Lagoon (Messier 8) and Trifid (Messier 20) Nebulas
Imaged September 6 and 7, 2023

The night skies finally cleared for a few days here in coastal San Diego, so I made hay while the moon shines! Here are two new Deep Sky Objects I have imaged.  The photons I captured left the nebulas 4000-6000 years ago!

LAGOON NEBULA, MESSIER 8 (M8)

The Lagoon Nebula is an emission nebula located in the constellation Sagittarius, in the Sagittarius arm of the Milky Way. It received its name due to the lagoon-shaped dark lane that appears above the bright “Hourglass” region. The dark lane divides the nebula in half. The Lagoon Nebula is home to some interesting astronomical features. At the center is the “Hourglass Nebula.” There is a funnel-like or tornado-like structure caused by a hot O-type star, that emanates massive amounts of ultra-violet light, heating and ionizing gases on the surface of the nebula. The Lagoon Nebula is also home to a number of Bok globules - dark, collapsing clouds of proto-stellar material. The Lagoon Nebula is classified as an HII region, where emission nebulae are created when young, massive stars ionize nearby gas clouds, composed primarily of hydrogen, with high-energy UV radiation. These stars have temperatures in excess of 10,000K. It is located about 5200 light-years away in the Sagittarius arm of the Milky Way. It is a relatively large nebula, subtending about 90x40 arc-minutes in size. That is about 3 x 1-1/3 full Moons. The Moon subtends about 30 arc-minutes or ½ a degree. With a visual magnitude of 6, the Lagoon Nebula is one of only two star-forming regions visible to the naked eye in mid-northern latitudes, the other being the Great Orion nebula, which is much brighter. 

TRIFID NEBULA, MESSIER 20 (M20)

The Trifid Nebula is a relatively young (300,000 years old) star-forming Hii region in Sagittarius of the Milky Way’s Saggitarius arm. Its name, Trifid, means “three-lobed.” This refers to the way it looks, and fact that it is an unusual combination of a star cluster, an emission nebula (the dense reddish-pink portion), a reflection nebula (the blue-colored portion), and a dark nebula, which creates the dark gaps and its trifurcated appearance. It is popular among amateur astronomers because it is relatively bright (Magnitude 6.3) and can be easily observed with a small telescope. Lying 5200 light-years distant, the Trifid Nebula subtends an angle of 28 arc-mins, just shy of the diameter of a full Moon.A bright, open cluster of young, hot O-type stars lie at the core of the emission nebula, partially obscured by thick dust lanes that block visible light. The intense radiation of the stars has blown away the dust and gas in the region surrounding the cluster. As a result, there is no longer any star-forming activity in the vicinity of the Trifid Nebula. Interestingly, the blue reflection nebula observed in images is not physically associated with the Trifid Nebula, but just happens to appear along the same line of sight. 

WEBB'S CROSS STAR CLUSTER, MESSIER 21 (M21)A serendipitous capture (just above the Trifid Nebula) is the open star cluster Messier 21, also designated NGC 6531 or Webb's Cross. The M21 cluster is located 3,930 light-years away from Earth with an apparent magnitude of 6.5.  This cluster is relatively young on the cosmological scale (about 6.6 million years old) and tightly packed, with a mass of over 783 solar masses.  A few blue giant stars have been identified in the cluster, but M21 is composed mainly of small dim stars.  As one can observe here, the cluster is positioned near the Trifid nebula, but is not associated with that nebulosity.  It forms part of the Sagittarius OB1 association. The stars in the cluster do not show a significant spread in ages, suggesting that the star formation was triggered all at once.  An interesting factoid, as of January 2022, Messier 21 is one of the few remaining objects within the Messier Catalog to not have been photographed by the Hubble Space Telescope.

Exposure Data and other Useful Information

Focus and Seeing: Vega was 4.9-5.0 FWHM, with smaller stars around M8 were 2.3-2.5 FWHM 

Exposure Information:·
Lights: 84x frames total; 46x 60 seconds, 38x 90 seconds·       
Darks: 50x 60sec, 50x 90sec·       
4x Master Darks (2x 60sec, 2x 90sec)·       
1x Master Bias·       
2x Bad Pixel Maps (1 created this session)

Equipment and Software·       
AstroTech AT70ED with ATR8 0.8x FF/Reducer and IDAS LPS-D3 filter imaged by an Ha-modified Canon T3i·       
Mount: EQM-35Pro with ASI 120-MM-mini with ZWO 30mm f/4 guide scope and camera controlled by PHD2·       
Session Control via BeeLink mini-PC running EQASCOM, Carte du Ciel, ASTAP, BYEOS, and Polemaster with remote control via Windows Remote Desktop from a laptop. 

The images were stacked and processed in Astro Pixel Processor, further polished in 32-bit mode using Photoshop and LightRoom, along with R-C Astro's NoiseXterminator and StarXterminator.