Dundee Astro - Planetary Notes

Mercury moves into inferior conjunction, between the Earth and Sun on 13 July but rapidly re-appears as a low but improving morning object, particularly at the end of that month, rising in the north-east around 03.00UT.

As mentioned, Venus starts June very obvious in the early evening sky with Jupiter moving ever closer, such that the pair meet on 09 June; Venus will then sit 1.6 degrees above Jupiter before pulling away from it as the period progresses. On 17 June, Venus will pass just over the top of the young crescent Moon (11% illuminated) making an interesting photo opportunity. For much of Canada and the USA this will be an occultation event, but not for the UK.

Night-on-night both Venus and Jupiter will first become visible at steadily lower altitudes in the west. All planets sit close to the ecliptic, and in June this is sinking ever lower as day turns to night, nonetheless Venus can easily be followed as a beacon in the western evening sky throughout this period. The Moon is nearby again on 17 July.

Mars is mired in morning twilight in this period. Nights are so short, in June particularly, that the ecliptic has not risen noticeably by sunrise; as a result, planets rising only shortly before dawn will inevitably sit low to the horizon in morning twilight. Nonetheless Mars is worth seeking out and may be followed telescopically into daylight if sensible precautions are taken to avoid the Sun. It rises around 02.30UT in early June but will be barely visible to the eye. Things are much better in early July when Mars rises an hour earlier and won’t be lost visually until perhaps 15 degrees high in the East. Late in July, Mars rises around 00.35UT, North-East, and rises to around 30 degrees high, due-East, before fading out. It will start to show a slight gibbous phase in the period and is just below 5 arcseconds (5”) in apparent size at the end of the month.

Mars is close to Uranus around 04 July with the pair visible in the same eyepiece on that date but with Mars at magnitude + 1.3 and Uranus at + 5.8 the latter certainly won’t be obvious.

Jupiter is sinking steadily in the western evening sky and is best seen at the start of June, becoming too low for sensible observation in July. Look for it appearing around 20 degrees high in the West on 01 June at 20.30UT. It will show a disk 33” across and, if seeing conditions are good, plenty of detail should be on view. By 01 July it won’t appear until around 21.00UT and only 5 degrees up in the north-west. I look forward to observing its dance with Venus over 09 and 10 June.

Saturn is a morning object, suffering initially from the same low angle of the ecliptic as Mars, but Saturn does rise earlier, around 02.00UT at the start of June, and is still visible an hour later, perhaps 10 degrees high in the east. As summer progresses, things improve. Mid-period Saturn rises around midnight UT and can be followed easily in astronomical twilight. It wont fade-out visually until nearly 3 hours later and will be more than 25 degrees up in the south-east. Late in July Saturn rises 2 hours before midnight UT and is becoming an object for serious observation in the early morning hours. By 02.00UT it will be nearly 35 degrees high in the south-east and a very prominent object. It won’t be lost visually until nearly 04.00UT when it will be 40 degrees up in the south; this makes it much better placed than during its last apparition. In the period its size grows from 39” to 43” across the rings, whose tilt opens to 9.2 degrees towards us; the widest for the year.

Of the Ice-Giants, Uranus is most easily found when close to Mars around 04 July. It does sit mid-way on a line joining the bright star Aldebaran in Taurus and the Pleiades cluster, so it can be found in morning twilight, especially later in the period, if these stars are still obvious. Neptune, though much dimmer, is better placed. In early June it sits around 8 degrees ahead of Saturn, along the line of the ecliptic, then stretches slightly to 10 degrees late in July. At magnitude +7.7 and 2.33” in apparent size it will be hard to find but if you hold your fist at arms length and look at the area one fist-width to the right of Saturn along the ecliptic, you will be in the right area to scan for this distant frozen planet.

Mercury is observable as an evening object in June and is well placed for equatorial and southern observers. While not so good from the UK it can be found, if at a low altitude. The best time is from the start of the month and leading up to Mercury’s Greatest Eastern Elongation (GEE) from the Sun on 15 June. From the first, look for Mercury appearing low in the north-west from 20.45UT, a little under 10 degrees high. Jupiter will be 20 degrees high in the west with spectacular Venus to the right and below Jupiter; both very conspicuous. Extend a line through these down to the horizon and Mercury will sit half way along, between Venus and the horizon. As June progresses Jupiter and Venus remain obvious, moving closer together and swapping places from the tenth, but Mercury will dim steadily and first appears ever later and lower, perhaps not until 21.15UT by GEE.