Popular Astronomy

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Fri, 29 Sep 2017 - Looking forward to October and November

In this period only the Ice Giant planets are visible at reasonable elevation at night with Uranus the best placed, reaching opposition on the 19th of October. The other major planets are only visible in the morning or early evening sky and at relatively low elevations, but some very interesting conjunctions occur in this period.


Having been reasonably well-placed in the morning sky in September, Mercury passes behind the Sun, in superior conjunction, on the 8th of October, so for the rest of the month is effectively hidden from our view. In November Mercury slowly becomes more accessible as an early evening object and reaches its greatest eastern (evening) elongation from the Sun on the 24th of November when it will trail the Sun by 22 degrees. It is not, however, well placed for observation from the Northern Hemisphere and on that date you may just glimpse it at around 1645 UT, 4 degrees below Saturn on a compass bearing of 225 degrees; just above the horizon in a darkening sky. As usual the further south you are the better your view; equatorial observers seeing Mercury in full darkness for nearly an hour on the 24th.


At the start of the period Venus rises at around 0350 UT, slightly north of due-east in the morning sky, and reaches some 22 degrees of elevation by sunrise at mid-UK latitudes. It shines at an obvious magnitude of -3.9 throughout the period and is a beacon of light above the horizon. In this position it is occasionally reported as a UFO so watch for interesting reports in the local papers! At more than 90% illuminated its size is relatively small, at little over 10 arcseconds in apparent diameter, but this is large enough to record subtle detail with infrared or ultra-violet photography. The planet can be followed into the morning sky and viewed at higher altitudes if sensible precautions are taken and the Sun kept well-away from either the viewfinder or the main telescope.


On the 5th of October Venus lies very close to Mars, a telescope of moderate focal length such as an ED80 or similar will easily catch both planets in the field of view of eyepieces down to around 10 mm and, again, the pairing can be followed into daylight for extended observation. Another excellent pairing happens on the 13th of November when Venus and Jupiter are separated by just 0.3 of a degree; look for them from around 0630 UT, at 5 degrees of elevation a little south of due east, when the same telescope and eyepiece combination will give a stunning view of this planetary pair. Do beware however as the duo are only separated from the Sun by 14 degrees on this date so take exceptional care to avoid blindness or equipment damage; the Sun rises shortly after 0730UT.


As mentioned, Mars is a low-down morning object, only slowly increasing in visibility through the period. In early October Mars rises at around 0410 UT for mid-UK latitudes, keeping close company with Venus but at a much less obvious magnitude of +1.8.  It is just 3.7 arcseconds in size and hardly grows any larger in the period. By early November it rises at 0355 UT and at 0345 UT by the end of the period when it can be followed for nearly 4 hours until a little before sunrise. Its northern hemisphere will be tilted somewhat towards us but since the end of November this year coincides with mid-summer on Northern-Mars there is only a slight chance of glimpsing a bright polar ice cap.


Jupiter is also a morning object but is rising in daylight for much of October. By Early November it might just be glimpsed in a brightening sky but wait for the end of the period for the best views. Do not miss its conjunction with Venus on the 13th of November, and from then on it can be followed from around 0605 UT rising in dark skies and observed into daylight with care. It will be interesting to watch for any major changes in its systems of belts and zones that have been hidden from amateurs over the last couple of months.


Saturn can now only be seen in the early evening skies. In early October look for it 20 degrees west of south from 1830 UT and follow it as the sky darkens, setting around 2045 UT. Initially its elevation above the horizon will be barely more than 10 degrees and this worsens throughout the period. By early November you can catch it from around 1730 UT in the darkening skies of late autumn but the planet is effectively then lost from mid-month onwards.


Which brings us to the Ice-Giants of Uranus and Neptune. These are the only planets visible well into the night during this period and Uranus reaches opposition, due-south at midnight UT, on the 19th of October when it will be at some 46 degrees of elevation above the horizon. Perhaps the best order to observe them is Neptune first, as that outermost of the major planets is past opposition and is already subsiding towards the west after midnight. In early October Neptune rises around 1700 ut in early-evening twilight and transits due south at 2220 ut; reaching some 30 degrees of elevation at that time.  Transit time mid-period is at 2015 ut and by the end of November this becomes 1820 ut, so viewing earlier in the period gives more extended observing time. It can be found close to the star λ Aquarius, also known as Hydor; a ‘finder chart’, usable until at least the middle of the period and with more information on observing both Neptune and Uranus, can be found on the SPA website at the following address:-




Neptune’s tiny blue-green disc is just 2.4 arcseconds in apparent size and shines at a distinctly telescopic magnitude of +7.8. At the eyepiece it will show nothing but some subtle colour shading but larger telescopes equipped with planetary cameras and filters designed to pass deep-red and infrared wavelengths may catch large pale storm features in the upper atmosphere. Tracking these features is important to planetary science and I would welcome any such images being sent in to the section.


The same can be said of Uranus. After catching Neptune swing your telescope across to the stars of Pisces and look a little more than a degree west and north of ο Psc (Torcularis Septentrionalis); again there is a finder chart at the above web address. Uranus’s slightly larger apparent size, greater elevation and increased brightness, on the edge of naked eye visibility from a dark site, make it easier to observe than Neptune and the same imaging-telescope, filter and camera will produce pictures with subtle banding and possibly more atmospheric storm features. By the end of the period Uranus transits due-south at 2105 ut, some 46 degrees above the horizon, so is very well placed for extended and detailed observation. Very well equipped observers may find it possible to image the rings of Uranus; please follow the links mentioned above for more information.



Added by: Alan Clitherow