Jupiter’s conspicuous opposition in the Balance
Jupiter is at its brightest and best in the constellation of Libra, the Weighing Scales or Balance, this month. Its opposition, when it stands directly opposite the Sun, occurs on the morning of the 9th but it is prominent every night as it transits low across the south from the south-east at nightfall to the south-west before dawn.
Venus, however, outshines it in the western evening sky and both Saturn and the increasingly striking Mars follow Jupiter into the southern morning sky.
The Sun climbs another 7° northwards during May as Edinburgh’s sunrise/sunset times change from 05:29/20:52 BST on the 1st to 04:36/21:45 on the 31st. Because twilight is also lengthening, official darkness in the middle of the night lasts for under one hour by May’s end.
The Moon is at last quarter on the 8th, new on the 15th, at first quarter on the 22nd and full on the 29th.
Venus stands 20° high in the west at sunset, sinking to set in the north-west by 23:40 on the 1st and one hour later by the 31st. Brilliant at magnitude -3.9, it begins the month 6° above-right of Taurus’ brightest star, Aldebaran, and tracks east-north-eastwards between the Bull’s horns to end May in mid-Gemini, below Castor and Pollux.
The young earthlit Moon makes an impressive sight almost 6° below-left of the planet on the evening of the 17th. Three days later, as Venus joins the region of sky covered by our chart, it passes 1.0° (two Moon-diameters) above-right of the star cluster M35 whose brightest stars may be glimpsed through binoculars from their distance of some 2,800 light years. Still on the far side of its orbit, Venus approaches from 217 million to 190 million km this month as its almost-full disk swells to 13 arcseconds in diameter.
After dominating our winter nights, Orion ducks below our western horizon as the evening twilight fades at present. The Plough is overhead and Leo high in the south with its main star Regulus which has a close encounter with the first quarter Moon on the night of 21st/22nd.
By our map times, Leo sis inking in the west and Jupiter is easily the most conspicuous object in the south though it stands barely 18° high for Edinburgh. Moving westwards in Libra, it lies close to the Moon on the 27th. Its motion takes it from 4° east (left) of the well-known double star Zubenelgenubi at present to lie just 1.0° north-east of the star on the 31st.
Jupiter is 658 million km away at opposition, shines at magnitude -2.5 and shows a 45 arcseconds wide disk through a telescope. Its two main darker cloud bands, its northern and southern equatorial belts, straddle a lighter equatorial zone. The famous Great Red Spot is gradually losing its status, however, being less than half as wide as it was a century ago and currently more salmon-pink in hue than red. It sits in a bay at the southern edge of the south equatorial belt and, like the many other Jovian cloud features, is carried smartly across the disk as the planet spins in just under ten hours.
Steadily-held binoculars show the four main moons of Jupiter, Io, Europa, Ganymede and Callisto which change their configuration to the east and west of Jupiter from night to night, sometimes disappearing as they hide behind Jupiter or cross the disk, along with their shadows.
If Jupiter’s low elevation makes telescopic views less than sharp, this is even more the case with Saturn which rises in the south-east at our map times and is 6° lower in the sky than Jupiter as it reaches the meridian just before dawn. Saturn improves from magnitude 0.4 to 0.2 as it creeps westwards above the Teapot asterism in Sagittarius. It lies 1,392 million km away at mid-month when its oblate globe is 18 arcseconds across set within 40 by 17 arcseconds rings that have their north face inclined at 26° to our view. Look for it 4° right of the Moon on the morning of the 5th.
Less than 2° below Saturn is the globular star cluster M22, a ball of thousands of stars that lies about 10,600 light years away and formed some 12 billion years ago. At about magnitude 5.1 and visible as a hazy glow through binoculars, it was the first globular to be discovered and is brighter than M13 in Hercules, the best globular in the northern sky.
Mars lies almost 15° east of Saturn at present and rises at Edinburgh’s south-eastern horizon at 02:46 on the 1st. As it more than doubles in brightness, from magnitude -0.4 to -1.2, it also speeds 12° eastwards from Sagittarius to Capricornus so that by the 31st it rises at 01:31 and its fiery glow is unmistakable above the south-south-eastern horizon before dawn.
Catch Mars below the Moon on the morning of the 6th. Telescopically, its disk swells from 11 to 15 arcseconds as its distance falls from 126 million to 92 million km. Its approach opens the optimum window for sending probes to the planet and NASA’s InSight lander to study “marsquakes” and the Martian interior is due for launch between 5 May and 8 June.
Meteors of the Eta-Aquarids shower, debris from Comet Halley, appear until the 20th as they radiate from a point that lies low in the east for an hour or so before dawn over Scotland. The shower peaks with some moonlight interference on the 6th and brings a fine shower for watchers further south but only a handful of meteors for us.
Diary for 2018 May
Times are BST
3rd 18h Venus 7° N of Aldebaran
4th 21h Moon 1.7° N of Saturn
5th – 6th Peak of Eta Aquarids meteor shower
6th 08h Moon 2.7° N of Mars
8th 03h Last quarter
9th 02h Jupiter at opposition at distance of 658 million km
15th 13h New moon
17th 19h Moon 5° S of Venus
22nd 03h Moon 1.5° N of Regulus
22nd 05h First quarter
27th 19h Moon 4° N of Jupiter
29th 15h Full moon
This is a slightly revised version, with added diary, of Alan’s article published in The Scotsman on April 30th 2018, with thanks to the newspaper for permission to republish here.
Impressive conjunction before dawn for Mars and Saturn
The Sun climbs almost 10° northwards during April to bring us longer days and, let us hope, some decent spring-like weather at last. Our nights begin with Venus brilliant in the west and end with three other planets rather low across the south. Only Mercury is missing – after rounding the Sun’s near side on the 1st it remains hidden in Scotland’s morning twilight despite standing further from the Sun in the sky (27°) on the 29th than at any other time this year.
Edinburgh’s sunrise/sunset times change from 06:44/19:51 BST on the 1st to 05:32/20:50 on the 30th. The Moon is at last quarter on the 8th, new on the 16th, first quarter on the 22nd and full on the 30th.
Mars and Saturn rise together in the south-east at about 03:45 BST on the 1st and are closest on the following day, with Mars, just the brighter of the two, only 1.3° south of Saturn. Catch the impressive conjunction less than 10° high in the east-south-east as the morning twilight begins to brighten.
Both planets lie just above the so-called Teapot of Sagittarius but they are at very different distances – Mars at 166 million km on the 1st while Saturn is nine times further away at 1,492 million km.
Brightening slightly from magnitude 0.5 to 0.4 during April, Saturn moves little against the stars and is said to be stationary on the 18th when its motion reverses from easterly to westerly. Almost any telescope shows Saturn’s rings which are tipped at 26° to our view and currently span some 38 arcseconds around its 17 arcseconds disk.
Mars tracks 15° eastwards (to the left) and almost doubles in brightness from magnitude 0.3 to -0.3 as its distance falls to 127 million km. Its reddish disk swells from 8 to 11 arcseconds, large enough for telescopes to show some detail although its low altitude does not help.
Saturn is 4° below-left of Moon and 3° above-right of Mars on the 7th while the last quarter Moon lies 5° to the left of Mars on the next morning.
Orion stands above-right of Sirius in the south-west as darkness falls at present but has all but set in the west by our star map times. Those maps show the Plough directly overhead where it is stretched out of shape by the map projection used. We can extend a curving line along the Plough’s handle to reach the red giant star Arcturus in Bootes and carry it further to the blue giant Spica in Virgo, lower in the south-south-east and to the right of the Moon tomorrow night.
After Sirius, Arcturus is the second brightest star in Scotland’s night sky. Shining at magnitude 0.0 on the astronomers’ brightness scale, though, it is only one ninth as bright as the planet Jupiter, 40° below it in the constellation Libra. In fact, Jupiter improves from magnitude -2.4 to -2.5 this month as its distance falls from 692 million to 660 million km and is hard to miss after it rises in the east-south-east less than one hour before our map times. Look for it below-left of the Moon on the 2nd, right of the Moon on the 3rd, and even closer to the Moon a full lunation later on the 30th.
Jupiter moves 3° westwards to end the month 4° east of the double star Zubenelgenubi (use binoculars). Telescopes show the planet to be about 44 arcseconds wide, but for the sharpest view we should wait until it is highest (17°) in in the south for Edinburgh some four hours after the map times.
Venus’ altitude on the west at sunset improves from 16° to 21° this month as the evening star brightens from magnitude -3.9 to -4.2. Still towards the far side of its orbit, it appears as an almost-full disk, 11 arcseconds wide, with little or no shading across its dazzling cloud-tops. Against the stars, it tracks east-north-eastwards through Aries and into Taurus where it stands 6° below the Pleiades on the 20th and 4° left of the star cluster on the 26th. As it climbs into our evening sky, the earthlit Moon lies 6° below-left of Venus on the 17th and 12° left of the planet on the 18th.
The reason that we have such impressive springtime views of the young Moon is that the Sun’s path against the stars, the ecliptic, is tipped steeply in the west at nightfall as it climbs through Taurus into Gemini. The orbits of the Moon and the planets are only slightly inclined to the ecliptic so that any that happen to be towards this part of the solar system are also well clear of our horizon. Contrast this with our sky just before dawn at present, when the ecliptic lies relatively flat from the east to the south – hence the non-visibility of Mercury and the low altitudes of Mars, Saturn and Jupiter.
The evening tilt of the ecliptic means that, under minimal light pollution and after the Moon is out of the way, it may be possible to see the zodiacal light. This appears as a cone of light that slants up from the horizon through Venus and towards the Pleiades. Caused by sunlight reflecting from tiny particles, probably comet-dust, between the planets, it fades into a very dim zodiacal band that circles the sky. Directly opposite the Sun this intensifies into an oval glow, the gegenschein (German for “counterglow”), which is currently in Virgo and in the south at our map times – we need a really dark sky to see it though.
Diary for 2018 April
Times are BST.
1st 19h Mercury in inferior conjunction on Sun’s near side
2nd 13h Mars 1.3° S of Saturn
3rd 15h Moon 4° N of Jupiter
7th 14h Moon 1.9° N of Saturn
7th 19h Moon 3° N of Mars
8th 08h Last quarter
16th 03h New moon
17th 13h Saturn farthest from Sun (1,505,799,000 km)
17th 20h Moon 5° S of Venus
18th 03h Saturn stationary (motion reverses from E to W)
18th 15h Uranus in conjunction with Sun
22nd 23h First quarter
24th 05h Venus 4° S of Pleiades
24th 21h Moon 1.2° N of Regulus
29th 19h Mercury furthest W of Sun (27°)
30th 02h Full moon
30th 18h Moon 4° N of Jupiter
This is a slightly revised version, with added diary, of Alan’s article published in The Scotsman on March 31st 2018, with thanks to the newspaper for permission to republish here.
Saturn’s opposition in the Balance
Our days lengthen during May until the period of true nighttime darkness dwindles to almost nothing by the month’s end. You might think that astronomers would be tempted to mothball their telescopes, but if they did they would miss the year’s best views of Saturn.
The beautiful ringed planet comes to opposition at a distance of 1,331 million km on the 10th when it lies in Libra, the Balance or Scales, and stands in the south in the middle of the night. The ochre deserts and white north polar cap of Mars are also observable, as are all the other brighter planets at one time or another. There may also be a spectacular meteor shower that has never been seen before.
Look overhead at nightfall to find the Plough and extend a curving line along its handle to reach the star Arcturus shining brightly in Bootes well up in the east-south-east. Continue that line, still bending, into the south-east where Mars is conspicuous and reddish in Virgo, above-right of Virgo’s leading star Spica. By our star map times, the Plough has moved to stand high in the west, Arcturus is high in the south, and Mars is in the south-west.
Following its own opposition on 8 April, Mars is now receding from us, from 96 million to 119 million km during May, and although it halves in brightness from magnitude -1.2 to -0.5 it still outshines Arcturus. Viewed telescopically, its disk shrinks from 15 to 12 arcseconds and only in moments of steady “seeing” can we discern its surface detail. The Red Planet’s slow westerly progress below the famous binary star Porrima halts on the 21st when it reaches a so-called stationary point before tracking eastwards again.
Saturn, creeping westwards in the middle of Libra and bright at magnitude 0.1, stands close to the horizon and beneath Arcturus at nightfall. By our map times, though, it is almost due south at an altitude of nearly 19° as seen from Edinburgh. This is 12° lower than Mars when it transits the meridian, so we see it through more of the Earth’s atmosphere and the seeing is likely to be worse. On the other hand, Saturn’s disk is bigger at 19 arcseconds while its superb ring system spans 42 arcseconds and has its north face tipped 22° towards us. This is a good time to look for the Cassini Division, the 4.800 km gap between the two main rings.
Binoculars show the star Zubenelgenubi, 5° to the west of Saturn, to be an obvious double star, while Zubeneschamali, to Saturn’s north, is held (perhaps mistakenly) by some observers to be one of the few greenish-hued stars in the sky. The Arabic names for these stars mean Southern and Northern Claw respectively and date from an era when they were also associated with the brighter nearby constellation of Scorpius the Scorpion. Use binoculars to scan 11° north of Zubeneschamali for the fuzzy blob of M5, a globular cluster of up to 500,000 stars at a distance of about 25,000 light years. Some observers rate it more highly than the more familiar M13 globular in Hercules and M3 in Canes Venatici, 12° to the north-west of Arcturus.
Jupiter remains prominent, and brighter than any star, in the west at nightfall but is close to setting in the north-west by our map times. At magnitude -2.0, it is tracking eastwards in the middle of Gemini, below Castor and Pollux, and shows a 34 arcseconds disk at midmonth.
Mercury is an evening star as it climbs to stand furthest east of the Sun, 23°, on the 25th. Between the 13th and 29th it stands about 10° high in the west-north-west forty minutes after sunset though it may be hard to spy without binoculars in the slowly-fading twilight. It dims from magnitude -0.6 to 1.0 between these dates. Venus is a brilliant morning star on magnitude -4.1 which rises in the east fifty minutes before the Sun on the 1st and one hour before sunrise on the 31st.
Sunrise/sunset times for Edinburgh change from 05:29/20:52 BST on the 1st to 04:36/21:45 on the 31st. Nautical twilight at dusk and dawn lasts for 105 minutes on the 1st and for all but the middle 24 minutes of the last night of May.
The Moon is at first quarter on the 7th, full on the 14th, at last quarter on the 21st and new on the 28th. The Moon is strongly earthlit when it stands just above Aldebaran in Taurus on the 1st evening. Catch it again below-left of Jupiter on the 4th, near Mars on the nights of the 10th and 11th and Saturn on the 13th and 14th.
The morning of the 24th may see slow meteors streaming away from a radiant point in the dim constellation of Camelopardalis the Giraffe, see north map. The prediction is made by analysts who have back-tracked the motion of a small comet whose official name is Comet 209P/LINEAR. Discovered as recently as 2004, its path carries it between the orbits of the Earth and Jupiter every 5.1 years and it is to pass harmlessly only 8,290,000 km from the Earth on the 29th, the ninth closest approach by a comet on record.
Only a few days earlier, it is thought that the Earth may encounter several streams of particles that were released by the comet between 1803 and 1924. Meteor rates could hit many hundreds per hour, if not storm force, though the peak of activity is predicted between 08:00 and 09:00 BST on the 24th, during daylight for Britain but ideal for observers in N America. Our pre-dawn hours could still be interesting, though.