September evening skies are a mixture of the summer Milky Way still found overhead and dominating the western sky with the dimmer and less obvious autumn constellations found in the eastern sky. High overhead is Cygnus and Lyra, both of which contain two stars of the Summer Triangle. The third Summer Triangle star is farther below in the sky found in Aquila. To the east of the Summer Triangle you’ll spot the Great Square of Pegasus. The Milky Way stretches through Cygnus and flows to the southwestern horizon where you’ll find Sagittarius. Facing north you’ll find Draco, Cepheus and Cassiopeia. The brightest objects this month in order of brightness is Jupiter, Mars, Arcturus, Vega, Capella, Saturn, Altair, Antares, Fomalhaut and Deneb. By the end of the month, Mars will be brighter than Jupiter.
Mars can change appearance from year to year more than any other planet depending on how close it is to Earth. Every 15 to 17 years Mars can really put on a show. We have a great opportunity to watch Mars grow in brightness and size through mid October; if you miss Mars this year it won’t be this bright again until July of 2033. You’ll easily find the bright red planet near the Moon on Sunday evening, Sept. 6 and Saturday evening Oct. 3.
Mars isn’t always spectacular for two reasons: it is fairly small and can be as close as 34 million miles or as far away as 249 million miles when both Mars and Earth are on opposite sides of the Sun. During a close approach Mars can shine at -3 magnitude with only Venus and the full Moon being brighter. At its farthest from the Earth Mars blends in with bright stars shining at +1.6 magnitude.
This month Mars is already an obvious reddish star rising in east in the late evening located in the dim constellation of Pisces. Mars started brightening in February and since mid-August, Mars is brighter than Sirius, our brightest star. By mid September Mars will be brighter than Jupiter. Mars will continue to brighten and appear larger until it is closest to Earth on Oct. 6 after which it reaches opposition on Oct. 13. At opposition Mars will shine at a brilliant magnitude of -2.62. At its closest this year Mars will be 38,780,000 miles from Earth.
Mars reaches opposition every 2.1 years when Mars, the Earth and Sun all lie in a straight line in space with the Earth in the middle. Mars is further from the Sun than Earth, so it takes the red planet 1.9 years to orbit the Sun and the Earth laps Mars every 2.1 years. When the planets pass each other Mars appears larger and brighter than at other times. Also since Mars is opposite the Sun, the planet is visible most of the night.
Not all oppositions of Mars result in a spectacular brightening of the red planet. In 2003 we were closer to Mars than we’d been in 60,000 years. All the planets orbit the sun in elliptical orbits; but the orbit of Mars is a more oval than Earths. Since Earth’s orbit is almost circular our distance from the Sun only varies by 3% during the year. Mars more oval orbit results in a variance of 20% in distance from the Sun. So when Mars and Earth pass each other in their orbits they are not always the same distance from each other. Our closest approach to Mars at opposition can range from 34,600,000 miles to 64,000,000 miles so naturally how big and bright Mars can get every other year varies dramatically. Mars brightness at opposition can vary from -3 magnitude to -1.4 magnitude. Mars apparent size at opposition can be 10 times larger during a very close encounter than it appears when it is farthest from Earth.
Mars opposition this year is not as close as the last two close oppositions in 2003 and 2018, but Mars is higher in the sky this year making it easier to view in northern latitudes.
Try to catch Mars every clear evening to watch it brighten then start to fade in late October as we pull away from our neighboring planet.
Mars can look red, orange, yellow or gold in color to the unaided. Mars is about 1/2 the size of the Earth with a diameter of 4,000 miles but it is interesting to think our tiny neighbor has more land area than Earth since roughly 2/3 of the Earth is covered by water. Mars has ice caps that appear to grow and shrink with their seasons, which last roughly twice as long as seasons on Earth. Mars has a giant canyon named Valles Marineris that is 3,000 miles long and dwarfs our Grand Canyon coming in at 277 miles long. Mars is also home to a giant volcano named Olympus Mons. It would basically cover the state of Wyoming and is roughly 17 miles high roughly 2.5 times higher than Mt. Everest above sea level.
When Mars is near opposition that is the best time to view Mars through a telescope primarily because it appears larger then and you can see more detail. Even small telescopes can usually catch the polar ice caps and maybe glimpse dark markings on the planet. Clouds along the limb or global dust storms can be visible and obscure any surface detail. You’ll probably need at least an 8-inch telescope with a high power eyepiece to see some of the dark markings on its surface. Color filters can help you catch more detail. A blue filter will enhance the ice caps, a red filter will lighten the desert area and darken the rest of the planet, a green filter will aid the overall contrast.