Blog Archives

Scotland’s Sky in May, 2019

Giant world Jupiter becoming obvious in May’s twilit nights

Sky maps looking north and south, showing the position of the main constellations at different times during the month.

The maps show the sky at 01:00 BST on the 1st, midnight on the 16th and 23:00 on the 31st. (Click on map to enlarge)

With its lengthening days and increasingly twilit nights, May is hardly a vintage month for stargazing from Scotland’s latitudes. Official (nautical) darkness for Edinburgh lasts for more than five hours around midnight as the month begins but dwindles to nothing by the start of June and does not return until 12 July

Edinburgh’s sunrise/sunset times change from 05:30/20:51 on the 1st to 04:37/21:45 on the 31st, while the Moon is new on the 4th, at first quarter on the 12th, full on the 18th and at last quarter on the 26th.

Our charts show Leo diving westwards as the Summer Triangle formed by Vega, Altair and Deneb is climbing in the east. After the Moon, our most obvious nighttime object is the planet Jupiter which rises in the south-east 30 minutes before our map times and reaches less than 12° high in the south before dawn. In fact, look for the Moon above-right of Jupiter on the night of the 19th and closer to the planet’s left on the 20th.

The giant world is now edging westwards against the stars of southern Ophiuchus and brightens from magnitude -2.4 to -2.6 as its distance falls from 678 million to 644 million km. The Jovian globe spans 45 arcseconds in mid-May and telescopes show that it is crossed by bands of cloud that lie parallel to its equator. The four principal moons of Jupiter are also easy targets, though sometimes one or more hide from view as they pass in front of, or behind, the disk or are eclipsed in Jupiter’s shadow.

Saturn trails almost two hours behind Jupiter but is fainter at magnitude 0.5 to 0.3. It lies in Sagittarius, below the Teaspoon asterism, where it stands above the Moon but low down in the south-south-east before dawn on the 23rd. Always an impressive sight through a telescope, though not helped by its low altitude, its disk appears 18 arcseconds wide at mid-month, circled by rings that measure 40 by 16 arcseconds.

Mercury and Venus are too deep in the morning twilight to be seen at present, though Mercury slips around the Sun’s far side on the 21st. The morning twilight also hinders views of the Eta-Aquarids meteor shower which peaks around the 6th-7th and brings swift meteors that stream from a point which hovers low in our east-south-eastern sky for two hours before sunrise.

Mars sets a few minutes before our star map times and may be hard to spot low down in our west-north-western evening sky. It stands between the horns of Taurus on the 1st and shines at magnitude 1.6 to rival the star Elnath, which lies 5° above Mars and marks the tip of the Bull’s northern horn.

Mars’ pinkish-orange hue is best appreciated through binoculars as the planet dims further to magnitude 1.8 and speeds 20° eastwards during May, crossing into Gemini at mid-month and sweeping only 0.2° north of the star cluster M35 (use binoculars) on the 19th. It recedes from 335 million to 363 million km during May but, at a mere 4 arcseconds in diameter, is too small to be of telescopic interest. Catch Mars above the slim earthlit Moon on the 7th.

NASA’s InSight lander used its sensitive French-built seismometer to detect its first likely marsquake on 6 April. The faint vibrations are now being studied for clues as to Mars’ interior. Another instrument, a German heat probe designed to drill up to five metres into the surface, seems to have encountered a rock and is currently stalled well short of its target depth.

The Plough looms directly overhead at nightfall and stands high in the west by our map times. If we extend a curving line along its handle, we reach the prominent star Arcturus which, at magnitude -0.05, is the brightest of all the stars in the sky’s northern hemisphere and, after Sirius, the second brightest (nighttime) star visible from Scotland, although both Vega and Capella come close.

Classed officially as a red giant star, though more yellow-orange in hue, Arcturus is slightly more massive than our Sun and perhaps 50% older. As such, it has depleted the hydrogen used to power its core through nuclear fusion, progressed to fusing helium instead and inflated to 25 times the Sun’s radius and 170 times its luminosity. Eventually, after shedding its outer layers, it will settle down as a dim white dwarf star comparable in size to the Earth.

At present, though, we admire it as the leading star in the constellation of Bootes which has been likened to a pale imitation of Orion or even an ice-cream cone. Bootes takes its name from the Greek for herdsman or plowman, apparently in relation to the seven stars of the Plough which were also known as the “Seven Oxen” in early times.

Arcturus’ own name comes from the Greek for “guardian of the bear”, another reference to its role in following Ursa Major across the sky. In truth, it is something of a temporary guardian since it is rushing past our solar system at 122 km per second at a distance of 36.7 light years and will likely fade from naked-eye view within (only) half a million years as it tracks south-westwards in the direction of Virgo and the bright star Spica.

It is in the north of Virgo, and roughly coincident with the “D” of the label for Denebola on our south star map, that we find the galaxy M87, the owner of the supermassive black hole whose image was released a few weeks ago. M87 is 54 million light years away and visible as a smudge in small telescopes.

Diary for 2019 May

Times are BST

5th           00h New moon

6th           15h Peak of Eta-Aquarids meteor shower

6th           23h Moon 2.3° N of Aldebaran

8th           01h Moon 3° S of Mars

11th         03h Moon 0.3° N of Praesepe

12th         02h First quarter

12th         16h Moon 3° N of Regulus

18th         22h Full moon

19th         18h Mars 0.2° N of star cluster M35 in Gemini

20th         18h Moon 1.7° N of Jupiter

21st          14h Mercury in superior conjunction

22nd         23h Moon 0.5° S of Saturn

26th         18h Last quarter

Alan Pickup

This is a slightly revised version, with added diary, of Alan’s article published in The Scotsman on April 30th 2019, with thanks to the newspaper for permission to republish here.

Scotland’s Sky in May, 2018

Jupiter’s conspicuous opposition in the Balance

The maps show the sky at 01:00 BST on the 1st, midnight on the 16th and 23:00 on the 31st. Arrows depict the motions of Jupiter during May and of Venus from the 20th. (Click on map to enlarge)

The maps show the sky at 01:00 BST on the 1st, midnight on the 16th and 23:00 on the 31st. Arrows depict the motions of Jupiter during May and of Venus from the 20th. (Click on map to enlarge)

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

Alan Pickup

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.