Dundee Astro - Planetary Notes

Mercury is between the Earth and the Sun (Inferior conjunction) on 11 April and then moves into
the morning sky. Looking East, the plane of the ecliptic is low towards sunrise so all ‘morning
planets will hug the horizon somewhat in this period; Mercury is no exception. It will be very close
to Venus on 19 April with Mercury rising first, around 0445UT, sitting almost directly above much
brighter and more obvious Venus, which rises 10 minutes later. The sky will already be bright for
this event and the best chance for UK observers is to find and follow Venus into daylight and to
look little more than a degree above it for faint Mercury. Mercury sinks below the ecliptic on 20
April and this planetary pairing is much better seen from the southern hemisphere.

Greatest Western Elongation (GWE) from the Sun is on 09 May by which time Mercury will sit only 4 or 5 degrees above the eastern horizon at sunrise for southern UK observers, however it will maintain this elevation at sunrise for the rest of the month as the ecliptic starts its slow springtime rise.

As mentioned, Venus, like Mercury, lies close to the eastern horizon at sunrise and is moving ever closer towards solar conjunction in early June. It comes close to both Uranus and Jupiter in May but these events will only be observable in daylight and at some risk to eyesight and equipment from the Sun. If you wish to catch Venus it is best seen in early April, rising around 0530UT but, even then, will be rising in twilight.

Mars is also a morning object, rising around 0455UT in early April, 0335UT mid period (by which time it will rise due-east) and 0215UT in late May; all times for mid-UK latitudes. From this it can be seen Mars is best observed later in the period when it will gain around 15 degrees of elevation by sunrise: It will also have grown to just above 5 arcseconds (5”) in apparent size, the point at which surface detail starts to be visible to imagers.

Mars does sit very close to Saturn in early April with the pair passing each other over the 10th and 11th but, again, this will be best followed into daylight from the UK. Mars is extremely close to Neptune on 29 Apr with the pair some 140” apart but the conjunction will be unobservable with Neptune too dim to see in morning twilight.

In early April, Jupiter will be very obvious, some 25 degrees high in the west a little after sunset. Shining at magnitude -2, its magnificent cloud topped disk will span some 34” in apparent size. For the first few days of the month Mercury will sit between Jupiter and the horizon but will be very low and thereafter sinks very rapidly towards conjunction: Jupiter will set around 2155UT in early April.

Jupiter moves steadily closer to Uranus with the pair meeting on 21 April. On that date Jupiter will start to be visible from around 1940UT in civil twilight; Uranus will sit a little above and north (right) of Jupiter with the separation around half a degree. This is a relatively rare conjunction so it is a shame it is not better placed from the UK. By mid-period Jupiter is setting around 2040UT, with the Sun only 10 degrees below the horizon, so is best seen early in the period if possible. Jupiter moves behind the Sun (conjunction) on 18 May.

Saturn is close to Mars and a low altitude morning object in this period. If you wish to find it, Saturn will rise around 0510UT, during morning twilight, in early April, thereafter at 0315UT mid period and 0120UT by late May; by which date it will gain some 20 degrees of elevation in the south-east at sunrise. On 31 May the Moon and Saturn rise at the same time with the planet 4 degrees north (left) of the Moon. The ring system will stretch nearly 40” across but will only be tilted some 2 degrees towards us presenting a very narrow aspect.

In early April Uranus can be found by scanning up and left of bright Jupiter for around 3.5 degrees along the line of the ecliptic. It will be most obvious from the end of twilight, from perhaps 2030UT, but will be only around 15 degrees high by then. The gap between planets closes steadily until 21 April when the twilight conjunction offers probably the last chance to easily find Uranus in this evening apparition.

Neptune has moved into the morning sky following its solar conjunction and is extremely close to Venus on 03 April and Mars on the 29th but neither conjunction is sensibly observable from the UK