Sources without a listed G magnitude. Left: sky distribution of 100,000 randomly selected Gaia sources without a G magnitude. The area displayed focuses on the inner Milky Way, but such sources are found all across the sky. Right: fraction of sources (out of a random sample of 3 million Gaia sources) without a G magnitude, computed in bins of Galactic latitude. The fraction is close to 0.3% over the entire sky but is significantly higher in regions close to the Galactic plane.