"Doppler boosting" is a well-known relativistic effect that alters the apparent luminosity of approaching radiation sources. "Doppler de-boosting" is the name of relativistic effect observed for receding light sources (e.g. relativistic jets of active galactic nuclei and gamma-ray bursts). "Doppler boosting" changes the apparent luminosity of approaching light sources to appear brighter, while "Doppler de-boosting" causes the apparent luminosity of receding light sources to appear fainter.

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... "Doppler de-boosting" has been successfully accounted for and observed in relativistic jets of AGN, it was ignored in the establishment of Standard candles for cosmological distances. A Standard candle adjustment of an Z>0.1 is necessary for "Doppler de-boosting", otherwise we would incorrectly assume that Standard Candles appear dimmer not because of "Doppler de-boosting" but because of the excessive distance, which would affect the entire Standard Candles ladder at cosmological distances. The ratio between apparent (L) and intrinsic (Lo) luminosities as a function of the redshift Z and spectral index α is given by the formula ℳ(Z) = L/Lo=(Z+1)α -3 and for Type Ia supernova appears as ℳ(Z) = L/Lo=(Z+1)-2. "Doppler de-boosting" may also explain the anomalously low luminosity of objects with a high Z without the introduction of an accelerated expansion of the Universe and Dark Energy.