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Thu, 19 Jan 2017 - Looking Forward; February and March 2017

Mercury starts this period well past its greatest western (morning) elongation from the Sun; so is drawing away from Earth and moving behind the Sun such that it will be in Superior Conjunction with it on the 7th of March. The apparent path followed by the planets is known as the ecliptic and at this time of year the ecliptic forms a very shallow angle with the south-eastern horizon as seen from the UK; as a result Mercury may only be glimpsed in the early part of February. This morning apparition will be much better seen by observers near the equator or further south. UK observers could try looking for it just breaking the horizon on a bearing of 130 degrees around 0700 ut during the first few days of February; after this Mercury is lost to us until around the 18th of March when it will reappear low in the west at dusk and then improve in visibility to the end of the period. Mercury reaches greatest eastern (evening) elongation from the Sun on the first of April so will be well seen from the UK in late March.


On the 20th of March at 1900 ut look for it almost due west at 5 degrees of elevation, at the same altitude and 10 degrees east of the much brighter Venus. On subsequent nights at the same time it will rise slightly higher, reaching nearly 15 degrees of elevation and just slightly north of due west on the 31st. It can then be followed until it sets around 2030 ut, in full darkness for mid UK latitudes.


In contrast, Venus is much better seen from the beginning of the period as it moves into inferior conjunction, between the Earth and the Sun, on the 25th of March. On the first of February it can be seen as a brilliant beacon in the western evening sky, visible for some 4 hours or more after sunset, but it is rapidly moving closer to the Sun so its period of visibility reduces, along with its illuminated phase as time goes on. It starts the period shining at magnitude -4.6 with a 39% illuminated disc some 31 arc seconds from pole to pole. By the 18th of February it has grown to 40 arc seconds in size and the phase has fallen to 26% illuminated. Now shining at magnitude -4.7, look for it at 30 degrees of elevation on a compass bearing of 240 degrees at 1800 ut on that date.

By mid-March Venus sits some 15 degrees directly above the Sun, as seen from the UK, so may be followed from sunset at around 1820 ut until it sets around 2000 ut. At this time it will show a narrow illuminated phase of just 4.3% while still shining at magnitude -4.3. Mid-March is a good time for researchers of the illusive ‘Ashen Light’ to observe the large shadowed phase of Venus for any signs of ghostly illumination. Occasionally reported by very experienced observers it has never be photographed so far as I know. Amateurs might perhaps try with cameras sensitive to infra-red light and using appropriate filters.


Mars sits close to Venus in the western evening sky for the first two weeks of February but, while Venus is large and brilliant, Mars is now very distant from Earth and, subsequently, appears very small in comparison. It is still an obvious red spark of light to the eye or in binoculars, shining at a magnitude of +1.1, fading to +1.3 during the month, but its size is below 5 arc seconds so even in a powerful telescope it will be hard to resolve anything but the largest of dark features on its surface. It is high summer in the southern hemisphere of Mars so there is the potential for very large, even planet engulfing, sand storms at its surface which may present you with a nearly uniform disc of dusky orange colour; reports of such storms obscuring major features is very useful for planetary climatologists studying Mars. In March Mars fades further to magnitude +1.5 and shows a phase illuminated some 95%.


Look for Mars in early February sitting some 5 or so degrees east and slightly above brilliant Venus from around 1700 ut. Once found it can be followed for over 4 hours, much of it at reasonable elevation and in full darkness. This period of visibility reduces as the period progresses but even by the last day of March it can be found due west at some 22 degrees of elevation at 19.30 ut, midway between Mercury and the 18% illuminated crescent Moon, and followed until it sets around 21.50 ut for mid UK latitudes.


Jupiter sits in Virgo, never far from the bright star Spica, throughout this period and is an excellent object for observation. Predominantly an early morning object it becomes more accessible as a late evening object as the period progresses. At the start of February it rises around 23.30 ut, a little south of due east and transits, due south, at 30 degrees of elevation at 0445 ut; still in full darkness. By the middle of the period it rises around 2140 ut and transits at 0300 ut and, by the end of March, it is rising around 1920 ut and transits at 0045 ut which means it can be followed in the evening sky at above 20 degrees of elevation from 2145 ut until 0345 ut the next morning. Its apparent size grows from 39 to 45 arc seconds in the period so very detailed observation should be possible given steady seeing conditions.


Recently there have been outbreaks of dark belt activity in the northern hemisphere of Jupiter and significant white- storm activity seen within the South Equatorial Belt which might result in this dark belt becoming partly bifurcated, split by a new, if temporary, light zone around parts of the planet. Jupiter increases steadily in brightness, from magnitude -2.3 to -2.5 in the period and should be observed whenever possible for major changes in its weather patterns. NASA’s Juno team welcomes good quality images of Jupiter to help with deciding on the imaging options for the orbiting Juno probe and details of how to send images can be found on the SPA website within the ‘Reference’ area of the planetary section.


Saturn is very much a morning object for observation from the UK but it never rises very high as seen from here since it currently sits below the ecliptic which, itself, lies close to the morning horizon at this time. In early February look for it to rise around 0522 ut, almost due south west and 15 degrees further north than the obvious bright red spark of Antares. It will have reached 10 degrees of elevation by 0645ut, as the sky starts to brighten for mid UK latitudes, and it will be lost soon afterwards. By early March it rises at 0325 ut but still only attains 14 degrees by morning twilight; by the end of the month it rises at 0130 ut and can be followed, just, until it transits, due south, at 0522 ut.


Saturn is relatively bright at magnitude +0.5 and grows in apparent size across it equator from 15.6 to17.0 arcseconds in the period. The rings will be more than 37 arcseconds across and will be very well presented, tilted some 26.5 degrees towards us with the northern hemisphere of the planet on view. Due to the low elevation the best views will be made using an Atmospheric Dispersion Corrector to reverse the rainbow-effect produced by the splitting of light as it passes through our own atmosphere at low angles, but any observer with a modest telescope should be able to appreciate views of this magnificent planet.


Uranus and, in particular, Neptune are drawing closer to the Sun as seen from Earth so are only accessible as early evening objects and best seen from early in the period. Uranus has a very close conjunction with Mars on the 27th of February, passing just over 0.5 of a degree south of the red planet; this event happens in daylight for the UK but the two planets can still be seen just 0.6 arcseconds apart on the 26th. At 1900 ut on that date Venus will be very obvious on a compass bearing of 260 degrees, some 20 degrees above the horizon; look 5 degrees higher and 10 degrees further south for the red spark of Mars; Uranus will be in the same field of view for low powered observation with a telescope, slightly lower and further south from Mars. If you miss the conjunction then, look in the same place at the same time on the evening of the 27th when Uranus will be below Mars with a separation only slightly larger than that of the previous night. With Mars shining at magnitude +1.3 and Uranus at +5.9 there will be significant contrast between the pair but sizes will be comparable at 4.3 and 3.4 arcseconds respectively.


Added by: Alan Clitherow