Question

This multiple exposure photograph shows the apparent retrograde motion of Mars. To make this picture, the photographer needed to combine individual photos of Mars taken over a period of:

1) about 3 nights
2) several months
3) one full night
4) about one hour

Answer 1

A photographer would need to combine photos taken over several months to depict Mars's apparent retrograde motion, as this motion is based on the relative motion of Earth and Mars in their orbits and cannot be captured in a short time frame.

Step-by-step explanation:

To capture the apparent retrograde motion of Mars in multiple exposure photography, the photographer would have needed to combine individual photos taken over a period of several months. The retrograde motion occurs because of the relative positions and movements of Earth and Mars in their orbits around the Sun. When Earth passes Mars in its orbit, Mars appears to move backward, or retrograde, against the background stars. This motion cannot be observed in a single night, as Mars's sidereal day is almost the same as Earth’s, which means the planet rotates nearly once every 24 hours. Therefore, it requires many nights of observation to note the full effect of retrograde motion. This process can be somewhat analogous to using a blink comparator, as Clyde Tombaugh did to discover Pluto, where changes in position over days or weeks were used to detect movement.