M38 - Starfish Cluster
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Messier 38, also known as NGC 1912, is an open star cluster located in the constellation Auriga, about 4,200 light-years from Earth. It was discovered in the first half of the 18th century by the Italian astronomer Giovanni Battista Hodierna and later independently cataloged by Charles Messier in 1764. The cluster spans roughly 21 arcminutes across the sky, which corresponds to an actual diameter of about 25 light-years.
M38 is classified as an intermediate-age open cluster, with an estimated age of around 220 million years. Its central region contains a large concentration of main-sequence stars of spectral types A and F, while the population also includes several red giants, indicating that some of its more massive stars have already evolved off the main sequence. The cluster’s integrated apparent magnitude is about 7.4, making it visible through binoculars under dark-sky conditions. In the same area of the sky lies Messier 36, a nearby but younger open cluster.
Observations
October 15, 2025, about 10:00 p.m. - Katowice Poland
urban conditions, very high level of light pollution
The spatial structure of M38 is irregular, with stars arranged in a pattern that reflects advanced gravitational dispersion. The relatively low central density suggests that the cluster is gradually dissolving under the influence of galactic tidal forces. Within its boundaries, several hundred gravitationally bound stars have been identified, and when fainter stars down to magnitude 15 are included, the total membership exceeds one thousand.
Spectroscopic measurements of radial velocities, together with photometric analyses in the UBV bands, indicate a metallicity close to the solar value, confirming that M38 is a typical open cluster within the Galactic disk. The proper motions of its member stars suggest that the cluster orbits the center of the Milky Way with a period of several hundred million years.
Messier 38 serves as a valuable target for studies of the dynamics and evolution of open clusters. Nearby lies another cluster, NGC 1907, situated only about 30 arcminutes away. Observations show that the two clusters are not gravitationally bound, although they may have been closer in the past, making this region an interesting field for investigating inter-cluster interactions.
Photo 1 Parameters:
- Total exposure time: 12 minutes (stack of 12 RAW frames at 60s each, using an appropriate number of dark, bias, and flat frames)
- ISO: 1600
- Maksutov-Cassegrain telescope (100/1400), prime focus exposure
- A filter was used to reduce the effects of artificial light pollution and atmospheric glow
- Mount: equatorial mount with tracking, aligned using the drift method and controlled by a custom-built system.
Further readings:
- Majaess D., Turner D.G., Lane D., In Search of Possible Associations between Planetary Nebulae and Open Clusters, Publications of the Astronomical Society of the Pacific, 119 (11), 2007, pp. 1349-1360
- Oliveira M.R., Fausti A., Bica E.L., Dottori H., NGC 1912 and NGC 1907: A close encounter between open clusters?, Astronomy and Astrophysics, 390 (1), 2002, pp. 103-108
- König M., Binnewies S., Bildatlas der Sternhaufen & Nebel, Kosmos, Stuttgart, 2023, p. 297
Marek Ples