century, noticed the star was a “nebulous cluster”. Further observation with larger telescopes revealed a rich star cluster of almost 300 blue-white stars with a wide range of luminosity.

• The Jewel Box is easy to find: it’s just 1 degree southeast of beta Crucis, the second brightest star of the Southern Cross. Coordinates are RA 12h54m, Dec -60d21m… this is the deep-southern sky.

NGC 4755, the kappa Crucis or “Jewel Box” cluster

Deeper Look

• A good pair of binoculars reveals kappa Crucis, also called NGC4755, as a pyramid of four bright stars. A small telescope at 25-50x reveals dozens more stars in two distinct clumps. It’s almost as if there are two overlapping star clusters, one with a half-dozen bright stars and one with scores of much fainter stars that require averted vision.

• Since the Jewel Box is just 10 million years old, most of its members are still blue-white main sequence stars. But near the cluster’s center, see if you can find a 7th magnitude red supergiant, one of the first of the cluster to evolve off the main sequence.

• This cluster is roughly the same age as the Double Cluster in Perseus, though it lies in the opposite direction in the galaxy, some 4,900 light years away from Earth.

A Bit of History

The 14th century writer Dante Aligherhi may have known about the four bright stars of the Southern Cross, perhaps hearing of them from explorers of the day. In his famed Divine Comedy, when he and Beatrice finally ascended from Hell on the far side of the world, they saw four brilliant stars which they took to represent the four principal virtues: Justice, Prudence, Fortitude, and Temperance.

Personal View

I will not forget my first view of Crux in the mountains of Chile, almost half a lifetime ago. The sky around the Southern Cross has an embarrassment of celestial riches, enough for countless nights of patient observation and contemplation. In the next issue, another memorable star cluster in this region of the sky…

Posted in Celestial Objects

Search: