Credit: Aldo Zanetti
Astronomical and Imaging Data
| RA: | 17h 37m 36.10s |
| DEC: | -03° 14′ 45.3″ |
| MAG: | 7.59 |
| Diameter: | 11′ |
| Const: | Oph |
| OTA | Celestron 9.25 Edge HD |
| Focal Length | 2350 |
| Camera | ASI1600MM |
| Site | Po Plain, Italy |
| Sky Quality | Bortle 7 |
Useful Informations
NGC 6402, also known as Messier 14 (M14), is a large globular cluster located in the constellation Ophiuchus. It’s a rich stellar system with several hundred thousand stars, notable for its significant population of variable stars and the observation of a rare nova event within its boundaries.
Physical Properties and Structure
M14 is located about 30,300 light-years from Earth and has a diameter of roughly 100 light-years. With a mass of approximately 1 million solar masses, it’s one of the more massive globular clusters in our galaxy. It’s classified as a Class VIII globular cluster, indicating that its stars are not as densely concentrated in its core as in other clusters, giving it a somewhat looser appearance. However, the overall shape is notably elongated.
The cluster’s stars are metal-poor, with a metallicity of about 1.2% of the Sun’s. This is a common characteristic of old stellar systems formed in the early universe. Recent studies using high-resolution spectroscopy have revealed that M14, like many other massive globular clusters, contains multiple stellar populations with distinct chemical compositions, hinting at a more complex formation history than previously thought.
Variable Stars and Novae
M14 is an excellent target for studying stellar variability. It’s known to contain at least 70 variable stars, many of which are of the RR Lyrae and W Virginis types. These are pulsating stars that are crucial for determining the cluster’s distance and for understanding stellar evolution.
Perhaps the most famous event associated with M14 is the nova explosion that occurred in 1938. The outburst was not discovered until 1964, when astronomers examined photographic plates from that period. The nova briefly outshone the brightest stars in the cluster, providing a direct observation of a thermonuclear runaway event on the surface of a white dwarf star in a binary system. This was only the second nova ever discovered in a globular cluster and the first to be captured on a photographic plate.