Mars Closest to Earth Tonight; Best View Until 2016
A graphic shows the last seven times Mars neared Earth while in opposition to the sun. When Earth is in between Mars and the sun, stargazers will see the red planet in full phase, similar to a full moon.
The images of Mars show the planet's relative size as it appeared each year to the Hubble Space Telescope while in opposition.
On December 18, 2007, Mars will be a mere 55 million miles away while in opposition—the nearest it will be to our world until 2016, astronomers say.
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.)
"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.
"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."
