Retrograde Motion of Mars

Winner in the 2023 IAU OAE Astrophotography Contest, category Still images with smartphones-mobile devices: Retrograde Motion of Mars, by Rob Kerby Guevarra.

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)