NGC 7243 is a large sparse open cluster located in the faint northern constellation of Lacerta. The cluster shines at magnitude +6.4 and is therefore just beyond naked eye visibility but easily seen with binoculars and small scopes. It spans 21 arc minutes of apparent sky, which is equivalent to about 2/3rds of the apparent diameter of the full Moon. In total, NGC 7243 contains about 40 stars including some blue, yellow and red members. It was discovered by William Herschel on September 26, 1788.

NGC 7243

Locating NGC 7243 is easy. It's positioned just a couple of degrees west of stars alpha Lac (α Lac - mag. +3.8) and 4 Lac (mag. +4.6). First magnitude Deneb (α Cyg - mag. +1.3) in neigbouring Cygnus is about 20 degrees further west and 5 degrees to the south. From latitudes greater that 41N the cluster is circumpolar and appears high in the sky or even overhead during the months of September, October and November.

Finder Chart for NGC 7243 (credit:- freestarcharts)

Finder Chart for NGC 7243 - pdf format (credit:- freestarcharts)

Through 7x50 or 10x50 binoculars, NGC 7243 appears as a loose gathering of stars with at least 10 resolvable. At 100x magnification through a 100mm (4-inch) refractor the cluster completely fills the field of view and is fully resolvable. About 40 stars can be seen in two distinct groups. The northwestern group contains about 10 stars in a triangular shape and the southwestern group up to 25 stars distributed almost quadrangle like. A dark lane connects the two sections. Positioned 4 degrees southwest of NGC 7243 is another sparse large open cluster, NGC 7209.

NGC 7243 is the brightest cluster in Lacerta and is object number 16 in the Caldwell Catalogue. It's located 2,800 light-years distant and has a spatial diameter of 17 light-years.

NGC 7243 Data Table

Object TypeOpen Cluster
Distance (light-years)2,800
Apparent Mag.6.4
RA (J2000)22h 15m 09s
DEC (J2000)49d 53m 51s
Apparent Size (arc mins)21 x 21
Radius (light-years)8.5
Age (years)100 Million
Number of Stars40
Other NameCollinder 448

Sky Highlights - September 2017

Neptune reaches opposition on September 5th

The Planets
This Month's Guide

Algol Minima
Algol eclipse dates and times for September

Northern Hemisphere
West:- Jupiter (mag. -1.7)
Southwest:- Saturn (mag. +0.5)
East:- Neptune (mag. +7.8)
South:- Neptune
East:- Uranus (mag. +5.7)
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
West:- Jupiter
Northwest:- Saturn
East:- Neptune
West:- Saturn
North:- Neptune
Northeast:- Uranus
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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