The Planets in December and January.

With Mercury and Venus on show in the morning sky, Mars still observable in the evening and Uranus showing new storm features at night, there is plenty to see in this observing period.

Mercury emerges from conjunction between the Earth and the Sun to appear in the early morning skies of December, putting on a good show for UK observers. On the 15th of the month Mercury reaches its greatest elongation to the west of the Sun, 21 degrees on this occasion, and is well placed for observation for a week either side of this date. Look for Mercury appearing on the south-easterly horizon from around 06.20 UT and then follow it as it rises, reaching 10 degrees of elevation by sunrise. Mercury keeps close company with Jupiter at this time and between the 21st and the 23rd of December they are only 1 degree apart. On New Year’s Day Mercury forms the lowest and most easterly element of a spectacular line up in the morning sky. Look for the waning crescent Moon, Venus, Jupiter and Mercury drawing a descending diagonal from due-south down to the south-eastern horizon.

After this, Mercury sinks closer to the Sun, morning on morning, moving towards superior conjunction behind the Sun at the end of January. If you do intend to watch the dance of the planets in the pre-dawn skies of January please remember to look west around 0511UT on Monday the 21st of January to watch the total eclipse of the Moon.

As mentioned, Venus is also in the morning sky during this period and from early December it becomes more and more obvious as it draws further from the Sun. In early December Venus gains more than 25 degrees of elevation in the south-east before sunrise and can easily be followed into daylight for observation at higher altitudes. On the 1st it shines at magnitude -4.65 and shows a 26% illuminated disc, increasing to 43% by the Christmas period. Greatest western elongation from the Sun, with Venus stretching 47 degrees from it, occurs on the 6th of January. On this date the visible phase should be exactly 50% however it is expected that the 50% phase will be seen a few days later. This is known as the SchrÖter effect after the Astronomer, Johann SchrÖter, who first noticed it in the late 18th Century. Usually 50% phase (dichotomy) is seen a few days late for morning apparitions and a few days early for evening ones. This effect is seen not just visually but also photographically and is thought to arise from the scattering of different wavelengths of light within the thick atmosphere of the planet.

Venus responds well to both infrared and ultraviolet imaging with low-contrast cloud features appearing at different depths in the atmosphere as revealed by these filters; an obvious phase difference can often be seen between the ultraviolet and the infrared on the same day. Later in the period Venus draws closer to the Sun again but remains an excellent observing target. Venus also draws closer to Jupiter; they are closest on the 22nd of January when they are 2.25 degrees apart.

Mars is becoming distant and small when seen from Earth however the rise of the ecliptic towards mid-winter means that the red planet appears much higher in UK skies than it did at opposition back in July. In early December Mars transits due-south around 1815UT at nearly 30 degrees of elevation and by New Year’s Eve transit time is in evening twilight at more than 35 degrees. After this Mars can still be followed into full darkness at considerable elevation with transit over 40 degrees up by the end of the month. Brightness falls from magnitude 0.0 to +0.8 and apparent size from 9 arc-seconds to 6 as the period progresses so it is best seen earlier in the period if possible. Look for Mars as darkness falls on December the 7th and find Neptune in the same eyepiece view, just 6 minutes of arc apart!
Like Mercury and Venus, Jupiter is moving into the morning sky in early December, and has its close conjunction with Mercury late in the month. Jupiter is certainly a good observing target, easily followed into morning daylight, as long as the usual safety precautions are taken. By January Jupiter is rising 2 hours before the Sun and this stretches to nearly 3 hours late in the month. Its brightness increases slightly from magnitude -1.7 to -1.9 and its apparent size grows from 31 to 33.5 arc seconds, meaning this is an excellent period to detect any large-scale changes in atmospheric features that have occurred while the planet was otherwise too close to the Sun for safe or effective observation.

Throughout December and January Saturn is, unfortunately, very close to the Sun as viewed from the Earth. On the 2nd of January the Sun and Saturn are in conjunction, that is they line up from our point of view, so the planet is unobservable safely for most of this period. You may glimpse Saturn right at the end of January, rising due south-east at around 0715UT.

Uranus is past opposition so will now transit before midnight then sink towards the western sky but is still the best late-night planetary target, riding relatively high against the background stars of Pisces. The planet is on the edge of naked-eye visibility, especially from a dark site, but is quite obvious in binoculars as a slightly de-focussed green ‘star’, which becomes a planetary disc under moderate to high magnification through a telescope. Uranus transits in full darkness at 2215Ut on December the first, around 1925Ut during the Christmas period and at the end of January in early twilight rather than darkness, at 1730UT. Transit is at over 45 degrees of elevation from the UK so Uranus is well placed for imaging throughout the period. Colour cameras show a green or blue-green disc with some subtle shading while monochrome cameras and deep-red or near infra-red filters may show some banding or even bright cloud features on this distant icy world.

I have been informed by the well-respected European amateur Marc Delcroix that a new, large-scale, storm feature has been discovered in the atmosphere of Uranus by American Blake Estes. The storm appears as a patch on the border of the bright northern polar zone and extends somewhat into the darker latitudes below it. Based on the observations made so far Marc has calculated the following “tentative ephemeris” for the storm. The main point of note is the estimated central meridian transit times for the storm; observations near these times on the dates given should help to tie down the exact rotation rate of the storm around the planet.

WinJUPOS 10.3.11 (Uranus), C.M. transit times, 2018/11/14  10:06
Object longitude: L = 270,0° – 24,7470°/d * (T – 2018 Oct 09,5)
Output format: Date UT (C.M. of System 1)
——————————————————————————
2018 Nov 26   04:16 ( 170°)
2018 Nov 27   13:07 ( 136°)
2018 Nov 28   05:33 ( 119°)   21:59 ( 102°)
2018 Nov 29   14:25 (  86°)
2018 Nov 30   06:50 (  68°)   23:16 (  51°)
2018 Dec 01   15:42 (  35°)
2018 Dec 02   08:08 (  18°)
2018 Dec 03   00:34 (   1°)   16:59 ( 344°)
2018 Dec 04   09:25 ( 327°)
2018 Dec 05   01:51 ( 310°)   18:17 ( 293°)
2018 Dec 06   10:43 ( 276°)
2018 Dec 07   03:08 ( 259°)   19:34 ( 242°)
2018 Dec 08   12:00 ( 225°)
2018 Dec 09   04:26 ( 208°)   20:52 ( 191°)
2018 Dec 10   13:17 ( 174°)
2018 Dec 11   05:43 ( 157°)   22:09 ( 140°)
2018 Dec 12   14:35 ( 124°)
2018 Dec 13   07:01 ( 107°)
2018 Dec 14   15:52 (  73°)
2018 Dec 15   08:18 (  56°)
2018 Dec 16   00:44 (  39°)   17:10 (  22°)
2018 Dec 17   09:36 (   5°)
2018 Dec 18   02:01 ( 348°)   18:27 ( 331°)
2018 Dec 19   10:53 ( 314°)
2018 Dec 20   03:19 ( 297°)   19:45 ( 280°)
2018 Dec 21   12:10 ( 263°)
2018 Dec 22   04:36 ( 246°)   21:02 ( 229°)
2018 Dec 23   13:28 ( 213°)
2018 Dec 24   05:54 ( 196°)   22:19 ( 178°)
2018 Dec 25   14:45 ( 162°)
2018 Dec 26   07:11 ( 145°)   23:37 ( 128°)
2018 Dec 27   16:03 ( 111°)
2018 Dec 29   00:54 (  77°)   17:20 (  60°)
2018 Dec 30   09:46 (  43°)
2018 Dec 31   02:12 (  26°)   18:38 (   9°)
2019 Jan 01   11:03 ( 352°)
2019 Jan 02   03:29 ( 335°)   19:55 ( 318°)
2019 Jan 03   12:21 ( 301°)
2019 Jan 04   04:47 ( 285°)
2019 Jan 05   13:38 ( 250°)
2019 Jan 06   06:04 ( 234°)   22:30 ( 217°)
2019 Jan 07   14:56 ( 200°)
2019 Jan 08   07:22 ( 183°)   23:47 ( 166°)
2019 Jan 09   16:13 ( 149°)
2019 Jan 10   08:39 ( 132°)
2019 Jan 11   01:05 ( 115°)   17:31 (  98°)
2019 Jan 12   09:56 (  81°)
2019 Jan 13   02:22 (  64°)   18:48 (  47°)
2019 Jan 14   11:14 (  30°)
2019 Jan 15   03:40 (  13°)
2019 Jan 16   12:31 ( 339°)
2019 Jan 17   04:57 ( 323°)   21:23 ( 306°)
2019 Jan 18   13:49 ( 289°)
2019 Jan 19   06:15 ( 272°)   22:40 ( 255°)
2019 Jan 20   15:06 ( 238°)
2019 Jan 21   07:32 ( 221°)   23:58 ( 204°)
2019 Jan 22   16:24 ( 187°)
2019 Jan 23   08:49 ( 170°)
2019 Jan 24   01:15 ( 153°)   17:41 ( 136°)
2019 Jan 25   10:07 ( 119°)
2019 Jan 26   02:33 ( 102°)
2019 Jan 27   11:24 (  68°)
2019 Jan 28   03:50 (  51°)   20:16 (  35°)
2019 Jan 29   12:42 (  18°)
2019 Jan 30   05:08 (   1°)   21:33 ( 344°)
2019 Jan 31   13:59 ( 327°)

The best way to capture it is with a larger aperture telescope using a monochrome planetary camera equipped with an infra-red pass filter; however certain one-shot-colour cameras have excellent sensitivity in the infra-red and can also be used with an IR pass filter to good effect. The main point is to try and capture this new storm if at all possible.

The same equipment can be used with good effect on Neptune with this target showing a slightly smaller disc at a distinctly telescopic magnitude of +7.85 against the stars of eastern Aquarius; look for it within 2 degrees of the star Hydor. Neptune is best observed in December or early in the New Year as it transits, due- south, at 1825UT in early December and at 1700UT by Christmas At these times it will still have some 30 degrees of elevation above the horizon but declines sharply to the west later in the period.

Alan Clitherow.