Glossarbegriffe: Opposition

Description: Wenn sich zwei astronomische Objekte am Himmel in (genau) entgegengesetzten Richtungen zu einem Beobachter befinden, spricht man von einer Opposition. Dabei müssen nicht beide Objekte für den Beobachter tatsächlich sichtbar sein. Wenn der Mond in Opposition zur Sonne steht, haben wir Vollmond: Dann sind Sonne, Beobachter auf der Erde und Mond in einer Linie, sodass der sichtbare Teil der Mondoberfläche vollständig von der Sonne beleuchtet wird. Wenn die Ausrichtung perfekt ist, sehen wir eine Mondfinsternis.

Wenn ein Planet, Komet oder Asteroid als "in Opposition" bezeichnet wird, bezieht sich dies im Allgemeinen auf die Sonne und Beobachter auf der Erde. Wenn ein Planet in Opposition steht, sieht er besonders hell aus, scheint sich in die entgegengesetzte Richtung als sonst zu bewegen ("rückläufige Bewegung", da sich die Erde auf ihrer Innenbahn schneller bewegt) und ist der Erde besonders nahe.

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Term and definition status: The original definition of this term in English have been approved by a research astronomer and a teacher
The translation of this term and its definition is still awaiting approval

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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A montage of images of Mars, seen here as a series of red dots in a squashed z-shaped pattern.

Retrograde Motion of Mars

Bildunterschriften: This image captures the celestial waltz of Mars as it demonstrates its intriguing retrograde motion against the background of fixed stars. This event, when Mars appears to backtrack in its orbit, arises from the different speeds at which Earth and Mars orbit the Sun. Earth’s faster movement occasionally positions it ahead of Mars, creating the illusion of the Red Planet moving in reverse from our perspective. This retrograde motion occurs when Mars is on the other side of the sky from the Sun, when it is said to be in opposition. Following Mars from 14 August 2022 to 5 April 2023, this smartphone image stands as a testament to perseverance and precision in the tranquil setting of Bataan, Philippines. Enduring unpredictable weather and ever-shifting celestial alignments, the photographer meticulously captured each shot at regular intervals of five to eight days. The process involved aligning 35 distinct images of Mars, taken without any external lens or telescope, alongside a stacked background image composed of 54 frames lasting 15 seconds each, portraying the starry expanse. Fusing these images involved precisely aligning them and cropping Mars in order to centre its position, revealing its retrograde movement against the backdrop of stars. This intricate process, blending the images seamlessly into the background by masking, highlights the planet’s unique motion. In the lower right corner, the Pleiades star cluster is visible.
Bildnachweis: Rob Kerby Guevarra/IAU OAE (CC BY 4.0)

License: CC-BY-4.0 Creative Commons Namensnennung 4.0 International (CC BY 4.0) icons

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