Abetti,
Giorgio Adams,
John Couch Adams,
Walter Sydney Airy,
George Biddell Aitken,
Robert Grant Alfvén,
Hannes Olof Gösta Ambartsumian,
Viktor Amazaspovich Amici,
Giovanni Battista Anaximander Antoniadi,
Eugène Marie Arago,
Dominique Argelander,
Friedrich Wilhelm August Aristarchus
of Samos Arp,
Halton Christian