Blog Archives

Scotland’s Sky in July, 2018

Dust storm rages on Mars as it stands closest since 2003

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

Mars comes closer to the Earth in July than at any time since its once-in-60,000-years record approach in 2003. It is just our luck that a dust storm that began a month ago now engulfs the entire planet so that the surface markings may now be glimpsed only through a patchy reddish haze.

Both current Mars rovers, Opportunity and Curiosity, are also affected. This is the most intense storm to impact Opportunity since it landed in 2004 and the vehicle has shut down because it lost power as the dust hid the Sun and coated its solar panels. It is hoped that, after the storm subsides, friendly gusts of wind will waft the dust from the panels and Opportunity will revive. If not, this would mark the end of a remarkable mission which had been planned, initially, to last for only 90 days. Its sister rover, Spirit, succumbed in 2010 after becoming stuck in soft soil.

Meanwhile, the more advanced Curiosity rover has been operating since 2012. Being nuclear powered, it is less vulnerable to the dust but its cameras are recording a dull reddened landscape beneath dusty orange skies.

For watchers in Edinburgh, Mars rises in the south-east just before midnight at the beginning of July and is conspicuous at magnitude -2.2 but only 11° high in the south during morning twilight. Look for it 4° below the Moon on the 1st as Mars moves westwards in the constellation of Capricornus.

Mars reaches opposition on the 27th when it stands opposite the Sun, rises during our evening twilight and is highest in the south in the middle of the night. By then it blazes at magnitude -2.8, making it second only to Venus in brilliance, and stands 58 million km away. A telescope shows it to be 24 arcseconds wide, with its southern polar cap tilted 11° towards us. Because Mars is edging inwards in its relatively elongated orbit, it is actually around 100,000 km closer to us on the 31st.

As Mars rises at its opposition on the 27th it once again lies below Moon, but this time the Moon is deep in eclipse as it passes almost centrally through the Earth’s shadow. The total phase of the eclipse, the longest this century, lasts from 20:30 to 22:13 BST and it is in the middle of this period, at 21:22, that the Moon rises for Edinburgh. By 22:13, and weather permitting, it may be possible to see the Moon’s dull ochre disk 5° high in the south-east. From then until 23:19, the Moon emerges eastwards from the Earth’s dark umbral shadow, and at 00:29 it is free of the penumbra, the surrounding lighter shadow.

The Earth stands at its furthest from the Sun for 2018 (152,100,000 km) on the 6th. Edinburgh’s sunrise/sunset times change from 04:31/22:01 on the 1st to 05:15/21:22 on the 31st. The Moon is at last quarter on the 6th and new on the 13th when a partial solar eclipse is visible to the south of Australia. First quarter on the 19th is followed by full moon and the total lunar eclipse on the 27th.

Our chart shows the corner stars of the Summer Triangle, Vega in Lyra, Altair in Aquila and Deneb in Cygnus, high in the south to south-east as the fainter corner stars of the Square of Pegasus are climbing in the east. The Plough stands in the middle of our north-western sky and the “W” of Cassiopeia is similarly placed in the north-east.

Venus sets before our chart times but is brilliant in the west at nightfall. It brightens from magnitude -4.0 to -4.2 but is sinking lower from night to night as it tracks southwards relative to the Sun. It passes 1.1° north of the star Regulus in Leo on the 9th as the much fainter planet Mercury (magnitude 0.4) stands 16° below-right of Venus. The little innermost planet stands furthest east of the Sun (26°) on the 12th but is a challenge to glimpse in the twilight this time around.

Venus lies to the left of the young earthlit Moon on the 15th, below-right of the Moon on the 16th and, by month’s end, stands less than 10° high at sunset before setting itself some 70 minutes later.

Jupiter lingers as a conspicuous evening object in the south-south-west at nightfall, sinking to set in the west-south-west one hour after our map times. Moving very little against the stars of Libra, it dims slightly from magnitude -2.3 to -2.1 and shows a 39 arcseconds disk when it lies below-left of the Moon on the 20th.

Saturn reached opposition on June 27 and is at its best at our star map times, albeit low in the south at a maximum altitude of less than 12° for Edinburgh. At magnitude 0.0 to 0.2, it is creeping westwards above the Teapot of Sagittarius where it lies near the Moon on the 24th and 25th. Its disk and wide-open rings appear 18 and 41 arcseconds wide respectively.

Our noctilucent, or “night-shining”, cloud season is now in full swing with sightings of several displays of these high-altitude blue-white clouds since late-May and further ones expected until August.

Often with a wispy cirrus-like appearance, noctilucent clouds are composed of ice-crystals at heights near 82 km and glimmer above our northern horizon where they catch the sunlight long after our more usual lower-level clouds are in darkness. Their nature is still something of a mystery but it may not be coincidental that the first definite record of them dates only as far back as 1885, just two years after the cataclysmic eruption of the Krakatoa volcano in Indonesia.

Diary for 2018 July

Times are BST

1st            03h Moon 5° N of Mars

6th            09h Last quarter

6th            18h Earth farthest from Sun (152,100,000 km)

9th            21h Venus 1.1° N of Regulus

11th          05h Jupiter stationary (motion reverses from W to E)

12th         06h Mercury furthest E of Sun (26°)

13th         04h New moon and partial solar eclipse S of Australia

14th         23h Moon 2.2° N of Mercury

16th         04h Moon 1.6° N of Venus

19th         21h First quarter

21st         01h Moon 4° N of Jupiter

25th         07h Moon 2.0° N of Saturn

27th         06h Mars at opposition at distance of 58 million km

27th         21h Full moon and total lunar eclipse

27th         22h Moon 7° N of Mars

29th         Main peak of Delta Aquarids meteor shower

31st         09h Mars closest to Earth (57,590,000 km)

Alan Pickup

This is a slightly revised version, with added diary, of Alan’s article published in The Scotsman on June 30th 2018, with thanks to the newspaper for permission to republish here.
Advertisements

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.