The author shares his encounters with Mars at perihelic opposition over the course of his years as an amateur astronomer.

Many stargazers know Mars makes a close approach to Earth every 15 to 17 years. These events, called perihelic oppositions, happen when the Sun, Earth, and Mars line up, with Mars on the opposite side of Earth from the Sun. Additionally, Mars is at its perihelion in its orbit, when it's closest to the Sun. We cherish these oppositions because Mars, being only half the size of Earth, needs to be close for us to see detail on its surface. Even though we pass the planet every two years due to our faster orbital velocity, the close pass between the two planets can vary from 35 million miles to 62 million miles. This year, the magic moment arrived on July 31st, when we came within 35.8 million miles of the mysterious red planet. The planet displayed a disk size of 24.3” arcseconds, which is about as big as it can get. (In the last close approach of 2003, Mars was only 34.6 million miles away and 25.11" in diameter.)

A lifelong dream realized — Roadrunner Observatory in the author's backyard at the base of the Superstition Mountains 35 miles east of Phoenix near Gold Canyon, Arizona
Bill Dellinges

It’s interesting (at least to me!) to look back at my Martian history (no, I’m not from Mars). My first experience of a Martian perihelic opposition occurred in 1956. I was a 13-year-old budding amateur astronomer armed with a funky but serviceable Criterion 4-inch Newtonian reflector. At the next pass in 1971, I had a 4-inch Unitron refractor — no gain in aperture but much better resolution! By the 1988 event, I had two new instruments that provided me with the best views of Mars I’ve ever had: a Celestron C-14 and a 5-inch APO refractor. Having finally joined the GoTo world in 2006, I have since replaced the C-14 with a Celestron CPC-11. This year, I was looking forward to my fifth close approach of Mars when the bad news arrived that Mars was experiencing one of its infamous dust storms.

Mars as imaged by Associate Editor Sean Walker on August 17, 2018 through a 12.5" Newtonian.

My first couple of looks at Mars in early August showed a nice large, orange disk completely devoid of any surface detail. Then came reports that the dust storm was clearing. Sure enough, on August 15th I could detect dark markings and the south polar cap on Mars — the Martian global dust storm had definitely abated! By comparing what I was seeing with a map of Mars, I saw that I had observed the prominent markings known as Syrtis Major, Sinus Meridiani, and the Hellas Basin. A great wave of relief swept through me. I had feared the dust storm might preclude any chance of seeing the Martian surface. Now I could get down to business.

Several resources aided me in identifying features on the planet. Sky & Telescope magazine has a handy “Mars Profiler” tool, where you can find which side of Mars is facing Earth on any given date and hour. I also have a Mars map that I copied from S&T back in June 2003 during the last apparition. Lastly, my 12-inch Mars globe helped me refamiliarize myself with Mars’s prominent surface features. (Disclaimer: I’m not getting any kickbacks from S&T!)

Now, don’t lament that you’ll have to wait another 17 years to witness the next perihelic opposition of Mars in 2035. That is, you do. But fear not, nature provides a loophole. If you check an ephemeris, you’ll notice that Mars still puts on a respectable performance two years before and after a perihelic opposition. Take for instance the next opposition on October 13, 2020. The closest approach to Earth occurs on October 6th, when Mars will be 38.58 million miles away with a disk diameter of 22.56”. Not bad. Better yet, its declination of +5o 27’ (compared to the current -25o 30”) puts it higher in the sky, meaning less atmosphere your telescope needs to punch through, and that means better resolution. We might see more detail on Mars in 2020 than this year, and maybe even one of Elon Musk’s Martian settlements…


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September 6, 2018 at 3:25 pm

Very good report here. The heliocentric solar system is on secure and firm footing in prediction and observations in astronomy - using good telescopes (unlike some YouTube videos promoting another universe, e.g. flat earth - geocentric view). A very fine image of Mars too taken on 17-Aug-18 using a 12.5 inch telescope. I enjoyed some great views of Mars using my 10-inch telescope on 23-Aug-18, [Great views of Mars tonight using the XT10i with Orion Sirius 10-mm plossl and TeleVue 1.8x barlow lens for 216x view and 0.24 degree true field of view. Mars was much brighter in the XT10i view than the 90-mm at 180x. Much more surface detail visible and color was yellow-orange. CM = 209 degrees at 2200 EDT with Utopia and Syrtis Major dark areas.]

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September 7, 2018 at 11:51 am


I congratulate anyone who is "mainly a visual observer." Comet Arend-Roland was about two years in your future when you became an amateur astronomer. Did you observe it?

I had a friend in 1976 who managed to get his hands on a Criterion 4-inch - it had great optics!

Doug Z

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September 8, 2018 at 11:53 am

No. I wasn't into comets till the 70's with Bennet and Kohoutek. Now I like to go after them. Though not an imager, I did take a pic of Hale-Bopp in 1997. To my surprise APOD asked me for in in 1999. See it there on 9/9/99.

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September 7, 2018 at 6:56 pm

IIRC, oppostions in July and August seemed the ones most plagued by dust storms (I remember one of the Mariner probes arrived at Mars in August 1971 during a very bad dust storm). The storms seem to be easing, so the 2020 opposition in October, besides being higher in the sky, occurs later in the year and probably won't have as bad a problem with dust as this year's opposition did.

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