MORE BACKYARD ASTRONOMY BLOG 12/1/2021
I am so pleased that I have captured NGC2338, The Rosette Nebula, right in the center of Huntington Beach with my backyard telescope. This is a bright emission nebula in the constellation of Monoceros. (Ever meet a person with that birth sign?)

So, what is this beautiful thing? It is an immense cloud of hydrogen gas and dust. The solar winds from that small cluster of stars are responsible for creating the porthole which we see and energizing the hydrogen gas, causing it to glow. I like to think that someday I might pass through that very porthole, and into heaven.The Rosette and the cluster of stars are floating about 5,000 light years above our city and measures roughly 130 light years in diameter. A light year (Ly) is the unit of measure we use for astronomical distances. Light travels at 186,000 miles per second or six trillion miles a year, give or take a mile or so. Quick math says that the Rosette is a mere 30,000 trillion miles away. Compared to other of my posts, it is just a stone’s throw away.

So, what causes the gas and dust to look like this? The Rosette is basically a neon sign. The nearby stars energize the gas, exciting it. The gas cloud lights up like a neon sign. Although the sign at the pub is filled with argon and Neon gases, not hydrogen. When electrical energy in the tavern sign flows from one end of the glass tube through the gas and on to the other end of the glass tube, the Argon lights up. They used the Neon for color.

Here, we find that this vast cloud comprises molecules of Hydrogen Alpha (Ha) gas, which glows red. We estimate the amount of hydrogen gas in this nebula to be 10,000 times more hydrogen than our sun.The Rosette is a prodigious star forming region, making new stars nearly as fast as China makes coal-fired generation plants. Rosette’s energy comes from the hot stars. That process is emission. 

The radiation from the young stars excites the atoms in the nebula, causing them to emit radiation themselves, producing the emission nebula we see. Every time they energize the nucleus of the hydrogen atom with a photon or a cosmic ray, the electron in that atom jumps to a higher level or distance from the nucleus. The nucleus can’t hold the electron at that level for long. When the electron falls from the third level to the second highest level, it releases the energy, that is the radiation which we see, a photon.

Sometimes the nucleus becomes unstable after a hit and transfers all its energy to the electron. The atom ejects the electron instantly, producing more of the light we see from this cloud.That poor little ejected Ha photon, and a pack of others from different gases, must travel all those 30,000 trillion miles to be counted on the chip of my camera and added to an array of camera pixels.

A long camera exposure is like an ice cube tray left out in the rain collecting differing amounts of rain drops in each cube. We process the differing amounts of photons registered as electrons on the CCD camera chip into the picture you see on this post.

The levels of photons converted into electrons in each pixel cube correspond to the brightness or darkness of each pixel in the photo. Telescopes are sometimes called photon buckets. The more photons an Astro photographer collects, the better the detail in the picture. My last galaxy photo was 10-12 hours of exposure from a galaxy 180 million trillion miles away. I collected my share, called it a night, and left the rest of the photons for the other astronomers.

I used Hydrogen Alpha, Oxygen III, and Sulphur II filters along with red, green, and blue filters to capture this image and simultaneously avoid the light pollution created by the unwanted photons. The II and III refer to the level or ionization of the electrons in the gas. By using different filters, I collect only the photons of the different gases. I save them separately in my computer. In post processing, I assign a color to each group.Altogether, I captured 90 images of 100 second exposures.

Half the exposures were gas, narrow-band, filters. The other 45 were color filters. I stacked the images with a stacking program called Astro Pixel Processor, like they were a deck of cards. Then I processed the stacked deck in another program called Astrophotography Tools. Altogether, the photo exposures took 2.5 hours. The post processing was about another ten hours, interspersed with feeding the dogs, my macaw and my fishys. I even spoke a few words to my lovely wife, Elizabeth, an astronomy widow. Hopefully, you will enjoy this photo.Clear skies—Ken Adler