Giant world Jupiter becoming obvious in May’s twilit nights
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
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.
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.
Jupiter rules our April nights
Venus dominated our evening sky for the first quarter of 2017, but it is now Jupiter’s turn in the spotlight. The conspicuous giant planet lies directly opposite the Sun in the sky on the 7th so that it rises in the east at sunset, reaches its highest point in the south in the middle of the night and sets in the west at sunrise.
Our charts show it in Virgo to the east of south as Taurus and Orion dip beneath the western horizon and the Plough looms overhead, stretched out of its familiar shape by our map projection. Regulus in Leo is in the south-west and almost level with Arcturus in Bootes in the south-east. Vega in Lyra and Deneb in Cygnus are beginning their climb in the north-east.
Sunrise/sunset times for Edinburgh change from 06:43/19:51 BST on the 1st to 05:31/20:50 on the 30th. The Moon is at first quarter on the 3rd, full on the 11th, at last quarter on the 19th and new on the 26th.
Venus rises only a little more than one hour before sunrise and, though brilliant at magnitude -4.2, may be difficult to spot low in the east before dawn. However, the other inner planet, Mercury, remains nicely placed in the evening and stands furthest east of the Sun (19°) on the 1st.
Thirty minutes after Edinburgh’s sunset on that day, Mercury is 12° high in the west and shines at magnitude 0.0. It should be possible to spy it through binoculars and eventually with the unaided eye as the twilight fades and the planet sinks to set another 96 minutes later. By the 8th, though, it is a couple of degrees lower and a quarter as bright at magnitude 1.6 as it is engulfed by the twilight. Inferior conjunction on the Sun’s near side occurs on the 20th.
Mars, magnitude 1.5 to 1.6 and above and to Mercury’s left at present, tracks east-north-eastwards this month to pass 5° below the Pleiades on the 15th and a similar distance left of the star cluster on the 26th. By then it sets late enough to be plotted near our north-western horizon at the star map times.
Its opposition means that Jupiter is at its brightest and closest, shining more brightly than any star at magnitude -2.5 and a distance of 666 million km. It lies 6° north-west (above-right) of Virgo’s leading star Spica as the month begins and tracks 3.7° westwards during April to pass 10 arcminutes or a third of a Moon’s-width south of the fourth magnitude star Theta Virginis on the 5th.
Jupiter lies close to the full Moon on the night of the 10th-11th when the Jovian disk appears 44 arcseconds wide if viewed telescopically, one fortieth as wide as the Moon.
Jupiter’s clouds are arrayed in bands that lie parallel to its equator, the dark ones called belts and the intervening lighter hued ones called zones. There are numerous whirls and spots, the most famous being the Great Red Spot in the southern hemisphere. The planet spins in under ten hours, so a resolute observer might view the entire span of its clouds in a single April night. The four main moons, visible through decent binoculars and easy through a telescope, lie on each side of the disk and change their configuration from night to night.
The beautiful planet Saturn rises in the south-east less than three hours after our map times and is the brightest object (magnitude 0.4 to 0.3) less than 15° above Edinburgh’s southern horizon before dawn. It is a shame that its low altitude means that we miss the sharpest and most impressive views of it rings which span 39 arcseconds in mid-April, and are tilted at 26° around its 17 arcseconds disk. After appearing stationary on the 6th, Saturn begins to creep westwards against the stars of Sagittarius – look for it below and left of the Moon on the 16th and right of the Moon on the 17th.
It is not often that I advertise the annual Lyrids meteor shower. As one of the year’s lesser displays, it yields only some 18 meteors per hour at best, all of them swift and some leaving glowing trains in their wake as they diverge from a radiant point to the right of Vega. The event lasts from the 18th to the 25th and peaks on the 22nd when moonlight should not interfere unduly this year. The Lyrid meteoroids were released by Comet Thatcher, last seen in 1861.
Bright comets have been rare of late, but fainter ones are observed frequently. One such has the jaunty name of comet 41P/Tuttle–Giacobini–Kresák and takes 5.4 years to orbit between the paths of Jupiter and the Earth. It passes within 21 million km of us on the 1st as it nears perihelion, its closest point to the Sun, on the 12th. I glimpsed it through binoculars from a superb dark-sky site at Kielder Forrest, Northumberland, last week when it was a diffuse seventh magnitude smudge close to Merak, the southern star of the Pointers in the Plough.
Although its path is not depicted on our chart, the comet is poised to sweep close to three of the stars identified in Draco, between the Plough and Polaris, the Pole Star. It passes 0.6° north of Thuban on the night of the 2nd-3rd, 1.5° south-west of Eta on the 11th (sadly, in full moonlight) and 0.6° west of Beta on the 18th-19th. During past perihelia, it has been seen to flare by several magnitudes for a few days at a time, so, if we are lucky, it may reach naked-eye visibility.
This is a slightly-revised version of Alan’s article published in The Scotsman on March 31st 2017, with thanks to the newspaper for permission to republish here.
Brilliant Venus plunges into the evening twilight
Stargazers will be hoping for better weather as Orion and the stars of winter depart westwards in our evening sky, Venus dives into the evening twilight and around the Sun’s near side, while all the other bright planets are on view too. Indeed, Venus has the rare privilege of appearing as both an evening star and a morning star over several days, provided our western and eastern horizons are clear.
Orion still dominates our southern sky at nightfall as Leo climbs in the east and the Plough balances on its handle in the north-east. The Sun’s northwards progress and our lengthening days mean that by nightfall at the month’s end Orion has drifted lower into the south-west, halfway to his setting-point in the west. He is even lower in the west-south-west by our star map times when it is the turn of Leo to reach the meridian and the Plough to be almost overhead.
Leo’s leading star, Regulus, sits at the base of the Sickle of Leo, the reversed question-mark of stars from which meteors of the Leonids shower stream every November. The star Algieba in the Sickle (see chart) appears as a glorious double star through a telescope. Its components are larger and much more luminous than our Sun and lie almost 5 arcseconds apart, taking some 510 years to orbit each other. The pair lie 130 light years away and are unrelated to the star less than a Moon’s breadth to the south which is only half as far from us.
The Sun travels northward across the equator at 10:28 GMT on the 20th, the moment of the vernal (spring) equinox in our northern hemisphere. On this date, nights and days are of roughly equal length around the globe. Sunrise/sunset times for Edinburgh change from 07:04/17:47 GMT on the 1st to 06:46/17:49 BST (05:46/18:49 GMT) on the 31st after we set our clocks forwards to BST on the morning of the 26th. The lunar phases change from first quarter on the 5th to full on the 12th, last quarter on the 20th and new on the 28th.
Look for the young earthlit Moon well to the left of the brilliant magnitude -4.6 Venus on the 1st when telescopes show the planet’s dazzling crescent to be 47 arcseconds in diameter and 16% sunlit. Venus’ altitude at sunset plummets from 29° in the west-south-west on that day to only 7° in the west on the 22nd as its diameter swells to 59 arcseconds and the phase shrinks to only 1% – indeed, a few keen-sighted people might be able to discern its crescent with the naked eye and this is certainly easy to spot through binoculars.
Venus dims to magnitude -4.0 by the time it sweeps 8° north of the Sun and only 42 million km from the Earth at its inferior conjunction on the 25th. This marks its formal transition from the evening to the morning sky, but because it passes so far north of the Sun as it does every eight years or so, Venus is already visible in the predawn before we lose it in the evening. In fact, it is 7° high in the east at sunrise on the 22nd, and it only gets better as the month draws to its close.
Before Venus exits our evening sky, it meets Mercury as the latter begins its best spell as an evening star this year. On the 20th, the small innermost planet lies 10° to the left of Venus, shines at magnitude -1.2 and sets at Edinburgh’s western horizon 78 minutes after the Sun. By the 29th, it is 10° high forty minutes after sunset and shines at magnitude -0.4, easily visible through binoculars and 8° to the right of the very young Moon.
Mars, near the Moon on the 1st and again on the 30th, dims from magnitude 1.3 to 1.5 this month as it tracks from Pisces into Aries. By the month’s end, it lies to the left of Aries’ main star Hamal and sets at our map times. It is now more than 300 million km away and its disk, less than 5 arcseconds across, is too small to be of interest telescopically.
The Moon has another encounter with the Hyades star cluster on the night of the 4th-5th, hiding several of its stars but setting for Scotland before it reaches Taurus’ main star Aldebaran. The latter, though, is occulted later as seen from most of the USA. The Moon passes just below Regulus on the night of the 10th-11th and meets the planet Jupiter on the 14th.
Jupiter, conspicuous at magnitude -2.3 to -2.5, rises in the east at 21:37 GMT on the 1st and only 31 minutes after Edinburgh’s sunset on the 31st. Now edging westwards above the star Spica in Virgo, it is unmistakable as it climbs through our south-eastern sky to cross the meridian in the small hours and lie in the south-west before dawn. Its disk, 43 arcseconds wide at mid-month, shows parallel cloud bands through almost any telescope, while its four moons may be glimpsed through binoculars as they orbit from one side to the other.
Saturn, the last of the night’s planets, rises in the south-east at 03:44 GMT on the 1st and almost two hours earlier by the 31st. Improving very slightly from magnitude 0.5 to 0.4 during March, it is the brightest object about 10° above the south-south-eastern horizon before dawn. Look for it 4° below-left of the Moon on the 20th.
This is a slightly-revised version of Alan’s article published in The Scotsman on February 28th 2017, with thanks to the newspaper for permission to republish here.
Nights begin with Venus and end at Jupiter
The end of British Summer Time means that we now enjoy six hours of official darkness before midnight, though I appreciate that this may not be welcomed by everyone. The starry sky as darkness falls, however, sees only a small shift since a month ago, with the Summer Triangle, formed by the bright stars Vega, Deneb and Altair, now just west of the meridian and toppling into the middle of the western sky by our star map times.
Those maps show the Square of Pegasus high in the south. The star at its top-left, Alpheratz, actually belongs to Andromeda whose other main stars, Mirach and Almach, are nearly equal in brightness and stand level to its left. A spur of two stars above Mirach leads to the oval glow of the Andromeda Galaxy, M31, which is larger than our Milky Way and, at 2.5 million light years, is the most distant object visible to the unaided eye. It is also approaching us at 225 km per second and due to collide with the Milky Way in some 4 billion years’ time.
Binoculars show M31 easily and you will also need them to glimpse more than a handful of stars inside the boundaries of the Square of Pegasus, even under the darkest of skies. In fact, there are only four such stars brighter than the fifth magnitude and another nine to the sixth magnitude, close to the naked eye limit under good conditions. How many can you count?
Mars is the easiest of three bright planets to spot in tonight’s evening sky. As seen from Edinburgh, it stands 11° high in the south as the twilight fades, shining with its customary reddish hue at a magnitude of 0.4, and appearing about half as bright as the star Altair in Aquila, 32° directly above it.
Now moving east-north-eastwards (to the left), Mars is 5° below-right of the Moon on the 6th and crosses from Sagittarius into Capricornus two days later. Soon after this, it enters the region covered by our southern star map, its motion being shown by the arrow. By the 30th, Mars has dimmed slightly to magnitude 0.6 but is almost 6° higher in the south at nightfall, moving to set in the west-south-west at 21:00. It is a disappointingly small telescopic sight, though, its disk shrinking from only 7.5 to 6.5 arcseconds in diameter as it recedes from 188 million to 215 million km.
We need a clear south-western horizon to spy Venus and Saturn, both low down in our early evening twilight. Venus, by far the brighter at magnitude -4.0, is less than 4° high in the south-west thirty minutes after sunset, while Saturn is 4° above and to its right, very much fainter at magnitude 0.6 and only visible through binoculars. The young earthlit Moon may help to locate them – it stands 3° above-right of Saturn on the 2nd and 8° above-left of Venus on the 3rd.
Mercury is out of sight in the evening twilight and Saturn will soon join it as it tracks towards the Sun’s far side. However, Venus’ altitude thirty minutes after sunset improves to 9° by the 30th when it sets for Edinburgh at 18:30 and is a little brighter at magnitude -4.1. Viewed telescopically, Venus shows a dazzling gibbous disk that swells from 14 to 17 arcseconds as its distance falls from 178 million to 149 million km.
Sunrise/sunset times for Edinburgh change from 07:20/16:31 on the 1st to 08:18/15:44 on the 30th. The Moon reaches first quarter on the 7th, full on the 14th, last quarter on the 21 and new on the 28th.
The full moon on the 14th occurs only three hours after the Moon reaches its perigee, the closest point to the Earth in its monthly orbit. As such, this is classed as a supermoon because the full moon appears slightly (7%) wider than it does on average. By my reckoning, this particular lunar perigee, at a distance of 356,509 km, is the closest since 1948 when it also coincided with a supermoon.
Of the other planets, Neptune and Uranus continue as binocular-brightness objects in Aquarius and Pisces respectively in our southern evening sky, while Jupiter, second only to Venus in brightness, is now obvious in the pre-dawn.
Jupiter rises at Edinburgh’s eastern horizon at 04:28 on the 1st and stands more than 15° high in the south-east as morning twilight floods the sky. It outshines every star as it improves from magnitude -1.7 to -1.8 by the 30th when it rises at 03:07 and is almost twice as high in the south-south-east before dawn.
Currently close to the famous double star Porrima in Virgo, Jupiter is 13° above-right of Virgo’s leader Spica and draws 5° closer during the period. Catch it less than 3° to the right of the waning earthlit Moon on the 25th. Jupiter’s distance falls from 944 million to 898 million km during November while its cloud-banded disk is some 32 arcseconds across.
The annual Leonids meteor shower has produced some stunning storms of super-swift meteors in the past, but probably not this year. Active from the 15th to 20th, it is expected to peak at 04:00 on the 17th but with no more than 20 meteors per hour under a dark sky. In fact, the bright moonlight is likely to swamp all but the brightest of these this year. Leonids diverge from a radiant point that lies within the Sickle of Leo which climbs from low in the east-north-east at midnight to pass high in the south before dawn.
This is a slightly-revised version of Alan’s article published in The Scotsman on November 1st 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.
November nights end with planets on parade
With the return of earlier and longer nights, astronomy enthusiasts have plenty to observe in November. As in October, though, the real highlight is the parade of bright planets in our eastern morning sky.
The first to appear is Jupiter which rises above Edinburgh’s eastern horizon at 02:04 GMT on the 1st and by 00:35 on the 30th. More conspicuous than any star, it brightens from magnitude -1.8 to -2.0 this month as it moves 4° eastwards in south-eastern Leo. It lies 882 million km away and appears 33 arcseconds wide through a telescope when it stands 4° to the left of the waning Moon on the 6th.
Following close behind Jupiter at present is the even more brilliant Venus. This rises 34 minutes after Jupiter on the 1st and stands 5° below and to its left as they climb 30° into the south-east before dawn. In fact, the two were only 1° apart in a spectacular conjunction on the morning of October 26 and Venus enjoys an even closer meeting with the planet Mars over the first few days of November.
On the 1st, Venus blazes at magnitude -4.3 and lies 1.1° to the right of Mars, some 250 times fainter at magnitude 1.7. The pair are closest on the 3rd, with Venus only 0.7° (less than two Moon-breadths) below-right of Mars, before Venus races down and to Mars’ left as the morning star sweeps east-south-eastwards through the constellation Virgo. Catch Mars and Venus 2° apart on the 7th as they form a neat triangle with the Moon, a triangle that contains Virgo’s star Zavijava.
Venus lies only 4 arcminutes above-left of the star Zaniah on the 13th, and 1.1° below-left of Porrima on the 18th. The final morning of the month finds it 4° above-left of Virgo’s leading star Spica. By then Mars is 14° above and to the right of Venus and 1.3° below-right of Porrima, while Jupiter is another 19° higher and to their right.
Venus dims slightly to magnitude -4.2 during November, its gibbous disk shrinking as seen through a telescope from 23 to 18 arcseconds as its distance grows from 110 million to 142 million km. Mars improves to magnitude 1.5 and is only 4 arcseconds wide as it approaches from 329 million to 296 million km.
Neither Mercury nor Saturn are observable during November as they reach conjunction on the Sun’s far side on the 17th and 30th respectively.
More than 15° above and to the right of Jupiter is Leo’s leading star Regulus, while curling like a reversed question-mark above this is the Sickle of Leo from which meteors of the Leonids shower diverge between the 15th and 20th. The fastest meteors we see, these streak in all parts of the sky and are expected to be most numerous, albeit with rates of under 20 per hour, during the morning hours of the 18th.
The Sun plunges another 7.5° southwards during November as sunrise/sunset times for Edinburgh change from 07:19/16:33 GMT on the 1st to 08:18/15:44 on the 30th. The Moon is at last quarter on the 3rd, new on the 11th, at first quarter on the 19th and full on the 25th.
As the last of the evening twilight fades in early November, the Summer Triangle formed by bright stars Vega, Deneb and Altair fills our high southern sky. By our star map time of 21:00 GMT, the Triangle has toppled into the west to be intersected by the semicircular border of both charts – the line that arches overhead from east to west and separates the northern half of our sky from the southern.
The maps show the Plough in the north as it turns counterclockwise below Polaris, the Pole Star, while Cassiopeia passes overhead and Orion rises in the east.
The Square of Pegasus is high in the south with Andromeda stretching to its left as quintet of watery constellations arc across our southern sky below them. These are Capricornus the Sea Goat, Aquarius the Water Bearer, Pisces the (Two) Fish, Cetus the Water Monster and Eridanus the River.
One of Pisces’ fish lies to the south of Mirach and is joined by a cord to another depicted by a loop of stars dubbed the Circlet below the Square. Like the rest of Pisces, they are dim and easily swamped by moonlight or street-lighting. Just to the left of the Circlet, one of the reddest stars known is visible easily though binoculars. TX Piscium is a giant star some 760 light years away and has a surface temperature of perhaps 3,200C compared with our Sun’s 5,500C.
Omega Piscium, to the left of the Circlet, is notable because it sits only two arcminutes east of the zero-degree longitude line in the sky – making it one of the closest naked-eye stars to the celestial equivalent of our Greenwich Meridian. The celestial counterparts of latitude and longitude are called declination and right ascension. Declination is measured northwards from the sky’s equator while right ascension is measured eastwards from the point at which the Sun crosses northwards over the equator at the vernal equinox.
That point lies 7° to the south of Omega but drifts slowly westwards as the Earth’s axis wobbles over a period of 26,000 years – the effect known as precession.
Below Pisces lies Cetus, the mythological beast from which Perseus rescued Andromeda. Its brightest stars, Menkar and Deneb Kaitos, are both orange-red giants, the latter almost identical in brightness to Polaris at magnitude 2.0. Another, Mira, takes 11 months to pulsate between naked-eye and telescopic visibility and is currently near its minimum brightness.
This is a slightly-revised version of Alan’s article published in The Scotsman on October 30th 2015, with thanks to the newspaper for permission to republish here. Journal Editor’s apologies for the lateness of the article appearing here.
A quarter-century for the Hubble Space Telescope
Just 25 years ago, scientists worldwide were celebrating the successful launch of the Hubble Space Telescope. We soon learned, though, that its precisely-figured 2.4-metre mirror had been built to the wrong shape, and we had to wait another three years before corrective optics could be installed to correct its blurred vision. Since then, Hubble has been returning research and a gallery of stunning images that have transformed our understanding of the Universe.
Its findings impact on every area of astronomy, and every distance-scale, from the farthest and earliest galaxies to the processes of star formation and images of objects in our solar system in unprecedented detail. It has also been a key player in the discovery that the entire Universe is expanding at an increasing rate because of a mysterious entity dubbed dark energy.
It is now six years since a shuttle visited to service it for the final time, and its instruments will eventually fail. Its orbit is also decaying because of the tiny atmospheric drag at its current altitude of 545 km, and it may spiral to destruction within another decade or so.
However, we expect that Hubble will still be alive when its successor, the James Webb Space Telescope, the JWST, is launched, hopefully in 2018. With a segmented 6.5-metre mirror, and working between visible and infrared wavelengths, this should build on Hubble’s legacy. The UK Astronomy Technology Centre at Edinburgh’s Royal Observatory has leading roles in the consortium from Europe and NASA that has built one of the JWST’s three main instruments, the Mid-InfraRed Instrument or MIRI.
As the Sun climbs another 7° higher at noon during May, Edinburgh’s days lengthen by almost two hours, although we lose much more than this of nighttime darkness. On the 1st, the Sun is more than 12° below Edinburgh’s horizon, and the sky effectively dark, for a little more than five hours, but by the month’s end this shrinks to only 32 minutes. More accurately, the sky would be dark for these periods were it not for the moonlight at the start and end of the month.
Sunrise/sunset times for Edinburgh vary from 05:30/20:51 BST on the 1st to 04:37/21:45 on the 31st while the Moon is full on the 4th, at last quarter on the 11th, new on the 18th and at first quarter on the 25th.
The conspicuous star Arcturus in Bootes is climbing in the east at nightfall to dominate the high southern sky by our map times although it pales by comparison with the planets Jupiter and Venus which lie further to the west.
Below and right of Arcturus is Virgo and the closest giant cluster of galaxies, the Virgo Cluster. Located some 54 million light years away, and one of Hubble’s earliest targets, it contains up to 2,000 galaxies, more than a dozen of which are visible through small telescopes under a dark sky. Its centre lies roughly midway between the stars Vindemiatrix in Virgo, and Leo’s tail-star Denebola (see map).
Another planet, Saturn, shines at magnitude 0.0 and almost rivals Arcturus in brightness when it reaches opposition at a distance of 1,341 million km on the 23rd. It is then best placed on the meridian in the middle of the night, though it stands only 15° above Edinburgh’s horizon so that telescopic views of its rings and globe, 42 and 18 arcseconds wide respectively, may be hindered by turbulence in our atmosphere.
Currently 1.2° north of the double star Graffias in Scorpius, Saturn creeps westwards into Libra by the day of opposition. The rings have their northern face tilted 24° towards us at present and although this will increase to 26° next year, Saturn itself slides another 2° further south. Catch Saturn to the right of the Moon on the 5th-6th.
This is the best time this year to glimpse Mercury in our evening sky. Until the 11th, it stands 10° or more above the west-north-western horizon forty minutes after sunset before it sinks to set more than two hours later. It dims from magnitude -0.3 on the 1st to 1.0 on the 11th and may be followed through binoculars for just a few more days as it sinks lower and fades to magnitude 1.7 by the 15th. Mercury stands furthest from the Sun (21°) on the 7th and passes around the Sun’s near side at inferior conjunction on the 30th.
The brilliant evening star Venus improves from magnitude -4.1 to -4.3 and is unmistakable in the west at sunset, sinking to set in the north-west after 01:00. From between the Horns of Taurus at present, it tracks eastwards into Gemini to stand 1.7° above-right of the star cluster M35 on the 9th (use binoculars) and end the month 4° to the south of Pollux in Gemini. Venus approaches from 148 million to 113 million km during the period as its gibbous disk swells from 17 to 22 arcseconds and its sunlit portion falls from 67% to 53%.
Jupiter still outshines every star, but is fainter than Venus and stands above and well to its left, their separation in the sky plummeting from 50° on the 1st to 21° on the 31st. Look for Jupiter in the south-west at nightfall at present and much lower in the west by our map times. This month it fades a little from magnitude -2.1 to -1.9 and tracks 3° eastwards to the east of the Praesepe star cluster in Cancer (use binoculars). The planet lies above the crescent Moon and 833 million km away on the 23rd when a telescope shows its cloud-banded disk to be 35 arc seconds across.