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Glossary term: Atmosphere

Description: Atmosphere is a layer of gas that surrounds a celestial body. It is maintained because of the gravitational pull of the celestial body and therefore it is densest at the surface and merges into interplanetary space at high altitudes.

For planets with solid or liquid surfaces the lower boundary of the atmosphere is clear. Stars have gaseous interiors so have no clear lower bound to their atmospheres. A stellar atmosphere normally refers to the outer gaseous layer of a star through which light from the interior travels out into space.

A magnetic field of a planet can protect its atmosphere from rapidly dissipating in space because of solar or stellar wind. In Earth's case, it also protects all organisms from genetic damage due to harmful effects of the solar wind and cosmic rays.

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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".

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The Moon in the far background and Earth's the blue of the Earth's atmosphere smoothly changes to the black of space

Moon and Earth's thin atmosphere

Caption: Taken from the International Space Station (ISS), approximately 400 kilometers above the ground, the picture shows the Moon far in the background and Earth's thin atmosphere. It appears blue as light in this wavelength is scattered more than in others by the gases in the upper layers. The photo was taken in March 2015 by a crew member. Clearly visible is the vanishingly small layer of gases compared to Earth's dimensions. There is no clear border between the atmosphere and space; it is a smooth transition with no sharp edges. The thickness to the upper limit of the stratosphere, roughly 50 kilometers, does not even amount to one percent of Earth's radius. Above 600 kilometers, particles reaching the critical escape velocity can leave into space. The total mass of the atmosphere is around 300 times less than that of all oceans combined or one million times less than Earth's total mass.
Credit: Earth Science and Remote Sensing Unit, NASA Johnson Space Center credit link

License: PD Public Domain icons


Venus as a circular disk against a dark background, with visible patterns and streaks in its atmosphere.

Atmosphere of Venus

Caption: This image of Venus was captured in ultraviolet light by the Pioneer Venus Orbiter and highlights features of the planet’s thick atmosphere that are not visible in ordinary light. Venus has a dense, cloudy atmosphere composed mainly of carbon dioxide. In ultraviolet wavelengths, patterns in the upper cloud layers become visible, revealing swirling structures and bright and dark bands caused by differences in the composition and motion of the atmosphere. These ultraviolet features help scientists map wind patterns, atmospheric circulation, and cloud dynamics high above Venus’s surface. Unlike Earth’s atmosphere, which is relatively transparent in visible light, Venus’s atmosphere is so thick that no direct view of the surface is possible from space without special instruments. The extreme pressure and temperature near Venus’s surface are consequences of this dense gaseous envelope, making Venus a dramatic example of how different planetary atmospheres can be. This image demonstrates how observing a planet’s atmosphere in different wavelengths, such as ultraviolet, reveals details about its structure and behaviour.
Credit: NASA credit link

License: PD Public Domain icons

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The Office of Astronomy for Education is hosted by the Haus der Astronomie on the campus of the Max Planck Institute for Astronomy in Heidelberg. The Office of Astronomy for Education is an office of the International Astronomical Union, with substantial funding from the Klaus Tschira Foundation and the Carl Zeiss Foundation. The Shaw-IAU Workshops on Astronomy for Education
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