Armenia marks Viktor Ambartsumian's birthday and Astronomy Day

September 18 marks renowned Armenian scientist Viktor Ambartsumian's 117th birth anniversary and has been celebrated as Astronomy Day in Armenia since 2009.

Victor Ambartsumian was one of the founders of theoretical astrophysics. He was best known for his theories concerning the origin and evolution of stars and stellar systems, including the discovery of stellar associations and the concept of active galactic nuclei.