Glossary term: Absolute Magnitude

Description: Absolute magnitude is a measure with two different definitions. Both relate to how bright objects appear under a special set of conditions. This allows the intrinsic properties of objects at different distances to be compared. This is in contrast to apparent magnitude which is a measure of how bright an object appears from the location of the observer.

For objects outside the Solar System such as stars and galaxies, absolute magnitude is defined as the apparent magnitude an object would have when viewed from a standard distance of 10 parsecs, ignoring the effects of interstellar extinction. This standardized number allows different objects to be compared by how intrinsically bright they are.

Within the Solar System, absolute magnitude is defined as the apparent magnitude an object such as an asteroid would have if viewed at a distance of one astronomical unit from the observer, while the object is at a distance of one astronomical unit away from the Sun, and at opposition. Note that an object in the Solar System can never match these conditions when viewed from Earth but the definition removes factors that depend on the locations of the object and the observer to allow Solar System objects in different locations to be compared.

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Term and definition status: This term and its definition have been approved by a research astronomer and a teacher

The OAE Multilingual Glossary is a project of the IAU Office of Astronomy for Education (OAE) in collaboration with the IAU Office of Astronomy Outreach (OAO). The terms and definitions were chosen, written and reviewed by a collective effort from the OAE, the OAE Centers and Nodes, the OAE National Astronomy Education Coordinators (NAECs) and other volunteers. You can find a full list of credits here. All glossary terms and their definitions are released under a Creative Commons CC BY-4.0 license and should be credited to "IAU OAE".