The problem is that the noise can swamp the signal. Another example of this would be doing astrophotography during the day. The sun doesn't block anything, it just makes the sky glow with "noise". Theoretically it has exactly as much signal from space as it does at night, but because the sun adds so much noise it's completely lost.
> "because the sun adds so much noise it's completely lost."
Do you mean that it would be conceptually possible to image planets or even deep-sky objects during the day with incredibly efficient denoising software? (I am a noob in astronomy)
I would be, yes. As early as the 1950’s, several avionics companies made daylight-capable star trackers (for jam-resistant long-distance airplane navigation) using chopper techniques. Those trackers were mostly mechanical, except for electronics to demodulate the star signal from the single pixel sensor.
