From the January 2022 issue

101 Must-See Cosmic Objects: The Southern Pleiades

By | Published: May 25, 2022 | Last updated on August 30, 2023
Marco Lorenzi

The Southern Pleiades (IC 2602) in the constellation Carina the Keel is a dazzling open cluster. It lies 550 light-years away and occupies a region 50′ in diameter. That’s 2.6 times as much area as the Full Moon covers.

IC 2602 contains about 75 stars surrounding blue, magnitude 2.7 Theta (θ) Carinae, so it’s sometimes referred to as the Theta Carinae Cluster. More commonly, however, observers call it the Southern Pleiades because its discoverer, French astronomer Nicolas Louis de Lacaille, compared it to the Pleiades (M45; see #8) in the northern constellation Taurus the Bull.

Astronomers originally thought IC 2602 was a young object, on the order of 15 million years old. Recent studies at the Anglo-Australian Observatory, however, have placed its age closer to 45 million years — which is still pretty young for an open cluster.

With a total magnitude of 1.9 (which makes it 52 percent as bright as M45), the Southern Pleiades ranks as the fifth-brightest open cluster in the sky. Most observers agree that, as with the northern Pleiades, IC 2602 looks better through binoculars. That’s because telescopes, though they provide increased magnification, have a more limited field of view and spread out the stars too much. If, however, you can use a short-focal-length scope with an eyepiece that gives a 1½° field of view, this collection of stars will knock your socks off.

Through such an instrument, it looks like you’re viewing two clusters with a 0.3°-wide gulf between them. The westernmost group includes Theta Carinae and two curving lines of stars that start at Theta. One heads north and the other south.

Some observers think that the eastern half of IC 2602 looks like a tiny Orion, whose stars have different relative brightnesses than those in the winter constellation.

Make sure to explore Astronomy’s full list of 101 cosmic objects you must see. New entries will be added each week throughout 2022.

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