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The Earth's orbit around the Sun with one planet orbiting outside the Earth's orbit and one orbiting inside

Opposition and Conjunction

image
Created for the OAE

Caption: This diagram shows the Earth's orbit around the Sun and the orbits of two other planets, one orbiting the Sun outside the Earth's orbit and one orbiting the Sun inside the Earth's orbit. At different times in the orbits of both of these planets, their positions appear to line up with the Earth and the Sun. At these points each planet would appear close to the Sun when viewed from Earth. When this happens each planet is said to be in conjunction with the Sun. For the planet that orbits the Sun within the Earth's orbit it can be in conjunction with the Sun twice in its orbit, once when it is between the Sun and the Earth and once when it is on the other side of the Sun from the Earth. When the planet is in conjunction between the the Sun and Earth it is said to be in inferior conjunction and when it is in conjunction on the far side of the Sun from the Earth it is said to be in superior conjunction. For the planet orbiting the Sun outside the Earth's orbit, it can sometimes be on the other side of the sky. At this point the Earth lies between the planet and the Sun. The planet in this case is said to be in opposition. Opposition and conjunction are not just limited to planets and other types of solar system objects such as dwarf planets, comets and asteroids can also be in opposition and conjunction. However only those objects that have an orbit that takes them outside the Earth's orbit can be in opposition. Conjunction is also used to refer to alignments in the sky between planets in the Solar System. For example when Jupiter and Venus appear very close on the sky when viewed from Earth they are said to be in conjunction with each other.
Credit: Aneta Margraf/IAU OAE

Termes del glossari: Conjunction , Opposition
Categories: Naked Eye Astronomy , Observational Astronomy , Solar System

License: Creative Commons Reconeixement 4.0 Internacional (CC BY 4.0) Creative Commons Reconeixement 4.0 Internacional (CC BY 4.0) icons

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Venus changes from being small and almost full to being large with only a thin crescent illuminated.

A Matter of Perspective

image
Created for the OAE

Caption: Second place winner in the 2023 IAU OAE Astrophotography Contest, category of Still images of phases of Venus. This exquisite series of images, captured from Santo Domingo, Dominican Republic, between 17 December 2019 and 25 May 2020, shows the phases of Venus as seen from Earth. As Venus and Earth orbit the Sun, we observe different portions of Venus’s sunlit half, similar to the Moon’s phases. The sequence clearly shows Venus as distant, small, bright and gibbous in the lower frames, and ends with Venus reaching the biggest apparent size of all planets (upper frames), very close to the Sun with a small elongation, and appearing as a thin crescent. In the last frame, only 2.8% of the planet’s surface is illuminated.
Credit: Christofer Baez/IAU OAE (CC BY 4.0)

Termes del glossari: Phase , Venus
Categories: Solar System
Tags: astrophotography

License: Creative Commons Reconeixement 4.0 Internacional (CC BY 4.0) Creative Commons Reconeixement 4.0 Internacional (CC BY 4.0) icons

This file on Zenodo ( image 339.56 kB)


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

Retrograde Motion of Mars

image
Created for the OAE

Caption: Winner in the 2023 IAU OAE Astrophotography Contest, category Still images with smartphones-mobile devices. 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.
Credit: Rob Kerby Guevarra/IAU OAE (CC BY 4.0)

Termes del glossari: Mars , Opposition , Pleiades
Categories: Naked Eye Astronomy , Solar System
Tags: astrophotography

License: Creative Commons Reconeixement 4.0 Internacional (CC BY 4.0) Creative Commons Reconeixement 4.0 Internacional (CC BY 4.0) icons

This file on Zenodo ( image 3.43 MB)


Jupiter with coloured horizontal bands of clouds. The shadow of the moon Io is seen as a dark circle in the top left

Jupiter, Io and its shadow, by Ralf Burkart, Germany

video
Created for the OAE

Caption: First place in the 2021 IAU OAE Astrophotography Contest, category Galilean moons. This time-lapse of Jupiter taken in 2017 from Germany beautifully illustrates the transit of one of the Galilean moons, Io, in front of Jupiter. As this is simply a moon casting a shadow on a planet it is equivalent to a lunar eclipse on Earth observed from further away. While the shadow of the moon is clearly visible from the beginning, it might be difficult to spot the moon itself against the background of the beautiful atmospheric bands of Jupiter the first time the video is seen. Watching it repeatedly allows appreciating the rapid motion and rotation in this fantastic observation.
Credit: Ralf Burkart/IAU OAE

Termes del glossari: Galilean Satellites , Gas Giant , Io , Jupiter , Moons , Orbit , Outer Planets , Planet , Transit
Categories: Solar System

License: Creative Commons Reconeixement 4.0 Internacional (CC BY 4.0) Creative Commons Reconeixement 4.0 Internacional (CC BY 4.0) icons

This file on Zenodo ( video 12.64 MB)


The planet Jupiter, seen here as a bright disk, is orbited by the four Galilean moons, seen here as bright dots

Jupiter Moons Movie2, by Nicolas Hurez, Paul-Antoine Matrangolo, and Carl Pennypacker, United States of America

video
Created for the OAE

Caption: Second place in the 2021 IAU OAE Astrophotography Contest, category Galilean moons. This sequence shows the orbit of the four Galilean moons around the planet Jupiter. Almost two entire orbits of the innermost moon, Io, can be seen, with the other moons (Europa and Ganymede, but in particular Callisto) being further away, orbiting noticeably slower. The images were obtained in 2018 with the Las Cumbres Global Observatory at different locations on Earth, allowing a continuous sequence of images over approximately half a week without gaps during the day. With clear skies and over the course of several nights, the motion of the Galilean moons can also be observed with binoculars (ideally steady your elbows on a surface).
Credit: Nicolas Hurez, Paul-Antoine Matrangolo and Carl Pennypacker/IAU OAE

Termes del glossari: Galilean Satellites , Gas Giant , Io , Jupiter , Moons , Orbit , Outer Planets , Planet
Categories: Solar System

License: Creative Commons Reconeixement 4.0 Internacional (CC BY 4.0) Creative Commons Reconeixement 4.0 Internacional (CC BY 4.0) icons

This file on Zenodo ( video 890.47 kB)


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