Marc Aaronson (ABD, 1950 – 1987)
George Ogden Abell (ABD, 1927 – 1983)
Antonio Abetti (İtalya, 1846 – 1928)
Giorgio Abetti (İtalya, 1882 – 1982)
Charles Greeley Abbot (ABD, 1872 – 1973)
Charles Hitchcock Adams (ABD, 1868 – 1951)
John Couch Adams (Birleşik Krallık, 1819 – 1892)
Walter Sydney Adams (ABD, 1876 – 1956)
Saul Adelman (ABD, (1944 -)
Agrippa (Yunanistan, bilinmiyor – 92)
Paul Oswald Ahnert (Almanya, 1897 – 1989)
Eva Ahnert-Rohlfs (Almanya, 1912 – 1954)
George Biddell Airy, (İngiltere, 1801 – 1892)
Robert Aitken, (ABD, 1864 – 1951)
Al Battani (Irak, 850 – 929)
Vladimir Aleksandrovich Albitzky (Rusya)
Albumasar (İran 787 - 886)
George Alcock (Birleşik Krallık, 1913 – 2000)
Harold Alden (ABD, 1890 – 1964)
Hannes Alfvén (İsveç, 1908 – 1995)
Lawrence H. Aller (ABD, 1913 – 2003)
Abd Al-Rahman Al Sufi, (İran, 903 – 986)
Viktor Amazaspovich Ambartsumian, (Ermenistan, 1912 – 1996)
John August Anderson, (ABD, 1876 – 1959)
Andronicus of Cyrrhus
Anders Jonas Ångström (İsveç, 1814 – 1874)
Eugène Michel Antoniadi (Yunanistan, Fransa, 1870 – 1944)
Petrus Apianus (Almanya, 1495 – 1557)
François Arago (Fransa, 1786 – 1853)
Sylvain Arend (Belçika, 1902 – 1992)
Friedrich Wilhelm Argelander (Almanya, 1799 – 1875)
Sisamlı Aristarkus, yaklaşık M.Ö. 310 – yaklaşık M.Ö. 230)
Christoph Arnold (Almanya, 1650 – 1695)
Svante Arrhenius (İsveç, 1859 – 1927)
Arzachel (Endülüs, 1028 – 1087)
Goryu Asada (Japonya, 1734 –1799)
Giuseppe Asclepi (İtalya, 1706 – 1776)
Joseph Ashbrook (ABD, 4 Nisan 1918 – 4 Ağustos 1980)
Arthur Auwers (Almanya, 1838 – 1915)
Adrien Auzout (Fransa, 1622 – 1691)
