On Jan. 15, Mars will reach a point in its orbit that astronomers call opposition. That evening, Mars will lie opposite the Sun from our perspective. It will rise at sunset, reach its highest point at midnight, and set at sunrise.
No matter when you go out, Mars will be somewhere in the sky. And it’ll be pretty bright, too. That’s because at opposition, Mars is about as close to Earth as it will get during this orbit. The actual closest approach occurs three days earlier, on Jan. 12.
Big and bright
On the 15th, Mars will shine at magnitude –1.4, essentially equaling the luminance of the brightest nighttime star, Sirius, which lies in the constellation Canis Major the Great Dog. You’ll find that star pattern roughly a quarter of the way across the sky to the south of Mars.
Mars will also appear larger than at any other time this year. Astronomers use angles to measure the span of celestial objects. At opposition, the Red Planet’s diameter will be 14.6 arcseconds, generally written as 14.6″. This isn’t much. For comparison, 1″ is the angle a dime subtends from a mile away.
To see any detail on Mars, even at opposition, you’ll need at least a medium-size telescope, an eyepiece that magnifies about 100x, and a night of good seeing (atmospheric stability). If the air is unsteady, the stars will be twinkling a lot and details — even through a telescope — will be washed out.
The changing sky
There’s another way to observe Mars, and this one doesn’t require a telescope. Note the position of Mars compared to the two bright stars above it. That pair is made of Castor and Pollux, which mark the heads of the constellation Gemini the Twins. Once you note the planet’s position, go out every few nights for a month. You’ll see Mars slowly move westward through Gemini with respect to Castor and Pollux.
However you observe it, go take a look at the Red Planet and maybe wonder if robotic spacecraft will ever find evidence of microscopic life there. Don’t wait for Mars’ next opposition, which won’t happen until Feb. 19, 2027. It will be a bit fainter and smaller then, so now’s the time. Good luck!
