Looking Forward to the Planets; June and July 2018

From mid-June to early July Mercury has a difficult evening apparition as viewed from the northern hemisphere. The planet is hidden behind the Sun on the 6th of June but moves into the evening sky mid-month and goes on to makes its greatest evening (eastern) elongation from the Sun on the 12th of July. On that date Mercury will trail the Sun by 26 degrees, however the shallow angle of its orbital path as seen from northern summer skies means Mercury makes no great elevation above the western horizon in this period. Look for it in the north-west shortly after sunset in late June and you may catch it just below 10 degrees of elevation but you are more likely to see it at around 5 degrees up as the sky darkens from 2140 UT.

Venus is nearby and much more obvious. From early June Venus will be clearly seen a little north of due west from 2100 UT as a bright evening ’star’ nearly 20 degrees above the horizon. Initially, as June progresses, the planet holds this position at each sunset because, while darkness falls later and later as we move into the summer, Venus is itself stretching further from the Sun with every evening. By the third week of June the steady decline of the ecliptic in the evening sky starts to lower Venus night on night such that, by the first of July the planet will first appear at only 15 degrees of elevation and will then continue to decline noticeably for the rest of the period. It will still be a brilliant beacon on the western horizon well into late July but is best observed early in the period if possible.

Mars will be observable and reaches opposition, directly opposite the Sun as seen from the Earth, on the 27th of July, however its own orbit at that time sits below the ecliptic which is already low during the hours of darkness; this means there is a limited window of opportunity to view Mars in this period. Early in June Mars rises in the south-east around 0035 UT and transits at sunrise for mid-UK latitudes, attaining around 15 degrees of elevation. As the month progresses things improve slightly such that by late June the red planet rises a little after 2200 UT and transits in morning twilight at 0222 UT; on the first of July Mars sits immediately below the nearly-full moon at this time. On opposition day Mars can be viewed from around 2255 UT, rising as darkness falls, to 0345 UT, setting in morning twilight but its transit elevation, due south, will only be around 12 degrees for most UK observers. In compensation the planetary disc will appear more than 24 arcseconds in diameter and surface features should be very obvious in good seeing conditions.

Jupiter was at opposition back in May so in this period the giant planet will still be easily visible for a substantial part of the night. On the first of June look for it almost due south from around 2145 UT, more than 20 degrees above the horizon with Jupiter shining at magnitude -2.5 and showing a disc some 44 arcseconds across at the equator; great detail will be on view in this period. Jupiter can be followed until 0230UT in early June. By the start of July Jupiter is past transit as evening twilight falls so becomes visible a little west of due south shortly after sunset but it can still be followed above 20 degrees of elevation until late evening and does not set until around 0045 UT. By late July Jupiter is declining into the south-west as summer twilight falls so is best observed early in the period.

Saturn moves along a very similar path to Mars in this period but rises ahead of the red planet so should be observed first. In early June it rises around 2220 UT, transits at 0200 UT and is then lost to morning twilight by 0330 UT. Just like Mars it reaches some 15 degrees of elevation when due south so is best seen around the time of southerly transit. The ring system is tilted towards us by 26 degrees so is very well placed for observation and, on a good night, will show considerable detail. Low altitude targets will benefit greatly from the use of an Atmospheric Dispersion Corrector (ADC) which will counter the ‘rainbow’ effect seen around low altitude targets. Saturn comes to opposition on the 27th of June when it can be followed from dusk to dawn. On that night the full Moon lies nearby and its glare will make it difficult but perhaps not impossible to note any ‘Seeliger’ effect during this opposition; that is a transient brightening of Saturn’s ring system that occurs as Sun, Earth and Saturn align. By early July Saturn is due-south at 2350 UT and at around 2140 UT late in the month. This means Saturn is easily viewed through the warm summer nights and is a ‘must-see’ target for this period.

The ice-giants start to make an appearance in this period with the outer most major planet, Neptune rising first and Uranus following. In early to mid-June neither planet reaches significant altitude in darkness but by July Neptune is above20 degrees of elevation in the south-East from around 0140 UT and may be observed against the background stars of Aquarius. By late July Neptune transits in a brightening sky at 0300 UT at above 30 degrees of elevation so can be followed for much of the night. Its tiny blue-green disc will be little more than 2 arc-seconds across and at magnitude 7.8 it will require binoculars to find and a powerful telescope to resolve but imagers equipped with larger apertures, a mono camera and filters that pass infrared light may like to try and target Neptune to look for bright atmospheric features.

Uranus is larger and brighter, on the edge of naked eye visibility from a good site but, in following Neptune, it only really becomes observable late in the period. In Mid-July it is rising around midnight UT and climbs on a steeper path than Neptune and is above 30 degrees of elevation as the sky brightens. By the end of July it will attain 40 degrees of elevation in the south-East by 0300UT so will be an excellent target for observation in the next reporting period.

Alan Clitherow.