Radio Sources in the Sky
Joachim Köppen Kiel July 2016

This tool shows the continuum radio fluxes of various celestial sources. Given the effective diameter of an antenna and the system temperature, the antenna temperature and the signal to noise ratio are computed for the present position of the mouse. If the angular size of the source is comparable or larger than the antenna HPBW, the antenna's main lobe picks up only a fraction of the true flux. This fraction is given by 1-fill with the beam filling factor fill = ang.diam²/(ang.diam² + 1.53 HPBW²) [1.53 is a shape correction factor for the main lobe from a uniformly illuminated disc antenna].

Emission from Galactic Centre and Anticentre is estimated only for a patch of about 1° square; an antenna with a wider beam will pick up more emission from adjacent areas.

Note that thermal radiation and absorption by the Earth atmosphere are not taken into account.

Vertical lines mark frequencies of 144, 432, 1420, 10380, and 24000 MHz. Horizontal lines indicate the levels of the Cosmic Microwave Background (2.7 K) and ground radiation (290 K). Thermal emission from the earth atmosphere is about 5 K at the zenith, but increases towards the horizon (like 1/sin(elevation)) and also for frequencies above about 20 GHz.

The angular diameter of each source is given in parentheses.


Solar system:
quiet Sun (0.5°)
active Sun
Moon (average distance, 0.5°)
Venus (min. distance, 0.16°)
Jupiter (min. distance, 0.01°)
Jupiter bursts (min. distance, 0.01°)
Our Galaxy:
Entire Milky Way (whole sky!)
Galactic Centre (approx. 1° square)
Galactic Anticentre (approx. 1° square)
Cas A (supernova remnant, 0.08°)
Crab nebula (Tau A, M1, NGC1952, 0.11°)
Crab pulsar
Orion nebula (HII region, M42, NGC1976, 1.1°)
NGC7027 (planetary nebula, 0.003°)
Extragalactic objects:
Cyg A (radio galaxy, 3C405, 0.03°)
Vir A (elliptical galaxy, M87, NGC4486, 0.11°)
Cen A (elliptical galaxy, NGC5128, 0.36°)
Large Magellanic Cloud (irreg. galaxy, 8°)
Small Magellanic Cloud (irreg. galaxy, 5°)
Andromeda spiral galaxy (M31, NGC224, 1° x 3°)
M33 (spiral galaxy, NGC598, 0.8°)
M51 (spiral galaxy, NGC5194/5195, 0.2°)
M82 (spiral galaxy, NGC3034, 0.08°)
3C273 (quasar, <0.0001°)


antenna effective diametre [m]
system temperature [K]
source angular diametre [deg]

Mouse position:

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