See Mars Near the Moon On Earth's Equinox Friday

This sky map shows how the moon and Mars will appear at 4 a.m. local time on Sept. 23, 2011, the fall equinox in the Northern Hemisphere, to skywatchers with clear skies at mid-northern latitudes CREDIT: Starry Night Software View full size image

On Friday, Sept. 23, the sun will cross the celestial equator, heading south, in the annual equinox marking the start of the fall season in the Northern Hemisphere and the spring in the south. But this year's equinox brings a special treat: the moon and planet Mars shining together at dawn.

The north's autumnal equinox will occur Friday at 5:05 a.m. EDT (0905 GMT). If you look high toward the east-southeast at sunrise, you’ll see a lovely crescent moon, and hovering above and to its left will be a modestly bright "star" with a yellow-orange tinge. That's no star, but rather the famous Red Planet, Mars.

The sky map of Mars and the moon here shows how they will appear on the Friday's equinox.

These days, Mars is coming up about five hours before sunrise — around 1:50 a.m. local daylight time.  It currently resides in the dim constellation of Cancer, the Crab. It's currently 173 million miles (278 million kilometers) from Earth and shines as brightly as a first-magnitude star. (Remember, astronomers measure the brightness of objects as "magnitude." The lower an object's magnitude, the brighter it appears.)

Mars is now a trifle brighter than the star Regulus in the nearby constellation of Leo, the lion, the 21st brightest star in the sky. The Red Planet is not the only bright planet skywatchers can in the early morning sky on Friday. The planet Jupiter will be shining high in the southern sky.

Mars is slowly approaching Earth, though it is still almost six months away from its closest point.

That's why if you train a telescope on that topaz-colored "star" to the moon's upper left on Friday morning, you’ll be disappointed; the disk of Mars has an apparent size that is only a 360th of the moon's width. 

Interestingly, autumn will arrive that morning for our Northern Hemisphere just 10 days after the spring equinox for the Martian northern hemisphere.

After Friday morning, Mars will continue to plod slowly east against the stars, and on the morning of Oct. 1 it will be positioned within the famous Beehive Star Cluster of Cancer — a very pretty sight in binoculars. 

If you use a telescope on that morning, you’ll be able to watch Mars pass extremely close to the 6.6-magnitude star SAO 98010. At 4 a.m. EDT (0800 GMT), they’ll be separated by a scant 18 seconds of arc. That’s equal to a hundredth the apparent width of a full moon. 

As Mars approaches Earth it will be getting progressively brighter and larger. In fact, by early next March it will appear nearly a dozen times brighter and almost three times larger than it is right now. 

To be sure, Mars has a lot of growing to do in the months ahead!

Editor's note: If you snap an amazing photo of Mars, the moon or any other skywatching target and would like to share the experience with SPACE.com for a possible story or photo gallery, please contact managing editor Tariq Malik at: tmalik@space.com.

Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for The New York Times and other publications, and he is also an on-camera meteorologist for News 12 Westchester, New York.