NGC 3766, also known as the Pearl Cluster, is a superb open cluster in Centaurus. At magnitude +5.3, it's faintly visible to the naked eye but challenging to spot against the numerous stars of the background Milky Way. The cluster was born in the Carina molecular cloud, a vast star-forming region that lies at approximately between 6,500 and 10,000 light-years distant. It includes the barely-stable star eta Carinae (η Car), which one-day will explode as a spectacular supernova.

NGC 3766 is a nice binocular target, a wonderful sight through telescopes and one of the jewels of the southern sky. With a declination of 61S, it's best seen from southern latitudes during the months of March, April and May. From many southern towns and cities, the cluster is circumpolar and therefore never sets. However, from northern locations above 29N it never rises above the horizon.

Nicholas Louis de Lacaille discovered NGC 3766 on March 5, 1752.

NGC 3766 (credit:- La Silla Observatory/ESO)

Finder Chart for NGC 3766 (credit:- freestarcharts)

Finder Chart for NGC 3766 - pdf format (credit:- freestarcharts)

The Pearl Cluster is located in the southwestern corner of Centaurus, 7 degrees west and slightly north of Acrux (α Cru - mag. +0.8). Positioned 1.5 degrees south of NGC 3766 is lambda Cen (λ mag. +3.1) and surrounding open cluster and associated emission nebula, IC 2944.

Binoculars show a compact cluster, spanning 12 arc minutes, with a number of stars resolvable. An 80mm (3.1-inch) refractor at 100x magnification reveals a stunning object with dozens of stars visible. Most members are white in colour, but the look is enhanced by a couple of nice 7th magnitude red stars. One red star is positioned left of the cluster centre, the other to the right. The appearance of NGC 3766 has been compared to the Wild Duck Cluster (M11) in Scutum and M37 in Auriga.

Through a medium 200mm (8-inch) scope, NGC 3766 is a stunning sight that appears bright, colourful and fully resolvable. At the extreme northern edge of the cluster lies eclipsing binary BF Cen, which varies between magnitudes +8.5 and +9.4 every 3.7 days. In total, 137 stars have been identified, but it's not clear how many of these are actually members.

NGC 3677 is 5,500 light-years distant and has a spatial diameter of 20 light-years. It's estimated to be 20 million years old.

NGC 3766 Data Table

NGC3766
NamePearl Cluster
Caldwell97
Object TypeOpen Cluster
ConstellationCentaurus
Distance (light-years)5,500
Apparent Mag.+5.3
RA (J2000)11h 36m 14s
DEC (J2000)-61d 36m 36s
Apparent Size (arc mins)12
Radius (light-years)10
Age (years)20 Million
Number of Stars137
Other NamesCollinder 248, Melotte 107

Sky Highlights - February 2017

Comets
Comet Encke (2P/Encke) now visible in the western sky during evening twilight
Now is the last good chance to see comet 45P/Honda-Mrkos-Pajdusakova before it dramatically fades

Conjunction
Mars passes less than 1 degree north of Uranus on February 27th

Minor Planet
Vesta now visible with binoculars and small telescopes.

The Planets
This Month's Guide

Algol Minima
Algol eclipse dates and times for February 2017

Northern Hemisphere
Evening
Southwest:- Venus (mag. -4.8), Mars (mag. +1.1 to +1.3), Uranus (mag. +5.9)
Midnight
East:- Jupiter (mag. -2.1 to -2.3)
Morning
South:- Jupiter
Southeast:- Saturn (mag. +0.6)

Southern Hemisphere
Evening
West:- Venus, Mars, Uranus
Midnight
East:- Jupiter
Morning
North:- Jupiter
East:- Saturn, Mercury (mag. -0.2 - first half of month)

Deep Sky
Naked eye / binoculars:-
Messier 45 - M45 - The Pleiades (Open Cluster)
The Hyades - Open Cluster
Messier 44 - M44 - The Praesepe (Open Cluster)
Messier 35 - M35 - Open Cluster
Messier 42 - M42 - The Great Orion Nebula (Emission/Reflection)

Small telescopes:-
Messier 36 - M36 - Open Cluster
Messier 37 - M37 - Open Cluster
Messier 38 - M38 - Open Cluster

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