Question: How to measure the flux density of radio sources in the sky, using single dish, VLA, or VLBA？ (how to do the flux scale in those measurements.) — Hongmin
Answer: Radio source fluxes are measured by radio telescopes, whether they be single antennas or interferometers like the VLA and VLBA, by measuring the electromagnetic energy from an object and converting it to a flux unit. The standard flux unit in radio astronomy is the “Jansky” (Jy), which is equal to 10^(-26) W/m^2/Hz. In order to convert measured fluxes into Jy one must make a measurement of a “flux standard”, or an astronomical object whose flux in Jy is well known. This then allows one to use the flux measurements from the standard source and the object under investigation to derive the flux in Jy for the object under study.