Jaan Einasto (born 23 February 1929) is an Estonian astrophysicist and one of the discoverers of the large-scale structure of the Universe.

[5] He attended the University of Tartu, where he received the Ph.D. equivalent in 1955 and a senior research doctorate in 1972.

For a long time, he was Head of the Division of Astronomy and Physics of the Estonian Academy of Sciences in Tallinn.

In 1974, in a seminal work with Kaasik and Saar at the Tartu Observatory, Einasto argued that "it is necessary to adopt an alternative hypothesis: that the clusters of galaxies are stabilised by hidden matter.

[7][8] Einasto showed in 1977 at a Symposium in Tallinn (Estonia) that the universe has a cell structure, in which the observed matter surrounds huge empty voids.