Balcony Stargazing

Astrophotography from a balcony in a heavily polluted city

Stargazing from a balcony has numerous advantages, the most obvious being the comfort to capture the sky's wonder from home, to keep the rig assembled and in-place, OTA thermal equilibration, and to do something else while acquiring frames.

However, these advantages come at a price! Quick description of main issues and solutions:

Polar & go-to alignments
The narrow sky window is challenging for polar alignment, as Polaris is not visible. Even rough alignment is challenging as reinforced concrete from the building tempers with accurate compass orientation. Ultimately I took drawings of the building and located the rough North position using walls. Similar result can be obtained from Google Earth and a bit of trigonometry. Azimuth is quite accurately set with a digital protractor. StarSense polar alignment is also of great help to refine polar alignment.
Go-to alignment is incredibly eased with StarSense module when used in manual (or manual auto mode). If the procedure is performed suitably (adding reference stars and synchronizing when necessary), objects are well centered on camera's sensor. Another advantage is that the module's camera is sensitive enough to detect stars in Bangkok's heavily polluted sky, and the number of stars detected can be used to get a rough seeing estimate: on worse seeing nights, 10-15 stars detected (below this, too few stars, SS will not platesolve), whereas 45-75 stars can be detected in best seeing nights. Of course these figures are purely indicative as the number of stars that can be detected within SS sensor's FOV varies from one night to another.

Sky obstruction & light pollution
From my shooting location, the sky field of view is at best 60deg wide, centered SE. The elevation is a maximum of 50deg over the horizon. Considering the light pollution that usually makes capture impracticable below 25deg, this leaves a short time to shoot frames, especially when autoguiding is used (piggy-backed on the optical tube, the guidescope gets obstructed before the imaging scope): 2 hours at best. The use of a OAG may help a bit in this respect. Short to mid exposures are thus preferred (30 to 180sec) to get enough frames to stack, and thus a better SNR. Owing to this acquisition time limitation, the use of an OSC is preferred, even if narrow-band imaging could give better results in city skies. A good filter is the Optolong L-Pro, exposure time can significantly be increased without saturation by the light pollution halos. Multi-sessions capture is also an option, particularly if object is faint and requires longer exposures (300sec and more).

The light coming from the living room surprisingly has a low influence on shooting, and avoiding asking my wife to shut light in the living room has a good influence on our relationship - less surprisingly ;)

Vibrations
Another aspect to consider are vibrations when walking around the scope and sliding the bay windows. Walking slowly, adding thick rubber pads below the tripod's leg and and leaving the iPad in the living room successfully mitigated this issue.

All pictures in the gallery were taken in these conditions when the location indicated is Bangkok.