Tonight – as darkness falls on September 9, 2016 – look for the moon to be at or near its first quarter phase. The brightest starlike object in the moon’s vicinity tonight is the red planet Mars. Mars forms a picturesque triangle on the sky’s dome with two other bright celestial gems, the golden planet Saturn and the ruddy star Antares. Mars is the brightest of the three, followed by Saturn and then Antares.
Mars is much like our planet Earth in several respects. The inner planets – Mercury, Venus, Earth and Mars – are all terrestrial (rocky) worlds. In contrast, the outer planets – Jupiter, Saturn, Uranus and Neptune – are often called gas giants and have no solid surfaces.
But Mars is like Earth in ways that the other terrestrial planets are not. Mars’ axial inclination is nearly the same as Earth’s; and a day on Mars (from noon to noon) is almost the same as on Earth. Mars’s axial inclination is 25.19 o as compared to 23.4o for Earth; and a day on Mars is 24.7 hours long as compared to 24 hours on Earth.
Like on Earth, Mars has seasons. Like on Earth, Mars’ rotational axis tilts maximally toward the sun at the solstices. Just like on Earth, the sun shines at zenith (directly overhead) at the equator on the equinoxes – so neither the north pole nor the south pole leans toward the sun nor away from the sun on the equinoxes. However, the Martian seasons last about twice as long as they do on Earth because Mars takes nearly two Earth-years to orbit the sun.
Looking ahead, the dates for the upcoming Martian solstices and equinoxes:
Nov. 28, 2016: Southern solstice (South Pole maximally pointed toward sun)
May 5, 2017: Equinox (sun going from south to north)
Nov. 10, 2017: Northern solstice (North Pole pointed maximally toward sun)
May 22, 2018: Equinox (sun going from north to south)
Oct. 16, 2018: Southern Solstice (South Pole pointed maximally toward sun)
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We find a certain juxtaposition between Earth’s and Mars’ seasons to be very intriguing, as illustrated by the tables below. Whenever an opposition of Mars happens around the time of Earth’s March or September equinox, Mars is at or near a solstice.
Whenever an opposition of Mars occurs around the Earth’s March equinox, then the Martian North Pole maximally leans in the direction of the Earth and sun.
On the other hand, when a Martian opposition happens near Earth’s September equinox, then it’s the Martian South Pole that maximally leans our way.
We look ahead to the Martian oppositions in March 2029 and September 2035:
|Date of Martian opposition||Date of Martian northern/southern solstice|
|March 25, 2029||March 3, 2029 (northern solstice)|
|September 15, 2035||September 20, 2035 (southern solstice)|
Also, whenever an opposition of Mars happens around the time of a solstice on Earth, then it’s near an equinox on Mars. We look back at the oppositions of June 2001 and December 2007:
|Date of Martian opposition||Date of Martian equinox|
|June 13, 2001||June 17, 2001 (equinox – north to south)|
|December 24, 2007||December 9, 2007 (equinox – south to north)|
Mars is known for its 79-year and 284-year cycles, whereby the Martian oppositions recur on nearly the same calendar date.
Bottom line: On September 9, 2016, use the moon to locate the planet Mars, a world that has numerous similarities to our planet Earth. Also, look nearby for a second planet, Saturn, and the bright star Antares.
Bruce McClure has served as lead writer for EarthSky's popular Tonight pages since 2004. He's a sundial aficionado, whose love for the heavens has taken him to Lake Titicaca in Bolivia and sailing in the North Atlantic, where he earned his celestial navigation certificate through the School of Ocean Sailing and Navigation. He also writes and hosts public astronomy programs and planetarium programs in and around his home in upstate New York.