Signal to Noise ratio: S/N usually proportional to at
least sqrt(telescope time*area) - or an even higher power of D,
depending on the exact observation. This is a major driver for larger
Where does astronomical noise come from?
With all that, the fact that we know anything at all is a testament to
the hard work of many people over millenia!
- Intrinsic statistical noise. Photon arrival is a random process
modelled by Poisson statistics.
- External Noise Sources (stuff out in the universe somewhere)
- Dust, both solar system and interstellar. Broadband extinction and reddening.
- Gas. Line absorption, e.g. interstellar hydrogen absorbs
shortward of 912 A.
- Foreground/Background sources. (Stars!)
- Solar and Galactic magnetic fields
- Atmospheric absorption
- Atmospheric emission
- Atmospheric dispersion and refraction
- Atmospheric scattering and polarization
- Atmospheric turbulence = seeing.
- Internal Noise Sources (Anything after the telescope entrance
- Optical limitations (PSF variation across field of view,
- Thermal variations ( = dome seeing)
- Pointing errors (vibration, tracking errors, wind shake)
- Variable throughput (mirror degradation)
- Electronic noise (readout noise, dark current, crosstalk)
- Detector imperfections (Biases, flat fielding, Charge
And now, let's look at some of what we've learned.
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