Is Jupiter’s Great Red Spot unfurling before our eyes?
The Sun reaches its most northerly point at 16:54 BST on the 21st, marking the summer solstice in our northern hemisphere. Between its setting in the north-west and its rising in the north-east, it follows only a shallow arc below Edinburgh’s horizon and stands, at most, 10.6° below Edinburgh’s due-north horizon at 01:14 BST. As a result, twilight persists throughout our June nights and we must stay up late to glimpse even the brighter stars and planets.
The sunrise/sunset times for Edinburgh change from 04:36/21:46 BST on the 1st, to 04:26/22:03 on the 21st and 04:30/22:02 on the 30th. The Moon is new on the 3rd, at first quarter on the 10th, full on the 17th and at last quarter on the 25th.
At times like these, some stargazers forsake their hobby for a couple of months while others switch to observing the Sun, or, perhaps, noctilucent clouds. This June, though, the giant planet Jupiter is well worth a look as it comes to opposition on the 10th. It is then closest to us (641 million km) and stands directly opposite the Sun, so that it rises in the south-east at sunset and passes (for Edinburgh) less than 12° high in the south in the middle of the night.
Conspicuous at magnitude -2.6 as it creeps westwards against the stars of southern Ophiuchus, Jupiter outshines every other object in our night sky except for the Moon which lies close to it on the night of the 16th-17th. A small telescope or good steadily-held binoculars reveal its four main moons, the Galilean moons, as they orbit from east to west of the planet in periods that range from 1.8 days for Io to 16.7 days for Callisto. Jupiter has more moons, 79 at the latest count, than any other planet, with Saturn’s tally of 62 coming second. Jupiter’s 75 lesser moons, though, are too small and dim to be spotted using any but the largest telescopes.
Jupiter’s globe is shrouded in clouds, mainly of ammonia crystals but tinted red and brown by other compounds which may include hydrocarbons. Telescopes show bands of darker cloud and a plethora of streaks and spots that transit smartly across the disk as the planet rotates in its sub-ten-hour day.
The most famous feature, the Great Red Spot, is an anticyclonic storm that may be more than 300 years old and was once larger than three Earths. It has shrunk significantly over the last century but observations over the past two weeks suggest something startling may be afoot and even that the spot may be disintegrating. It appears that 10,000-km-long streamers of reddish gas, perhaps methane-rich, are peeling away from the spot into the adjacent cloud band, the South Equatorial Belt, that circles the planet. Likened by some to the spot unfurling, nothing on this scale has been seen before so it is just as well that NASA’s Juno probe has a ring-side view as it orbits Jupiter.
Some 30° to the east of Jupiter, below the so-called Teaspoon of Sagittarius, is our Sun’s other gas giant planet, Saturn. Rising in the south-east about one hour before our map times, it brightens slightly from magnitude 0.3 to 0.1 to rival the two brightest stars on our south map – Vega in Lyra which stands very high in the east-south-east and Arcturus in Bootes in the middle of our south-western sky. When Saturn lies just left of the Moon on the night of the 18th, it lies 1,361 million km away and a telescope shows its disk and rings to span 18 and 41 arcseconds respectively.
The constellations of Ophiuchus and Hercules sprawl across the meridian at the map times, though our twilight means that this is not the best month for spotting M13, the Great Globular Cluster in Hercules (see map). Discovered by Edmond Halley of comet fame in 1714, this ball of hundreds of thousands of stars is some 160 light years across, 22,200 light years away and is thought to have formed 11.65 billion years ago. Under the best conditions, binoculars show it as a fuzzy circular patch around two-thirds as wide as the Moon.
Although Venus is brilliant at magnitude -3.9, it rises in the north-east around 40 minutes before the Sun and is unlikely to be noticed in Scotland’s dawn twilight. Mars is now as dim as magnitude 1.8 and becoming much harder to spot low down in our north-western evening twilight. Tracking eastwards in Gemini to pass below Castor and Pollux, it sets for Edinburgh at 00:05 BST on the 5th when it is 4° to the right of the slender young earthlit Moon. Mercury, much easier at magnitude -0.7, lies 11° below-right of Mars at that time and is 4° above the horizon one hour after sunset between the 5th and 19th. Mercury passes 0.2° above Mars on the 18th and stands furthest east of the Sun (25°) on the 24th.
Scotland’s noctilucent cloud season is just beginning and we can look forward to occasional displays of these “night-shining” clouds until August. Often with a bluish-white sheen, they may appear as wisps, streaks and whirls and merge into banks with cirrus-like herring-bone patterns. The clouds are formed when ice crystallises on dust particles in a narrow range of altitudes near 82 km. Here they are high enough to catch the sun’s light when our more typical lower-level terrestrial clouds are in darkness, from, say, one hour after sunset until one hour before sunrise. They rarely reach more than 20° above the horizon and favour directions towards the north-west at nightfall shifting to the north-east before dawn.
Diary for 2019 June
Times are BST
3rd 11h New moon
4th 17h Moon 4° S of Mercury
5th 16h Moon 1.6° S of Mars
7th 09h Moon 0.5° N of Praesepe
8th 21h Moon 3° N of Regulus
10th 07h First quarter
10th 16h Jupiter at opposition at distance of 641 million km
16th 20h Moon 2.0° N of Jupiter
17th 10h Full moon
18th 16h Mercury 0.2° N of Mars
19th 05h Moon 0.4° S of Saturn
21st 16:54 Summer solstice
24th 00h Mercury furthest E of Sun (25°)
25th 11h Last quarter
30th 17h Moon 2.3° N of Aldebaran
This is a slightly revised version, with added diary, of Alan’s article published in The Scotsman on May 31st 2019, with thanks to the newspaper for permission to republish here.
Dust storm rages on Mars as it stands closest since 2003
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)
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.
Saturn at its best as summer begins
The Sun reaches its most northerly place in the sky at the summer solstice on the 20th, regarded by many as the start of summer in our northern hemisphere. Contradictorily, though, the days around then are also classed as midsummer though the actual days of any midsummer celebrations vary from country to country. More sensibly, in my view, the Met Office defines summer to span the months of June to August which would place the middle of summer in mid-July and, consequently, means that summer begins on June 1.
The solstice occurs late on the 20th, at 23:34 BST, while sunrise/sunset times for Edinburgh change from 04:35/21:47 on the 1st, to 04:26/22:03 on the 20th and 04:31/22:02 on the 30th. Scotland’s nights remain twilight throughout, with little hope of spotting the fainter stars and, from the north of the country, only the brighter stars and planets may be seen.
One is the beautiful ringed world Saturn which stands opposite the Sun in the sky on June 3, only twelve days after Mars’ closest opposition since 2005. Both planets shine brightly in the south at our star map times as they track westwards across the sky. Unfortunately, Saturn climbs less than 14° above Edinburgh’s horizon and Mars is a degree or so lower still so telescopic views are hindered by their low altitudes.
Having stood at its closest (75 million km) on May 30, Mars fades from magnitude -2.0 to -1.5 as it recedes to 86 million km while telescopes show it contracting from almost 19 to 16 arcseconds in diameter, still large enough to show some detail on the disk. It tracks 5° westwards into the heart of Libra this month, its motion slowing to a halt on the 30th before resuming as an easterly progress that will persist for the next two years.
Saturn’s disk is similar in size, 18 arcseconds at opposition, but its rings are 42 arcseconds wide and have their north face tipped 26° towards us. Not since 2003 have the rings been so wide open to inspection. It dims slightly, from magnitude 0.0 to 0.2 as it creeps westwards in southern Ophiuchus about 7° above-left of Antares in Scorpius.
Third but not least in our planetary line-up, Jupiter is prominent at magnitude -2.0 in the south-west as the sky darkens at present, but sinks lower with each day and sets in the west a little more than one hour after our map times. Now moving eastwards below the main figure of Leo, it passes within 0.1° south of the magnitude 4.6 double star Chi Leonis on the 10th and dims a shade to magnitude -1.9 by the 30th.
Of the other naked-eye planets, Mercury stands 24° west of the Sun on the 4th and, while well placed for observers south of the equator, is swamped in our predawn twilight. Venus reaches superior conjunction on the Sun’s far side on the 6th and is not visible either.
The Moon is new on the 5th, close to Jupiter on the 11th, at first quarter on the 12th, above Spica in Virgo on the 14th, above-right of Mars on the 17th, close to Saturn on the 18th, full in the 20th and at last quarter on the 26th.
Our star charts show the stars of the Summer Triangle, Vega, Deneb and Altair, climbing in the east to south-east as the Plough stands high in the north-west. The curve of the Plough’s handle extends to the brightest star visible at our map times, Arcturus in Bootes. Look some 20° above and to the left of Arcturus for the pretty arc of stars that make up Corona Borealis, the Northern Crown, which, because it is incomplete, should perhaps be called the Northern Tiara.
Corona’s leading star has the dual names of Gemma, for an obvious reason, and Alphecca which derives from the Arabic for “the bright of the broken ring”. At magnitude 2.2, though, it was surpassed briefly and unexpectedly exactly 150 years ago, in 1866, by the appearance of a nova (“new star”) just beyond the crown’s south-eastern edge.
Now called T Coronae Borealis (or T CrB), this reached magnitude 2.0 but plunged below naked eye visibility after only eight days to became slightly variable in brightness as a telescopic object just fainter than the tenth magnitude. To much surprise it burst into prominence again in 1946 though this time it was already fading at magnitude 3.2 when it was first spotted.
T CrB thus earned its nickname as the Blaze Star and became the brightest known of ten such recurrent novae in the sky. Studies over the past year show it slightly brighter and bluer than usual and hint that a new outburst may occur at any time, so this is one to check regularly.
Another variable star, R CrB, is usually near the sixth magnitude and the brightest star within the crown. However, normally for a few weeks or months every few years, it fades to become a dim telescopic object when, so it is thought, clouds of soot form in its atmosphere and block its light. Strangely, it has yet to recover following a record-breaking fade in 2007 and was still near the 14th magnitude a few days ago.
Despite our summer twilight, Scotland is best placed to see noctilucent or “night-shining” clouds which may appear cirrus-like and often bluish low down between the north-west after sunset and the north-east before dawn. Formed by layers of ice-crystals near 82 km in height, these are Earth’s highest clouds and able to shine in the sunlight long after our normal clouds have dimmed to darkness.
This is a slightly-revised version of Alan’s article published in The Scotsman on June 1st 2016, with thanks to the newspaper for permission to republish here.
Mercury to transit face of Sun on 9th
May is seldom an outstanding month for astronomy for observers at Scotland’s latitudes. The Sun’s northwards progress, welcome as it is, leads to later and briefer nights and, as the month ends, twilight begins to persist throughout the night even over the south of the country.
Two astronomical events occur this May, though, that should arouse our interest. The first is the transit by Mercury across the Sun’s face on the 9th which, if the weather holds, should be our best opportunity until 2049 to view its inky silhouette against the Sun. The month also sees Mars approach closer to us and appear brighter than at any time since 2005.
I must repeat the usual serious warning about the dangers of observing the Sun. To prevent permanent damage to your eyes, never look directly at the Sun through a telescope or binoculars, or even stare at it with the unaided eyes. We may project the solar image onto a shaded white card using a pinhole, binoculars or a small telescope, but note that using a large telescope for this may damage its eyepiece.
Sadly, Mercury’s outline will be too small to view by pinhole-projection, and nor will we see it using so-called eclipse glasses. In my opinion, though, it is best to equip your telescope with a certified solar filter to cover the objective (“big”) end of your instrument and block all the harmful radiation.
The precise times we experience the transit can vary by a couple of minutes across the Earth. For Scotland, Mercury begins to encroach on the eastern (left) edge of the solar disk at 12:12 BST and it takes a little more than three minutes before its outline is complete against the Sun. After crawling across the southern half of the Sun it finally leaves at the south-western (lower-right) edge at 19:41.
At a mere 12 arcseconds in diameter, though, it appears only 1/150th as wide as the Sun and a fifth as wide as did Venus during its transit in 2012. Whereas there are more than a dozen transits of Mercury each century, the next one by Venus is not until 2117 and we must be patient until 2125 for the next to be observable from Scotland.
The Sun climbs 7° northwards during May as sunrise/sunset times for Edinburgh change from 05:28/20:53 BST on the 1st to 04:36/21:46 on the 31st. The Moon is new on the 6th, at first quarter on the 13th, full on the 21st and at last quarter on the 29th.
Other than during its transit, Mercury is not visible for us at all this month, and neither is Venus which is lost in the glare on the Sun’s far side.
Jupiter, though, remains prominent in the heart of our southern sky at nightfall where it is slow moving in southern Leo and reaches a stationary point on the 10th before edging eastwards again. May has it dimming slightly from magnitude -2.3 to -2.0 as it recedes from 723 million to 791 million km and its disk shrinks from 41 to 37 arcseconds in diameter. Catch it near the Moon on the 14th and 15th.
By our star chart times, Leo and Jupiter are sinking into the west and our southern sky is dominated by the bright star Arcturus, the equally bright planet Saturn and, most conspicuous of all, the Red Planet, Mars. The Plough is tumbling westwards from the zenith as the Summer Triangle formed by the bright stars Vega in Lyra, Deneb in Cygnus and Altair in Aquila, occupies our lower eastern sky.
Mars rises in the south-east at 23:14 BST on the 1st and at sunset on the 22nd, the day it stands directly opposite the Sun in the sky at opposition. Our chart plots it low down in the south-south-east about one hour before it reaches its highest point, albeit less than 13° above Edinburgh’s southern horizon.
It lies 5° above the red supergiant star Antares in Scorpius at present but is retrograding, or moving westwards, against the stars and enters Libra towards the end of the period as it brightens from magnitude -1.5 to rival Jupiter at magnitude -2.0 at opposition. Because it is on the inwards leg of its somewhat eccentric orbit, it is actually closest to us at 75,280,00 km on the 30th, almost a million km closer than on the day of opposition.
Mars’ low altitude means that views of its reddish disk, only 18 arcseconds wide at opposition, may be less sharp (under “poorer seeing”) than if it stood high in the sky. Even so, telescopes should show the small northern polar cap, tipped 10° towards us, and other surface features as they drift slowly to the right across the disk. Those features return to almost the same position from one night to the next since Mars’ day is 40 minutes longer than that of the Earth. Mars comes 17 million km closer during its next opposition in 2018, but will be 4° lower still in our sky so we should make the most of any chance to view it this time around.
Shining to the east (left) of Mars is Saturn which this month brightens from magnitude 0.2 to 0.0 as it creeps westwards in southern Ophiuchus. It always rewards us with stunning telescopic views, its disk being (like Mars) 18 arcseconds wide but set within a glorious ring system that spans 41 arcseconds and has its north face inclined towards us at 26°. Look for the Moon above Mars late on the 21st and closer still to Saturn on the next night.
This is a slightly-revised version of Alan’s article published in The Scotsman on April 30th 2016, with thanks to the newspaper for permission to republish here.
Smallest planet Mercury at its best for the year
It is surprising just how quickly our evening sky changes during April. If we look to the south-west as the twilight fades tonight, the foremost winter constellation of Orion stands well clear of the horizon, with Sirius sparkling to his left and Taurus and the Pleiades to the right, almost due west. By the month’s end, though, Orion has all-but-set as nautical twilight ends in the evening and only Betelgeuse at Orion’s shoulder remains (barely) in view, as shown by our monthly star chart. Taurus is setting, too, and Sirius has already gone.
Jupiter remains a striking object which is ideally placed for study in our evening sky as it slips westwards in the southern part of Leo, some 14° below and to the left of Regulus. Having stood at opposition, directly opposite the Sun, on March 8, the giant planet is unmistakable in the south-east at nightfall at present and passes 41° high in the S only thirty minutes before our map times.
Those maps have the Plough overhead, dragged out and distorted by the map projection used, while Virgo and the star Spica are nearing the meridian to the left of Jupiter. Spilling northwards from Virgo into the constellation of Coma Berenices is a region sometimes called the Realm of the Galaxies. This includes the Virgo cluster of well over 1,000 galaxies whose core lies some 54 million light years away and is roughly coincident with the “D” of “Denebola” on the chart.
More than a dozen of these Virgo galaxies are visible through medium-sizes telescopes and have entries in Charles Messier’s 18th century list of comet-like smudges in the sky. While it is impractical to plot their locations on our chart, a Web search and dark moonless skies over the next fortnight should allow some to be spotted.
The Sun climbs more than 10° northwards during April as sunrise/sunset times for Edinburgh change from 06:42/19:52 BST on the 1st to 05:30/20:51 on the 30th. New moon on the 7th is followed by first quarter on the 14th, full moon on the 22nd and last quarter on the 30th.
This month, Jupiter recedes from 676 million to 723 million km, dims only slightly from magnitude -2.4 to -2.3 and shrinks in diameter from 44 to 41 arcseconds. Binoculars show its four main moons and also show Jupiter passing only 7 arcminutes (one quarter of a Moon-breadth) above-left of the magnitude 4.6 star Chi Leonis on the 8th.
Jupiter loses its status as our sole evening planet this month. One of its usurpers is Mars which, as we’ll see, rises before midnight later in the period. The other is Mercury which emerges from the Sun’s glare over the coming week at the start of its best evening apparition of the year.
By the evening of the 8th, Mercury shines brightly at magnitude -0.9 and stands almost 8° high in the west-north-west 40 minutes after sunset. The very young crescent Moon, only 3% illuminated and brightly earthlit, lies 6° to its left but we will need a clear horizon, and perhaps even binoculars, to pick them out of the twilight. On the next evening, Mercury is 17° below-right of the still-spectacular earthlit Moon while, on the 10th, the Moon stands against the V-shaped Hyades star cluster in Taurus and sets as it draws close to the bright star Aldebaran.
As the Moon continues onwards, eventually to shine alongside Regulus on the 16th and Jupiter on the 17th, Mercury climbs to stand furthest east of the Sun (20°) on the 18th. By then, the innermost and smallest planet is 11° high 40 minutes after sunset and sets itself more than 90 minutes later still. It is fainter, though, at magnitude 0.2 and it dims further to magnitude 1.5 by the 25th when it is 2° lower and 7° below-right of the Pleiades. As Mercury dives towards the Sun’s near side, it is heading for a spectacular transit across the Sun’s face on May 9.
Mars is brightening rapidly as it draws closer to us on its way to opposition on May 22. It rises in the south-east about one hour after our chart times and from the 21st onwards rises before midnight as seen from Edinburgh. The best time to see it, though, is just before dawn when it reaches its highest point, admittedly only low down in the south. At magnitude -0.5 it is already the brightest object (after the Moon) down there, and by the month’s end it is more than twice as bright at magnitude -1.4.
Mars is currently in Scorpius, 6° north-north-west of the red supergiant star Antares, but it tracks 1.5° eastwards to a stationary point in Ophiuchus on the 17th before doubling back into Scorpius. Meantime, it approaches from 118 million to 87 million km and its disk swells from 12 to 16 arcseconds wide. Telescopes should reveal some markings on it desert surface, and perhaps its northern polar cap, but its low altitude is likely to make for poor observing conditions.
Not far to Mars’ left, and another victim of its low altitude, is the glorious ringed world Saturn. The second brightest object low in the south before dawn, it improves from magnitude 0.4 to 0.2 as it edges 1° westwards in Ophiuchus. Saturn lies almost 1,400 million km away in mid-April when its rotation-flattened disk is 18 arcseconds across and the rings span 40 arcseconds, their north face tipped 26° earthwards.
The Moon stands 4° above Mars before dawn on the 25th and a similar distance above-left of Saturn on the next morning.
This is a slightly-revised version of Alan’s article published in The Scotsman on April 1st 2016, with thanks to the newspaper for permission to republish here.
Jupiter conspicuous at opposition in Leo
The Sun, now climbing northwards at its fastest pace for the year, crosses the equator of the sky at 04:30 GMT on the 20th, the time of our vernal equinox. It then rises due east and sets due west, and days and night are equal in length around the globe.
The Sun’s progress means that our nights are falling rapidly later, an effect that appears to enjoy a step-change when we set our clocks forward to British Summer Time on the 27th, though, in this instance, the daylight we gain in the evening is lost in the morning. It is noticeable, too, that the stars at nightfall are shifting quickly to the west. Orion, for example, dominates in the south as darkness falls at present, but has tumbled well over into the south-west by the month’s end.
The Plough is nearing the zenith at our map times and it is the squat figure of Leo the Lion and the prominent planet Jupiter that dominate our southern sky. Jupiter is edging westwards beneath Leo’s hindquarters and passes just below the fourth magnitude star Sigma Leonis over the first few days of the month. Above and to its left is Denebola, the Lion’s tail, while further west (right) is Leo’s leading star Regulus in the handle of the Sickle. Algieba (see chart) appears as a glorious double star through a telescope.
Jupiter comes to opposition on the 8th when it stands opposite the Sun so that it rises in the east at sunset and is unmistakable as it climbs through our south-eastern evening sky to pass 40° high on Edinburgh’s meridian in the middle of the night. Eleven times wider than the Earth and yet with a day lasting under ten hours, it is 664 million km distant at opposition and shines at magnitude -2.5, more than twice as bright as any star other than the Sun.
View Jupiter through binoculars or a telescope, and the fun really begins. Binoculars show its four main moons, Io, Europa, Ganymede and Callisto, which change their relative positions to east and west of the planet’s disk from night to night as they orbit almost directly above the equator. Were it not for Jupiter’s glare, we could see all four of these with the naked eye.
With numerous sulphurous volcanoes, Io is the most geologically active body we know, while Europa is the only one of the four to be smaller than our Moon and is thought to harbour a deep ocean of water beneath its icy crust. This makes it so irresistible as a potential home for life that the US Congress has urged NASA to add a lander craft to a planned mission to Europa over the next decade.
The Jovian disk appears 44 arcseconds wide when we view it through a telescope at present. Even a small telescope shows its main cloud belts but the smaller cloud features that indicate Jupiter’s rotation are more of a challenge. The famous Great Red Spot in the southern hemisphere is a storm that has raged for at least 185 years but is now shrinking noticeably.
By the time Jupiter is sinking in the west before dawn, the two brightest objects low in the south are Mars and Saturn. Mars stands 18° to the right of Saturn and is slightly the brighter of the two at present – their magnitudes being 0.3 and 0.5 respectively, with both of them outshining the red supergiant star Antares in Scorpius which lies more than 5° lower and between them. The Moon stands above-left of Mars on the 1st, above Saturn on the 2nd, and above and between them both on the 29th.
This month Saturn improves only slightly to magnitude 0.4 and hardly moves in southern Ophiuchus, being stationary in position on the 25th. Mars, tracking eastwards from Libra to Scorpius, more than doubles in brightness to magnitude -0.5 as it approaches from 161 million to 118 million km. It also swells in diameter from 9 to 12 arcseconds and telescopes are starting to show surface features, including its north polar cap. There is no comparison, though, with the beauty of Saturn whose superb rings have their north face tipped Earthwards at 26°, near their maximum tilt, and stretch across 38 arcseconds. Saturn’s disk is 17 arcseconds wide and has much more subdued cloud belts than Jupiter.
Although Venus is brilliant at magnitude -3.9, we have slim hopes of seeing it deep in our south-eastern twilight for just a few more mornings. Mercury, already lost from view, reaches superior conjunction on the Sun’s far side on the 23rd.
The sunrise/sunset times for Edinburgh change from 07:03/17:48 GMT on the 1st to 06:45/19:50 BST (05:45/18:50 GMT) on the 31st. The Moon is at last quarter on the 1st, new on the 9th, at first quarter on the 15th, full on the 23rd and at last quarter again on the 31st.
New moon on the 9th brings the first and best of this year’s four eclipses when a total eclipse of the Sun occurs along a path that travels eastwards across Indonesia before swinging north-eastwards over the Pacific to end to the north of Hawaii. Surrounding areas enjoy a partial eclipse but there is nothing to see from Europe. The Moon slims the outer and lighter shadow of the Earth during a penumbral lunar eclipse on the 23rd. Also best seen over the Pacific, it is partly visible from most of the Americas and eastern Asia, but only a minor fading of the southern part of the Moon may be expected.
This is a slightly-revised version of Alan’s article published in The Scotsman on March 1st 2016, with thanks to the newspaper for permission to republish here. Journal Editor’s apologies for the lateness of the article appearing 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.
This is a slightly-revised version of Alan’s article published in The Scotsman on April 29th 2014, with thanks to the newspaper for permission to republish here.
Mars shines brightly at opposition in Virgo
Six years have passed since Mars was as close and bright as it is this month, but two other planets outshine it and a fourth, Saturn, will soon be at its best for the year. There are also two of 2014’s four eclipses but, as with the second pair in October, neither is of much interest for observers in Scotland.
For the moment, our evening sky retains a flavour of stellar feast we enjoyed over the winter. Orion is still on show in the south-west at nightfall below the conspicuous planet Jupiter. Orion’s Belt now lies almost parallel to the horizon, a line along it pointing to the left towards Sirius, our brightest nighttime star, and to the right towards Aldebaran and the Pleiades in Taurus. By our star map times, though, Orion has all but sunk below our western horizon.
Jupiter, however, continues as our brightest evening object bar the Moon. As it slips 3.5° or seven Moon-widths eastwards in the middle of Gemini during April, it fades a little between magnitude -2.2 and -2.0 and its telescopic diameter shrinks from 38 to 35 arcseconds. The earlier in the night that we catch it, the higher it stands and the sharper the view of its cloud-banded disk. By our map times Jupiter is some 30° high in the west and on its way to setting in the north-west four hours later.
The month begins with impressive views of the young earthlit Moon in the west at nightfall. It is only 5% illuminated on the 1st as it stands 14° high forty minutes after sunset. Look for it below the Pleiades on the 2nd, below the Aldebaran-Pleiades line on the 3rd and 6° below Jupiter on the 6th as it nears first quarter.
Mars reaches opposition on the 8th when it lies 93 million km away and shines at magnitude -1.5 so that its orange-red beacon rivals Sirius in brightness if not in colour. By definition, it stands opposite the Sun in the sky so that we find it climbing from the eastern horizon as the evening twilight fades to pass 28° high on Edinburgh’s meridian two hours after our map times. As the arrow on our south map shows, Mars tracks 10° westwards in Virgo during April, from 5° above the magnitude 1.0 Spica today to lie 1.6° below-left of the famous binary star Porrima as the month ends.
Often the day of opposition is when a planet is closest to us but Mars is approaching the Sun in its orbit and is 450,000 km closer to us on the 14th than on the 8th. Through a telescope, its ochre disk is 15 arcseconds wide and shows dusky markings and the dwindling white smudge of its north polar ice cap, tipped about 22° towards us.
The full Moon lies below Mars on the evening of the 14th and is approaching Spica as it sets for Edinburgh at 06:08 BST on the 15th. Only 14 minutes before this, and while it is less than 2° above the west-south-western horizon in the twilight, it begins to enter the outer shadow of the Earth, the penumbra. Sadly, we have no hope of seeing any dimming of the lunar disk before it sets. Observers in the Americas are much better placed to view the resulting total eclipse of the Moon which is total from 08:07 until 09:26 BST (03:07 to 04:25 EDT).
Sunrise/sunset times for Edinburgh change from 06:44/19:51 BST on the 1st to 05:32/20:50 on the 30th while the duration of nautical twilight at dawn and dusk stretches from 84 to 105 minutes. After first quarter on the 7th, the Moon is full during the eclipse on the 15th, at last quarter on the 22nd and new on the 29th when a small area of Antarctica and perhaps a few penguins experience an annular eclipse of the Sun. A partial solar eclipse is visible from Australia and the southern Indian Ocean.
On course to reach opposition in May, Saturn rises at Edinburgh’s east-south-eastern horizon at 23:31 on the 1st and only 36 minutes after sunset by the 30th, climbing to pass 18° high on the meridian four hours after our map times. Improving from magnitude 0.3 to 0.1, it edges westwards in Libra and draws ever closer to the Moon overnight on the 16th-17th when Saturn’s disk is 18 arcseconds wide while its stunning rings span 42 arcseconds.
Mercury is hidden in the dawn twilight until it passes around the Sun’s far side on the 26th. Venus, brilliant as a morning star, rises in the east-south-east seventy minutes before sunrise on the 1st and in the east only 51 minutes before the Sun on the 30th. Dimming from magnitude -4.3 to -4.1, its gibbous disk shrinks from 22 to 17 arcseconds in diameter.
It is less than a month since results from NASA’s WISE spacecraft appeared to rule out any Jupiter or Saturn-sized planet lurking unseen in the outermost solar system. Now we learn that a new dwarf planet, dubbed 2012 VP113, has been found to have an orbit that comes no closer to the Sun than 80 times the Earth’s distance, further than any other known object in the solar system. Thought to be a ball of rock and ice perhaps 450 km wide, it may be six times further away at its farthest, and take perhaps 5,000 years to complete each orbit.
Surprisingly, 2012 VP113’s orbit is similarly orientated to those of some other remote bodies, including the only other comparable object, Sedna. There is speculation that this is because they are influenced by a larger undiscovered world, perhaps a super-Earth, even further out.
This is a slightly-revised version of Alan’s article published in The Scotsman on April 2nd 2014, with thanks to the newspaper for permission to republish here.
Orion and Jupiter are unmistakable at nightfall
March sees Jupiter high and conspicuous in our southern sky at nightfall as Mars brightens considerably and rises well before midnight on its way to opposition in April.
Meanwhile, the Sun’s climb northwards means that it is already two and a half times higher in Edinburgh’s sky at midday than it was at our winter solstice on 21 December and by the end of March it will stand 38° high, almost four times higher than it did at midwinter. The moment when it crosses the equator comes this year at 16:57 GMT on the 20th and marks our spring or vernal equinox. Although this is often cited as the first day of spring, meteorologists now use 1 March as this milestone.
The days are lengthening, too, and the sunrise/sunset times for Edinburgh change from 07:04/17:47 GMT on the 1st to 05:46/18:49 GMT on the 31st. We set our clocks forwards to British Summer Time on the 30th, so the latter times translate to 06:46/19:49 BST. With nautical twilight persisting for 84 minutes, effective darkness does not arrive until 21:13 BST as the month ends, less than one hour after our map times.
Another consequence is that our sky at nightfall is changing quickly. The glorious constellation of Orion the Hunter, for example, stands proudly in the south at nightfall at present but has shifted lower into the south-west by the 31st, taking with him Taurus and his faithful companion, Sirius the Dog Star. Our maps show him even lower in the west-south-west as his place near the meridian has been claimed by Leo the Lion whose main star Regulus shines in the handle of the reversed question-mark of stars known as the Sickle.
Meanwhile, Ursa Major is soaring from the east to overhead. As I mentioned last time, it was in the galaxy M82 in Ursa Major that a group of students in London discovered one of the brightest and closest supernovae for several years. After peaking as an easy telescopic object near magnitude 10.5 in early February, that stellar explosion has now dimmed to be closer to the twelfth magnitude.
It is Jupiter that really catches the eye during our March evenings. As the brightest object high in the southern sky at nightfall, it is slow-moving against the stars of Gemini, above and to the left of Orion and just 1.8° to the south of the third magnitude star Mebsuta. In fact, it reaches a so-called stationary point on the 6th when its westerly or retrograde progress against the stars reverses to a more usual easterly or direct motion. Such apparent changes in motion result from our changing vantage point on the moving Earth.
The giant planet recedes from 695 million to 767 million km and dims slightly from magnitude -2.4 to -2.2. Binoculars show its four main moons while telescopes sometimes reveal the inky shadows of one or other of the moons on its cloud-banded globe which shrinks from 42 to 38 arcseconds. Chances to view Jupiter at its sharpest while high in the sky are beginning to run out – by our map times it is already sinking towards the west and it sets in the north-west before dawn.
Our second conspicuous evening planet is Mars which rises in the east-south-east one hour before our map times and crosses our lower southern sky during the early hours. After its own stationary point on the 1st, 6° north-east of Spica in Virgo, it moves to lie 5° north of Spica on the 31st, as indicated by the arrow on our chart. Spica is a blue-white star of magnitude 1.0 and considerable fainter than the distinctively reddish hue of Mars which again doubles in brightness from magnitude -0.5 to -1.3.
Due to reach opposition in April, Mars approaches from 121 million to 95 million km during March as its diameter swells from 12 to 15 arcseconds, large enough for surface markings to be glimpsed through decent telescopes. The northern hemisphere of Mars experienced its own midsummer in mid-February and the small white button of the northern polar ice cap is tipped 20° towards us in mid-March.
Saturn, magnitude 0.4 to 0.3 and at a stationary point in Libra on the 3rd, rises in the east-south-east less than two hours after our map times and trails some 25° behind Mars, and slightly lower, as it crosses our southern sky before dawn. Venus continues as a brilliant morning star though its altitude in the south-east at sunrise falls from 12° to 8° and it fades a little from magnitude -4.6 to -4.3. Viewed telescopically, it shrinks from 33 to 22 arcseconds in diameter and changes from a crescent to slightly gibbous in form. While Venus is furthest west of the Sun (47°) on the 22nd, Mercury lies 28° west of the Sun on the 14th but is probably too low in the predawn twilight to be seen from Scotland.
The Moon is new on the 1st, at first quarter on the 8th, full on the 16th, at last quarter on the 24th and new again on the 30th. Look for the young earthlit Moon low in the west-south-west at nightfall on the 3rd and 4th. It lies south of the Pleiades on the 6th and against the stars of the Hyades near Aldebaran in Taurus on the 7th. After passing south of Jupiter on the 10th, it lies below Regulus on the 14th and between Mars and Spica as they rise on the 18th. It has a close conjunction with Saturn on the morning of the 21st and stands just above Venus on the 27th.