Finding the right spot for a permanent observatory is more involved than it might seem. You can't just plonk it anywhere in the garden and hope for the best — there are a surprisingly large number of factors to weigh up, and getting it wrong at this stage means living with the consequences for years.
The stars align
I drew up a list of requirements before even walking the garden with a measuring tape. The site needed to have:
- An unobstructed view to the south, ideally down to 20° altitude or lower
- Minimal light spill from the house windows and neighbours
- Firm, level ground suitable for a concrete pad
- Reasonable access for construction materials
- Power available within a sensible cable run
Surveying the Garden
I spent three clear evenings doing a proper survey, using a compass and a simple angle-measuring app to map out obstructions at different azimuths. The results were more nuanced than expected.
The far corner of the garden looked promising from the house, but a mature sycamore on the south-west boundary clips the view at around 28° in that direction — not ideal for targets transiting in the south-west. The middle of the lawn, frustratingly, turned out to be the best compromise.
Light Pollution
Lancaster isn't the darkest of skies — Bortle 5 on a good night — but the local horizon is the bigger issue. Neighbour security lights, a street lamp to the north-east, and the ambient glow from the town centre all needed mapping.
I used an app called Dark Sky Meter over several nights to build up a picture of the sky quality at different times and in different directions. The south is significantly darker than the north, which confirms the importance of that clear southerly view.
The Decision
After all the surveying, the choice came down to a 4m × 3m footprint roughly in the centre of the garden, offset slightly to the east. It gives a clear southern horizon to around 15°, avoids the worst of the neighbour's security light, and sits on the only genuinely level part of the lawn.
Not perfect — but in backyard astronomy, nothing ever is. The next step is getting a concrete pad down before the autumn weather closes in.