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.
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