Abbé Georges Édouard Lemaître
(1894–1966) Belgian astronomer and cosmologistLemaître was born at Charleroi in Belgium. After serving in World War I, he studied at the University of Louvain in Belgium from where he graduated in ...
Abd al-Ramān al-Ṣūfī
(903–86)Arabastronomer (Latinized name Azophi), born in modern Iran. His Book of the Fixed Stars (c.964) contained a star catalogue and atlas based on Ptolemy's*Almagest, revised in the spirit of ...
Abell Catalogue
A catalogue of 2712 rich clusters of galaxies published in 1958 by the American astronomer George Ogden Abell (1927–83) from inspection of the Palomar Observatory Sky Survey photographs. The ...
Abell cluster
A cluster of galaxies listed in the Abell Catalogue. To appear in the catalogue, a cluster must satisfy selection criteria which include containing more than 50 galaxies and having a dense ...
Abell radius
A radius of about 2 megaparsecs within which at least 50 galaxies of a particular range of brightness must be found if the cluster is to qualify as an Abell cluster.
aberration
The small apparent difference between the observed direction of a star and its true direction (see diagram). It is due to the combined effect of the observer's motion across the path of incoming ...
ablation
The wearing away of the outer layers of a body by melting, erosion, vaporization, or some other process due to aerodynamic effects as the body moves at high speed through a planetary atmosphere. ...
ablation age
The period of time since the outer glassy layers of a tektite solidified following ablation during its re-entry into the Earth's atmosphere. The ablation ages of known tektites vary from about ...
ablation shield
The heat shield on a spacecraft to protect it during re-entry. The intense heat generated by friction during the high-speed entry of the craft into the Earth's atmosphere burns away ablative ...
