NGC 6541, also known as Caldwell 78, is a globular cluster in the southern constellation of Corona Australis. It shines at mag. +6.3 and therefore just beyond naked eye visibility, but easily seen with binoculars and small scopes. Although often overlooked and not as spectacular as the great southern showpiece globulars, it's still a fine object in its own right.

NGC 6541 was discovered by Niccolò Cacciatore at the Palermo Astronomical Observatory, Sicily, on March 19, 1826. James Dunlop independently found it a few months later on July 3, 1826. The cluster is best seen from southern regions during the months of June, July and August. From locations north of latitude 47N, it never rises above the horizon.

NGC 6541 (credit:- NASA, ESA, and The Hubble Heritage Team (STScI/AURA))

Finder Chart for NGC 6541 (credit:- freestarcharts)

Finder Chart for NGC 6541 - pdf format (credit:- freestarcharts)

To find NGC 6541 look towards the southwest corner of Corona Australis. It lies 4 degrees west-northwest of Alpha Telescopii (α Tel - mag. +3.5) with the bright curved tail and sting of Scorpius positioned a few degrees further northwest. Located a third of a degree from NGC 6541 is SAO 228708 (mag. +4.9). This star acts as a good marker, appearing in the same binocular and low power telescope field of view.

In total, NGC 6541 spans 15 arc minutes of apparent sky. Binoculars show a much smaller, hazy glow about 3 arc minutes across that obviously non-stellar. Small scopes do somewhat better. Through an 80mm (3.1-inch) instrument, it appears almost twice the size and hints on resolution.

The brightest member stars at the edges are resolvable at high magnifications through a 200mm (8-inch) telescope. The core remains bright, compact but unresolved. With a 350mm (14-inch) scope or larger, NGC 6541 is a dazzling sight with many stars visible. It becomes gradually denser as you move towards the core, but resolving the core remains challenging.

NGC 6541 is very old at almost 13 billion years. It was once thought to be about 16 or 17 billion years old, which would make it older than the current accepted 13.7 billion year age of the Universe! However, recent cluster age measurements have rectified the issue.

NGC 6541 is 22,800 light-years distant, which corresponds to a spatial diameter of 100 light-years. It contains approx. 150,000 stars.

NGC 6541 Data Table

NGC6541
Caldwell78
Object TypeGlobular Cluster
ConstellationCorona Australis
Distance (light-years)22,800
Apparent Mag.+6.3
RA (J2000)18h 08m 03s
DEC (J2000)-43d 42m 57s
Apparent Size (arc mins)15
Radius (light-years)50
Age (years)12.93 Billion
Number of Stars150,000

Sky Highlights - September 2017

Opposition
Neptune reaches opposition on September 5th

The Planets
This Month's Guide

Algol Minima
Algol eclipse dates and times for September

Northern Hemisphere
Evening
West:- Jupiter (mag. -1.7)
Southwest:- Saturn (mag. +0.5)
East:- Neptune (mag. +7.8)
Midnight
South:- Neptune
East:- Uranus (mag. +5.7)
Morning
West:- Neptune
South:- Uranus
East:- Venus (mag. -3.9), Mars (mag. +1.8) (from second week), Mercury (mag. +0.5 to -1.3) (from second week)

Southern Hemisphere
Evening
West:- Jupiter
Northwest:- Saturn
East:- Neptune
Midnight
West:- Saturn
North:- Neptune
Northeast:- Uranus
Morning
West:- Neptune
Northwest:- Uranus
Northeast:- Venus
East:- Mars (end of month)

Deep Sky

Small telescopes:-
Messier 13 - M13 - Great Hercules Globular Cluster
Messier 92 - M92 - Globular Cluster
Messier 11 - M11 - The Wild Duck Cluster (Open Cluster)
Messier 7 - M7 - The Ptolemy Cluster (Open Cluster)
Messier 6 - M6 - The Butterfly Cluster (Open Cluster)
Messier 4 - M4 - Globular Cluster
Messier 8 - M8 - Lagoon Nebula (Emission Nebula)
Messier 16 - M16 - Eagle Nebula (Emission Nebula with Open Cluster)
Messier 20 - M20 - Trifid Nebula (Emission and Reflection Nebula)

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