Observatory location

Where should the observatory be located? The two obvious criteria were sky quality and convenience. Tycho's stars were relatively bright, so a dark site was not needed, but stars to 6th magnitude should be easily found. Convenience has two components, ease of operation and ease of repair. Computers make operation easy almost independent of location, but repair is another matter. I already have a large scope in a dark site, operated remotely from my house, but it is a two and a half hour drive (140 miles) just to push a reset button. For a new instrument and an aging observer, proximity was a strong driver.

My house is between Baltimore and Washington, D.C., and it would be hard to find a poorer site from which to do astronomy. My skies are about 8 or 9 on the Bortle scale.

On a clear, moonless, night I can see, by eye, only to third magnitude. Most constellations are hard to make out. On normal nights, only a few stars are visible. However, with some optical aid, Tycho's stars are easily found. Thus, I did not need to have a distant location.

I started to look for nearby buildings to place my observatory upon, but did not find any obvious sites. My area is heavily wooded, so I needed a location significantly above ground level. Tycho's stars range down to -30 degrees declination, and some of his techniques involve observing stars below Polaris.

I asked myself whether my roof could possibly serve as the observatory location, so I climbed up a did a multi-day/night survey. My absolute minimum requirements were that I could observe the Sun at the winter solstice and that I could also easily observe Polaris. I had one roof section that had a moderate slope (2:12) between two much steeper sections.

With chalk in hand, I marked out possible places for the observatory. There was a fortunate gap in the treeline directly to the south, but many trees to the north. The roof peaks on my house also limited the altitudes observable. Only to the west could I observe to low altitudes. Here are some photos from my rooftop search. The left photo shows my northerly view over my north roof section. Polaris was within a degree of the tree on the left side. Nothing below Polaris was available. The right photo shows my southerly view where there was, luckily, a gap in the trees that permitted access over the south roof to declinations as low as -26 degrees, but only at az 170 to 190 degrees.

So the observatory could not be too close to the south roof without losing negative declinations, and not so close to the north roof that Polaris was blocked. There was also a request, from the management, that the telescope not be visible from the front of the house, so locations to the east were limited, and gravity provided an obstacle to the west (roof edge).

So you can see from my chalk markings that the possible locations were extremely limited:

I finally decided that there was an acceptable roof location that met almost all my needs. What was lost was a few of Tycho's most southerly stars, and any access to stars below Polaris. The surrounding treeline meant that I would get very few observations at low altitudes so that I would have a hard time measuring refraction effects. I accepted these limitations so that the scope would be close by and easily maintainable. I only later realized that this would also limit my access to Venus, needed to locate the first point of Aries.

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