Location, Location, Location

are the three most important factors when it comes to success, according to many wise counselors.

Location certainly matters when it comes to success in observing the sky. In my back yard observing area, I can only have partial success. I am limited by the trees of the back yard and the roof line of my house. I am limited by the amount of urban light that limits my best unaided observations to magnitude 4. I am limited by the intrusion of light from my own windows and from backyard lights of my neighbors. I am limited by the heat that rises from the shingles of my home, roiling the air with turbulence.

But my backyard location leads to increased probability of success too. My least obstructed view of the sky is to the south. That is good, because as the seasons change this area gives the most chance to see new large swaths of the sky. My urban light problem is much less bothersome as that of friends that live just 15 minutes away toward the center of San Antonio. From their beautiful perch looking over downtown, I can seldom see anything dimmer than second magnitude stars. They have great sunsets, but pretty poor conditions for seeing any of the galaxies on the Messier list. Another great advantage of my location is that by driving an hour west or northwest, I can move below some of the darkest skies in the United States.

My location in near San Antonio also means that I have access to a large number of objects which are not visible from further north. It's true that I can not see the Big Dipper during winter evenings, like I grew up being able to do in Ohio. However, the full tail of the scorpion is very obvious in the summer, along with its treasure trove of Messier objects. From further north this part of the sky is much closer to the southern horizon than it is here.

Observing from a location in the northern hemisphere certainly gives me a different view of the sky than my friends in Australia have. Obviously, I can not see the constellations furthest south and have never observed those two close galaxies associated with the Magellanic clouds.

Another aspect of the northern hemisphere observing location recently occurred to me. A decade ago I needed to find a way to teach my son how to identify the waxing and waning moon. I remembered a scene from Karate Kid - a movie he had seen - in which the master taught his apprentice how to strengthen his arm muscles by waxing his old car. "Wax on - Wax off" with the right hand and then the left was his mantra. I taught my son that the "Wax on" motion with the right hand could remind him that the waxing moon was lit up by the sun on the moon's right side looking south or southwest, and that the waning moon would be lit on the moon's left side.

This fall, as I was looking through different telescopes at the moon, I was trying to determine whether I was looking at the moon's east or west on the right side of the eyepiece and whether the moon's north or south pole was at the top of the eyepiece view. It was clear that with binoculars, the Moon's north was at the top of the view and the moon's east was to the right, just like in a map of the United States. That view differs with different telescopes - a topic complex enough that it is worth writing a blog on the subject sometime in the future.

However, from my backyard it was clear that the first quarter moon was to my south at sunset. As I looked at this waxing moon, its right side was lit by the sun. The moon's north pole was up and its eastern side was to my right.

I asked myself the thought experiment question, "What would I be seeing from Perth, Australia at sunset today?" The answer surprised me after I puzzled through it. I would be looking north at the first quarter moon. This waxing moon would be lit by the sun on my left. The moon's south pole would be up and its eastern edge would be to my left. Everything about the view would be completely backwards from my northern hemisphere viewing area.

This understanding may be completely obvious to southern hemisphere observers. They are used to having to translate texts to their point of view. But it was an understanding that had escaped me for the first 55 years of my life. It was a good feeling to finally come to a new understanding of a very basic idea.