The Southern Beehive Cluster is a bright, dense open cluster located 1,300 light-years away in the constellation Carina (the Keel). With an apparent magnitude of 3.8 and an apparent size of 30 arcminutes, the cluster is visible to the unaided eye. It is also known as the Sprinter and the Diamond Cluster. It is catalogued as NGC 2516 in the New General Catalogue and Caldwell 96 in the Caldwell catalogue.
The Southern Beehive Cluster lies in the far southern sky and is largely unfamiliar to northern observers. However, its brightness and size make it a popular target for amateur astronomers in the southern hemisphere. Like its northern counterpart, the Beehive Cluster (Messier 44), the Southern Beehive appears as a hazy patch in clear, dark skies. Its angular size is comparable to that of the full Moon.
The Southern Beehive Cluster has a tidal radius of about 32.6 light-years (10 parsecs) and a vast halo of stars spanning 1,630 light-years (500 parsecs), corresponding to 20 degrees on the sky. It has an estimated mass of up to 100,000 solar masses.
Southern Beehive Cluster (NGC 2516), image created using Aladin Sky Atlas software from the Centre de Données astronomiques de Strasbourg and public data in FIT format from DSS (Digitized Sky Survey) (CC BY-SA 4.0)
NGC 2516 has a central overdensity and two tails (the halo), one leading the orbit of the cluster and the other trailing it. The core of the cluster and the extended halo are the same age, around 150 million years.
Astronomers have proposed that the halo structures may be tidal tails composed of stars that escape the cluster due to the galactic tide. Alternatively, the stars may have formed in a more dispersed complex, such as a giant molecular filament instead of a molecular cloud.
The Southern Beehive Cluster contains 1,106 candidate members brighter than magnitude 18 in the G-band, located within a few degrees of the cluster’s centre, based on the data obtained with the Gaia space observatory. Other studies, which looked at stars up to a magnitude fainter, found 1,860 and 3,003 member stars.
The open cluster NGC 2516 hosts two red giant stars that shine at 5th magnitude and three relatively bright visual double stars, catalogued as HJ 4031, HJ 4027, and I 29. These pairs can be resolved in a small telescope.
In 2023, a team of astronomers led by Gang Li of the Institute of Astronomy, Department of Physics and Astronomy, KU Leuven, performed photometric and spectroscopic observations of the Southern Beehive Cluster with the ESA’s Gaia space observatory, NASA’s Transiting Exoplanet Survey Satellite (TESS), and the FEROS instrument (Fiber-fed Extended Range Optical Spectrograph) at ESO’s La Silla Observatory in Chile.
The team analyzed the light curves of a sample of 301 stars and discovered many different types of variable stars in the cluster. These included 24 g-mode pulsators (Gamma Doradus variables and slowly pulsating B stars), 35 p-mode pulsators (Delta Scuti variables), five eclipsing binary systems, and 147 stars that vary in brightness because of surface modulations.
This image captures some of the shimmering stars in the outskirts of the open cluster Caldwell 96. Also known as NGC 2516 or the Southern Beehive (for its similarity to the Northern Hemisphere’s Beehive Cluster), this loosely bound swarm of stars was first recorded by the French astronomer Nicolas-Louis de Lacaille in 1751. It is a popular observing target for stargazers in the Southern Hemisphere. Because it is so bright, Caldwell 96 is visible with unaided eye in dark skies. It appears as a hazy patch, but a pair of binoculars will resolve some of its roughly one hundred stars. Part of what makes Caldwell 96 such an appealing target for observers is its brightness, but it is also notable for hosting at least three double stars that can be visually separated with a small telescope. Double stars are pairs of individual stars that appear very close together from our vantage point here on Earth. This may be because the two stars in question are gravitationally bound, orbiting around a common point, or because two unrelated stars appear very close together by chance alignment but are really at different distances from Earth. The former category is also known as a binary star system, but the double stars in Caldwell 96 fall into the second category — what are known as “optical” double stars. Observers in the Southern Hemisphere can view the cluster and its double stars most easily during late summer. The above image of Caldwell 96 is comprised of observations taken by Hubble’s Wide Field and Planetary Camera 2 at ultraviolet, visible, and infrared wavelengths. These observations were part of a survey that took advantage of Hubble’s sensitive camera to learn more about the structures of distant galaxies and to understand the motion of star clusters. Credit: NASA, ESA, R. Griffiths (Carnegie Mellon University); S. Casertano (Space Telescope Science Institute), and J. MacKenty (Space Telescope Science Institute); Processing: Gladys Kober (NASA/Catholic University of America) (CC BY 2.0)
Facts
The Southern Beehive Cluster was discovered by the French astronomer Nicolas-Louis de Lacaille from the Cape of Good Hope in 1751. Abbé Lacaille spent several years charting the southern skies from South Africa. He observed almost 10,000 stars and discovered 42 nebulous objects during his stay. He spotted NGC 2516 with a ½-inch refractor.
Like the Southern Pleiades (Theta Carinae Cluster, IC 2602), the Southern Beehive Cluster takes its name from its brighter and larger northern counterpart, the Beehive Cluster (Messier 44). Also known as Praesepe, M44 is much better known to observers in the northern hemisphere because, unlike NGC 2516, it is visible from most northern locations. Located in the region between Regulus in the constellation Leo and Pollux in Gemini, Praesepe has an apparent size of 95 arcminutes and an apparent visual magnitude of 3.7. It lies at more than half the distance of the Southern Beehive, only 610 light-years away, in the constellation Cancer.
The Southern Beehive is one of the many bright deep sky objects in the southern celestial hemisphere that were not included in the Messier catalogue. The French astronomer Charles Messier made his observations from Paris, France, and NGC 2516 stays below the horizon for much of the northern hemisphere.
Like many of these objects, the Southern Beehive was included in the Caldwell catalogue, compiled by Sir Patrick Moore as a complement to the Messier catalogue in 1995. Like Messier objects, Caldwell objects are visible in amateur telescopes.
NGC 2516 is believed to have formed in the same stellar nursery as the open star cluster Mamajek 2, discovered in 2006 in the constellation Ophiuchus. The two clusters have a similar age and metallicity. In 2008, a team of astronomers proposed that they formed in the same star-forming region around 135 million years ago. The team found an age of 140 million years for the Southern Beehive and 120 ± 25 for Mamajek 2.
This image transports you to the most advanced visible-light astronomical observatory in the world: the Very Large Telescope (VLT), located at ESO’s Paranal Observatory in Chile. The shadowy figure gazing at the dark skies is photographer Babak Tafreshi, as captured by his fellow ESO Photo Ambassador Petr Horálek. For a moment, place yourself in Babak’s — or indeed Petr’s — shoes. Here, you are king of the cosmos. The site is silent, dark, still. You stare up at the pristine Chilean night sky, which, with its extremely low levels of both light pollution and water vapour, offers spectacular nighttime scenery to delight any astrophotographer or stargazer. With your trusty camera on hand, a night of amazing photo opportunities lies ahead; you anticipate spending clear hour after clear hour documenting the heavens, with no fear of cloudy weather appearing, uninvited, to spoil the view. The Large Magellanic Cloud is visible at the centre of the frame, while Canopus, the brightest star in the constellation Carina (The Keel), watches over the starry scene to the upper right. The Southern Beehive Cluster (NGC 2516) can be spotted in the upper left corner, near the orange giant Avior. Image credit: P. Horálek/ESO (CC BY 4.0)
Location
The Southern Beehive Cluster is located in the southern constellation of Carina. It appears 3.3 degrees west-southwest of Avior (Epsilon Carinae). Avior is the third brightest star in Carina, after Canopus and Miaplacidus. It is part of the False Cross, a bright asterism that is often mistaken for the Southern Cross. The asterism is formed by Avior with Aspidiske in Carina and Alsephina and Markeb in Vela. A line extended from Markeb through Avior leads to the Southern Beehive.
NGC 2516 is visible to the unaided eye on a clear night. About a hundred stars can be resolved using binoculars. Small telescopes will also resolve several double stars in the cluster.
The location of the Southern Beehive Cluster (Caldwell 96, NGC 2516), image: Stellarium
The bright Omicron Velorum Cluster (IC 2391, Caldwell 85) lies in the same region of the sky. Like the Southern Beehive, it can be found using the stars of the False Cross. It appears in the constellation Vela, near the bright Alsephina.
The False Cross, the Southern Beehive (NGC 2516) and the Omicron Velorum Cluster (IC 2391),
image credit: ESO/Digitized Sky Survey 2 (CC BY 4.0)
At declination -60° 52’, the Southern Beehive Cluster never rises above the horizon for observers north of the latitude 29° N. It stays low above the horizon from locations in the northern tropical latitudes and is best seen from the southern hemisphere.
The best time of the year to observe the Southern Beehive Cluster and other deep sky objects in Carina is during the month of March, when the constellation climbs higher above the horizon in the early evening.
Southern Beehive Cluster – NGC 2516
| Constellation | Carina |
| Object type | Open cluster |
| Right ascension | 07h 58m 06.5s |
| Declination | −60° 48′ 00’’ |
| Apparent magnitude | 3.8 |
| Apparent size | 30.0’ |
| Distance | 1,300 light-years (399 parsecs) |
| Age | 100 – 200 million years |
| Diameter | 12 light-years |
| Names and designations | Southern Beehive Cluster, the Sprinter, Diamond Cluster, NGC 2516, Caldwell 96 (C96), Collinder 172 (Cr 172), OCl 776.0, C 0757-607, Theia 613, MWSC 1393 |
The Southern Beehive (NGC 2516), image credit: ESO/Digitized Sky Survey 2 (CC BY 4.0)