A while ago, I made a post describing the process I go through in planning an image. In said post I used an image of Rho Ophiuchi I was planning on taking as an example. I planned to take the picture at the Golden State Star Party, and promised to provide an update once it was done. Well GSSP has come and gone, and I have no pictures. So what went wrong?
I’ll bet it won’t take most of you very long to guess what. It was cloudy. If you remember, my plan was to take half the picture in Yosemite, and the other half at GSSP. Yeah.. that may have been optimistic.
Strangely, I’ve learned a lot about clouds through my astrophotographic journey, so here’s a short meteorology lesson. A lot of the clouds that I come across at my summer imaging sites are “Convection Clouds.” These clouds are formed by a process called Convection. On a hot summer day, the ground heats up, warming the air. The warm air rises high into the altitude where it begins to cool off. This cold air falls down, and the cycle repeats. Fortunately for me, convective clouds are usually my friend. See, in order for convective clouds to survive, they need convection. Convection is powered by heat, usually from the sun. Once the sun sets the process looses it’s energy source and stops. This means that in theory once night falls, convective clouds should dissipate.
So why does this matter for the Rho Oph picture? Shouldn’t I have had clear skies? Unfortunately things like water, trees, grass, rocks, etc, are good at holding heat. This means it takes a while for the process to die off… which means it gets clear, but much later in the night. Rho Oph is a southern target, and thus starts low in the sky, and gets lower as the night goes on. By the time the convective clouds had dissipated, I had lost my target.
The good new is the clouds dissipated eventually, meaning I could still take pictures. This is why we bring backup targets! I ended up shooting M17 at Yosemite, and a variety of targets at GSSP. I’ll be posting them soon!