For the amateur astronomer in a city, the biggest obstacle is light pollution, mainly from street lighting. Until recently, most street lights were sodium discharge lamps, initially low pressure (LPS), but later high pressure (HPS). These lamps gave good and efficient lighting although the LPS lamps gave poor colour rendering (better with HPS).
For amateur astronomers, because sodium lamps produce virtually monochromatic light in a small wavelength band averaging about 593 nm, the light pollution (skyglow) could be removed by using optical glass filters although nowadays the filtering can be achieved via astronomy software for astrophotograhy.
For this discussion colour temperature is important; that is the temperature at which a black body would emit radiation of the same colour as a given object. The relationship between colour and temperature is familiar to astronomers because it is how stars are classified. The colour temperature of LPS is 1800 K while the SON type of HPS has a colour temperature of 2700 K (the higher the colour temperature, the bluer the light). HPS lamps give a wider colour spectrum, but can still be filtered.
Like many cities across the world, the City of Edinburgh Council (CEC) has begun to replace sodium street light luminaires with light-emitting diode (LED) clusters. The case for this change is that LEDs are more energy efficient (using less electricity) and give a nearly full spectrum of light. The colour temperature of CEC’s LEDs is between 3700 and 4300 K. (For comparison moonlight has a colour temperature of 4100-4150 K and for daylight it is about 6000 K.) As a result, LED street lights emit much more blue-rich light than HPS lamps. This can impede night sky observations and also affect the health of humans, plants and animals. There is even evidence that exposure to this blue light can increase the risk of breast and prostate cancer.
Unfortunately for amateur astronomers, blue light is far more polluting than red or yellow light as the amount of light scattered by small particles in the atmosphere is inversely proportional to the wavelength. Blue light also contributes to glare, a growing problem in brightly-lit cities .
This is a matter that greatly concerns the International Dark-Sky Association (IDA) . Its Fixture Seal of Approval (FSA) provides objective, third-party certification for luminaires that minimize glare, reduce light trespass and do not pollute the night sky. In 2014 the FSA programme began requiring lighting that has a colour temperature of 3000 and lower (up to 3220 K actual measured value). However, with the rapid pace of technological advance in the lighting industry, the IDA is likely to reduce its recommendation to 2700 K or lower. The IDA seeks the best possible scenario for new LED installations and retrofits to replace old technology without increasing light output and minimizing short wavelength emissions while also decreasing operational costs and energy consumption.
In April this year I asked CEC if they would be following the IDA’s recommendations, but their response was to claim that their design and specifications are in line with current British Standards (these appear to require LEDs to have a minimum colour temperature of 4000 K). Understandably, CEC would be reluctant to change its specification for LEDs.
ASE is the only amateur organisation in Edinburgh that can legitimately express a view on this matter. Consequently ASE should press CEC to correct its present specification to reduce light pollution to reduce skyglow, if for no other reason of which there are many. Without this change, Edinburgh residents are unlikely to see much of the night sky and amateur astronomers will be frustrated.
- ‘Night skies get the blues’ by Gabriel Popkin in Physics World, March 2015.
This article is based on a short presentation given to the ASE by Steuart Campbell on the 6th of April 2018. Steuart is a science writer, a member of the ASE and a regular contributor to the Journal. His website is www.steuartcampbell.com
Jupiter’s conspicuous opposition in the Balance
Jupiter is at its brightest and best in the constellation of Libra, the Weighing Scales or Balance, this month. Its opposition, when it stands directly opposite the Sun, occurs on the morning of the 9th but it is prominent every night as it transits low across the south from the south-east at nightfall to the south-west before dawn.
Venus, however, outshines it in the western evening sky and both Saturn and the increasingly striking Mars follow Jupiter into the southern morning sky.
The Sun climbs another 7° northwards during May as Edinburgh’s sunrise/sunset times change from 05:29/20:52 BST on the 1st to 04:36/21:45 on the 31st. Because twilight is also lengthening, official darkness in the middle of the night lasts for under one hour by May’s end.
The Moon is at last quarter on the 8th, new on the 15th, at first quarter on the 22nd and full on the 29th.
Venus stands 20° high in the west at sunset, sinking to set in the north-west by 23:40 on the 1st and one hour later by the 31st. Brilliant at magnitude -3.9, it begins the month 6° above-right of Taurus’ brightest star, Aldebaran, and tracks east-north-eastwards between the Bull’s horns to end May in mid-Gemini, below Castor and Pollux.
The young earthlit Moon makes an impressive sight almost 6° below-left of the planet on the evening of the 17th. Three days later, as Venus joins the region of sky covered by our chart, it passes 1.0° (two Moon-diameters) above-right of the star cluster M35 whose brightest stars may be glimpsed through binoculars from their distance of some 2,800 light years. Still on the far side of its orbit, Venus approaches from 217 million to 190 million km this month as its almost-full disk swells to 13 arcseconds in diameter.
After dominating our winter nights, Orion ducks below our western horizon as the evening twilight fades at present. The Plough is overhead and Leo high in the south with its main star Regulus which has a close encounter with the first quarter Moon on the night of 21st/22nd.
By our map times, Leo sis inking in the west and Jupiter is easily the most conspicuous object in the south though it stands barely 18° high for Edinburgh. Moving westwards in Libra, it lies close to the Moon on the 27th. Its motion takes it from 4° east (left) of the well-known double star Zubenelgenubi at present to lie just 1.0° north-east of the star on the 31st.
Jupiter is 658 million km away at opposition, shines at magnitude -2.5 and shows a 45 arcseconds wide disk through a telescope. Its two main darker cloud bands, its northern and southern equatorial belts, straddle a lighter equatorial zone. The famous Great Red Spot is gradually losing its status, however, being less than half as wide as it was a century ago and currently more salmon-pink in hue than red. It sits in a bay at the southern edge of the south equatorial belt and, like the many other Jovian cloud features, is carried smartly across the disk as the planet spins in just under ten hours.
Steadily-held binoculars show the four main moons of Jupiter, Io, Europa, Ganymede and Callisto which change their configuration to the east and west of Jupiter from night to night, sometimes disappearing as they hide behind Jupiter or cross the disk, along with their shadows.
If Jupiter’s low elevation makes telescopic views less than sharp, this is even more the case with Saturn which rises in the south-east at our map times and is 6° lower in the sky than Jupiter as it reaches the meridian just before dawn. Saturn improves from magnitude 0.4 to 0.2 as it creeps westwards above the Teapot asterism in Sagittarius. It lies 1,392 million km away at mid-month when its oblate globe is 18 arcseconds across set within 40 by 17 arcseconds rings that have their north face inclined at 26° to our view. Look for it 4° right of the Moon on the morning of the 5th.
Less than 2° below Saturn is the globular star cluster M22, a ball of thousands of stars that lies about 10,600 light years away and formed some 12 billion years ago. At about magnitude 5.1 and visible as a hazy glow through binoculars, it was the first globular to be discovered and is brighter than M13 in Hercules, the best globular in the northern sky.
Mars lies almost 15° east of Saturn at present and rises at Edinburgh’s south-eastern horizon at 02:46 on the 1st. As it more than doubles in brightness, from magnitude -0.4 to -1.2, it also speeds 12° eastwards from Sagittarius to Capricornus so that by the 31st it rises at 01:31 and its fiery glow is unmistakable above the south-south-eastern horizon before dawn.
Catch Mars below the Moon on the morning of the 6th. Telescopically, its disk swells from 11 to 15 arcseconds as its distance falls from 126 million to 92 million km. Its approach opens the optimum window for sending probes to the planet and NASA’s InSight lander to study “marsquakes” and the Martian interior is due for launch between 5 May and 8 June.
Meteors of the Eta-Aquarids shower, debris from Comet Halley, appear until the 20th as they radiate from a point that lies low in the east for an hour or so before dawn over Scotland. The shower peaks with some moonlight interference on the 6th and brings a fine shower for watchers further south but only a handful of meteors for us.
Diary for 2018 May
Times are BST
3rd 18h Venus 7° N of Aldebaran
4th 21h Moon 1.7° N of Saturn
5th – 6th Peak of Eta Aquarids meteor shower
6th 08h Moon 2.7° N of Mars
8th 03h Last quarter
9th 02h Jupiter at opposition at distance of 658 million km
15th 13h New moon
17th 19h Moon 5° S of Venus
22nd 03h Moon 1.5° N of Regulus
22nd 05h First quarter
27th 19h Moon 4° N of Jupiter
29th 15h Full moon
This is a slightly revised version, with added diary, of Alan’s article published in The Scotsman on April 30th 2018, with thanks to the newspaper for permission to republish here.
Impressive conjunction before dawn for Mars and Saturn
The Sun climbs almost 10° northwards during April to bring us longer days and, let us hope, some decent spring-like weather at last. Our nights begin with Venus brilliant in the west and end with three other planets rather low across the south. Only Mercury is missing – after rounding the Sun’s near side on the 1st it remains hidden in Scotland’s morning twilight despite standing further from the Sun in the sky (27°) on the 29th than at any other time this year.
Edinburgh’s sunrise/sunset times change from 06:44/19:51 BST on the 1st to 05:32/20:50 on the 30th. The Moon is at last quarter on the 8th, new on the 16th, first quarter on the 22nd and full on the 30th.
Mars and Saturn rise together in the south-east at about 03:45 BST on the 1st and are closest on the following day, with Mars, just the brighter of the two, only 1.3° south of Saturn. Catch the impressive conjunction less than 10° high in the east-south-east as the morning twilight begins to brighten.
Both planets lie just above the so-called Teapot of Sagittarius but they are at very different distances – Mars at 166 million km on the 1st while Saturn is nine times further away at 1,492 million km.
Brightening slightly from magnitude 0.5 to 0.4 during April, Saturn moves little against the stars and is said to be stationary on the 18th when its motion reverses from easterly to westerly. Almost any telescope shows Saturn’s rings which are tipped at 26° to our view and currently span some 38 arcseconds around its 17 arcseconds disk.
Mars tracks 15° eastwards (to the left) and almost doubles in brightness from magnitude 0.3 to -0.3 as its distance falls to 127 million km. Its reddish disk swells from 8 to 11 arcseconds, large enough for telescopes to show some detail although its low altitude does not help.
Saturn is 4° below-left of Moon and 3° above-right of Mars on the 7th while the last quarter Moon lies 5° to the left of Mars on the next morning.
Orion stands above-right of Sirius in the south-west as darkness falls at present but has all but set in the west by our star map times. Those maps show the Plough directly overhead where it is stretched out of shape by the map projection used. We can extend a curving line along the Plough’s handle to reach the red giant star Arcturus in Bootes and carry it further to the blue giant Spica in Virgo, lower in the south-south-east and to the right of the Moon tomorrow night.
After Sirius, Arcturus is the second brightest star in Scotland’s night sky. Shining at magnitude 0.0 on the astronomers’ brightness scale, though, it is only one ninth as bright as the planet Jupiter, 40° below it in the constellation Libra. In fact, Jupiter improves from magnitude -2.4 to -2.5 this month as its distance falls from 692 million to 660 million km and is hard to miss after it rises in the east-south-east less than one hour before our map times. Look for it below-left of the Moon on the 2nd, right of the Moon on the 3rd, and even closer to the Moon a full lunation later on the 30th.
Jupiter moves 3° westwards to end the month 4° east of the double star Zubenelgenubi (use binoculars). Telescopes show the planet to be about 44 arcseconds wide, but for the sharpest view we should wait until it is highest (17°) in in the south for Edinburgh some four hours after the map times.
Venus’ altitude on the west at sunset improves from 16° to 21° this month as the evening star brightens from magnitude -3.9 to -4.2. Still towards the far side of its orbit, it appears as an almost-full disk, 11 arcseconds wide, with little or no shading across its dazzling cloud-tops. Against the stars, it tracks east-north-eastwards through Aries and into Taurus where it stands 6° below the Pleiades on the 20th and 4° left of the star cluster on the 26th. As it climbs into our evening sky, the earthlit Moon lies 6° below-left of Venus on the 17th and 12° left of the planet on the 18th.
The reason that we have such impressive springtime views of the young Moon is that the Sun’s path against the stars, the ecliptic, is tipped steeply in the west at nightfall as it climbs through Taurus into Gemini. The orbits of the Moon and the planets are only slightly inclined to the ecliptic so that any that happen to be towards this part of the solar system are also well clear of our horizon. Contrast this with our sky just before dawn at present, when the ecliptic lies relatively flat from the east to the south – hence the non-visibility of Mercury and the low altitudes of Mars, Saturn and Jupiter.
The evening tilt of the ecliptic means that, under minimal light pollution and after the Moon is out of the way, it may be possible to see the zodiacal light. This appears as a cone of light that slants up from the horizon through Venus and towards the Pleiades. Caused by sunlight reflecting from tiny particles, probably comet-dust, between the planets, it fades into a very dim zodiacal band that circles the sky. Directly opposite the Sun this intensifies into an oval glow, the gegenschein (German for “counterglow”), which is currently in Virgo and in the south at our map times – we need a really dark sky to see it though.
Diary for 2018 April
Times are BST.
1st 19h Mercury in inferior conjunction on Sun’s near side
2nd 13h Mars 1.3° S of Saturn
3rd 15h Moon 4° N of Jupiter
7th 14h Moon 1.9° N of Saturn
7th 19h Moon 3° N of Mars
8th 08h Last quarter
16th 03h New moon
17th 13h Saturn farthest from Sun (1,505,799,000 km)
17th 20h Moon 5° S of Venus
18th 03h Saturn stationary (motion reverses from E to W)
18th 15h Uranus in conjunction with Sun
22nd 23h First quarter
24th 05h Venus 4° S of Pleiades
24th 21h Moon 1.2° N of Regulus
29th 19h Mercury furthest W of Sun (27°)
30th 02h Full moon
30th 18h Moon 4° N of Jupiter
This is a slightly revised version, with added diary, of Alan’s article published in The Scotsman on March 31st 2018, with thanks to the newspaper for permission to republish here.
Elusive Mercury is second evening star alongside Venus
Orion is striding proudly across the meridian as darkness falls, but, even before the twilight dims, we have our best chances this year to spot Mercury low down in the west and close to the more familiar brilliant planet Venus.
Both evening stars lie within the same field-of-view in binoculars for much of March, so the fainter Mercury should be relatively easy to locate using Venus as a guide. Provided, of course, that we have an unobstructed horizon. Mercury never strays far from the Sun’s glare, making it the most elusive of the naked-eye planets – indeed, it is claimed that many astronomers, including Copernicus, never saw it.
Blazing at magnitude -3.9, Venus hovers only 9° above Edinburgh’s western horizon at sunset on the 1st and sets 64 minutes later. Mercury, one tenth as bright at magnitude -1.3, lies 2.0° (four Moon-breadths) below and to its right and may be glimpsed through binoculars as the twilight fades. Mercury stands 1.1° to the right of Venus on the 3rd and soon becomes a naked eye object as both planets stand higher from night to night, becoming visible until later in the darkening sky.
By the 15th, Mercury lies 4° above-right of Venus and at its maximum angle of 18° from the Sun, although it has more than halved in brightness to magnitude 0.2. The slender young Moon sits 5° below-left of Venus on the 18th and 11° above-left of the planetary pairing on the 19th. Earthshine, “the old Moon in the new Moon’s arms”, should be a striking sight over the following few evenings.
On the 22nd, the 30% illuminated Moon creeps through the V-shaped Hyades star cluster and hides (occults) Taurus’ leading star Aldebaran between 23:31 and 00:14 as they sink low into Edinburgh’s west-north-western sky.
Falling back towards the Sun, Mercury fades sharply to magnitude 1.4 by the 22nd when it passes 5° right of Venus and becomes lost from view during the following week. At the month’s end, Venus stands 15° high at sunset and sets two hours later.
The Sun climbs 12° northwards in March to cross the sky’s equator at the vernal equinox at 16:15 on the 20th, which is five days before we set our clocks forward at the start of British Summer Time. Sunrise/sunset times for Edinburgh change from 07:04/17:47 GMT on the 1st to 06:46/19:49 BST (05:46/18:49 GMT) on the 31st. The Moon is full on the 2nd, at last quarter on the 9th, new on the 17th, at first quarter on the 24th and full again on the 31st.
Orion is sinking to our western horizon at our star map times while the Plough, the asterism formed by the brighter stars of Ursa Major, is soaring high in the east towards the zenith. To the south of Ursa Major, and just reaching our meridian, is Leo which is said to represent the Nemean lion strangled by Hercules (aka Heracles) in the first of his twelve labours. Leo appears to be facing west and squatting in a similar pose to that of the lions at the foot of Nelson’s Column in Trafalgar Square.
Leo’s Sickle, the reversed question mark that curls above Leo’s brightest star Regulus, outlines its head and mane and contains the famous double star Algieba whose two component stars, both much larger than our Sun, take more than 500 years to orbit each other and may be seen through a small telescope. Regulus, itself, is occulted as they sink towards Edinburgh’s western horizon at 06:02 on the morning of the 1st.
Jupiter, easily our brightest morning object, rises at Edinburgh’s east-south-eastern horizon at 00:47 GMT on the 1st and at 23:41 BST (22:41 GMT) on the 31st, climbing to pass around 17° high in the south some four hours later. Brightening from magnitude -2.2 to -2.4, it is slow moving in Libra, being stationary on the 9th when its motion reverses from easterly to westerly. Jupiter is obvious below the Moon on the 7th when a telescope shows the Jovian disk to be 40 arcseconds wide.
If we look below and to the left of Jupiter in the south before dawn, the three objects that catch our attention are the red supergiant star Antares in Scorpius and, further from Jupiter, the planets Mars and Saturn.
Mars lies in southern Ophiuchus, between Antares and Saturn, and is heading eastwards into Sagittarius and towards a conjunction with Saturn in early April. The angle between the two planets falls from 17° to only 1.5° this month as Mars brightens from magnitude 0.8 to 0.3 and its distance falls from 210 million to 166 million km. Mars’ disk swells from 6.7 to 8.4 arcseconds, becoming large enough for surface detail to be visible through decent telescopes. Sadly, Mars (like Saturn) is so far south and so low in Scotland’s sky that the “seeing” is unlikely to be crisp and sharp.
Incidentally, on the morning of the 19th Mars passes between two of the southern sky’s showpiece objects, being a Moon’s breadth below the Trifid Nebula and twice this distance above the Lagoon Nebula. Both glowing clouds of hydrogen, dust and young stars appear as hazy patches through binoculars but are stunning in photographs.
Saturn, creeping eastwards just above the Teapot of Sagittarius, improves from magnitude 0.6 to 0.5 and has a 16 arcseconds disk set within its superb rings which span 37 arcseconds at midmonth and have their northern face tipped towards us at 26°. The waning Moon lies above-left of Mars on the 10th and close to Saturn on the 11th.
Diary for 2018 March
Times are GMT until March 25, BST thereafter.
1st 06h Moon occults Regulus (disappears at 06:02 for Edinburgh)
2nd 01h Full moon
4th 14h Neptune in conjunction with Sun
5th 18h Mercury 1.4° N of Venus
7th 07h Moon 4° N of Jupiter
9th 10h Jupiter stationary (motion against stars reverses from E to W)
9th 11h Last quarter
10th 01h Moon 4° N of Mars
11th 02h Moon 2.2° N of Saturn
15th 15h Mercury furthest E of Sun (18°)
17th 13h New moon
18th 01h Mercury 4° N of Venus
18th 18h Moon 8° S of Mercury
18th 19h Moon 4° S of Venus
20th 16:15 Vernal equinox
23rd 00h Moon occults Aldebaran (23:31 to 00:14 for Edinburgh)
24th 16h First quarter
25th 01h Start of British Summer Time
27th 02h Moon 1.8° S of star cluster Praesepe in Cancer
31st 14h Full moon
This is a slightly revised version, with added diary, of Alan’s article published in The Scotsman on February 28th 2018, with thanks to the newspaper for permission to republish here.
Conspicuous Jupiter leads trio of planets before dawn
February’s main planetary focus is the trio of Jupiter, Mars and Saturn in our predawn sky while Venus and Mercury begin spells of evening visibility later in the period. As the night falls at present, though, our eyes are drawn inevitably to the sparkling form of Orion in our south-eastern sky. Perhaps the only constellation that most people can recognise, it is one of the very few that has any resemblance to its name.
It is easy to imagine Orion’s brighter stars as the form of a man, the Hunter, with stars to represent his shoulders and knees, and three more as his Belt. Fainter stars mark his head, a club and a shield, the latter brandished in the face of Taurus the Bull, while his Sword, hanging at the ready below the Belt, contains the fuzzy star-forming Orion Nebula, mentioned here last month.
Since he straddles the celestial equator, the whole of Orion is visible worldwide except from the polar regions. Observers in the southern hemisphere, though, are seeing him upside down as he crosses the northern sky during their summer nights. For us, Orion passes due south about one hour before our map times.
The line of Orion’s Belt slants down to our brightest nighttime star, Sirius, in Canis Major which is one of the two dogs that accompany Orion around the sky. The other, Canis Minor, stands higher to its left with the star Procyon. This, with Sirius and Betelgeuse in Orion’s shoulder, form the equilateral Winter Triangle whose centre passes some 30° high in the south at our map times.
The Belt points up to Aldebaran in Taurus and, much further on, to the eclipsing variable star Algol in Perseus which we highlighted last month. This month Algol dims to its minimum brightness at 22:09 GMT on the 7th, 18:58 on the 10th and 23:54 on the 27th.
The Sun climbs 9.5° northwards during February as sunrise/sunset times for Edinburgh change from 08:07/16:46 on the 1st to 07:07/17:45 on the 28th.
A total lunar eclipse occurs when the Moon is full on 31 January, but finishes before the Moon rises for Scotland. The Moon lies close to Regulus in Leo on the 1st and is at last quarter on the 7th. The new moon on the 15th brings a partial solar eclipse for Antarctica and southernmost South America. First quarter occurs on the 23th when, late in the afternoon, it occults Aldebaran – a telescope should show the star disappearing behind the Moon from 16:37 to 17:47 as viewed from Edinburgh. The Moon is not full again until 2nd March.
Jupiter, brighter than Sirius and the most conspicuous of our morning planets, rises at Edinburgh’s east-south-eastern horizon at 02:27 on the 1st and 00:51 by the 28th, and climbs to pass 17° high in the south before we lose it in the dawn twilight. Creeping eastwards in Libra, it brightens from magnitude -2.0 to -2.2 while, viewed telescopically, its cloud-banded disk swells from 36 to 39 arcseconds is diameter.
Mars follows some 12° to the left of Jupiter on the 1st, rising in the south-east at 03:41 and shining at magnitude 1.2 less than a Moon’s breadth below the multiple star Beta Scorpii, Graffias, as they climb into the south. The planet tracks quickly eastwards against the stars, sweeping 4° north of the magnitude 1.0 red supergiant Antares on the 10th and making this a good month to compare the two. The name Antares means “rival to Mars” and both are reddish and, this month at least, very similar in brightness. By the 28th, Mars stands 27° from Jupiter, rises at 03:24 and shines at magnitude 0.8.
Saturn, now also a morning object as it creeps eastwards above the Teapot of Sagittarius, rises in the south-east at 06:13 on the 1st and by 04:37 on the 28th when it shines at magnitude 0.6 and is 17° to the left of Mars before dawn. Catch the waning Moon above-left of Jupiter before dawn on the 8th, above Mars on the 9th and above-right of Saturn on the 11th.
Venus is brilliant at magnitude -3.9 as it pulls slowly away from the Sun into our evening twilight but we need a clear west-south-western horizon to see it. Its altitude at sunset doubles from 4° on the 8th to 8° by the 28th, by which day it sets more than one hour after the Sun. As the month ends, use binoculars to look a couple of degrees below-right of Venus for the fainter magnitude -1.3 glow of Mercury as the small innermost planet begins its best evening apparition of the year.
For a real challenge, try to spy the very young Moon when it lies just 1.2° below-left of Venus soon after sunset on the 16th. Barely 20 hours old, the Moon is only 0.7% illuminated and may be glimpsed as the thinnest of crescents. It is more noticeable, and impressively earthlit, as it climbs steeply away from the Sun over the following days.
This is a slightly revised version of Alan’s article published in The Scotsman on January 31st 2018, with thanks to the newspaper for permission to republish here.
Inconstant stars in stunning New Year sky
Our evening sky is bursting with stellar interest but devoid of bright planets. Instead, Mars partners Jupiter in the predawn in the south-east to south while the impending spectacle of the annual Quadrantids meteor shower is rather blunted by bright moonlight.
The charts show Taurus high on the meridian, above and to the right of the unmistakable form of Orion whose brightest stars are the distinctly reddish supergiant Betelgeuse and the contrasting blue-white supergiant Rigel.
Between them lie the three stars of Orion’s Belt, while hanging below the middle of these is his fainter Sword with the Orion Nebula. The latter’s diffuse glow, visible to the unaided eye under decent conditions and obvious through binoculars, comes from a region where new stars and planets are forming. It lies some 1,350 light years away and is one of the most intensively studied objects in the entire sky.
Two iconic variable stars, Algol and Mira, are well placed in the evening. Algol in Perseus, the archetype of eclipsing variable stars, has two unequal stars that orbit around, and hide, each other every 2 days 20 hours and 49 minutes. Normally Algol shines at magnitude 2.1 and is almost identical in brightness to the star Almach in Andromeda, 12° to its west and labelled on the chart.
However, when Algol’s fainter star partially obscures its brighter companion, their combined light dips to magnitude 3.4, one third as bright, in an eclipse that lasts for about 10 hours and can be followed with nothing more than the naked eye. This month, Algol is at its mid-eclipse faintest at 02:45 on the 13th, 23:34 on the 15th and 20:23 on the 18th.
Mira, by contrast, is a single red giant star that pulsates in size and brightness every 332 days on average. It lies well to the west of Orion in Cetus, the sea monster of Greek mythology which was slain by Perseus when he rescued Andromeda.
During a typical pulsation, Mira varies between about magnitude 3.5, easy for the naked eye, and the ninth magnitude, probably needing a telescope. Unlike Algol, whose variability is like clockwork, Mira is less predictable and it has been known to touch the second magnitude, as it did in 2011. Now is the time to check, for it is close to its maximum as the year begins. Markedly orange in colour, it dims only half as quickly as it brightens so should remain as a naked-eye object throughout January.
Named for the extinct constellation of Quadrans Muralis, the Quadrantids meteors diverge from a radiant point in northern Bootes which lies low in the north at our map times and climbs to stand high in the east before dawn. Meteors are seen between the 1st and 6th but peak rates persist for only a few hours around the shower’s peak, due this time at about 21:00 on the 3rd when 80 or more meteors per hour might be counted by an observer with the radiant overhead in a clear moonless sky. However, with the radiant low in the north and moonlight flooding the sky at the time, expect to see only a fraction of these, perhaps trailing overhead from north to south.
Earlier on the 3rd, at 06:00, the Earth reaches perihelion, its closest point to the Sun in its annual orbit. Edinburgh’s sunrise/sunset times change from 08:44/15:49 on the 1st to 08:09/16:44 on the 31st. The Moon is full at 02:25 on the 2nd, only four hours after it reaches its closest point to the Earth for the entire year. There is a relatively modern obsession in dubbing such an event a supermoon, because the Moon appears 17% wider than it does when at its furthest. The difference between an average full moon and this one, though, is hardly “super” and far from obvious to the eye.
The Moon’s last quarter on the 8th is followed by new on the 17th, first quarter on the 24th and full again on the 31st when it passes through the southern half of the Earth’s shadow in a total lunar eclipse. Sadly, the event is over before sunset and moonrise for Britain.
Venus slips around the Sun’s far side to reach superior conjunction on the 9th and leave Jupiter as our brightest morning planet. Seen from Edinburgh, the latter rises in the east-south-east at 04:04 on the 1st and is climbing more than 15° high into the south before dawn. Conspicuous at magnitude -1.8 to -2.0, it creeps 4° eastwards to the east of the famous double star Zubenelgenubi in Libra and rises at 02:30 by the month’s end.
Mars, much fainter at magnitude 1.5, lies almost 3° above-right of Jupiter on the 1st and tracks more quickly eastwards to stand only 14 arcminutes (half a Moon’s breadth) below Jupiter before dawn on the 7th. The pair lie below the waning Moon in our predawn sky on the 11th when Jupiter’s cloud-banded disk 34 arcseconds wide and visible through any telescope, while Mars is still too small to appear interesting. Mars is brighter at magnitude 1.2 and stands 12° to the left of Jupiter by the 31st.
Mercury, bright at magnitude -0.3, may be glimpsed through binoculars as it hovers very low above our south-eastern horizon for more than 90 minutes before sunrise until the 8th. Given a clear horizon it may still be visible on the 15th when it stands 2.6° below-right of the vanishingly slender waning Moon. Saturn, half as bright at magnitude 0.5, lies 4° right of the Moon on that morning but is easier to spot by the month’s end when it rises almost two hours before the Sun.
This is a slightly revised version of Alan’s article published in The Scotsman on December 30th 2017, with thanks to the newspaper for permission to republish here.
Geminid meteors sparkle during long December nights
December brings us spectacular night skies and arguably the richest meteor shower of the year, the Geminids. We still have the Summer Triangle of bright stars, Vega in Lyra, Deneb in Cygnus and Altair in Aquila, high in the south-west at nightfall while the unmistakable figure of Orion dominates the midnight hours, surrounded by his cohort of familiar winter constellations. By the predawn, the Plough sails overhead and the night’s only conspicuous planets shine to the south of east.
Our longest nights, of course, occur around the winter solstice when the Sun reaches its most southerly point in its annual trek around the sky. This occurs at 16:28 GMT on the 21st when Edinburgh’s night, measured from sunset to sunrise, lasts for 17 hours and 3 minutes, which no less than 10 hours and 39 minutes longer than at June’s summer solstice.
Sunrise/sunset times for Edinburgh during December vary from 08:19/15:44 on the 1st to 08:42/15:40 on the 21st and 08:44/15:48 on the 31st. The Moon is full on the 3rd, at last quarter on the 10th, new on the 18th and at first quarter on the 26th,
By our map times, the Summer Triangle has toppled low into the west and is being followed by the less impressive Square of Pegasus. The Square’s top-left star, Alpheratz, belongs to Andromeda whose other main stars, Mirach and Almach, line up to its left. A spur of fainter stars above Mirach leads us to the Andromeda Galaxy, whose oval glow reaches us from 2.5 million light years away.
Orion is in the east-south-east, his Belt pointing up Aldebaran and the Pleiades in Taurus and down to where the brightest nighttime star, Sirius in Canis Major, rises less than one hour later.
The Moon lies to the right of Aldebaran and below the Pleiades on the night of 2nd-3rd, to the left of Aldebaran a day later and comes around again to occult the star in the early hours of the 31st. We need a telescope to see Aldebaran wink out at the Moon’s limb at 01:01 and reappear at 01:57 as seen from Edinburgh.
It is from a radiant point near Castor in Gemini, north-east of Orion, that meteors from the Geminids shower diverge between the 8th and 17th although, of course, the meteors fly in all parts of the sky. With negligible moonlight this year, and given decent weather, we are in for a stunning display of sparkling long-trailed meteors whose paths point back to the radiant. Rates for an observer under an ideal dark sky could peak at more than 100 per hour at the shower’s peak on the night of the 13th-14th, though most of us may glimpse only a fraction of these.
Although most meteors originate as cometary debris, the Geminids appear to be rocky splinters from the 5 km-wide asteroid, Phaethon, which dives within 21 million km of the Sun every 523 days. In what is its closest approach to the Earth since its discovery in 1983, Phaethon sweeps only 10.3 million km from the Earth on the 16th when a telescope might show it as a tenth magnitude speck speeding past Alpheratz.
December’s second shower, the Ursids, derives from Comet Tuttle and is active between the 17th and 25th, peaking on the 23rd. Typically it yields fewer than ten meteors per hour so I rarely mention it here – I believe my last time was 37 years ago – but very occasionally it rivals the Geminids in intensity, if only for a few hours. The radiant point lies near the star Kochab in Ursa Minor and is plotted on our northern chart.
The unprecedented interstellar asteroid, discovered using a telescope in Hawaii and featured here hast time, has now been called 1I/’Oumuamua. This indicates that it is our first known interstellar visitor and employs the Hawaiian word ’Oumuamua to reflect its supposed status as a scout from the distant past. Further observations imply that it is remarkably elongated, being at least five times longer than it is wide.
Venus shines brilliantly at magnitude -3.9 very low in the south-east as the night ends, but is soon lost from view as it dives towards the Sun’s far side. It leaves Jupiter as our most prominent (magnitude -1.7 to -1.8) morning object. The giant world rises at Edinburgh’s east-south-eastern horizon at 05:31 on the 1st and 04:07 on the 31st, climbing southwards in the sky to stand some 15° high before dawn. Tracking eastwards in Libra, it passes 0.7° north of the celebrated double star Zubenelgenubi on the 21st.
Mars, fainter at magnitude 1.7 to 1.5, lies 16° above-right of Jupiter on the 1st when it is also about half as bright as Virgo’s star Spica, 3° below and to its right. As Mars tracks east-south-eastwards from Virgo to Libra it almost keeps pace with the Sun, so that it rises at around 03:50 throughout the month. By the 31st, it stands 3° from Jupiter, with Zubenelgenubi below and to Mars’ left in the same binocular field of view. The waning Moon forms a nice triangle with Mars and Spica on the 13th and with Mars and Jupiter on the 14th.
Saturn sets in our bright evening twilight as it heads towards conjunction beyond the Sun on the 21st. Mercury slips around the Sun’s near side on the 13th to become best placed as a morning star between Christmas and New Year. Between the 21st and 31st it brightens between magnitude 0.8 and -0.3, rises 100 or more minutes before Edinburgh’s sunrise and stands around 8° high in the south-east thirty minutes before sunrise.
This is a slightly revised version of Alan’s article published in The Scotsman on November 30th 2017, with thanks to the newspaper for permission to republish here.
At the recent Member’s Evening on 3 November 2017, Mark Phillips gave a presentation about his experience of astro imaging.
Here is a link to the Prezi presentation (use the arrows at the bottom of the screen to navigate):
Astro imaging is a large topic so the presentation covers, at a general level, the sorts of imaging that I do with my own equipment. It describes the techniques, software and equipment I use, and shows some of the results. I hope it will be an encouragement to others to try astro imaging maybe for the first time or maybe to get back into it again.
You can see more of my images and projects on my astronomy website: http://www.forthimage.co.uk/
Here are some links to the software mentioned in the presentation:
- Cartes du Ciel: https://www.ap-i.net/skychart/en/start
- EQMOD: http://eq-mod.sourceforge.net/
- Astrophotography Tool (APT): https://www.ideiki.com/astro/Default.aspx
- PHD Guiding 2: https://openphdguiding.org/
- ASCOM: https://ascom-standards.org/
- FireCapture: http://www.firecapture.de/
- Deep Sky Stacker: http://deepskystacker.free.fr/english/index.html
- Autostakkert: https://www.autostakkert.com/
- Registax: http://www.astronomie.be/registax/
- Microsoft ICE: https://www.microsoft.com/en-us/research/product/computational-photography-applications/image-composite-editor/
Mark has been a member of the ASE for just over a year, having found us through his love of astro imaging.
Astronomers spot a mystery interstellar visitor
Comets have always been of particular interest. Appearing without warning, and sometimes with impressive tails, it was not surprising that they were regarded as portents of battles to be won or lost and of the passing of kings.
It was in 1705 that Edmond Halley first published the orbit of the comet that now bears his name. This, and the more than 5,000 comets that have been studied since, have all proved to be members of our solar system.
Some, like Halley, follow closed elongated orbits, returning to perihelion in the Sun’s vicinity every few years. Many more, though, trace almost parabolic paths as they dive towards the Sun from the Oort cloud, a spherical reservoir of icy worlds at the edge of the Sun’s influence – if they ever return to perihelion it may not be for millions of years. A handful, though, receive a sufficient gravitational boost as they pass a planet that they are flung beyond the Oort cloud into interstellar space, never to return.
Now astronomers have sighted a faint object which appears to have originated far beyond the Oort cloud, perhaps as an escapee from another star. Discovered by the Pan-STARRS 1 telescope in Hawaii on 18 October, it had already reached its perihelion within 38 million km of the Sun nine days before and passed 24 million km from the Earth on the 14th. Dubbed at first Comet/2017 U1 (PanSTARRS) because of its highly eccentric comet-like orbit, its name was changed to A/2017 U1 on 25 October when observers failed to detect any trace of a tail or hazy coma surrounding its small nucleus, probably less than 200 metres wide. So, for the moment, it is classed as an asteroid.
Its path though is certainly hyperbolic, having entered the solar system at a relative speed of 26 km per second from a direction close to the bright star Vega in the constellation Lyra. This is also close to the direction that our solar system is moving at 20 km per second with regard to the stars around us, so it may be expected that interstellar intruders, be they comets or asteroids, are most likely to appear from this region. As our first known visitor from interstellar space, frantic efforts are underway to investigate its spectrum and nature before it recedes forever from view in the direction of the Square of Pegasus.
Vega, itself, is the brightest object very high in the south-west at nightfall, falling into the west by our star chart times as Pegasus and Andromeda occupy our high meridian. Orion is rising in the east below Taurus whose brightest star, Aldebaran, is occulted by the bright Moon on the morning of the 6th. Use a telescope to watch it slip behind the Moon’s lower-left limb between 02:27 and 03:26 as seen from Edinburgh
Our sole bright evening planet, Saturn at magnitude 0.5, is easy to miss as it hangs low in the south-west at nightfall, sinking to Edinburgh’s horizon at 18:40 on the 1st and by 16:58 on the 30th. We may need binoculars to spy it in the twilight 5° left of the young earthlit Moon on the 20th and 8° below-right of the Moon a day later. Mercury stands 22° east of the Sun on the 24th but is unlikely to be visible from our latitudes.
The other naked-eye planets are all in our predawn sky. Mars rises in the east just before 04:00 throughout November, climbing to stand 15° to 20° high in the south-east before its magnitude 1.8 pinprick is swallowed by the twilight. This month, it tracks 19° east-south-eastwards in Virgo to pass 3° north of Virgo’s leading star Spica on the 28th. Mars stands to the right of the waning Moon on the 15th when a telescope show it as only 4 arcseconds wide – too small to see any detail.
Venus continues as a brilliant morning star of magnitude -3.9, but it stands lower each morning as it approaches the Sun’s far side. Currently above and left of Spica but speeding east-south-eastwards into Libra, it rises a little more than two hours before the Sun on the 1st and one hour before sunrise by the 30th.
Jupiter, about to emerge from the Sun’s glare below-left of Venus, climbs to pass a mere 16 arcminutes, or half the Moon’s diameter, below-right of Venus on the 13th. Conspicuous at magnitude -1.7, the Jovian disk appears 31 arcseconds wide as compared with only 10 arcseconds for Venus. On the 17th, the incredibly slim earthlit Moon lies above-left of Venus and to the left of Jupiter while the later stands 18° above-right of Venus by the 30th.
Sunrise/sunset times for Edinburgh change from 07:20/16:32 on the 1st to 08:18/15:45 on the 30th. The Moon is full on the 4th, at last quarter on the 10th, new on the 18th and at first quarter on the 26.
The annual Leonids meteor shower lasts from the 15th to the 20th and peaks on the night of the 17th-18th. Its meteors, all of them very fast and many leaving glowing trains in their wake, emanate from the Sickle, the reversed question-mark of stars above Regulus in Leo. This rises in the north-east at 22:00, with most Leonids visible during the predawn hours as it climbs through our eastern sky. The shower has given some spectacular meteor storms in the past, notably in 1966 and 1999, but the parent comet, Comet Tempel-Tuttle, is now near the farthest point of its orbit and rates may be around a dozen meteors per hour. For once, though, moonlight is no hindrance.
This is a slightly revised version of Alan’s article published in The Scotsman on October 31st 2017, with thanks to the newspaper for permission to republish here.
Saturn at full tilt as Comet Halley’s meteors fly
Our charts capture the sky in transition between the stars of summer, led by the Summer Triangle of Deneb, Vega and Altair in the west, and the sparkling winter groups heralded by Taurus and the Pleiades star cluster climbing in the east. Indeed, if we look out before dawn, as Venus blazes in the east, we see a southern sky centred on Orion that mirrors that of our spectacular February evenings. October also brings our second opportunity this year to spot debris from Comet Halley.
As the ashes of the Cassini spacecraft settle into Saturn, the planet reaches a milestone in its 29-years orbit of the Sun when its northern hemisphere and rings are tilted towards us at their maximum angle of 27.0° this month. In practice, our view of the rings’ splendour is compromised at present by its low altitude.
Although it shines at magnitude 0.5 and is the brightest object in its part of the sky, Saturn hovers very low in the south-west at nightfall and sets around 80 minutes before our map times. The rings span 36 arcseconds at mid-month while its noticeably rotation-flattened disk measures 16 arcseconds across the equator and 14 arcseconds pole-to-pole. Catch it below and to the right of the young crescent Moon on the 24th.
The Sun moves 11° further south of the equator this month as sunrise/sunset times for Edinburgh change from 07:16/18:48 BST (06:16/17:48 GMT) on the 1st to 07:18/16:34 GMT on the 31st, after we set our clocks back on the 29th.
Jupiter is now lost in our evening twilight as it nears the Sun’s far side on the 26th. Saturn is not alone as an evening planet, though, for both Neptune and Uranus are well placed. They are plotted on our southern chart in Aquarius and Pisces respectively but we can obtain more detailed and helpful diagrams of their position via a Web search for a Neptune or Uranus “finder chart” – simply asking for a “chart” is more likely to lead you to astrological nonsense.
Neptune, dimly visible through binoculars at magnitude 7.8, lies only 0.6° south-east (below-left) of the star Lambda Aquarii at present and tracks slowly westwards to sit a similar distance south of Lambda by the 31st. It lies 4,346 million km away on the 1st and its bluish disk is a mere 2.3 arcseconds wide.
Uranus reaches opposition on the 19th when it stands directly opposite the Sun and 2,830 million km from Earth. At magnitude 5.7 it is just visible to the unaided eye in a good dark sky, and easy through binoculars. Currently 1.3° north-west of the star Omicron Piscium and also edging westwards, it shows a bluish-green 3.7 arcseconds disk if viewed telescopically.
North of Aquarius and Pisces are Pegasus and Andromeda, the former being famous for its relatively barren Square while the fuzzy smudge of the Andromeda Galaxy, M31, lies 2.5 million light years away and is easy to glimpse through binoculars if not always with the naked eye.
Mercury slips through superior conjunction on the Sun’s far side on the 8th and is out of sight. Venus remains resplendent at magnitude -3.9 in the east before dawn though it does rise later and stand lower each morning. On the 1st, it rises for Edinburgh at 04:44 BST (03:44 GMT) and climbs to stand 20° high at sunrise. By the month’s end, it rises at 05:30 GMT and is 13° high at sunrise. Against the background stars, it speeds from Leo to lie 5° above Virgo’s star Spica by the 31st.
Mars is another morning object, though almost 200 times dimmer at magnitude 1.8 as it moves from 2.6° below-left of Venus on the 1st to 16° above-right of Venus on the 31st. The pair pass within a Moon’s breadth of each other on the 5th and 6th when Venus appears 11 arcseconds in diameter and 91% sunlit and Mars (like Uranus) is a mere 3.7 arcseconds wide.
Comet Halley was last closest to the Sun in 1986 and will not return again until 2061. Twice each year, though, the Earth cuts through Halley’s orbit around the Sun and encounters some of the dusty debris it has released into its path over past millennia. The resulting pair of meteor showers are the Eta Aquarids in early-May and the Orionids later this month. Although the former is a fine shower for watchers in the southern hemisphere, it yields only the occasional meteor in Scotland’s morning twilight.
The Orionids are best seen in the morning sky, too, and produce fewer than half the meteors of our main annual displays. This time the very young Moon offers no interference during the shower’s broad peak between the 21st and 23rd. In fact, Orionids appear throughout the latter half of October as they diverge from a radiant point in the region to the north and east of the bright red supergiant star Betelgeuse in Orion’s shoulder and close to the feet of Gemini. Note that they streak in all parts of the sky, not just around the radiant.
Orionids begin to appear when the radiant rises in the east-north-east at our map times, building in number until it passes around 50° high in the south before dawn. Under ideal conditions, with the radiant overhead in a black sky, as many as 25 fast meteors might be counted in one hour with many leave glowing trains in their wake. Rates were considerably higher than this between 2006 and 2009, so there is the potential for another pleasant surprise.