1. (astronomy) an observational branch of astronomy, which deals with the study of X-ray emission

Encyclopedia: X-ray astronomy

• Christian name
• Christian religion
• Christian Schonbein
• Christian Science
• alsike
• also
• also known as
• also-ran
• Alsobia
• Alsobia dianthiflora
• Alsophila
• Alsophila pometaria
• Alstonia
• Alstonia scholaris
• alstroemeria
• Alstroemeria pelegrina
• Alstroemeriaceae
• alt
• Altace
• Altai Mountains
• Altaic
• Altaic language
• Altair
• altar
• altar boy