[mpetroff]

BICEP3 actually uses a >20 year old CCD camera with analog video output (BICEP Array uses newer cameras, with more modern sensors). Daytime star pointings are possible by using a low-pass filter to block visible light and take advantage of the sensitivity of CCD / CMOS sensors to the near infrared, where the daytime sky is more transparent, combined with baffling.

[joshvm]

I would add it also uses an ancient analog TV for manual sighting in combination with the GUI for semi-auto centroiding. I always thought that was funny to see, but it seems to work well enough. Also, inserting that baffle is somewhat terrifying because it slots into a hole next to the main vacuum window and if you dropped it on the membrane, bad things would happen. Always fun to bump into Polies here :)

[mpetroff]

> Always fun to bump into Polies here :)

Definitely! I wasn't expecting to see a mention of BICEP while reading HN from Pole, particularly not on something as arcane as its star camera.

[gunian]

how hard would this be to set up for a total hardware noob? and how good or useful would the data be?

i know gaia data for instance is available for free but if one used just a homemade telescope could any useful celestial data be acquired?

[joshvm]

It depends what you mean by useful. On its own, all you're doing is taking pictures of the sky and figuring out where the camera was pointing (and its field of view). Where it's useful is calibrating the pointing direction of other systems. It's fun to try the software at home (there is a public web interface), you just need a camera that can take long enough exposures to see stars without too much noise.

One of the more "useful" backyard astronomy tasks that is achievable for a dedicated amateur is variable star observation (eg AAVSO), because many stars don't need huge telescopes to observe and it's very expensive for a big observatory to stare at a single patch of sky for weeks. Nowadays we have instruments like LSST which is basically designed for this sort of surveying, but public data are still useful. And you do need to know exactly where you're pointing, so either you do this manually by pointing at a bunch of target stars, or you can use a guide scope that solves the field for you.

[mpetroff]

With images taken at night, you can run the images through Astrometry.net, which is a blind astrometric solver and will provide you with RA / Dec for most images, as long as you have at least a dozen or two stars visible. The code compares asterisms formed by multiple stars to index files built from Gaia or other similar data. This is the technique that's used more frequently for microwave telescopes located where there's a normal diurnal cycle, e.g., CLASS. The smaller the field of the view, the higher the precision, but it also works fine with a camera with a zoom lens.

BICEP, however, is located at the South Pole on a moving ice sheet, requiring frequent updates to its pointing model, and has six months of continuous daylight, so daytime star pointing observations are required. This requires a different technique. Instead of looking at asterisms with multiple stars, the optical pointing telescope is pointed at a single star using an initial pointing model, the telescope pointing is adjusted until the star is centered, and the offset is recorded. This measurement process is repeated for the few dozen brightest stars, which acquires the data needed for refining the pointing model.