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StarGazer
Each week most PBS stations air Star
Gazer with Jack Horkheimer, the world's first and only weekly TV series
on naked-eye astronomy. The images on this page illustrate the show for
the week of Monday,
April 2, 2001.
The Planet Mars Is Getting Ready to Back Up! And You Can Watch It Shift Into Reverse From Your Own Back Yard
Mars is near the constellation Scorpius in April. Stargazers at mid-northern latitudes will only be able to see Scorpius in the hours before sunset, very low along the southern horizon. Antares is the brightest star in Scorpius.
The retrograde motion of Mars is shown in this picture. After moving eastward away from Scorpius, Mars appears to change course and move west from mid-May to mid-July before again shifting direction and heading east.
The retrograde motion that we see in the sky occurs when Earth "passes" the slower-moving Mars as they lap around the sun. Click here to watch a short (~600 kb) QuickTime movie showing Earth and Mars moving around the sun. Note the date that is displayed in the top left corner. Remember that the retrograde motion we see takes place between mid-May and mid-July.
