Jansky to Microwatt per m2

Jansky to µW/m² conversion

Radio astronomers measure spectral flux density in janskys (Jy). One jansky is defined as 1 Jy = 10⁻²⁶ W/m²/Hz. Want the same flux back in W/m²/Hz? Divide the jansky value by 10²⁶. From there, multiplying by 10⁶ gets you to µW/m²/Hz.

Flux density is a spectral quantity, so the total power a receiver actually collects per unit area hinges on the bandwidth: P (W/m²) = S (W/m²/Hz) × Δν (Hz). Take the quiet Sun at 100 MHz, which sits around 5×10⁶ Jy. Run that through a 1 MHz channel and you land near 5×10⁻⁹ W/m², or 5 µW/m² for every square meter of antenna collecting area.

Applications

You need to move between janskys and SI flux units whenever radio astronomy measurements have to line up with telecommunications budgets, the ITU‑R noise floor recommendations (Rec. P.372), CCIR thermal noise references, or satellite link analyses that quote receiver sensitivity in dBW/m²/Hz. Spectrum coordination relies on it too, when someone has to gauge how much interference active services dump into protected radio astronomy bands.

FAQ

Why use jansky at all? Most celestial sources are faint, ranging from microjansky up to a few thousand jansky. The unit spares you the awkward exponents you would otherwise carry around in W/m²/Hz.

Is the conversion frequency-dependent? No. At any frequency, 1 Jy stays 10⁻²⁶ W/m²/Hz. What shifts with frequency is the spectrum of the source itself.

How do I get total power instead of spectral density? Take the flux density and multiply it by your receiver's effective bandwidth in hertz. That gives you power per unit area in W/m².