From the photographer: “Mars and Saturn spent most of the year 2016 close to each other north of bright star Antares in Scorpius. Mars was in opposition in late May shining at magnitude -2. Saturn’s own opposition was in early June, as the ringed planet shone as bright as magnitude 0. Here Saturn and Mars can be seen in retrograde motion together in eastern Libra, Scorpius and Ophiuchus. Photography started on 2015 December 15 and the last frame is from 2016 November 21.”
Saturn’s apparent motion is back and forth along the flattened, compact loop, while Mars follows the wider S-shaped track from upper right to lower left through the frame. Mars and Saturn don’t actually reverse direction in their orbits. Instead, their apparent backwards or retrograde motion with respect to the background stars is a reflection of the orbital motion of the Earth itself. Retrograde motion can be seen each time Earth overtakes and laps planets orbiting farther from the Sun, the Earth moving more rapidly through its own relatively close-in orbit.



comments (5)

  • Hector dueno Reply

    What a great work apod today retrograde. Hope you. Have a sponsor for such work–you do not lack in appreciative admirers (me too)!

    September 14, 2016 at 11:53 pm
  • Alan Kennedy Reply

    Great work, and thanks for sharing!
    I’ve been watching the triangle formed by Antares, Saturn and Mars for months and really like seeing it so “simply” put

    September 15, 2016 at 12:25 am
  • Phil Visser Reply

    Excellent explanation and visualization of retrograde motion. Super video!

    September 15, 2016 at 6:31 am
  • Sally Greenspirit Reply

    Truly awesome work! I admire your dedication and determination to record this event. Thank you and congratulations for making it available to all thru APOD!

    September 15, 2016 at 12:53 pm
  • Michael Reply


    September 19, 2016 at 2:14 pm

Leave a comment