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Monthly Newsletter of the Durban Centre November 2016

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Monthly Newsletter of the Durban Centre November 2016 Page 1 Monthly Newsletter of the Durban Centre November 2016 Page 2 Table of Contents Chairman’s Chatter ………………………………………...……… 3 Touring Clusters and Stars in Ophiuchus ……………..……… 4 At the Eyepiece ……………………………………..…………….... 8 A Strange Little Planet …………………………………………….. 9 The Cover Image - Trifid …..….……..……………...…………… 10 The 5 Numbers That Explain a Telescope ........……………… 12 Bits and Pieces ...……………………………..…………………… 16 The Month Ahead ..…………….…………………………...……... 17 Inaugural SA - China Bilateral Conference ………………….... 18 Minutes of the General Meeting 12 October 2016 …………… 19 Supermoon …………………………………………………………. 19 Public Viewing Roster ……………………………………………. 20 Member Submissions Disclaimer: The views expressed in nDaba are solely those of the writer and are not necessarily the views of the Durban Centre, nor the Editor. All images and content is the work of the respective copyright owner Page 3 Chairman’s Chatter By Mike Hadlow Dear Members, The year is nearly over and we seem to be fully into the rainy season with both of our last public viewings being cancelled because of either cloud or rain. In addition, we were to view the moon on ‘International Observe the Moon Night 2016’ which occurred on 8 October and attend the Toti Conservancy Full moon walk on the 16th but both these nights were cloudy and raining and the events never took place. We must however be thankful that we’ve had some good rain over the last month. On other fronts the society was busy with other activities including sending representatives to the Urban Breakfast hosted by the eThekwini Municipality and our public relations representative Logan Govender being a guest speaker at both a Rotary and Progress luncheon meetings. The workshop on the operation of the society’s telescope by members of the society for public viewing was completed. Thanks to those who participated we now have eight teams to assist in public viewings. A viewing roster has been prepared and will be published on our website. Our guest speaker for the monthly meeting held on the 13th was Prof Mike Watkeys, his talk was titled, “How geologists know there has been climate change through geological history”. Being a geologist I found it really enjoyable, confirming many of my beliefs about climate change and I’m sure all present really enjoyed it. Our last formal general meeting of the year will be held on 9 November and the main speaker will be Logan Govender. The December general meeting will be held on 14 December and will be our end of year annual dinner. On this point please give your name to Richard if you will be attending the annual dinner. Remember, this will be the night of our raffle draw and you may come away from the evening with a new telescope. Please everyone get those ticket sales in. Also, Richard has reminded me to ask those of you who have not yet paid your membership fees please to do so. Whilst on the subject of money please remember to pay Richard for Sky guides you may have ordered. The next public viewing will be on the 28 October but unfortunately rain is predicted and it will likely be cancelled. Looking forward to seeing you all on 9 November. Wishing you clear skies and great viewing. Mike Page 4 Touring Clusters and Stars in Ophiuchus August 13, 2016 By Brian Ventrudo As befits a large constellation at the edge of the Milky Way, Ophiuchus is packed with deep-sky sights for observers with small and large telescopes. Open and globular star clusters abound here, along with many fine double stars. Let’s have a short tour of a handful of the highlights of the constellation, moving from easy objects to more difficult sights. One of my favorite regions of the sky is centered near the little asterism called Taurus Poniatowski. The little bull-shaped asterism on the northeastern edge of Ophiuchus is easy to spot in dark sky. It was named in 1777 by Abbe Poszobut after King Stanislaus Poniatowski of Poland. It’s a pretty little group. In binoculars, the background is flecked with fainter 9th and 10th-magnitude stars that straggle off the western edge of the Milky Way. The V-shaped head of the bull consists of three stars: 67, 68, and 70 Ophiuchi. The two stars at the back end of this little beast are γ and β Ophiuchi (Cebalrai). Page 5 … Ophiuchus The region in and around Taurus Poniatowski in the constellation Ophiuchus. This maps shows the asterism as well as star clusters IC 4665, IC 4756, NGC 6633, and planetary nebula NGC 6572. Now grab your telescope and direct your optics and attention to the star 70 Ophiuchi in the head of Taurus Poniatowski. 70 Oph is one of the best-known and widely studied binary star systems. It’s relatively nearby, just 16 light years away. You’ll need about 75x to resolve the pair cleanly with a telescope. The two components of 70 Oph have magnitude 4.2 and 5.9; the brighter star is yellow-gold while the fainter looks orange-red, with some observers reporting a tinge of violet. The pair is separated by about 5″. Move your telescope out of focus just a touch to see the colours best. Each star has an intrinsic brightness only a fraction that of our Sun. The components of 70 Oph complete a revolution about their common center of mass in just 88 years. So this is one of the few double stars you can see move appreciably during a human lifetime. Wide-angle image of the region of Taurus Poniatowski showing open star clusters IC 4665, IC 4756, and NGC 6633. Page 6 … Ophiuchus Up for a couple more open clusters? Then look east and slightly north of the head of Taurus Poniatowski to see a pair of splendid star groups, NGC 6633 and IC 4756. Some call this pair the “Ophiuchus Double Cluster”, which isn’t exactly accurate because the latter lies just over the border in the constellation Serpens Caput Cauda. IC 4756 is much larger, covering a full degree of sky, so it’s an excellent cluster for observing with binoculars or with low magnification in a telescope. NGC 6633 is smaller and tighter and can handle a little more magnification. Both clusters are the same distance away, about 1,300 light years, so their comparative sizes reflect their true dimensions. Open cluster NGC 6633 Now to a couple of globular clusters. The pair M10 and M12 inside the pentagon of Ophiuchus are fainter than the more famous globular cluster M5 in Serpens. But they still look good in a small scope. M10 lies just 1o west of the orange star 30 Ophiuchi. M10 appears brighter than its neighbour M12, and certainly more concentrated towards the center. The cluster is visible in binoculars or a finderscope as a dim smudge. In a 4” scope at 70x, you will see some granularity on the outer edges of the cluster. A 6” or larger scope resolves a couple of dozen stars towards the center. M12 is just 3o northeast of M10. The two are visible in the same finder field of view, and even in a wide-field telescope at low magnification. The cluster is certainly less dense than M10, and a good 6” scope may resolve some stars near the core. Try a range of magnification to see what works best for you. M10 lies some 14,000 light years from Earth, while M12 is about 16,000 light years distant. Since they are physically separated by just 2,000 light years, a planet around a star in either cluster would see the other cluster shine at a brilliant 2nd magnitude M 10 M 12 Images by John Gill Page 7 … Ophiuchus Location of globular clusters M10 and M12 in the pentagon of Ophiuchus. Back to Taurus Poniatowski for the most challenging object on this tour, the pretty little planetary nebula NGC 6572, sometimes called the “Emerald Eye Planetary”. The name comes from the somewhat greenish hue of this small bright gem-like nebula. The colour comes from the light emitted by OIII oxygen ions excited by the nebula’s hot central star. Look for this little celestial jewel above the horns of Taurus Poniatowski, and about 1.3o southeast of the star 71 Ophiuchi (see the first map at the top of the page). This 8th-magnitude nebula appears quite small, so it looks star-like at low magnification (<50x). The nebula reveals a small disk only at 70x or higher. Try as much magnification as you can to bring out detail in this tiny object. At 100x, you may begin to see a diffuse elliptical halo. Try an OIII or UHC filter if you have one to bring out more contrast and detail. Most planetary nebulae last for just 50,000 years or so before they expire, which is not long in astronomical terms. But NGC 6572 is young even by these standards: it’s just 2,600 years old. So it will likely expand, dim slightly, and change its shape slowly over the coming centuries. Page 8 At The Eyepiece For November 2016 by Ray Field THE MOON is First Quarter on the 7th, FULL on the 14th, Last Quarter on the 21st and NEW on the 29th. The Moon is near Saturn on the 2nd, Venus on the 3rd, Mars on the 6th, Aldebaran on the 15th, Regulus on the 21st, and near Jupiter and Spica on the 25th. (See diagrams at the bottom of pages 52 and 53 of SKYGUIDE for the relevant positions of the Moon and planets.) MERCURY is visible low over the west in the evening in the twilight.
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