Today Earth and Mars will be closer together than at any time during the last 12 years. Stargazers won't want to miss the Red Planet blazing bright in the midnight sky.
June 21, 2001 -- Check most any astronomer's 2001 calendar and you'll find June 21st circled. It's a big day for astronomy! For starters, June 21st marks the beginning of northern summer and the longest day of the year north of the equator. The Sun will climb to its highest point in the sky at 7:38 UT (3:38 EDT), a moment known as the summer solstice.
Then, just a few hours later, something extraordinary will happen to that solstice Sun. With hundreds of astronomers watching intently, the New Moon will slide across our star's fiery disk for a rare total solar eclipse. The Sun's ghostly corona will dance across the sky for nearly four minutes -- but, alas, only over southern Africa where the narrow path of totality makes landfall.
If you're among the billions who will miss the eclipse in remote Africa, don't despair. There's one more astronomical wonder on June 21st that anyone can enjoy: a close encounter with the planet Mars.
Earth and Mars have been growing steadily closer for months, and today around 0615 UT the two worlds will lie only 0.45 AU (67 million km) apart -- the nearest they've been in a dozen years. Mars is simply dazzling when it's so close to Earth, and finding it is easy, says astronomy professor George Lebo, a NASA Summer Faculty Fellow at the Marshall Space Flight Center. "Simply go outside between 10 pm and 2 am local time," he says, "and look toward the south. Mars is brighter than any other star in the sky and it has a distinctive reddish-orange color -- you can't miss it."
Mars rises in the east around sunset and can be seen for most of the night. But as Lebo suggests, the hours around midnight offer the best view, because that's when the Red Planet is highest in the sky. Midnight sky watchers at mid-northern latitudes will spot Mars hovering about 30 degrees above the southern horizon. For southern hemisphere stargazers, Mars will lie almost directly overhead.
Even city dwellers with troublesome light pollution can spot the planet. Blazing at visual magnitude -2.3, Mars will outshine everything in the sky except Venus and the Sun itself. The Moon will be New on June 21st (and busy blocking out the Sun in southern Africa), so Mars will be even brighter than Earth's satellite.
If you happen to be watching Mars with dark-adapted eyes from an extremely dark site, be sure to look at the ground around you. Can you see a faint shadow? The light outlining your silhouette could be from Mars! It's not every day you can see your "Mars shadow," but this week is a good time to try.
Earth and Mars are on the same side of the Sun this month. They were aligned most directly on June 13th --a date astronomers call opposition -- but the pair won't make their closest approach until 8 days later, on June 21st, because of the substantial eccentricity of Mars' orbit.
Mars will remain blazing bright for weeks to come, fading slowly as northern summer wanes and fall approaches. Throughout the coming months the Red Planet will linger in a region of the sky that's home to the very center of our galaxy. This will be a treat for dark sky observers who can see the faint Milky Way, a hazy band of stars that bisects the sky along the galactic plane. The Milky Way cuts through the teapot-shaped constellation Sagittarius and brightens near its spout -- right by Mars. There lies the galactic center, the lair of a supermassive black hole around which our entire pinwheel galaxy spins. (Don't bother looking for the black hole, you can't see that!)
Of course, Mars and the galactic center are very far apart despite their seeming proximity. A spacecraft from Earth traveling at light speed would arrive at the Red Planet in only a few minutes. Reaching the inner regions of our galaxy would take an extra 30,000 years!
We don't yet have spacecraft that can travel so fast, but you can still visit Mars at the speed of light -- through a telescope. The nearby Red Planet will be a whopping 21 arcseconds across this week and next. "One arcsecond is a tiny angle, about the size of a dime viewed from a distance of 1.5 miles," explains Lebo. "Even twenty-one arcseconds is small to the unaided eye, but it's plenty big for telescopes." This week a modest six-inch reflecting telescope could reveal normally invisible details including martian clouds and icy polar caps. See Sky and Telescope's "A Grand Return of Mars" for more information.
If you don't own a telescope, looking at Mars with your unaided eye is still a wonderful way to enjoy this planetary close encounter. So don't wait. Mars is out there now, fiery red and beckoning from your own back yard!