Mercury starts October very low in the western evening sky. Greatest Eastern Elongation is on 12 October but the ecliptic is so low at sunset, Mercury is unlikely to be spotted from mid-UK latitudes. The planet is in inferior conjunction, directly between the Earth and the Sun, on 04 November but then starts a good morning apparition for northern hemisphere observers. Greatest Western Elongation (GWE) is on 21 November and Mercury can easily be followed before sunrise from around the 12th until the end of the month. For that period Mercury brightens from +0.7 to -0.68 magnitude, its illuminated phase grows from 21 to 83% while its apparent size falls from 8.5 to 5.6 arcseconds (5.6”). Look for Mercury low in the east-south-east from 06.00UT and watch it rise to over 10 degrees elevation before sunrise.
Mercury is at perihelion (closest to the Sun in its orbit) on 10 November. 16 days after this it has its largest radial velocity away from the Sun, which is of interest for observations of Mercury’s sodium tail. 16 days after perihelion is close to the GWE on 21 November so around and a little after that date the illusive sodium tail of Mercury will be well placed for imaging. The tail is visible in reflected sunlight but for much of Mercury’s orbit that light sits in a solar atmospheric absorption line and can’t be seen from Earth. Around 16 days before and 16 days after perihelion Mercury’s radial velocity towards or away from the Sun, Doppler-shifts that light out of the absorption line making it visible. Specialist sodium band pass filters will make it more obvious but the tail has been imaged with just a DSLR if the sky is exceptionally transparent.
Venus reaches inferior conjunction on 24 Oct and, like Mercury in early October, is not really visible to UK observers. From the start of November it can be seen in the morning, rising in the east-south-east from around 06.00UT but will be lost to the sunrise within around 40 minutes. Late in November it rises from around 04.00UT and becomes once more a spectacular ‘morning star’. It will shine at -4.6 magnitude and climb 25 degrees high in the south-south-east by sunrise. The very narrow crescent of the waning Moon is close by on the morning of 07 November making a photogenic pairing.
In early October, Mars rises a little before midnight UT and is well up in the south-east by sunrise (around 05.25UT). At that time it will be nearly 50 degrees high for much of the UK, sitting below Castor and Pollux and shining slightly brighter than that pair at +1 magnitude. At 5.7” in apparent size it will start to show real detail to both observers and imagers and will steadily improve through the period. The Moon will be very close on the morning of 05 October. Mars’s subsequent motion will carry it through the constellation of Cancer, passing directly through M44, the Beehive Cluster, from the 10th to the 12th.
By Early November Mars rises around 23.00UT and reaches nearly 55 degrees high at sunrise, almost due-south. Its will have moved steadily from Cancer towards Regulus in Leo and will be joined there by Jupiter, the pair growing ever closer until 16 November when Mars will sit above and just over 1 degree from Jupiter. Mars will be shining at +0.7 while Jupiter is much brighter at -2.1 magnitude. Late in November Mars rises around 22.35UT and transits, due south, 50 degrees high at 05.40UT, still in darkness. It will sit next to Regulus and be noticeably brighter. Its apparent size will be nearly 8” by then.
As mentioned, Jupiter is a morning object that improves in visibility throughout the period. Rising around 01.25UT early in October, it chases Mars up the ecliptic and reaches around 40 degrees elevation towards the south-east at sunrise. At 33.4” in apparent size it will show great detail in steady morning skies. Mid-period, Jupiter rises just before midnight UT and will be lost to dawn just before it passes due-south around 06.50UT. Late in November Jupiter-rise is at 22.10UT and transits at 05.20 in full darkness. At 39” in size it will be a spectacular target.
November sees a number of observable ‘Mutual Events’ between the four main moons of Jupiter. This means our viewpoint allows us to see one moon pass in front of another causing an occultation (O) or the shadow of one moon to fall on the face of another, known as an eclipse (E). No observable night-time eclipses occur for the UK in November but the following occultations are visible:-
04 November 02.22 to 02.29 Ganymede (O) Io
07 November 04.12 to 04.24 Europa (O) Ganymede
08 November 04.34 to 04.40 Io (O) Ganymede
11 November 05.13 to 05.20 Ganymede (O) Io
Saturn is at opposition on 04 October, so is the most accessible planetary target in the period being on show for nearly all the hours of darkness and close to its best in the comfortable early evening hours through November. Find it due-south at midnight UT, nearly 40 degrees high for much of the UK on opposition night. Its slightly flattened disk will stretch 19.7” across the equator while the rings extend to 45.9”. The southern aspect of Saturn is tilted towards us so we view the ‘underside’ of the ring system which, in early October, is tilted 7.6 degrees away from exactly edge-on. This is a much more open view than at the last opposition and Saturn is also higher in the sky making this an excellent period to view it. The well known ‘Opposition Surge’ effect may make the rings appear particularly bright a day or so either side of opposition night.
Mid period, Saturn will transit around 21.53UT and late in November at 19.54UT. Its elevation at transit will have dropped a couple of degrees by then and its size shrinks to 18.7” across the disk; 43.5” for the rings which will have then closed slightly to 6.1 degrees.
Uranus is also a small but viable target sitting in Taurus, midway between the Pleiades cluster (M45) and bright Aldebaran; the ‘eye’ of the Bull. South transit in early October is at 03.31UT with Uranus around 58 degrees high. Its pale green disk will only be 3.7” across, shining at +5.67 magnitude so track down a faint green ‘star’ in that region and add power to see its disk. Early in November Uranus transits at 01.30UT, still 58 degrees high, while late in the month transit is close to midnight UT as the planet comes to opposition on the 25th. On that night, the Moon is nearby which will not help finding a faint target but I do recommend trying to observe Uranus sometime in this period even if only to tick it off a list.
Neptune starts October a little past opposition and is harder to find. South transit will initially be at 23.30UT with this distant ‘ice-giant’ 37 degrees high from mid UK latitudes. It sits in a region of faint stars between Pisces and Cetus so, in this period, is most easily found by scanning west from Saturn along the path of the ecliptic. The pair are 9 degrees apart initially, 7 degrees in early November when Neptune transits at 21.25UT, and 6.5 degrees late in the period. By then south-transit will be at 19.30UT, still 36 degrees high. Neptune is below naked eye visibility at around +7.7 magnitude and is just 2.36” across throughout this period. Like Uranus, scan for a tiny, slightly fuzzy blue-green ‘star’ and add power to capture its disk.
Alan Clitherow