Mars 2003: Loop-the-Loop in Aquarius
The Red Planet makes a curly-cue track (red) through Aquarius between mid-June and early November. |
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Long before it was imagined as a home to extraterrestrials, Mars had established itself in the human imagination.
Its tawny color, which contrasts beautifully with the deep blue of a twilight sky, is unique among the planets. Mars undergoes exceptional changes in brightness within a single apparition -- and its peak brightness varies from one appearance to the next. And in the months when Mars shines best, near opposition, the Red Planet takes a seemingly chaotic whirl through the starry sky.
Mars will make its signature loop among the stars over the coming weeks. The planet is now gliding swiftly eastward through the stars of the constellation Aquarius, but its pace will slow until, on July 29, its motion parallel to the ecliptic halts completely.
And then something peculiar happens: Mars reverses course.
All of the planets display periods of westward, or retrograde, sky motion, but Mars puts on the best show. This year, it heads west through Aquarius until September 27, when it halts, reverses course again, and resumes its stately eastward slide.
It's a wonderful display of celestial geometry. The combined orbital motions of Earth and Mars create the appearance of a celestial loop-the-loop. Mars seems to be moving backward because the Earth is actually approaching and overtaking it. Since the distance between Earth and Mars is smallest at this time, the Red Planet shines brightest and presents its largest angular size to telescopic observers.
Mars also reaches its closest point to the sun, or perihelion, just days after we pass it. Since perihelic oppositions only occur once every fifteen years or so, our view of Mars this summer represents the best of the decade.
In 2003, Mars traces a tight five-degree-wide oval. But the pattern it makes changes size and shape from opposition to opposition, depending on where in its orbit Mars happens to be when we pass it. The retrograde loop in 2005 is best described as a zigzag. And the 2010 loop covers almost twice as much sky as this year's, which is the smallest of the decade. (See Celestial Delights for more details on Mars oppositions through 2010.)
Circumstances for the Mars Loop in 2003
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