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

August 31, 2018
Northern-Sun Print
Ps. 19:1 The heavens declare the glory of God; the skies proclaim the work of his hands. September. Hot and muggy. Kids back in school but then sent home early because it’s too hot in the unairconditioned classrooms! That’s what usually comes to mind first when I think about September. Right on the heels of those thoughts comes thoughts of nice, clear nights - not too cold, but with lots of dew is what usually comes next. Judging by the way things are going as I write this article in the last week of August, this year’s September is quite likely going to start out that way. Time to get that order in for a new Dew Zapper for my telescope and guidescope! I’m going to want to keep those optics dew free and you will too because the four planets that have entertained us all summer are quickly heading west, setting earlier and earlier. We’ll need clear, clean optics to get the best views before they get too low to see well through the thick atmosphere near the horizon. And, Comet 21P/Giacobini-Zinner has returned. Some say this time around, it might become visible to the unaided eye this month. There haven’t been any naked-eye comets to watch for several years so let’s talk about the comet first. Comet 21P/Giacobini-Zinner was first discovered discovered by astronomer Michel Giacobini at the Côte d’Azur Observatory in Nice, France on the night of December 20th, 1900. It was recovered two orbits later by Ernest Zinner on October 23rd, 1913. This comet does not usually get very bright, generally only around +8th magnitude. Most people cannot see objects fainter than around +7.4. This year, though, 21P/Giacobini-Zinner will pass very close to Earth on September 11th. Now when I say, “very close” I don’t mean we are in any danger of colliding with it - it will still be 0.392 AU (36.5 million miles) away - but that’s still pretty close for a comet! Comet 21P/Giacobini-Zinner is no stranger to the inner solar system. It has a period (orbit) of only 6.6 years and every year we pass through the dust it leaves behind creating the annual Draconid Meteor Shower. Since this comet has made many trips close to the Sun, it does not usually boil off a lot of dust anymore and that dust is what makes the streaks we call meteors, flash across the sky. There have been a few exceptions though. For example, in 2011, the Draconids topped out at a zenithal hourly rate of 400 meteors per hour! I have not heard anyone predicting anything like that for this year, but you just never know, so if the weather cooperates, it might be worth (In my opinion, it’s ALWAYS worth,) getting out under the stars and just enjoying the beautiful sky and cool evening air. Adding some pretty meteors are like icing on the cake and lots of meteors is like icing with sprinkles! Closest approach will be September 11th but we won’t plow through the stream until October 7th and 8th. The moon will be new on October 9th so the waning crescent should not interfere much with the shower. As far as the planets this month, Venus sets about 2 hours after the Sun at the beginning of the month (a little after 9 PM) and a little after 7 PM at the end of the month. Venus goes from almost 50% lit on the 1st to only about 17% lit on the 30th - a very pretty crescent! In order to see the phases of Venus, you will need at least a small telescope at 35X to 50X magnification of more. On the 30th, Venus will appear about 46” (46 arc seconds) wide. Because it is so bright, I find it is usually best to observe Venus while the sky is still blue and my pupils have not opened too much. Moving to the southwest, Jupiter is still shining very brightly and will also be visible in the twilight sky. Jupiter does not set until around 10:30 on the first, but by the 30th disappears below the horizon a little before 9! Jupiter is “between the claws” of the Scorpion this month. On the first it is very close to the southern claw: Zubenelgenubi (don’t you love saying that name?). As the month goes on, Jupiter pulls away from Zubenelgenubi and forms a nice almost equilateral triangle with the southern claw and Zubeneschamali. I love how that one rolls off the tongue too, don’t you? Just don’t try to say them too fast; you might break something! Moving farther to the east, we find Saturn still hanging out just above the teapot asterism in Sagitarius. Saturn is always a treat in the eyepiece of a good telescope. Do try to get out with your favorite local astronomy club and make sure someone aims a scope at this jewel of the Solar System for an unforgettable astronomical treat! Clear Skies!

Article Photos

Milkyway image by Jim Bonser

 
 

 

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