M46
Messier 46 or M46, also known as NGC 2437, is an open cluster of stars in the slightly southern constellation of Puppis. It was discovered by Charles Messier in 1771. Dreyer described it as "very bright, very rich, very large." It is about 5,000 ly away. There are an estimated 500 stars in the cluster with a combined mass of 453 M☉ and it is thought to be a mid-range estimate of 251.2 million years old. The cluster has a very broadest tidal radius of 37.8 ± 4.6 ly (11.6 ± 1.4 pc) and core radius of 8.5 ± 1.3 ly (2.6 ± 0.4 pc). It has a greater spatial extent in infrared than in visible light, suggesting it is undergoing some mass segregation with the fainter (redder) stars migrating to a coma (tail) region. The fainter stars that extend out to the south and west may form a tidal tail due to a past interaction.
The planetary nebula NGC 2438 appears to lie within the cluster near its northern edge (the faint almost rainbow array of colored smudge at the top-center of the image), but it is most likely unrelated since it does not share the cluster's radial velocity.
M46 is about a degree east of M47 in the sky, so the two fit well in a binocular or wide-angle telescope field.
Sky chart shows the position of Messier 46 in the sky. The first chart has a field of view of 60°.
Source: The Sky Live
Acquiring and processing details
It's actually one of my first real open clusters I imaged until now (except for the Pleiades and NGC 457, ET-Cluster). I took only for 1.3 hrs of data, just to see how well I would get it with this amount of subframes. I was also curious about the stars, would they blowout, give natural color? I should have performed photometric color calibration, but maybe I will do that later. Processing PixInsight, stacking done in Astro Pixel Processer. Some color adjustments where done in Affinity Photo 1.9. Anyway I'm quite pleased with the result.
- Date: March 6 - 2021
- Integration Time: 1.3 hrs
- Telescope: TS Photoline 130/910 x 0.79 at f5.5
- Mount: Skywatcher EQ6-Synscan Go-To
- Camera: ZWO ASI1600MM-Cool
- Filters: 19x120" L, 5x120" R, 8x120" G, 6x120" B
Some interesting objects that can also be seen besides M46 and NGC 2438. The attentive viewer can see a small red planetary nebula about 30 'north of NGC 2438. It concerns PK 231 + 04.1 or also M 1-18 (Minkowski 1-18), a faint nebula that needs an OIII filter and a telescope of at least 35 cm aperture if you want to observe it visually.
The German-American astronomer Rudolph Minkowski was best known for his spectroscopic work on supernovae. But he was also interested in "gaseous nebulae" and created a catalog of planetary nebulae in the 1940s that he had identified with the 60- and 100-inch telescopes on Mount Wilson. In three articles written in 1946, 1947, and 1948 for the Publications of the Astronomical Society of the Pacific entitled "New Emission Nevulae," he listed nearly 200 real (or probable) planetary nebulae.
Another interesting object is the Calabash Nebula, 5 'north-east of NGC2438. This nebula is not clearly visible to me, but there is an appearance of it. The Calabash Nebula, also known as the Rotten Egg Nebula, is a 1.4 light-year protoplanetary nebula (PPN) located about 5,000 light-years from Earth in the constellation Puppis. The name "Calabash Nebula" was first suggested in 1989 in an early paper on the expected nebula dynamics, based on the nebula's appearance. The Calabash is almost certainly a member of the open cluster Messier 46, as it has the same distance, radial speed and self-motion. You can see the nebula in the attached image of the Schulman telescope.