The brightest emission nebula in the sky, Messier 42, was a great target to test extended object spectroscopy with my new ALPY 600. I set the telescope to track the core, just off the Trapezium, and the science camera to take 12 exposures of 100 seconds each.
Emission nebulae are huge clouds of primordial elements that are energized by nearby stars, typically stars formed by and within the nebula. The most common element in the universe, hydrogen, is the main component. Other light elements, such as helium, oxygen, nitrogen, and sulfur, may become ionized by the strong ultraviolet energy of the nearby stars and begin emitting light in predictable frequencies.
Due to amp glow in my ASI183MC at this exposure length, I calibrated the raw files with a hand full of darks. I then simply averaged all of the images together. Here is a stretched view of the raw spectrum,
You might note that the spectrum contains only a few very distinct lines in the visible region. To the far right, the white blob is likely leakage from the infrared illumination of the security camera in the dome.
I processed the data in BASS, calibrating simply by the few well-known emission lines. I did not use any kind of flat correction nor response correction, so the color camera I used will not give accurate relative intensities. However, it does show well the primary constituent elements of M42,
The green color of the nebula, which may be quite noticeable in a decent aperture visual telescope, primarily comes from doubly ionized oxygen. Some of the Balmer series of hydrogen emission lines are present in the spectrum, these being primarily α (alpha) in the deep red and β (beta) in the cyan. Although nebula are typically very strong in Hα, the cones in the human eye are poor at responding to its long wavelength. This makes many nebula very hard to see in a visual telescope in all but the darkest of skies. Most terrestrial cameras, which attempt to accurately model human color perception, are also poor at recording Hα. Finally, there are noticeable amounts of ionized Helium and Nitrogen.