NGC 7243
An open cluster in Lacerta discovered by William Herschel in 1788.
NGC 7243, also known as Caldwell 16, is an open star cluster in the northern constellation Lacerta. Discovered by William Herschel on September 26, 1788, it has an apparent magnitude of +6.4. The cluster is positioned near the naked-eye stars Alpha Lacertae and 4 Lacertae, the latter being an A-class double star, as well as the planetary nebula IC 5217. Its distance is roughly 878.0 parsecs.
Classified as Trumpler type II 2m, the cluster shows moderate star dispersion, average brightness, and average richness. A 2003 study identified 211 candidate members down to magnitude 15.5, with a combined mass falling within a certain range. The main sequence turnoff gives an age estimate, and the brightest star has a magnitude of 8.43, with the earliest spectral type being B5 III.
Over a decade of observations culminating in 2016 revealed 37 eclipsing binary systems and 26 pulsating variable stars within the cluster. One exoplanet transit candidate, designated J221550.6+495611, was also identified.
Quick Facts
- Epoch
- J2000.0
- Constellation
- Lacerta
- Ra
- 22 · 15 · 16.0
- Dec
- +49 · 50 · 07
- Dist Ly
- 878.0 pc
- Appmag V
- +6.4
- Mass Msol
- 348 · to · 522
- Names
- Caldwell 16, Cr 448
Facts from the source article.
Lore & Background
NGC 7243 was discovered on September 26, 1788 by German-English astronomer William Herschel. It has a Trumpler class of II 2m, indicating moderate dispersion, average brightness, and average richness of stars. A 2003 study identified 211 candidate members down to magnitude 15.5, with a combined mass range and age estimate derived from the main sequence turnoff. The cluster's brightest component has a magnitude of 8.43, and the earliest spectral type is B5 III.
Reader's Guide
NGC 7243 is notable for its proximity to naked-eye stars and the planetary nebula IC 5217, making it a useful reference point in the constellation Lacerta. Over a decade of observing campaigns culminating in 2016 revealed 37 eclipsing binary star systems and 26 pulsating variables within the cluster, as well as one exoplanet transit candidate designated J221550.6+495611. These findings contribute to the understanding of stellar evolution and binary star dynamics in open clusters. The cluster's moderate richness and brightness make it accessible to amateur astronomers, while its variable star population offers ongoing research opportunities.
Did You Know?
- It contains 37 eclipsing binary star systems identified by 2016.
- One exoplanet transit candidate, J221550.6+495611, was identified in the cluster.
Frequently Asked Questions
What exactly is NGC 7243?
It is an open star cluster in the constellation Lacerta, listed as Caldwell 16 in the fan-favourite deep-sky catalogue. William Herschel first recorded it on 26 September 1788, and it presents at an apparent magnitude of roughly 6.4.
How far away is NGC 7243 and how bright is its brightest star?
The cluster sits about 878 parsecs from the Solar System, placing it at a moderate distance within the Milky Way. Its single brightest member glows at magnitude 8.43, so the whole group is well beyond the naked-eye limit.
Where should I point my scope to find NGC 7243?
Look in the region between the naked-eye stars Alpha Lacertae and 4 Lacertae, the latter being an A-class double star. The small planetary nebula IC 5217 also lies nearby and makes a useful landmark for star-hopping.
What does the Trumpler type II 2m classification tell me about NGC 7243?
It indicates a cluster with a moderate spread of stars, average overall surface brightness, and a middling richness of members. A 2003 membership study identified 211 candidate stars down to magnitude 15.5.
Why is NGC 7243 included on the Caldwell list?
Stuart Caldwell compiled his catalogue to cover fainter Northern-Hemisphere targets that complement the brighter Messier objects, and NGC 7243 fits that niche. At magnitude 6.4 it rewards dark-sky observers with binoculars or a modest telescope.
More in Caldwell Objects 1-16
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