October 24, 2008

In Today's One Minute Astronomer...

47 Tucanae: The Sky's Best Globular

Today, a fine globular cluster. It's not the brightest, it's not the biggest, but it may very well be the prettiest. 47 Tucanae lies deep in the southern skies and, in a perfect world, is something we all see through a telescope at least once in our lives.

The Basics

• 47 Tucanae is a remarkable cluster, the second brightest globular in the sky and easily visible with the naked eye in the far southern constellation Tucana, the Toucan. You can find it just a few degrees west of the Small Magellanic Cloud.

• It's one of the closest clusters to the Sun: just 14,700 light years away. This star cluster spans an area as large as the full moon.

• Unlike the brighter Omega Centauri globular cluster, 47 Tuc appears more concentrated near the core. Through an 8” or larger telescope, its center seems to burn like a flame. Steven James O'Meara says the sight of 47 Tucanae through a telescope is like “cracking open a geode and finding it filled with gold dust”.

47 Tucanae, as it might appear through a 10-12' scope

A Deeper Look

• Like many globulars, 47 Tucanae (also called NGC 104) contains the remnants of long-dead stars. Astronomers have found more than 20 fast-rotating pulsars scattered throughout the cluster.

• 47 Tucanae is bright enough to display a yellowish hue. That's not surprising since, like most globular clusters, the stars in 47 Tuc are ancient, low-mass reddish-orange stars. But the Hubble Space Telescope discovered dozens of blue stars, although blue stars burn hotter and should have long disappeared from this cluster. It seems these hotter stars formed by the slow merger of two low-mass red stars into massive hot blue stars.

How To Find It

47 Tucanae, also called NGC104, is a naked-eye object easily visible near the Small Magellanic Cloud. Here's a map looking south-southeast.

47 Tucanae at RA 00h 24m 05.67s Dec -72° 04m 52.6s

Personal View

Although I'm a big fan of small high-quality refractors, they are not up to the job of showing the best views of globulars. No, you need big aperture… at least 8 inches… to best see these old beautiful clusters. A good 12” Dobsonian will give you a dazzling view of 47 Tucanae.

Finally... the perfect guide to the stars of the southern hemisphere. Maps, myths, legends, and a complete overview of the exotic wonders of the southern skies. No telescope required. Learn more…