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By Jim Bonser (jbonser@usa.net)Touring the Skies

June 28, 2018
Northern-Sun Print
Ps. 19:1 The heavens declare the glory of God; the skies proclaim the work of his hands. “Greetings, greetings, fellow stargazers!” This was how Jack Horkheimer always opened his show on public television. Like this column, Jack usually stuck to what you could see in the night sky with nothing more than your eyes or, occasionally, binoculars. I miss Jack - he passed away in August of 2010. I started watching Jack’s show called ‘Star Hustler’ soon after I renewed my interest in astronomy in the early 1990’s. When the internet came along, Jack renamed his show to ‘Star Gazer’ because suddenly searching for the old name was returning hits by the search engines that were not suitable for children (or anyone else, for that matter). I liked Jack’s friendly, simple approach to describing the constellations and the locations of the planets. His talks went a long way towards bring me up to speed as I learned my way around the night sky. I owe him a lot, and as I said, I miss him and his cheerful greeting. Jack would have been especially excited to talk about the planets visible this month, especially the Red Planet: Mars. Mars moves much more slowly in its orbit around the Sun than we do here on Earth and Mars is quite small, only about two times bigger than The Moon, or about half the diameter of Earth. The orbit of Earth around the Sun is almost a perfect circle but the orbit of Mars is not so perfect, in fact, Mars has one of the most eccentric orbits of all the planets (if you don’t count Pluto as a planet). All of this adds up to making it very difficult to observe any details on the Martian surface because Mars looks so small. Fortunately, every so often, the Sun and Earth and Mars line up at the same time that Mars is closest to the Sun. This means it is closer than usual, but don’t worry, there is no danger of a collision. Even at closest approach, we will be a little more than 57 million kilometers (over 35 million miles) apart. Mars won’t quite be at perihelion when it reaches opposition on July 26th. Perihelion doesn’t occur until September 16th so we are actually closest to Mars a few days later, on July 31th. Nevertheless because of the special circumstances we just talked about, astronomers give this rendezvous a special name: “perihelic opposition” because Mars is at perigee or closest to the Sun at or very near opposition. The last time there was a perihelic opposition of Mars was back in August of 2003. I remember that event very well. I was with a group of close friends at the Ames Area Amateur Astronomer’s observatory. We were all anxious to get the best view of Mars probably in our lifetimes. We were told back then that it was the closest we had been to Mars in thousands of years. It was a beautiful night, no clouds and pleasant temperatures and Mars looked amazing in the club’s 12” reflector. Let’s hope this one turns out as well. Mars will not be quite as close as it was in 2003 and so it will appear slightly smaller in a telescope than it did back then but not by much, only 0.8”. Remember, the double quote marks means arc-seconds to astronomers so you would read that .8 arc-seconds. There will be more close approaches of Mars such as the one in 2020, but we will have to wait until September of 2035 for another one as close as this so be sure to get out to your local astronomy club’s observatory and get a good look at the elusive surface markings of Mars! And while you are there, be sure to ask for a view of the other bright planets in the evening sky: Saturn, Jupiter and Venus. Jupiter will be around 30 degrees off the southwest horizon at dusk this month, setting near midnight. A bright gibbous Moon will stand only about 3 and degrees above Jupiter on July 20. Saturn is in Sagittarius about 4 degrees above Kaus Borealis (Lambda Sagittarii), the star that marks the top of the teapot asterism’s lid. This month, Mars starts out with roughly the same apparent diameter as Saturn’s disk: Mars 20.9” vs Saturn18.4”, but Mars ends the month with a very nice 24.3” appearing much bigger than Saturn in a telescope. Saturn’s rings are wide open and look spectacular in even a modest sized telescope. Mercury is visible at dusk in the first couple weeks of the month. A very beautiful crescent Moon will be a couple Moon diameters above Mercury on July 14th. Mercury will set about 9:30 that night so look for it early. Finally, Venus shines at an incredibly bright -4.1 magnitude above the western horizon on the 1st which increases slightly to -4.3 on July 31st. For comparison, Mars is at -2.8 at closest approach on the 31st and Jupiter goes from -2.3 on the 1st to -2.1 on the 31st. The Moon pays Venus a visit on the 15th. I hope the clouds stay away that night, it will be a beautiful pairing. I began by quoting Jack’s introduction to his show so I think it is only fitting to end this month’s article just as he did: “Always remember: Keep Looking Up!”.

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