Looking Forward to the Planets in June and July 2020

Mercury is at its greatest eastern (evening) elongation from the Sun on the 4th of June and will become visible to UK observers on a compass bearing of 300 degrees, some 10 degrees above the horizon on that date; look for it around 40 minutes after sunset. This is a good evening apparition of Mercury and should not be missed if possible. The planet can be followed from the beginning of the month until at least the 10th at greater than 5 degrees of elevation from around 2100 UT. It will shine at magnitude +0.5 and show an obvious phase. Mercury moves between the Earth and the Sun on the 1st of July (inferior conjunction) before reaching its greatest western (morning) elongation on the 22nd. This morning apparition is slightly less favourable than the evening one that preceded it but you can follow Mercury from its rise, around 0250 UT, to a little before sunrise by which time it will have attained some 10 degrees of elevation on that date and a few days either side.

Venus starts this period in inferior conjunction then moves into the morning sky and steadily improves in visibility, but for most of June the planet is too low and close to the Sun for ready observation. By Early July Venus rises around 0215 UT, some 90 minutes before sunrise, and reaches around 12 degrees of elevation as the Sun breaks the horizon. In mid-July Venus rise is 0140 UT, 2 hours and 20 minutes ahead of the Sun, gaining 20 degrees of elevation by sunrise and by the end of July Venus rises at 0115 UT, 3 hours and 15 minutes before the Sun and gains nearly 30 degrees of elevation as the Sun breaks the horizon. Throughout July Venus shines at a brilliant magnitude of -4.4, far outshining any other twilight object other than the Moon and can, with great care, be followed into daylight for observation at higher altitudes. In July the illuminated phase grows from 19% to 42% and its apparent size, pole to pole falls from 43 to 28 arcseconds. This is an excellent morning apparition for UK observers.

Mars is also in the morning sky in this period and, like Venus, improves steadily in visibility. It rises at 0110 UT in early June, some 15 degrees south of due-east, and gains 20 degrees of elevation by sunrise. At magnitude 0.0 it will be less obvious than Venus but its red colour will help you to pick it out from the background stars of Aquarius. By early July Mars rises at or just before midnight UT, due-east and now below the head of Pisces. By sunrise Mars will be above 30 degrees of elevation in the south-east, and shining at magnitude -0.5. In late July the figures are, rise at 2230 UT, near the tail of Pisces, reaching more than 40 degrees of elevation by sunrise, almost due-south. It brightness will be magnitude -1.0 and from early June to late July its apparent size will grow from 9 to nearly 15 arcseconds. Mars can and should be observed throughout this period and improves even further as the year progresses!

Both Jupiter and Saturn reach opposition in this period, Jupiter on the 14th and Saturn on the 20th of July. From this it is easy to see that both giant planets are close to a line-of-sight from Earth and sail through the heavens in close formation throughout the period. Jupiter rises first, around 2320 UT in early June, with Saturn following 13 minutes afterwards; both planets rising in the south-east. Jupiter will be quite the most obvious of the pair, shining at magnitude -2.6 and will show an equatorial diameter nearly 45 arcseconds in apparent size. At the same time Saturn shines at magnitude +0.4 with a planetary diameter of 18 arcseconds and the rings stretching to 41 arcseconds, well presented and tilted towards us by nearly 22 degrees. Even in the bright morning skies of June the pair can be followed until nearly sunrise when they will be approaching due south. At south transit Jupiter will gain just 16 degrees of elevation with Saturn marginally higher. Steady seeing conditions will reward with good detail within the cloud decks of both planets but an atmospheric dispersion corrector will help combat the effects of viewing these relatively low altitude targets.

By early July Jupiter rises at 2120 UT and reaches south transit at 0112 UT with Saturn transiting 26 minutes later, ‘though still at disappointingly low elevations. On the 14th of July Jupiter transits around 0100 UT, still at 16 degrees of elevation and has grown slightly to 47 arcseconds in size. Saturn’s opposition night on the 20th of July sees the ringed planet shine at magnitude +0.1 with its disc a little more than 18 arcseconds across and the glorious rings 43 arcseconds in size. For a few nights either side of opposition some observers note a brightening of Saturn’s rings, known as the Opposition Surge or Seeliger effect, but this may be hard to see with Saturn at such a low elevation. Both planets can be observed from close to dusk until dawn for most of this period and I would encourage you to do so when possible.

Of the outer ‘Ice-Giant’ planets Neptune rises first, low in the east, and is initially close to Mars. On the 14th of June Neptune sits just above Mars, separated by less than 2 degrees so a small refractor with a low-power eyepiece will easily show the two planets in the same field of view. At magnitude +7.9 Neptune will appear as a small blue ‘star’ until more magnification starts to show its tiny 2.3 arcsecond disc. By early July Neptune rises before midnight UT, now a little west of Mars, and gains 30 degrees of elevation in the south-east by sunrise. By the end of July Neptune transits due south at over 30 degrees of elevation at 0256UT, in morning twilight, so observers will see it best later in this period.

Uranus follows behind Neptune and in early June is too close to the Sun in the morning sky for sensible observation. By late July Uranus rises at 2240 UT, at the feet of Aries the Ram, trailing Mars by 23 degrees. By the time the sky has noticeably started to brighten, with the Sun still 10 degrees below the horizon, Uranus has gained nearly 40 degrees of elevation in the south-east, sitting between Mars and Venus. Its magnitude of +5.6 will require binoculars or a small telescope to pinpoint it but it will appear as a green or blue-green gem and it is well worth seeking out.

Alan Clitherow