47 Tucanae or 47 Tuc is a spectacular globular cluster located in the southern constellation of Tucana. At magnitude +4.5, it appears to the naked eye as a slightly fuzzy star similar to the head of a tail-less comet. Always hidden from view for European and North American observers, 47 Tuc was discovered by French astronomer Nicolas Louis de Lacaille on September 14, 1751. Initially Lacaille though he had found a comet until further inspection revealed its true nature.

47 Tuc is the second brightest globular in the sky, only Omega Centauri is more brilliant. It has an extremely dense core and is one of the most massive globular clusters surrounding the Milky Way. The cluster is located 2.5 degrees west of the Small Magellanic Cloud (SMC) and from most of the Southern Hemisphere it's circumpolar and never sets. In contrast from latitudes of 18N or greater, the globular can never be seen as it fails to rise above the horizon.

47 Tucanae (ESO/Cioni/VISTA/Cambridge Astronomical)

Through 7x50 or 10x50 binoculars, 47 Tuc appears as a bright starlight nucleus surrounding by a halo of soft pearly light. It's clearly non-stellar in nature. Telescopically the cluster is stunning and a showpiece object of the night sky. It total it spans 31 arc minutes of apparent sky, almost exactly the same diameter as the full Moon. For comparison, 47 Tuc is 50% larger and 3x brighter than M13 "the Great Hercules Globular Cluster" widely regarded as the finest globular in the northern section of the sky.

A small 100mm (4-inch) scope reveals a bright compact core surrounded by a large 15 arc minute sphere with the brightest members resolvable. Even through small telescopes it's a superb sight. A 200mm (8-inch) instrument shows a swarm of stars in a glittering 3D view. The dense centre remains unresolvable in stark contrast to the less dense outer regions. Overall it's a breathtaking object for all sizes and types of telescopes.

47 Tuc is located 16,700 light-years from Earth and contains at least 500,000 stars. These include exotic stars with at least 23 blue stragglers and 23 millisecond pulsars known. The globular is estimated to be 13.1 billion years old.

Finder Chart for 47 Tucanae

Finder Chart for 47 Tucanae - pdf format

47 Tucanae Data Table

Name47 Tucanae
Object TypeGlobular Cluster
Distance (kly)16.7
Apparent Mag.4.5
RA (J2000)00h 24m 05s
DEC (J2000)-72d 04m 51s
Apparent Size (arc mins)31 x 31
Radius (light-years)75
Age (years)13.1 Billion
Number of Stars>500,000
Notable FeatureSecond brightest globular cluster after Omega Centauri

Sky Highlights - April 2017

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