Picture of the Ring Nebula (M57) taken with a Canon T2i DSLR and an RSpec Star Analyser 100 diffraction grating on a 10-inch Ritchey-Chretien telescope at f/9. The diffraction grating generated the spectra seen in the image. Well to the right of each star is the star’s spectrum. The Ring Nebula is the ring-shaped object just to the left of center in the image. Its spectrum also appears to its right. Interestingly, its spectrum appears to consist of only two wavelengths, a red one and a cyan one. The red one is H-alpha (656 nm). The cyan-colored one is O-III (501 nm). We don’t see a broad spectrum because the Ring Nebula, like most nebulae in the Milky Way galaxy, is an emission nebula. The picture is a stack of 60 one-minute unguided exposures.
[OPN 2023 Photo Contest Second Place]
—Robert Vanderbei, Princeton University, Belle Mead, NJ, USA