's 2021 data release Many projects have attempted to bridge the gap in knowledge caused by the Zone of Avoidance. The dust and gas in the Milky Way cause
extinction at optical wavelengths, and foreground stars can be confused with background galaxies. However, the effect of extinction drops at longer wavelengths, such as the
infrared, and the Milky Way is effectively transparent at radio wavelengths. Surveys in the infrared, such as
IRAS and
2MASS, have given a more complete picture of the extragalactic sky. Two very large nearby galaxies,
Maffei 1 and
Maffei 2, were discovered in the Zone of Avoidance by
Paolo Maffei by their infrared emission in 1968. Even so, approximately 10% of the sky remains difficult to survey as extragalactic objects can be confused with stars in the Milky Way. Projects to survey the Zone of Avoidance at radio wavelengths, particularly using the
21 cm spin-flip emission line of neutral atomic
hydrogen (known in astronomical parlance as
H I line), have detected many galaxies that could not be detected in the infrared. Examples of galaxies detected from their HI emission include
Dwingeloo 1 and
Dwingeloo 2, discovered in 1994 and 1996, respectively. Recent astronomical studies revealed a supercluster of galaxies, termed the
Vela Supercluster, in the
Great Attractor's theorized location. ==See also==