Dundee Astro - Planetary Notes

Venus is a very obvious morning object. It reaches Greatest Western Elongation (GWE) from the Sun on the first of June, rising in the east around 02.15UT, and climbing to nearly 15 degrees of elevation by sunrise for UK observers on that date. The steady rise of the ecliptic, as night turns to day, will carry Venus with it such that by early July it will be 20 degrees high at sunrise and at magnitude -4.2 it will be easy to find in morning twilight; late in July Venus will stretch to around 25 degrees of elevation in the east at sunrise. In the period its apparent size, pole to pole, falls from 24 arcsecond (24”) to 14.5” while the illuminated phase grows from 50% to 75%. This is an excellent period to try and see or image dark cloud features at the deep-blue end of the spectrum.

Mars is in the later stages of its evening apparition and will first be visible around 30 degrees high in the west, shortly after sunset. On 01 June Mars sits 5 degrees right and just below the 37% illuminated Moon which on that day may help you find Mars earlier, perhaps in daylight. After this, Mars sinks steadily lower with each sunset such that by mid period you will first see it at around 15 degrees of elevation, almost due-west, in early twilight. The Moon is again nearby on 29 June, this time Mars sits 2 degrees to the left and slightly above it. By late July you will be lucky to see Mars 10 degrees high after sunset though, again, the Moon is a good pointer, a couple of degrees below and slightly left of Mars on 28 July. In the period the apparent size of Mars falls from 5.5” to 4.4” so visit it as early as possible to have a chance of catching surface detail.

Jupiter is not really observable in June, ‘though you may catch it below 10 degrees high on a compass bearing of 300 degrees, shortly after sunset in the first few days of the month. Solar conjunction is on 24 June, after which Jupiter moves slowly into the morning sky. In early July Jupiter rises in the north-east around 3.25UT but the sky will be very bright by then. Your best chance is to wait until the second half of the month when it rises 50 minutes or more earlier, and improves steadily from there. Late in July Jupiter rises around 02.00UT and will sit 20 degrees left of Venus along the ecliptic; by then you will be able to follow magnitude -1.9 Jupiter to more than 15 degrees high in the east-north-east before the sun rises. At 32.6” in apparent size there should be notable detail on view.

Saturn is a good and improving morning object throughout this period, first rising around 01.40UT, almost due-east, and gaining around 17 degrees of elevation by sunrise for mid-UK latitudes. By late June, Saturn is rising before midnight UT and it keeps close company with Neptune throughout the period, sitting a degree or so below and right of that distant Ice-Giant. Of interest the Moon passes above the pairing on 19 June and again on 16 July, with all three sitting comfortably in binoculars or a low-powered telescopic view.

Mid period, Saturn gains 30 degrees of elevation in the south-east by sunrise and will transit (due-south) around 35 degrees high at 03.30UT, in morning twilight, by the end of July. The ring system will be tilted towards us by just 3.6 degrees in this period but will stretch to 43” in width, with the planetary disk stretching to nearly 19”; Saturn is certainly well worth seeking out in this period.

Just as Neptune sits close to Saturn, Uranus is close to Venus in early July, giving your best chance to find it from around the beginning to the 10th of the month. Venus sits 3 degrees below Uranus on the 5th and 6th with Uranus midway between Venus and the Pleiades on the 4th. By late July, Uranus is more than 30 degrees high in the east before sunrise and scanning below the Pleiades will help you spot it.

Mercury is observable as an evening object in June and is well placed for equatorial and southern observers. It is not so good from the UK but can still be found. Mercury will be stretching away from the Sun and improving through June, but initially will be too low and dim to find; it sits a couple of degrees directly above Jupiter on 09 June but the pair will be low in the north-west at sunset as seen from the UK. Greatest Eastern Elongation (GEE) from the Sun occurs on 04 July but Mercury may be seen at a reasonable altitude above the horizon from around 21 June; perhaps 6 or 7 degrees high in the west-north-west. It will maintain this altitude, when first visible, until just after GEE when it will sink rapidly back towards the horizon; conjunction is at the end of the month.