More astronomy posting! This time! Emission Nebulae.
Emission nebulae are where gas and dust in the galaxy collapses under gravity to form new stars, with new planets around those stars. Each of these objects are in the process of forming solar systems. When especially hot stars are formed in these nebulae, they emit ultraviolet radiation which 'powers' the nebula, and causes it to glow in visible light.
Let's look at the best such nebula in the sky visible from the northern hemisphere: Messier 42, aka The Great Nebula in Orion. It is seen in winter or early spring evenings in the northern hemisphere, or summer and early autumn in the southern hemisphere. (It is near enough to the equator to be visible from most latitudes.)
We'll zoom in starting from binoculars, moving up to a small toy telescope, and then a large 10" reflector.
Text transcription, and more sketches including a beautiful view with a large telescope, below the read-more!
2022-Feb-19 - 09:00 PM EST
M42 - 7x50 (tripod-mounted)
The belt & sword of Orion will both fit into the fov at once, but the edges are too blurry to be worth sketching. The sword is easily defined by 6 bright stars, two of which are in the nebula and correspond to the Trapezium and the "tail" of M42. [by which I meant the three linear bright stars next to the Trapezium] The nebula is faint w/ direct vision but easy & quite broad with averted vision.
The bright stars of the sword just barely fit in the fov, and the nebula is a blurry fuzzy gray blob in direct vision. Trapezium is barely split. W/ averted vision, the boxy part can be seen as a blurry highlight, and the wings can be glimpsed, as well as M43 nebula.
The wings are these sort of branching structures you sometimes see in M42, especially with averted vision. I assure you the wings are not for spaceflight, they're purely decorative. (that joke kills at public observing sessions)
These sketches are made with black pencil on white paper, while looking through the eyepiece of binoculars and telescopes. The drawings were then digitally inverted. The goal in DSO sketching is to produce an image without embellishment that reproduces the detail that you were able to detect in the eyepiece. Thus, astronomy sketches are the most realistic depictions of what it looks like to look through a telescope. The one caveat is that an experienced observer will be able to see more than a novice, and detail that was at the very limit of detection may be represented by features which are still fairly easy to see on the drawing.
This is to-date probably the best, most accurate, and most detailed sketch of a deep-sky-object I have ever done by looking through a telescope. It was seen with a 10" Newtonian reflector under suburban light polluted skies. I have seen the nebula even better under darker skies, but my sketches are generally more rudimentary when I do dark sky trips, since I'm trying to get as much done as I can. Note that compared to the last two images, which were taken with prisms to erect the image, this view through a Newtonian reflector telescope is rotated 'upside down.'
2022-Feb-19-09:54 PM EST
M42 - 250P - 11mm 82° - UHC Filter (109x)
Trapezium easily split. Fifth star [the "E" star] faintly visible [w/o UHC filter; with the UHC filter it was too dim]. There is a sharp-edged boxy region with some visible mottling at the center of the nebula. A fainter glow creates the "head" and "plumage" of a bird-like figure, with the wings extending at east and west, with a great extent in averted vision. One wing, the eastern one, is bifurcated. M43 is faint but visible in direct vision and appears almost cometary, with a fat tail facing M42.
Here is a sketch of M42 seen with a 90mm aperture Maksutov-Cassegrain called a Celestron C90. It's a step up from the Mak60, but the wings are much more indistinct.
Here's another view of the nebula with a 10" Dobsonian, in essentially the same conditions as the one above, just spending a little less time getting the details right. In some ways this impression is a little more realistic, in terms of what you're actually likely to see.
Here are two summer sky treats in Sagittarius. Messier 8 (the Lagoon Nebula) and Messier 20 (the Trifid Nebula). M21 is an open star cluster.
This drawing was done with a 76mm aperture toy tabletop dobsonian called the Celestron FirstScope.
Here are two sketches from two different nights in 2020 of the Messier 17 Swan Nebula in Sagittarius, seen with a 6" Dobsonian reflector. And here's a nicer sketch from 2021-July-4, with a 10" Dobsonian.
A bright fuzzy bar in a fairly rich star field, not far from the sagittarius star cloud. A dimmer spur comes off the southwest side, looping slightly so it resembles a swan's craned head. Very subtle "wings" are visible as puffs of nebulosity smeared out to the southeast.
And here is the Eagle Nebula. The famous Pillars of Creation are within this nebula, though they are unattainable targets to the visual observer.
M16 - Eagle Nebula
10" f/5 Dobsonian, 32mm Plossl, UHC filter
It took me a while to figure out that I had already found it, that the whole time I was trying to find it by star hopping off of what i thought was a nearby cluster, I was leaving M16 itself the whole time. The nebula is very dim, especially by Messier standards, requiring a UHC filter to even see, and really rewarding averted vision. The brightness is quite exaggerated in my drawing, or else you wouldn't be able to see it on your screen. No chance of seeing the pillars of creation, hah!
Many famous nebulae like the Horsehead for example are not really visible because their surface brightness is just too low. They would require absurdly large aperture telescopes (16" minimum) under perfectly dark skies.
For some reason I can't find a digital scan of my 2021 10" dob sketch of Messier 8. Maybe I'll go crack open the ol' log book and try and find it later.
Globular star cluster Messier 9 by Hubble Space Telescope
Messier 9, or M9, is a fascinating globular star cluster located in the constellation Ophiuchus. Discovered by Charles Messier in 1764, it’s one of the older clusters in our galaxy, estimated to be around 12 billion years old. It sits about 25,800 light-years away from Earth and is relatively close to the galactic center—only about 5,500 light-years from it, which is pretty tight-knit compared to many other globulars.
M9 contains a couple hundred thousand stars packed into a roughly spherical region about 90 light-years across. It’s not the brightest or most prominent cluster—magnitude-wise, it’s around 7.7, so you’d need a small telescope or decent binoculars to spot it under good conditions. What’s cool about it is its mix of stars: mostly old, low-mass ones, with a good dose of metal-poor stars (meaning they’re low in elements heavier than helium), which ties into its ancient origins.
It’s also got some variable stars—like RR Lyrae types—that astronomers use to gauge distances and study stellar evolution. The cluster’s been shaped by its proximity to the galactic core, too; tidal forces have likely stripped away some of its outer stars over billions of years, giving it a slightly squashed look.
Let’s dive into the history and structure of Messier 9 (M9)
History
Messier 9 was first cataloged by Charles Messier on May 19, 1764. Messier, a French astronomer obsessed with hunting comets, spotted it while charting objects that could be mistaken for them. He described it as a "nebula without stars," which makes sense—through his modest 18th-century telescope, M9 would’ve looked like a faint, fuzzy blob. It wasn’t until later, with better instruments, that astronomers like William Herschel resolved it into a dense cluster of stars in the 1780s. Herschel’s observations helped shift the understanding of these "nebulae" into what we now know as globular clusters.
M9’s historical significance grew as astronomers pieced together its age and context. By the 20th century, studies of its stellar population—especially its metal-poor stars—pegged it as one of the Milky Way’s ancient relics, formed roughly 12 billion years ago. That’s not long after the Big Bang itself, making M9 a window into the early galaxy. Its proximity to the galactic center also hints at a turbulent past, shaped by gravitational tussles with the Milky Way’s core over eons.
Structure
M9 is a classic globular cluster: a tight, roughly spherical ball of stars held together by gravity. It spans about 90 light-years in diameter, though its core is much denser—most of its estimated 200,000+ stars are crammed into the inner regions. The cluster’s classified as a Shapley-Sawyer Concentration Class VIII, which means it’s not the most densely packed (Class I is the tightest), but it’s still got a noticeable core concentration that loosens up toward the edges.
Its structure’s been sculpted by its environment. Being just 5,500 light-years from the galactic center—closer than most globulars—M9 feels the Milky Way’s tidal forces strongly. These forces stretch and distort it slightly, stripping away some outer stars over time. This gives it a less perfectly spherical shape than more isolated clusters, with a bit of flattening or elongation detectable in detailed observations.
The stellar makeup is telling, too. M9 is dominated by old, low-mass stars—red giants and main-sequence stars nearing the end of their lives. Its metallicity (the fraction of elements heavier than helium) is low, around 1/50th that of the Sun’s, confirming its early formation before the galaxy had much heavy-element recycling. You’ll also find variable stars like RR Lyrae types pulsing in its core, which are handy for measuring its distance (around 25,800 light-years from us) and studying its dynamics. No fancy young star-forming regions here—just a quiet, ancient assembly.
The cluster’s compactness and its tidal wear-and-tear make it a great case study for how globulars evolve near the galactic core.
Let’s connect Messier 9’s history to the Milky Way’s formation and then zoom into its core dynamics
History and the Milky Way’s Formation
M9’s ancient age—around 12 billion years—places it among the first generation of globular clusters formed in the Milky Way. Back then, the galaxy was a chaotic mess of gas, dust, and smaller proto-galaxies merging into what we know today. Globular clusters like M9 are thought to have condensed out of massive gas clouds during this early epoch, before the galactic disk fully took shape. Its low metallicity—elements heavier than helium are scarce at about 1/50th the Sun’s level—backs this up. The universe hadn’t had time to churn out much “metal” through stellar fusion and supernovae yet, so M9’s stars are made of nearly pristine primordial stuff: mostly hydrogen and helium.
Being just 5,500 light-years from the galactic center suggests M9 formed in the galaxy’s inner halo or bulge region, where star formation kicked off early and fast. Some theories propose that clusters like M9 could even be remnants of dwarf galaxies or smaller stellar systems that got swallowed up by the growing Milky Way. Over billions of years, as the galaxy settled into its spiral structure, M9’s orbit kept it close to the core, exposing it to intense gravitational forces. These interactions likely stripped away some of its mass—stars on the outskirts got peeled off into the galactic halo—linking its history directly to the Milky Way’s violent assembly. It’s like a fossil record of the galaxy’s youth, preserved despite the chaos around it.
Core Dynamics
Now, zooming into M9’s core—it’s where the action (or what passes for action in a 12-billion-year-old cluster) happens. The core is dense, with stars packed so tightly that their mutual gravity drives some wild dynamics. M9’s a Class VIII globular, so its core isn’t as insanely concentrated as a Class I cluster (like M15), but it’s still compact enough for stellar interactions to shape its evolution. The inner region’s probably only a few light-years across, stuffed with thousands of stars buzzing around at high speeds—tens to hundreds of kilometers per second.
This density leads to stellar collisions and close encounters, though actual smash-ups are rare because stars are small compared to the space between them. More common are gravitational “slingshots” that fling lower-mass stars outward, leaving heavier ones—like white dwarfs or neutron stars—to sink toward the center via a process called mass segregation. Over time, this concentrates the core even more. M9’s core might even harbor a few exotic remnants—maybe a low-mass black hole or binary systems of compact objects—though nothing’s confirmed yet.
The variable stars, like RR Lyrae types, are a big deal here. They pulse with regular brightness changes, driven by internal instabilities, and their presence in the core helps map its structure. These stars also hint at dynamical heating: as stars interact gravitationally, energy gets redistributed, puffing up the core slightly against total collapse. Meanwhile, the tidal pull from the galactic center keeps tugging at the cluster, counteracting some of that inward squeeze and giving M9’s core a delicate balance between contraction and disruption.
So, M9’s history ties it to the Milky Way’s formative brawls, while its core is a slow-motion dance of gravity and survival.
Grok AI
Constellation Ophiuchus
Globular star cluster Messier 9 (M9) on the star map in Constellation Ophiuchus
A small addition to what AI said
The globular star cluster M9 is observed through the most densely populated regions of the Milky Way, rich in both stars and hydrogen nebulae, as well as interstellar dust, which partially hides this cluster from us. The absorption of light by the cluster and the filaments of dust nebulae against its background were noticed by Lord Rosse in the 19th century. The not quite round observed shape of the cluster is also due to dust screening.
In addition, the cluster is moving away from the Solar System at a very high speed - more than 200 kilometers per second. From this we can conclude that the globular star cluster M9 is not constantly near the galactic center, but only for a short time - its orbit is most likely highly elongated, and for most of its galactic year the cluster is on the periphery of the Galaxy or at an average distance from the core, possibly (and most likely) in the galactic halo, and not in the plane of the spiral arms. But now it is passing through the galactic plane and actively losing stars (but who knows - maybe it is acquiring new ones to replace the lost ones, capturing them on its way... although the mechanism of such capture has not yet been studied by science and is only assumed). But the approach to the core of the Galaxy, of course, greatly weakens the gravitational bonds between the stars of the cluster, which leads to large losses in the number of stars every couple of hundred million years, when the cluster again returns to the central part of the Galaxy.
Astronomers observe the globular star cluster Messier 9. Vision by Grok AI
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The famous Great Nebula in Orion in the center and the Running Man Nebula at the top. RAW imaging stacked in Deep Sky Stacker and then processed in Adobe and LR. 250 images comprised to make this image.
The Lagoon Nebula, also known as Messier 8, M8 or NGC 6523 (Emission nebula)
The Lagoon Nebula, also known as Messier 8, M8 or NGC 6523 (Emission nebula), is drawn by the Grock AI
Messier 8, commonly known as the Lagoon Nebula, is a stunning emission nebula located in the constellation Sagittarius. Here's a concise overview:
Overview
Designation: Messier 8 (M8), also cataloged as NGC 6523 (the nebula itself) and NGC 6530 (the associated open star cluster).
Type: Emission nebula with an embedded open star cluster.
Location: Approximately 4,000–6,000 light-years from Earth in the Sagittarius arm of the Milky Way.
Size: Spans about 110 by 50 light-years, with an apparent size of roughly 90 by 40 arcminutes in the sky (about three times the size of the full Moon).
Magnitude: Approximately 6.0, making it visible to the naked eye under dark skies, though binoculars or a telescope enhance the view.
Characteristics
Appearance: The Lagoon Nebula is named for its wide, lagoon-like dust lane that divides it, visible in photographs and through telescopes. It glows with a reddish hue due to ionized hydrogen (H II regions), energized by the intense radiation from young, hot stars within it.
Star Formation: M8 is a stellar nursery, actively forming new stars. The open cluster NGC 6530, embedded within the nebula, contains numerous young, hot stars, including O-type stars, which illuminate and ionize the surrounding gas.
Notable Features:The "Hourglass Nebula," a smaller, bright region within M8, is a site of intense star formation.Several Bok globules—dark, dense clouds of gas and dust—are visible, some of which may collapse to form new stars.
Observation
Best Time to Observe: Summer months (June to August) in the Northern Hemisphere, when Sagittarius is prominent in the night sky.
Location in Sky: Near the bright star Lambda Sagittarii and the Teapot asterism in Sagittarius.
Equipment: Visible with the naked eye in dark skies, but binoculars or a small telescope reveal more detail, including the cluster and nebulosity. Long-exposure photography highlights its vivid colors and intricate structure.
Scientific Significance
The Lagoon Nebula is a key object for studying star formation and the evolution of massive stars. Its proximity and brightness make it a prime target for both amateur astronomers and professional researchers using advanced telescopes, such as the Hubble Space Telescope and the Very Large Telescope.
Grok AI
Constellation Sagittarius
Additional information from human
It is considered to be the second brightest nebula in the Earth’s sky, and one of two hydrogen nebulae visible to the naked eye (for an observer in the middle latitudes of the Northern Hemisphere). The first to come to mind is the Orion Nebula. Is there anything comparable to it in the sky? — Yes — There is the Lagoon Nebula.
But it is not easy to see the Lagoon with the naked eye. Its integral brightness is about 6m — right at the limit of the eye’s penetrating ability. If it is possible to see it without optics somewhere, then only high in the mountains. And it is not at all surprising that the Lagoon was discovered using a telescope, even the simplest one. Different sources give different discoverers. It is believed that this nebula was observed by Giovanni Hodierna back in 1654 or even earlier — in fact, in the era of Galileo. But then, telescopic study of the skies was not yet mainstream in astronomy, not everyone was in a hurry to talk about it. And Hodierna’s discovery did not become generally known at the time. That is why the French astronomer Guillaume le Gentil, who discovered a wispy foggy cloud in the constellation Sagittarius a century later, is sometimes mentioned as the discoverer of the Lagoon Nebula.
The Lagoon is located literally in the direction of the center of the Milky Way Galaxy, at a distance of 5,200 light years from us (until recently, distance estimates varied greatly — from 4 to 6 thousand light years, but in any case, the Lagoon is still very far from the center of the Milky Way). Interestingly, the famous Orion Nebula, often mentioned in connection with the Lagoon, is located almost in the opposite direction — away from the center of the Galaxy (but a little closer to us — 1,300 light years, which means that the Lagoon is much larger and brighter than the Orion Nebula … would be under equal conditions).
The M8 nebula has a physical diameter of 50 to 100 light years (it is oblong), in its huge volume young hot — sometimes very massive — stars are intensively born. It is the same maternity hospital for new galactic luminaries as the Orion Nebula.
The lagoon is adjacent to a large number of other interesting objects, which the constellation Sagittarius is rich in. Sometimes it seems that Sagittarius has attracted most of the pearls of visual and photographic astronomy. But the center of the Galaxy is to blame for everything — it is to it that both Nebulae and star clusters gravitate, which are most often present in the central parts of hydrogen nebulae — they are born in them. Laguna also has its own cluster — NGC 6530.
The visualization provided as an example is based on an astrophotography by Andre Helmuth and Jan Beckman, published on the Astrobin website — there this image became the winner of regular ratings, and in terms of detail it competes with the best professional photographs, although it was made using a telescope with a mirror diameter of 12 inches — quite serious, but not too big in comparison with the multi-meter giants of the top observatories.
Open star cluster Messier 7, also known as the Ptolemy Cluster
Open star cluster Messier 7, is drawn by the Grok AI
Messier 7, also known as M7, the Ptolemy Cluster, or NGC 6475, is an open star cluster in the constellation Scorpius. Here's some key information about M7:
Basic Information:
Type: Open Star Cluster
Constellation: Scorpius
Catalog Numbers: Messier 7, NGC 6475
Right Ascension: 17h 53m 51.2s
Declination: -34° 47' 34"
Distance: Approximately 980 light-years from Earth
Physical Characteristics:
Age: Estimated to be about 200 million years old.
Number of Stars: Contains roughly 80 to 100 stars, with some estimates going up to several hundred.
Diameter: The cluster spans about 25 light-years across. Visually, it covers about 80 arcminutes, making it one of the larger and more prominent open clusters in the sky.
Visual Appearance:
Magnitude: M7 has an apparent magnitude of about 3.3, making it visible to the naked eye under good viewing conditions. It's one of the brighter objects in the Messier catalog.
Color: The stars in M7 vary in color, with many being blue and white, indicative of hotter, younger stars.
Historical Observations:
Discovery: M7 was one of the first objects known to ancient astronomers. It was cataloged by Ptolemy in his "Almagest" around 130 AD, thus sometimes called the Ptolemy Cluster.
Messier Catalog: Charles Messier added it to his catalog in 1764 as M7.
Observing M7:
Visibility: It's best observed in the summer months in the Southern Hemisphere or the late spring/early summer in the Northern Hemisphere, when Scorpius is well placed in the evening sky.
Telescopic Observation: With binoculars or a small telescope, M7 resolves into a beautiful cluster of stars, with many individual stars visible even in modest instruments.
Scientific Significance:
Study of Star Formation: Open clusters like M7 are crucial for understanding stellar evolution since all stars within such a cluster formed at roughly the same time from the same molecular cloud.
Astrophysical Research: Measurements of the brightness and color of stars in M7 help in determining their ages, distances, and evolutionary paths.
Source: Grok AI
Addition to brief information from AI
In the middle northern latitudes, the Ptolemy cluster is not observable. There, it either does not rise or does not rise to a height sufficient for confident visibility. And only starting from the latitude of the subtropics can it be observed with light optics, and even further south - in the tropical zone of the northern hemisphere - with the naked eye.
Claudius Ptolemy conducted his observations from Egyptian Alexandria. And more northern astronomers of antiquity did not notice this cluster. Because its integral brightness - 3m - decreased significantly as it approached the horizon due to atmospheric absorption.
A small remark regarding the number of stars in this cluster
There are about a hundred identified participants. Why do astronomers talk about several hundred stars possibly included in the cluster?
Because for the stable existence of a cluster of 25 light years (moreover, the radius of gravitational dominance for this cluster is estimated at 40 light years), its mass must be at least 800 solar masses. On average, each visible star must have a mass of about 10 solar masses, and this is a fairly large mass - the mass of a supergiant star. But such are not observed in the cluster - there are mainly stars of medium masses and luminosities. Consequently, a significant part of the cluster is represented by dwarf stars, like the Sun or less massive.
By the way, if we place our Sun at a distance of 1000 light years (approximately this distance is removed from us by the Ptolemy cluster), then without taking into account the absorption of light by the interstellar medium, it would have only 13 stellar magnitude, and such stars - background and not only - in the visible limits of this cluster are a great number. But the amount of light absorption in the direction of the center of the Galaxy (and this is the direction we are looking when observing the Ptolemy cluster) is significant. And the main part of the stellar population of the cluster is most likely weaker than the 15th stellar magnitude. All objects of such brightness have not yet been studied by astronomers.
But astronomers have studied the distribution of stars by mass in open clusters, from which we can draw a simple conclusion: If we observe a certain number of bright and clearly visible stars in a particular open cluster, then most likely the total number of all stars in the cluster is at least 10 times greater.
New image from the Wide Field Imager on the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile, shows the bright star cluster Messier 7, aka NGC 6475
A messier marathon is a star gazing where we try to spot all one hundred ten objects in one night. Although it is a difficult task, it is doable with some stargazing organizations offering certificates to those completing the marathon.
