After the hiatus while I compiled my Nightscape Odyssey notes and photos, I now return to my longer term project: “Coffee Table Nightscapes”, a collection of photos acquired over the years, often on business trips or summertime travels. I don’t pretend to be a competitor to APOD, where you will find spectacular astronomical imagery each and every day; rather, this is a low key way to share a few pictures that I enjoyed taking, with people that may appreciate them.
I resume the series with this image that someone else took. The Veil Nebula is a striking object in the sky and a popular target for astrophotographers. The view in the eyepiece of the telescope shows a faint fuzzy gray wisp of cloud, but cameras record something else. I was curious about what its actual visual appearance would be, if we could actually see it in full color.
The Veil Nebula is a supernova remnant– a star exploded, casting off a shell of gas that expands outward. The gas is hot and ionized and emits light at characteristic wavelengths. Hydrogen glows red at a characteristic 656nm, and also a blue-green at 486nm. Ionized oxygen emits green-blue light at 501nm. Most pictures of the Veil show a bright red cloud because the red H-alpha light is easy to record on film and CCD sensors. It is a challenge to display the blue-green colors because it falls in the gap between the blue and green-sensitive layers of film, and other imaging systems.
Figuring out how to make an image that was “colorimetrically correct” took me down a particular path of color science that resulted in a paper presented at the annual Color Imaging Conference. This image was my primary example among others, that were featured in the poster presentation (scroll to the end to see them). If you are still not convinced, try getting through the full technical details published in the Journal of Imaging Science.
The pictures I will be subsequently sharing are not this technically demanding. Whether simple or complex, simply enjoy them for their visual and inspirational value.
If you are interested in my occasional contributions to Thor’s Life-Notes, I invite you to follow along.