Why would Mars appear to move backwards? Most of the time, the apparent motion of Mars [
http://www.nineplan…] in Earth's sky [
http://antwrp.gsfc.…] is in one direction, slow but steady in front of the far distant stars. About every two years, however, the Earth passes Mars [
http://antwrp.gsfc.…] as they orbit around the Sun. During the most recent such pass in August, Mars loomed [
http://antwrp.gsfc.…] particularly large and bright [
http://antwrp.gsfc.…]. Also during this time, Mars appeared to move backwards in the sky, a phenomenon called retrograde motion [
http://alpha.lasall…]. Pictured above is a series of images digitally stacked so that all of the stars images coincide. Here, Mars appears to trace out a loop [
http://mars.jpl.nas…] in the sky. At the top of the loop, Earth passed Mars and the retrograde motion [
http://astron.berke…] was the highest. Retrograde motion [
http://antwrp.gsfc.…] can also be seen for other Solar System [
http://www.nineplan…] planets. In fact, by coincidence, the dotted line to the right of the image center is Uranus doing the same thing.
Explanation
Why would Mars appear to move backwards? Most of the time, the apparent motion of Mars [
http://www.nineplan…] in Earth's sky [
http://antwrp.gsfc.…] is in one direction, slow but steady in front of the far distant stars. About every two years, however, the Earth passes Mars [
http://antwrp.gsfc.…] as they orbit around the Sun. During the most recent such pass in August, Mars loomed [
http://antwrp.gsfc.…] particularly large and bright [
http://antwrp.gsfc.…]. Also during this time, Mars appeared to move backwards in the sky, a phenomenon called retrograde motion [
http://alpha.lasall…]. Pictured above is a series of images digitally stacked so that all of the stars images coincide. Here, Mars appears to trace out a loop [
http://mars.jpl.nas…] in the sky. At the top of the loop, Earth passed Mars and the retrograde motion [
http://astron.berke…] was the highest. Retrograde motion [
http://antwrp.gsfc.…] can also be seen for other Solar System [
http://www.nineplan…] planets. In fact, by coincidence, the dotted line to the right of the image center is Uranus doing the same thing.
Explanation
