Mars Closest to Earth Tonight; Best View Until 2016
Kelly Hearn
for National Geographic News
December 18, 2007
The bright yellowish-orange "star" poised above the constellation Gemini
is actually the planet Mars, and tonight the icy world will make its closest
approach to Earth until 2016.
Earth passes Mars every 26 months, overtaking it in an "orbital race" as
both bodies go around the sun. (Explore planetary orbits using an interactive
solar system.)
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"Earth comes close to Mars because our planet is moving faster in its
orbit, catching up to and passing Mars," said Jaymie Mark Matthews, an
astronomer at Canada's University of British Columbia.
Tonight's passage happens while Mars is in retrograde motion, or
appearing to move westward across the night sky.
"Thus, for the three months around closest approach, the yellowish-orange
planet will appear to move slowly backward from the constellation Gemini into
Taurus," said Edward Murphy, an astronomer at the University of Virginia.
The exact distance between the two worlds varies during a close
encounter, because the planets' orbits are elliptical.
Murphy calculates that today Earth is roughly 55 million miles (88
million kilometers) apart from Mars, a figure backed by Matthews.
But experts say tonight's glimpse of the red planet will be nothing
compared to the show-stopping passage of August 27, 2003, when a mere 35
million miles (56 million kilometers) stood between the two bodies.
"That was when the red planet came closer than it had ever been since the
time Neanderthals walked the Earth," Matthews said.
Best Views
Though Mars won't be as close to Earth as it was in 2003, tonight's
viewing might be better for some sky-watchers.
That's because Mars won't be as close to the Earth's horizon as it was
four years ago, thanks to the astronomical geometry of this year's planetary
opposition.
Opposition is when Earth is between the sun and a planet, so the planet
appears in the opposite side of the sky as the sun. During the Northern
Hemisphere's winter Earth tilts away from the sun and toward Mars.
"That's a good sign for sky-gazers at latitudes of about 40 to 45 degrees
north," Matthews said.
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RELATED
a.. Holiday Sky Show: Five Planets to Shine in Predawn (December 16,
2004)
b.. Planets: Photos, Stats, Charts, More
c.. Gallery: New Hi-Res Color Images of Mars Released (October 11,
2007)
"For them, Mars will pass almost straight overhead during the night."
And for those at mid-northern latitudes, Mars will be up all night long,
Murphy said.
Mars fans who miss out on tonight's show will still get a few good weeks
of viewing.
"Although tonight is the night of closest approach, the distance between
Earth and Mars is changing very slowly," Matthews said.
"Mars will look good all month and will still be very good until late
January."
People with even the most basic telescopes should be able to see Mars's
bright icy poles and dark features, according to Space.com.
The planet will also be visible with the naked eye, and its opposition
means that it appears in full-phase, similar to a full moon.
But Matthews cautioned against unrealistic expectations.
"Ignore email messages saying that Mars will look as big as the full moon
in the sky," he said.
(Read: "'Mars Spectacular' E-Mail Hoax Spins On" [August 26, 2005].)
"Even in August 2003, at a telescopic magnification of about a hundred
times, Mars would have had the same angular size as the full moon seen with the
naked eye."
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