Video from the rover shows Curiosity’s shadow moving across the surface of Mars for 12 hours while it was parked. When NASA’s Curiosity Mars rover is not moving, it is the 4,002nd day of the mission. It works quite well as a sundial, as seen in two black-and-white videos recorded on November 8, the Martian day or sol. The rover captured its own shadow moving across the Martian surface using black-and-white hazard avoidance cameras, or Hazcams.

Instructions for recording the video were part of the final set of commands given to Curiosity just before the start of Mars solar conjunction, the period when the Sun is between Earth and Mars. Missions delay sending spacecraft commands to Mars by several weeks during this time, as plasma from the Sun can interfere with radio communications. (The missions were not fully in touch: they still radioed regular medical checks along the link.)

Rover drivers often rely on Curiosity’s security cameras to spot rocks, cliffs and other hazards that might be risky to cross. But because the rover’s other activities were deliberately interrupted before docking, the team decided to use the Hazcams to record 12-hour snapshots for the first time, hoping to capture clouds or dust devils that could provide more information about the Red Planet’s weather.

When the images landed on Earth after being reconnected, scientists didn’t see any weather, but a pair of 25-frame videos they put together captured the passage of time. The video shows Curiosity’s skyline changing from 5:30 a.m. to 5:30 p.m. local time as the day changes from morning to afternoon to evening.

The first video, featuring views from Hazcam’s front, looks southeast across Geddies Vallis, a valley on Mount Sharp. Curiosity has been climbing the 3-mile (5-kilometer) mountain base in Gale Crater since 2014.

As the sky brightens at sunrise, the shadow of the rover’s 2-meter (7 ft) robotic arm moves to the left and Curiosity’s front wheels emerge from the darkness on either side of the frame. Also visible on the left is the circular calibration target mounted on the shoulder of the robot arm. Engineers are using the target to test the accuracy of the Alpha Particle X-ray Spectrometer, an instrument that detects chemical elements on the surface of Mars.

At midday, the Hazcam front camera’s automatic exposure algorithm is set to an exposure time of approximately one-third of a second. As night falls, this exposure time increases to up to a minute, causing typical sensor noise known as “hot pixels” that appear as white snow in the final image.

Curiosity’s rear Hazcam captured the shadow of the rover’s back in this 12-hour image overlooking the floor of Gale Crater. Various factors, including a black spot, a distorted view of the Sun, and rows of white pixels moving away from the Sun, have contributed to the various image artifacts.NASA/JPL-Caltech

The second video shows the rear Hazcam looking northwest, down the slopes of Mount Sharp toward the floor of Gale Crater. The rover’s right rear wheel is visible along with the shadow of Curiosity’s power system. The small black image that appears in the middle left of the video in frame 17 is the result of cosmic radiation hitting the camera sensor. Likewise, the bright blink and other noise at the end of the video are a result of heat from the spacecraft’s power system affecting the Hazcam image sensor.

These images were reprojected to correct for Hazcam’s wide-angle lenses. The mottled appearance in the images, which is especially striking in the rear camera video, is caused by 11 years of Martian dust settling on the lenses.