This is the Bubble Nebula. It’s estimated to be 10 light-years across and 7,100 light-years from Earth. It’s an emission nebula located in the constellation Cassiopeia, contained within a large molecular cloud. It’s shaped by stellar winds from a massive central star. The winds push against the slower-moving gas of the nebula, creating the bubble-like structure.
The interaction between the stellar wind and the nebula’s gas causes the shell to glow brightly in visible light. The winds from the central star are so powerful they move at speeds up to 4 million miles per hour! The age of the nebula is estimated to be a few hundred thousand years, which is actually pretty young in astronomical terms.
Astrophotography: A Time-Consuming Endeavor
The amount of time spent collecting and processing the data to create this one picture is rather astounding. It’s compiled from 192 separate five-minute exposures. That’s a total of 16 hours worth of pictures.
That doesn’t include all the additional “calibration frames” that are also accumulated. These frames compensate for imperfections in the optical chain that is used to accumulate the data. Things like dust motes on the lens and the inexact nature of outputs from individual pixels of camera sensors. Note that the deep-space light signal can be as little as a few photons a minute!
There are also many times when the pictures don’t meet expectations for various reasons and must be redone. For example, if there’s a lot of air turbulence, the seeing conditions can be affected negatively. Even if the sky looks perfectly clear, the turbulence at higher altitudes can interfere with getting nice small star sizes. This can lead to a handful of pictures being discarded. And the telescope has to be refocused several times throughout the night. These extra tasks easily add one hour per night, so 8 additional hours were invested in this case where data was collected across that many nights..
There’s also setup and tear-down time. These 16 hours of images were taken over 8 separate nights. Each evening, the equipment had to be set up in our driveway, and then taken down at the end. I would estimate that between the two, it took approximately 30 to 45 minutes each time, adding another 4 hours conservatively. I would estimate between the two that it took approximately 30 to 45 minutes of time. So conservatively, that added another 4 hours.
Finally, there’s the processing time. All the images are stacked and calibrated, and the resulting picture goes through many additional processing steps. It’s part science and part art. Then a final image is produced. Total processing time in this case was roughly 10 hours. Sometimes it takes a few hours longer, and sometimes a little less; depends on the project. And depends on how much time the photographer wants to spend trying to get it just right.
So, for this particular project, I’ve invested somewhere around 38 hours of time. The only thing to add is I did other things while the pictures were being taken once the process started. I monitored the result of each individual picture that was taken along the way, but between those five-minute timeframes, I was watching TV or doing something else. But I also had to stop and address problems and refocus the setup. I had to remain involved in overseeing the operation as it’s ongoing.
To summarize, astrophotography is a very rewarding hobby that can deliver beautiful results. But it has a pretty high learning curve. And along the way, there are nights where you may spend hours and not get anything accomplished due to equipment issues or bad seeing. Or maybe clouds roll in unexpectedly shortly after you get things set up. And the amount of time spent even when things go right is a large number of hours.
So, to be a happy amateur astrophotographer, you must enjoy staying up late and, importantly, have the patience of Job!
