The Planets in June and July 2019

Mercury starts June as an early evening object, stretching steadily eastwards of the Sun to reach its greatest eastern (evening) elongation of 25 degrees on the 23rd of the month. It will initially increase its elevation at the same time, night on night, however the brightness of early summer evenings can make it hard to spot. Sunset is not until around 2015 UT at mid-UK latitudes and Mercury won’t be seen until around 2100 UT or soon afterwards, initially just above the north-western horizon. By mid-June it will be seen to have gained more elevation but it is best observed from the UK a few days before greatest elongation since the plane of the ecliptic starts to decline noticeably as twilight falls at this time of the year, dragging Mercury down with it even as the planet stretches further from the Sun.

Look for Mercury in a photogenic pairing with Mars on the evening of the 18th of June when the pair sit just 15 minutes of arc apart, above the north-western horizon and below the star Castor; visible from around 2115 UT onwards. Mars and Mercury are close from at least the 15th to the 20th of June. Equatorial and Southern observers will, of course, be treated to a much better view of this event. Mercury reaches inferior conjunction between the Earth and the Sun of the 21st of July and will just become visible in the early morning twilight by the end of the month.

Venus is a morning object, drawing steadily closer to the Sun and, eventually passing behind it, at superior conjunction, in August. In early June it rises in the north-east in morning twilight around 0315 UT and is best observed by following it into daylight. Separation from the Sun is only 20 degrees and reducing, so all normal precautions must be taken to protect eyesight and equipment from damage by the Sun. At magnitude -3.9 Venus should be easy to find and then follow and will show a disk more than 90% illuminated and around 10 arcseconds in apparent diameter. By early July separation from the Sun will have fallen to 12 degrees and Venus is effectively lost to the majority of observers unless they have specialist equipment.

As mentioned, Mars is in the evening sky of early June, visible from around 2100 hours onwards on a bearing of around 295 degrees and a little less than 15 degrees up for most UK observers. Its prograde (easterly) motion against the background stars at this time helps to prolong its visibility but it is best to observe it in early June and as soon as the sky starts to darken. At a magnitude of +1.8 it should be relatively easy to find but at below 4 arcseconds in size only large-scale detail is likely to be seen on its disc. On the 5th of June it will be found a little west of a young crescent Moon and close by Mercury a few days either side of the 18th. Mars is again close by Mercury on the 6th of July but at very low altitude and it will be lost to most UK observers soon after.

Jupiter is undoubtedly the best object to observe in this period, reaching opposition from the Sun on the 10th of June when it will be due south at midnight UT and visible for all of the short summer night. Sadly this will occur at no great elevation due to the low altitude of the ecliptic during the summer months. Its brightness of magnitude -2.6 will make it obvious against the stars of Ophiuchus and its well-known dark belts and light zones will be visible as well as the Great Red Spot during periods of good seeing. An Atmospheric Dispersion Corrector (ADC) will greatly improve the view allowing significantly more detail to be seen on this low-altitude target.

On the 5th of June a double shadow-transit event may be seen from 0035 UT. The Jovian moon Ganymede and its shadow track across the southern edge of Jupiter’s North Polar Region and Io casts its shadow on the North Equatorial Belt. The split between a moon and its shadow will be obvious even though it is only 5 days before opposition. A similar event happens from 0329UT on the 12th of June but will be harder to discern because each moon will sit almost directly above its own shadow. Sadly Jupiter will be close to setting at this time and hard to observe from the UK.
Jupiter can easily be observed right until the end of July and beyond.

Saturn rises around 2 hours after Jupiter and follows a near identical path across the sky. Its ring system still well open, tilted around 24 degrees towards the Earth with the northern pole on view to us. Just like Jupiter observing it will benefit from the use of an ADC and, with good local seeing conditions, considerable detail may be seen in this beautiful object. Saturn comes to its own opposition from the Sun on the 9th of July and it will be interesting to see if there is an apparent surge in brightness of the ring-system on the day or so either side of opposition. This ‘Seeliger Effect’ or ‘opposition surge’ may be hard to spot at such low altitudes.

Of the ice-giant planets, Uranus is poorly placed early in this period being lost in morning twilight until July. Neptune is a little better placed, rising after 0100UT in early June and reaching more than 20 degrees of elevation in the south-east by Sunrise. Mid period Neptune is rising before midnight UT, a little south of due-east, and can be followed for the rest of the night. Uranus rises around 0030 UT and, again, may be followed until the sky is too light. By late July both planets are sensibly observable with Neptune transiting due south around 0250 UT with more than 30 degrees of elevation against the background stars of Aquarius. At the same time Uranus will be found near the head of Cetus, the whale somewhat further east and at nearly 40 degrees of elevation. Both planets will be well placed for observation in the next period.

Alan Clitherow