M8, M20, and M23 – the Lagoon Nebula, the Trifid Nebula, and the nearby open cluster
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Nebulae are clouds of interstellar gas and dust or vast regions of space containing similar material. In the past, this term also referred to galaxies other than our own.
Molecular clouds, a type of nebula, consist mainly of molecular hydrogen (H2) and carbon monoxide (CO). These clouds typically have low temperatures, around 10K. In certain regions, they condense into dense cores, serving as birthplaces for new stars. Factors such as size, temperature, and chemical composition determine the size and life cycle of the stars that form within the cloud.
One of the most beautiful nebular objects in the night sky is, in my opinion, the Lagoon Nebula. It is listed as the eighth entry in the Messier catalog (M8). It is a diffuse nebula and an H II region located in the constellation Sagittarius, approximately 4,100 light-years from Earth. The Lagoon Nebula has a diameter of about 33 light-years and, under ideal conditions, can be seen with the naked eye as a faint, fuzzy patch of light with an apparent magnitude of 5.8m and angular dimensions of 90' by 40'. Nearby, there are other fascinating objects, such as the Trifid Nebula (M20) and the open cluster M23.
Considering that all these objects lie within the constellation Sagittarius, they can be observed from our geographic latitudes primarily during the summer months.
Observations
July 11, 2019, around 11:30 PM – Jaworzno (Poland), garden
urban conditions, high level of light pollution
During my observations, I first captured a photograph with a relatively wide field of view. The objects in the frame were positioned fairly low above the southern horizon, where light pollution was particularly intense. The photograph was taken without a telescope, using only a telephoto lens with variable focus.
The Lagoon Nebula is an active star-forming region, so it is no surprise that it is illuminated from within by young, bright stars. Some of these “stellar infants” form the open cluster NGC 6530, which contains between 50 and 100 stars only a few million years old. When observed with the naked eye, the nebula appears pale and almost colorless. This is due to the physiology of our eyes, which are not well-suited to distinguishing colors in low-light conditions. However, long-exposure photographs reveal that the Lagoon Nebula is distinctly pink.
Just north of the Lagoon lies the Trifid Nebula, which is similar in many ways to the previously described nebula—although it is much dimmer, and its exact distance from Earth remains uncertain. Estimates range from approximately 2,000 to as far as 9,000 light-years.
The last object marked in the photograph is Messier 23, an open star cluster. It is located 2,150 light-years from Earth. Its actual diameter is about 15 light-years, while its apparent diameter is 27'. The cluster contains more than 150 relatively young stars, aged between 220 and 300 million years, with the brightest stars reaching a magnitude of 9.2m.
Encouraged by the good results of the previous exposure, I decided to capture another photograph, this time maximizing the lens's focal length to increase magnification (and reduce the field of view) to focus solely on the region of the Lagoon and Trifid Nebulae. The result can be seen in Photo 2.
The Lagoon Nebula is located approximately 4,100 light-years from Earth. It is a stellar nursery where many stars are only a few million years old—too young for any form of life as we know it to have evolved there. Due to the youth of newly formed stars and planets, it is unlikely that evolution could have produced any complex biological structures. However, if an observer were viewing Earth from this great distance using a hypothetical supertelescope, what might they see?
Our hypothetical alien astronomer might witness the Slavs establishing a settlement in Trzcinica—a heavily fortified stronghold and one of the oldest on Polish territory. Meanwhile, the first ziggurats were being built in the Mesopotamian cities of Ur, Eridu, and Uruk. Around the same time, ancient Egypt was emerging from the First Intermediate Period, which marked the transition between the Old and Middle Kingdoms—a time characterized by the collapse of centralized power, internal conflicts for control over the country, and social unrest.
As for natural phenomena, it is worth mentioning the last eruption of Mount Mariveles, which shook the Philippines during that era.
All of these events occurred roughly four thousand years ago, meaning that the light carrying information about them is only now reaching the Lagoon Nebula. Let us remember that when we observe the night sky, we are seeing celestial objects as they were in the distant past—stargazing is, therefore, a journey through time, accessible to anyone who looks up at the sky.
June 30, 2024, around 11:00 PM – Jaworzno (Poland), garden
urban conditions, high level of light pollution
It is always a pleasure to return to familiar places, especially those associated with fond memories. Such was the case that night when my observations once again took me to the region of Sagittarius. This time, I successfully captured an image of the Trifid Nebula using a Newtonian reflector telescope (Photo 3).
Here, we can finally see why the Trifid Nebula is named as such—the dark lanes of matter visibly divide this beautiful cloud of interstellar gas and dust into three distinct sections.
During this session, I also took a closer look at the open cluster M23 (Photo 4).
M23 is located 2,150 light-years from Earth. Its apparent diameter on the celestial sphere is 27 arcminutes, while its actual diameter is about 15 light-years. The cluster contains more than 150 stars, with the brightest reaching a magnitude of 9.2m and the total magnitude of the cluster being 6.9m. M23 is estimated to be between 220 and 300 million years old.
Photo 1 Parameters:
- Total exposure time: 20 minutes (stack of 20 RAW frames at 60s each, using an appropriate number of dark, bias, and flat frames)
- Canon EOS 60D
- ISO: 2500
- Lens: zoom type (used at f = 120mm)
- Aperture: f/4 (the smallest possible for the lens used)
- Mount: equatorial mount with tracking, aligned using the drift method and controlled by a custom-built system
Photo 2 Parameters:
- Total exposure time: 20 minutes (stack of 20 RAW frames at 60s each, using an appropriate number of dark, bias, and flat frames)
- Canon EOS 60D
- ISO: 500
- Lens: zoom type (used at fmax = 250mm),
- Aperture: f/4 (the smallest possible for the lens used),
- Mount: equatorial mount with tracking, aligned using the drift method and controlled by a custom-built system.
Photo 3 Parameters:
- Total exposure time: 50 minutes (stack of 50 RAW frames at 60s each, using an appropriate number of dark, bias, and flat frames)
- Canon EOS 60D
- ISO: 800
- Newton telescope (150/750), 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.
Photo 4 Parameters:
- Total exposure time: 20 minutes (stack of 50 RAW frames at 60s each, using an appropriate number of dark, bias, and flat frames)
- Canon EOS 60D
- ISO: 800
- Newton telescope (150/750), 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:
- Lefloch B., Cernicharo J., Pardo J. R., Star formation in the Trifid Nebula, Astronomy & Astrophysics, 489(1), 2008, str. 157-171
- Tothill N. F. H., Gagné M., Stecklum B., Kenworthy M. A., The Lagoon Nebula and its Vicinity, w: Reipurth B. (ed.), Handbook of Star Forming Regions, vol. II., Astronomical Society of the Pacific, 2008
- Frommert H., Kronberg Ch., Messier 8, dostępne online: http://www.messier.seds.org/m/m008.html [dostęp: 11.07.2024]
Marek Ples