Dundee Astro - Planetary Notes

Mercury passes behind the Sun on 14 June to start its evening apparition and is very close to Venus on 17 June, but this pairing won’t be observable. Even by late July neither will be obvious from the UK as they will appear at very low altitude in the north-western evening sky. Greatest Eastern (evening) Elongation (GEE) of Mercury from the Sun will be on 22 July but the ecliptic sits very low in summer evening twilight so this apparition of Mercury will be disappointing from the UK.

Venus starts June behind the Sun, with Superior Conjunction (SC) on 04 June. Its own orbit passes above the ecliptic on 06 June and is at its highest above the ecliptic on 20 June but, as mentioned, the ecliptic itself is very low at sunset. Even by the end of July, Venus sets only 35 minutes after the sun so, despite its dazzling brightness of magnitude -3.9, it will be very hard to spot before it sets. It is, perhaps, obvious to say that it will be putting on a much better show from the southern hemisphere.

Mars is a better target from the start and throughout this period. It rises around 02.10UT in early June with the Sun still 10 degrees below the horizon. At magnitude +1 and only 5 arcseconds (5”) in apparent size it will hardly be obvious but it does improve as time moves on. On 03 June it rises only 3 degrees south (right) of the slender waning crescent Moon which may help with finding and following Mars. Around that date Mars reaches some 15 degrees of elevation, due east, by sunrise and, to risk repeating myself, is better seen from further south.

Mid-period, Mars is rising at 01.00UT, in astronomical twilight, again with the Moon nearby on 01 and 02 July. Now it will reach nearly 20 degrees of elevation in the east by sunrise so is becoming a more viable target. By late July Mars rises just before midnight UT and can be followed for around 4 hours before fading out in morning twilight, 35 degrees high in the eastern morning sky. At magnitude +0.85 it will be clearly visible but significantly outshone by nearby Jupiter which rises 25 minutes after Mars. At just under 6” in apparent size, Mars will start to show larger surface details, especially to imagers, as it rises higher in the morning sky.

Jupiter is also improving throughout the period. In early June it rises barely ahead of the Sun but by mid-period it rises in twilight around 01.50UT and reaches 15 degrees of elevation in the east by sunrise; on 03 July the slim, waning crescent Moon sits directly above Jupiter making its magnitude -2 disk very easy to find and follow to higher altitudes. On 31 July Jupiter rises at 00.15 UT, with the Moon once more close by. Jupiter will show a disk 34” across and clear detail should become available as the planet reaches more than 30 degrees of elevation in the east in late twilight.

Saturn rises ahead of Jupiter in this period, only slightly south of due-east and at around 01.20UT at the start of June. By 03.20UT it will start to be lost to the brightening sky but will be 15 degrees high in the south-east. By the start of July Saturn will rise around 23.25UT and by the time it is lost, will be more than 25 degrees up on a compass bearing of 150 degrees, at around 03.10UT. By late July Saturn can easily be followed, for mid-UK latitudes from around 21.30UT as it rises in a darkening sky, then passes south-east at 00.05UT and will go on to transit, due-south, around 02.50UT at more than 30 degrees of elevation. At magnitude +0.76 it will be the brightest star-like object in eastern Aquarius and will be very obvious.

On 09 June Saturn is at ‘quadrature’ when the Earth, Saturn, Sun angle forms 90 degrees, at which time the planet normally casts a very obvious shadow on its own ring structure behind it. In this period the rings are closing and are not-quite edge on to the Earth, forming a thin but striking line bisecting the planet. With one half of the rings cut by the planet’s own shadow the ring will have an odd ‘sickle-blade’ appearance on its western side; a very interesting observing target.

Uranus is not readily observable in early June; rising around 03.10UT in an already bright morning sky. By early July things have improved only slightly with Uranus rising around 01.15UT, midway between Mars and Jupiter; on 02 July the Moon sits almost above Uranus which may help you to pin it down, however the brightening twilight will rapidly wash out the +5.85 magnitude planet. On 16 July Uranus sits directly above Mars so will be easier to track down, and by late July, will be rising at 23.20UT in properly dark skies. It will be some 25 degrees high when passing due-east around 02.20UT in skies dark enough to allow you to find its 4” wide disk. To find it in late July extend a line from Jupiter, through Mars and upwards by one length and Uranus will lie near its end.

Neptune is a hard target in this period due to its low brightness of +7.7 magnitude, however it rises, due-east, around 01.40UT in early June and trails some 11 degrees behind Saturn, following it in a climbing arc for the rest of the night. By early July Neptune rises at 23.30UT and again follows Saturn up the arc of the ecliptic. In late July Neptune rises around 21.40UT in a slowly darkening sky and passes south-east at 00.55UT, still 11 degrees behind Saturn but almost level with it above the horizon. Look for a blue-green ‘star’ in the scattering of similar brightness objects between Pisces and Cetus and add power to single-out its 2.33” disk.