Terms in astronomical observation

Polarized (bias): measure the background noise before CCD is enabled (0 s.

Dark stream (dark): The Hot electrons produced by CCD itself. The number is very small, generally 1 ~ 2/s, which can be ignored. The exposure time is the same as the actual observation time.

Flat field: first, a uniform color light is used to illuminate the CCD to obtain the ratio of electrons produced by each part of the CCD. Then, the actual data measured in the future is divided by the ratio.

Wavelength calibration: the CCD is illuminated by several beam with known wavelengths as the scale to correct the waveform.

Zhongtian: the moment in which the celestial body passes through the Meridian Circle in its Sunday Motion

Seeing: Used in the unstable atmosphere of the Earth, there is always a weak hot air above the telescope, so that the star image is always blinking and boiling at a high magnification. The intensity of such flashes is called atmospheric vision.