What Sun, Moon, and Ground tell you about your Antenna ...
Joachim Köppen DF3GJ ... Kiel Mar 2023

Some brief explanations

Measurements of the radio noise of the Sun, Moon, the ground, and the empty sky are used to determine three estimates for the system temperature (or noise figure) of a radio telescope. It makes use that the Sun, Moon, and the ground emit thermal radiation, which corresponds to their physical temperatures. The ground can well be assumed to have the ambient temperature, which is close to 290 K. At frequencies above about 15 GHz, the Sun's radio emission is independent of its acitivity, and the temperature can be taken as that for the quiet Sun (Benz, 2009). The Moon's average surface temperature is 213 K, but varies during one month within a range which increases with frequency, from ±10 K at 10 GHz to ±100 K at 300 GHz (Foster 1969; see also here). Thus, the three bodies can be considered to have known temperatures, and to serve as calibrating sources.

Frequency [GHz]
HPBW [°]



Zenith attenuation [dB]

at Elevation [°]
Line-of-sight attenuation

Moon noise temp.

Mouse position

Noise figures and System temperatures

Notes on the examples:
  • SRT is the Small Radio Telescope, devised by the MIT Haystack Observatory, for spectroscopy at the 1420 MHz line of neutral hydrogen. Its diameter is 2.3m, and the system temperature about 250 K. With a HPBW of 6.5° the Moon is barely detectable.
  • The ESA-Dresden radio telescope uses conventional satellite TV equipment: a 1.2 m offset dish and a normal LNB, with a system temperature of about 170 K and HPBW of 1.5°. It is used for solar and lunar observations.
  • The 24 GHz antenna at DL0SHF has a diameter of 3.7 m. After improvements of the feed, its system temperature has been brought to about 250 K (2021).
  • The 47 GHz antennas of CT1BYM (measured data from PA0EHG's 47 GHz Performance Table)