Geminids suffer in the supermoonlight
The Sun reaches its farthest south at our winter solstice at 10:44 GMT on the 21st, as Mars and the brilliant Venus stand higher in our evening sky than at any other time this year. This is not a coincidence, for both planets are tracking eastwards and, more importantly, northwards in the sky as they keep close to the ecliptic, the Sun’s path over the coming weeks and months. Meantime, Jupiter is prominent during the pre-dawn hours while Orion is unmistakable for most of the night and strides proudly across the meridian at midnight in mid-December.
As the sky darkens this evening, Pegasus with its iconic, but rather empty, Square is nearing the meridian and the Summer Triangle (Vega, Deneb and Altair) stands high in the south-west.
By our map times, Altair is setting in the west and Orion stands in the south-east, the three stars of Belt pointing down to where Sirius, our brightest night-time star, will soon rise. Sirius, the red supergiant Betelgeuse at Orion’s shoulder and Procyon in Canis Minor, almost due east of Betelgeuse, form a near-equilateral triangle which has come to be known as the Winter Triangle.
Above Orion is Taurus, home to the Pleiades star cluster and the bright orange giant star Aldebaran, the latter located less than halfway between us and the V-shaped Hyades cluster.
Look for the almost-full Moon below the Pleiades and to the right of Aldebaran and the Hyades on the evening of the 12th and watch it barrel through the cluster during the night, occulting (hiding) several of the cluster’s stars on the way. As they dip low into the west on the following morning, the Moon occults Aldebaran itself, the star slipping behind the Moon’s northern edge between 05:26 and 05:41 as seen from Edinburgh. Even though this is the brightest star to be occulted this year, the Moon’s brilliance means we may well need a telescope to view the event.
Sunrise/sunset times for Edinburgh vary from 08:20/15:44 on the 1st to 08:42/15:40 on the 21st and 08:44/15:48 on the 31st. The Moon is at first quarter on the 7th and full on the 14th when, once again, it is near its perigee, its closest point to the Earth. Despite the fact that the Moon appears a barely perceptible 7% wider than it does on average, we can look forward to yet another dose of over-hyped supermoon hysteria in the media. The Moon’s last quarter comes on the 21st and it is new on the 29th.
Sadly, the Moon does its best to swamp the annual Geminids meteor shower which lasts from the 8th to the 17th and is expected to peak at about 20:00 on the 13th. Its meteors are medium-slow and, thankfully, there are enough bright ones that several should be noticeable despite the moonlight. Without the moonlight, and under perfect conditions, this might have been our best display of 2016, with 100 or more meteors per hour.
Geminids are visible in all parts of the sky, but perspective makes them appear to diverge from a radiant point near the star Castor in Gemini, marked near the eastern edge of our north map. This radiant climbs from our north-eastern horizon at nightfall to pass high in the south at 02:00.
Venus stands 10° above Edinburgh’s southern horizon at sunset on the 1st and shines spectacularly at magnitude -4.2 as it sinks to set in the south-west almost three hours later. The young earthlit Moon stands 10° above-right of Venus on the 2nd, 5° above the planet on the 3rd and, one lunation later, 20° below-right of the Moon on Hogmanay. By then, Venus is twice as high at sunset and (just) brighter still at magnitude -4.3. A telescope shows its dazzling gibbous disk which swells from 17 to 22 arcseconds in diameter as the sunlit portion shrinks from 68% to 57%.
As Venus speeds from Sagittarius to Capricornus, so Mars keeps above and to its left as it moves from Capricornus into Aquarius and into the region of sky above our south-western horizon at the map times. Mars is only a fraction as bright, though, and fades from magnitude 0.6 to 0.9. It also appears much smaller, only 6 arcseconds, so that telescopes now struggle to reveal any surface features. Spot Mars to the left of the Moon on the 4th and below-right of the Moon on the 5th.
Mercury is farthest east of the Sun, 21°, on the 11th but hugs our south-western horizon at nightfall and is unlikely to be seen. It reaches inferior conjunction between the Sun and Earth on the 28th by which time Saturn, which passes beyond the Sun on the 10th, might just be glimpsed low above the south-eastern horizon before dawn. On the 27th, it shines at magnitude 0.5 and lies 7° below-left of the slender waning Moon.
Jupiter is conspicuous at magnitude -1.8 to -1.9 and the real star of our morning sky. Rising in the east for Edinburgh at 03:04 on the 1st and 01:31 on the 31st, it climbs well up into our southern sky before dawn where it stands above Virgo’s leading star Spica and draws closer during the month.
Jupiter, Spica and the Moon form a neat triangle before dawn on the 23rd, when Jupiter is 850 million km away and appears 35 arcseconds wide through a telescope. Any decent telescope shows its parallel cloud belts, while binoculars reveal its four main moons which swap places from side to side of the disk as they orbit the planet in periods of between 1.8 and 17 days.
This is a slightly-revised version of Alan’s article published in The Scotsman on December 1st 2016, with thanks to the newspaper for permission to republish here.
The phrase ‘Big Bang’ was coined in 1949 by astronomer Fred Hoyle as a label for a cosmological model of the universe, although one with which he happened to disagree. However, the theory itself had an earlier origin.
Many think that George Lemaitre, a Belgian Roman Catholic priest, astronomer and professor of physics at the Université Catholique de Louvain was the first to suggest cosmic expansion. In his 1927 report, ‘A homogeneous universe of constant mass and growing radius accounting for the radial velocity of extragalactic nebulae’, he proposed that the universe expanded from the finite static state imagined by Einstein. But only in 1931, at a meeting of the British Association on the relation between the physical universe and spirituality (sic), did he propose that the universe originated in a ’primeval atom’ (but this was 2 years after Edwin Hubble had demonstrated cosmic expansion).
Many think it was mathematician Alexander Friedmann who, unknown to Lemaitre, proposed a similar solution to Einstein’s equations in 1922.
However, what seems to be little known is the fact that both Friedmann and Leamaitre were forestalled by the American writer and poet Edgar Allan Poe.
In 1848 (79 years before Lemaitre and 74 years before Friedmann), he wrote Eureka: A Prose Poem, also subtitled ‘An Essay on the Material and Spiritual Universe’. It was his last major work and his longest non-fiction work at nearly 40,000 words. It was based on a lecture he gave on the 3rd of February 1848 in the Society Library in New York entitled ‘On The Cosmography of the Universe’. He died the following year.
Poe dedicated the work to Alexander von Humboldt, whose book Kosmos he must have read, at least the first two volumes. It was Humboldt who coined the word ‘cosmos’ (from the Greek kosmos) in the sense that modern cosmology uses it, to describe everything that exists in the universe, or the universe itself. In the volumes Poe must have read, he examined what was then known of the Milky Way, cosmic nebulae, and planets. The first volume was so popular that it sold out in two months.
Eureka describes Poe’s intuitive conception of the nature of the universe with no reference to any scientific work done to reach his conclusions (well there were none). His general proposition was ‘Because Nothing was, therefore All Things are’.
That is a bit vague, but it seems to suggest that the universe came out of nothing! Hasn’t modern science come to that conclusion? Indeed, he proposed that it had an origin: Poe contended that the universe filled with matter after a single, high-energy particle exploded and that, since the energy of the explosion is pushing matter outward, the universe must be expanding.
A reviewer in the New York Review of Books in February last year observed that :
‘This by itself would be a startling anticipation of modern cosmology, if Poe had not also drawn striking conclusions from it, for example that space and ‘duration’ [i.e. ‘time’] are one thing, that there might be stars that emit no light, that there is a repulsive force that in some degree counteracts the force of gravity, that there could be any number of universes with different laws simultaneous with ours, that our universe might collapse to its original state and another universe erupt from the particle it would have become, and that our present universe may be one in a series.’
Apart from suggesting a Big Crunch, Poe was the first to explain Olbers’ Paradox (the night sky is dark despite the vast number of stars in the universe); I wrote about this in the Journal 8 years ago . Poe claimed, as many do now, that the universe is not old enough to fill the sky with light. The universe may be infinite in size, he thought, (we think that now don’t we?) but there hasn’t been enough time since the universe began for starlight, travelling at the speed of light, to reach us from the farthest reaches of space. A Wikipedia page on the Paradox recognises Poe’s priority in this matter.
Response to Eureka was overwhelmingly unfavourable and the lecture on which it was based received negative reviews such as ‘hyperbolic nonsense’, but one newspaper called in ‘a noble effort’. Many were bored by the lecture which evidently was too long and rambling. However, Poe considered Eureka to be his masterpiece. He believed that the work would immortalize him because it would be proven to be true. Indeed, much of what he claimed has been verified and some, like Arthur Eddington, praised it. Albert Einstein called it ‘a beautiful achievement of an unusually independent mind’.
Eureka was published in a small hardcover edition in March 1848 by Wiley & Putnam priced at 75 cents. Poe persuaded George Putnam, to publish Eureka after claiming the work was more important than Isaac Newton’s discovery of gravity (Newton did not discover gravity, but he did explain it)! Putnam paid Poe $14 (3-4 hundred dollars today) for the work. Poe suggested an initial printing of at least one million copies, but Putnam settled on 750, of which 500 were sold that year.
The book can still be bought in various editions and it can also be read online . The National Library of Scotland has two copies, one of them the original 1848 edition, apparently once owned by the poet Dante Gabriel Rossetti.
What Poe suggested in this inspired work, with no antecedents, except perhaps Humboldt, is astonishing in its prescience. He deserves more recognition for his insights.
Finally, Poe has a Scottish connection. He was briefly at school in Irvine in 1815 when the Allans, his foster family, visited Britain. Let’s celebrate him.
- The New York Review of Books, February 5, 2015 – “On Edgar Allan Poe” by Marilynne Robinson
- ASE Journal No. 57, September 2008 – “Why is it dark at night?” by Steuart Campbell
- Eureka by Edgar Allan Poe, 1848. For an analysis of the work, see Eureka, an annotated edition by Stuart and Susan F Levine, University of Illinois Press, 2004.
This article is based on an illustrated talk given to the ASE by Steuart Campbell on 4 November 2016. Steuart is a member of the ASE and a regular contributor to the Journal.
W. David Woods (2016). NASA Saturn V – 1967-1973 (Apollo 4 to Apollo 17 & Skylab) – Owner’s workshop manual – An insight into the history, development and technology of the rocket that launched man to the Moon. Haynes Publishing, Yeovil, Somerset. ISBN 978 0 85733 828 0. Hardcover, 27.2×20.8×1.4 cm. 172 pages, several photos or illustrations per page. £22.99 rrp.
ASE members will recall the author’s fascinating talk on how Apollo flew to the Moon. He has written other books on spaceflight, including co-authorship of the Haynes manuals on Gemini and the Lunar Rover. About 50 years after NASA settled on the Saturn IB and V designs as carrier for the Apollo programme, Woods places this iconic machine centre-stage and makes the engineering the story itself.
The first chapter deals with the history leading up to the Saturn rocket, not least Wernher von Braun and the German A-4, which under its belligerous assignation “V2” inflicted tens of thousands of casualties among the British population and the slave labourers that were forced to build it. Originally interested in spaceflight for its own sake, von Braun was again lead figure when NASA made spaceflight a civilian project again.
The main chapters deal with the rocket from the bottom up. The F1 engine is described in good and consistent detail. This is followed by the chapter about the S-IC stage – the first stage of the Saturn V and powered by five F1 motors. Description of the J2 engine is a bit shorter due to similarities with the F1. Both the second S-II stage and the third S-IVB stage are powered by five and one J2 motors resp. The bulk of the volume and mass of the rocket is necessarily in the tanks for liquid oxygen and fuel (kerosene in the S-IC and liquid hydrogen in the S-II and S-IVB). The IU instrument unit atop the third stage is given its own chapter as the brains of the rocket.
The penultimate chapter draws it all together and takes us through an average flight from launch to lunar transit injection and final disposal of the third stage. The average flight was not without complications, and so a variety of real flights serve to illustrate the problems that did occur on occasion.
The final chapter is about Skylab, which seems strange at first. The book otherwise refrains from speaking about the Apollo missions after the S-IVB had done its job and was usually orbiting the Sun or had crashed into the Moon. Launching the space station (without crew) was the last flight of a Saturn V. But also, Skylab itself was a modified S-IVB and in that sense part of the last Saturn V to fly.
It is fascinating to learn in some detail how these rocket motors work. There is elegance in the design, for example how the propellants are used to lubricate, and to drive the turbo pumps that then pump those same propellants to the combustion chamber. I was surprised that the iconic bell shape of the rocket motor nozzles is not solid metal cast or shaped from sheets, but is merely a collection of hundreds of parallel tiny metal pipes bonded together to make the shape required for best performance as an exhaust nozzle. One of the propellants is fed through these pipes down the nozzle wall and back up, both to cool the nozzle and to warm up the propellant, or even evaporate the liquid hydrogen prior to combustion.
The book has a lavish collection of high quality photographs and purpose-made drawings and diagrams, which make good use of colour. It does not so much work as a picture book, the text and pictures go together and match closely. Still, some diagrams illustrate more than the point in hand, such as the plot of g-force versus time into the rocket flight, which also illustrates how short the first-stage flight is compared to the second stage. In the text the level of detail is good and consistent.
There are a variety of technical terms used in the Saturn V programme. Some sound serious like “max-Q”, others may confuse like the two-page lecture on specific impulse in relation to weight and mass, resp. Others are refreshingly intuitive like the “pogo phenomenon” that could make astronauts very uncomfortable at times.
Should you wonder at the end, why some Apollo flights are hardly mentioned – Apollo 7, the three Skylab crew flights and the Apollo-Soyuz rendezvous – this is because they flew on the lesser, two-stage Saturn IB, which was sufficient to reach Earth orbit. Saturn V was all about the Moon, even if not much of the rocket itself reached the Moon. Some of its third stages flew by the Moon to enter solar orbit, others were crashed into the Moon to be monitored by seismometers already in place.
Horst is currently Secretary of the Astronomical Society of Edinburgh and was the Journal’s previous editor, prior to it’s online incarnation.
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.
Mars bright in evenings as ExoMars probe arrives
As we plunge into the final quarter of the year, our lengthening nights offer a procession of stellar views that stretch from the Summer Triangle in the evening to the stunning star-scapes around Orion during the morning hours. The brighter planets, though, are on show only low down around dusk and dawn.
The middle of the Summer Triangle stands some 60° high and due south as darkness falls tonight. Its brightest corner star, Vega in the constellation Lyra, lies just south-west of overhead, while Deneb in Cygnus is even higher in the south-east and Altair in Aquila lies below them on the meridian.
With no hindering moonlight over the next few evenings, now is a good time to spy the Milky Way as it arches almost overhead after dusk, climbing from Sagittarius on the south-south-western horizon and flowing through the heart of the Triangle on its way to Deneb and the “W” of Cassiopeia high in the north-east. Of course, unless we can find a dark site, away from the pollution of street lighting and the like, we may have trouble seeing the Milky Way or indeed any but the brighter stars on our chart.
Edinburgh’s sunrise/sunset times change this month from 07:16/18:47 BST (06:16/17:47 GMT) on the 1st to 07:18/16:34 GMT on the 31st after we set clocks back one hour with the end of BST on the morning of the 30th. The Moon is new on the 1st, at first quarter on the 9th, full on the 16th (the hunter’s moon), at last quarter on the 22nd and new again on the 30th.
Venus stands nearly 5° high in the south-west at sunset and sets itself only 43 minutes later on the 1st. By the 31st it is barely a degree higher in the south-south-west at sunset but remains visible for 73 minutes so is easier to spot if we enjoy an unobscured outlook. It blazes at magnitude -3.9 and stands 4° below-right of the slender earthlit Moon on the 3rd when its gibbous disk appears 12 arcseconds wide and 85% sunlit if viewed telescopically.
In the month that the first European-Russian ExoMars spacecraft reaches Mars, the planet is the brightest object low in the south-south-west as the twilight disappears. ExoMars consists of a Trace Gas Orbiter to study rare gases, and particularly methane, in Mars’ atmosphere and it also has the experimental Schiaparelli lander.
Mars fades slightly from magnitude 0.1 (almost equal to Vega) to 0.4 this month as it tracks 21° eastwards above the so-called Teapot of Sagittarius, clipping the top star of the Teapot’s lid (Kaus Borealis) on the 7th. The planet recedes from 160 million to 187 million km during October while its gibbous disk shrinks to 7.5 arcseconds in diameter which, with its low altitude, makes telescopic study all the more challenging. It lies below the Moon on the 8th.
A little fainter than Mars, and a little lower to Mars’ right in this evening’s sky, is the ringed planet Saturn. This shines at magnitude 0.6 in southern Ophiuchus and appears 16 arcseconds across, with its glorious rings spanning 36 arcseconds. Saturn lies to the left of the earthlit Moon on the 5th and dips lower with each evening until it is passed by Venus late in the month – catch Saturn 3° above Venus on the 29th.
By our map times, both Saturn and Mars have set and the Summer Triangle has toppled over into the west. High in the south is the Square of Pegasus, a line along its right-hand side pointing down to the southern bright star Fomalhaut in Piscis Austrinus the Southern Fish. Just to the right of this line, and 2° south-west (below-right) of the star Lambda Aquarii (magnitude 3.7), is the farthest of the Sun’s planets, Neptune. At magnitude 7.8 and a distance of 4,350 million km on the 1st, we need binoculars and a better chart to identify it, and probably a large telescope to glimpse its bluish disk only 2.3 arcseconds wide.
To the east of Aquarius lies the constellation of the two fish, Pisces, and the second most distant planet, Uranus, which stands directly opposite the Sun at opposition on the 15th at a distance of 2,835 million km. At magnitude 5.7 it is near the limit of naked-eye visibility under the darkest of skies, but is an easier binocular or telescope target with its diameter of 3.7 arcseconds.
Orion rises in the east less than two hours after our map times and strides across the meridian before dawn. To its north and east lies Gemini and between the two is the radiant point for the annual Orionids meteor shower. This is visible during our morning hours throughout the second half of the month and peaks at rates around 25 meteors per hour between the 21st and 24th. Its meteors are swift, with many leaving glowing trains in their wake, and represent the dusty debris laid down by Halley’s Comet.
The night ends with Mercury which is conspicuous at magnitude -0.7 and rises in the east 109 minutes before the Sun on the 1st, climbing to stand 9° high forty minutes before sunrise. By the 11th, as its favourable morning show draws to a close, it rises 76 minutes before sunrise. On that morning, the even brighter Jupiter lies only 0.7° below-right of Mercury as the giant planet climbs away from the Sun’s far side. By the 28th, Jupiter rises at about 05:40 BST and is an impressive sight 1.5° below the earthlit waning Moon.
This is a slightly-revised version of Alan’s article published in The Scotsman on October 1st 2016, with thanks to the newspaper for permission to republish here. Journal Editor’s apologies for the lateness of the article appearing here.
Harvest moon eclipsed on the 16th
Two eclipses and a couple of notable space exploration milestones make September an interesting month for astronomers. I’ll postpone until the close of this note, though, my thoughts on the exciting news that Proxima Centauri, the closest star to our Sun, has a planet which is probably rocky, slightly larger than the Earth and in the star’s so-called habitable zone where liquid water might exist.
The first eclipse, an annular or “ring” eclipse of the Sun, occurs on the 1st with the Moon too distant to hide the Sun completely. Instead, a dazzling ring of sunlight remains visible along a narrow path that stretches across Central Southern Africa into the Indian Ocean. Surrounding areas enjoy a partial solar eclipse but nothing is seen as far north as Europe
Of greater interest for us is a penumbral eclipse of the Moon on the 16th during which the Moon passes through the southern outer part of the Earth’s shadow, the penumbra. The event lasts from 17:55 to 21:54 BST although, as seen from Edinburgh, the Moon only rises in the east at 19:29. Maximum eclipse occurs 25 minutes later, at 19:54, when all but the southern 9% of the Moon is within the penumbra. Little darkening of the disk may be noticeable, except near the northern edge which is closest to the Earth’s umbra where all direct sunlight is extinguished.
Since this full moon is the one closest to the autumnal equinox, due at 15:21 BST on the 22nd, it is also called the harvest moon. The tradition is that the bright moon stands at a similar altitude in the eastern sky over several evenings at this time, so permitting the harvesting hours to be extended.
The Sun tracks 11.5° southwards during September to cross the celestial equator at the equinox when day and night have approximately equal lengths around the Earth. Sunrise/sunset times for Edinburgh change from 06:18/20:06 BST on the 1st to 07:14/18:50 on the 30th. The moon is new on the 1st, at first quarter on the 9th, full on the 16th, at last quarter on the 23rd and new again on 1 October.
Jupiter is now lost from view as it nears conjunction on the Sun’s far side on the 26th. It leaves Venus as an evening star, but even though Venus is brilliant at magnitude -3.9 it stands less than 5° above Edinburgh’s horizon at sunset and sets itself within the next 45 minutes. Catch it, if you can, in the west as September begins, shifting to the south-west by the month’s end.
Mars, Saturn and the star Antares in Scorpius form a triangle low in the south-west as darkness falls at present, with Saturn above Antares and Mars a few degrees to their left. Saturn is magnitude 0.5 while Mars is brighter and noticeably reddish, though it fades from magnitude -0.3 to 0.1 as it speeds 18° eastwards and further away. By month’s end, its motion brings it onto our chart and close to the so-called Teapot of Sagittarius, just setting in the south-west.
Look for the Moon close to Saturn on the 9th and above Mars on the 10th when, if viewed telescopically, the two planets appear 16 and 10 arcseconds wide respectively, with Saturn’s wide-open rings spanning 37 arcseconds.
Mercury begins its best morning appearance of the year late in the month. From the 24th onwards, it rises in the east more than 95 minutes before the Sun and reaches more than 8° high forty minutes before sunrise. It is furthest west of the Sun (18°) on the 28th and is magnitude -0.5 when it lies alongside the slender earthlit Moon on the 29th.
Just a day later, on the 30th, Europe’s Rosetta spacecraft is destined to end its mission when it collides with Comet Churyumov-Gerasimenko, the rubber-duck shaped body it has been orbiting and investigating since August 2014. The collision will be gentle but radio contact and data-collection is likely to be lost as the craft settles on the comet’s surface.
Earlier in the month, during a month-long launch window beginning on the 8th, NASA’s OSIRIS-REx spacecraft is due to embark on its seven-years mission to collect and return samples from the surface of Bennu, a small asteroid which has been given an outside chance of having a catastrophic impact with the Earth late in the next century.
Proxima Centauri lies at a distance of only 4.25 light years but is much too dim to be seen without a telescope, A small red dwarf star, it is less than 15% as massive and wide as our Sun and has less than 0.2% of the Sun’s energy output. Also called Alpha Centauri C, it was discovered in 1915 by the Edinburgh-born astronomer Robert Innes and lies 15° to the east of the Southern Cross in a part of the sky we never see from Britain. It is thought to form a triple star system with Alpha Centauri A and B, a tight binary of more Sun-like stars that lie 2° away in the sky.
The newly discovered world has been dubbed Proxima b but it is something of a stretch to call it Earth-like. It orbits its star in a year of 11.2 Earth-days at a distance of less than 8 million km where it is blasted by X-rays from dramatic flares that we see erupting on Proxima’s surface – far from ideal for life. It is also probably tidally locked – keeping its same face towards the star – and we do not even know (yet!) that it has water, never mind life.
This is a slightly-revised version of Alan’s article published in The Scotsman on September 1st 2016, with thanks to the newspaper for permission to republish here.
Perseids rain as Mars approaches his rival
Every year at this time the Earth sweeps through the stream of meteoroids released by Comet 109P/Swift-Tuttle which passed just inside the Earth’s orbit in 1992 and is not due to return until 2126. And every year at this time, some of those meteoroids plunge into our upper atmosphere at 59 km per second, producing a rich display of bright meteors, many leaving glowing trains in their wake. According to some claims, this year’s meteor spectacle could be even better than usual.
The meteors appear in all parts of the sky but, since they are moving in parallel, perspective causes their paths to point away from a so-called radiant point in the constellation Perseus. It has already been active for a week, but it is expected to peak at about 13:00 BST on the 12th when, typically, an observer beneath the radiant and with a perfect dark sky might count 80 or more Perseids per hour. Of course, this year’s peak occurs in daylight for Scotland, but we should still enjoy high rates on our nights of 11/12th and 12/13th.
The radiant, plotted on our north star map, stands in the north-east at nightfall and climbs to lie just east of overhead before dawn. As the radiant climbs, so we face more directly into the Perseids stream and meteor rates climb in sympathy. This means that our morning hours are favoured and we have the extra advantage that the Moon sets in the middle of the night on the critical nights, though moonlight will hinder evening watches. Another bonus is that the nights are much less cold than they are for the year’s other two major showers which occur in the depths of winter.
The suggestions that the Perseids might be particularly active in 2016, with perhaps twice as many meteors as usual, derive from the fact that Jupiter approaches the Perseids stream every 12 years and its gravity might be diverting a segment of the stream closer to the Earth on each encounter. Indeed, there does seem to be a 12-years periodicity in enhanced Perseids displays with the last one in 2004, so we may be due for another special show this month.
Sunrise/sunset times for Edinburgh change from 05:17/21:19 BST on the 1st to 06:16/20:09 on the 31st. The Moon is new on the 2nd, at first quarter on the 10th, full on the 18th and at last quarter on the 25th.
Our chart depicts the Summer Triangle, formed by Deneb, Vega and Altair, high on the meridian as the Plough sinks in the north-west and the “W” of Cassiopeia climbs in the north-east, above the Perseids radiant. The large but rather empty Square of Pegasus balances on a corner in the east-south-east while the Teapot of Sagittarius is toppling westwards on our southern horizon. To its right, and very low in the south-west, is Saturn, the only bright planet visible at our map times.
Saturn hardly moves this month, being stationary against the stars on the 13th when it reverses from westerly to easterly in motion. It lies in Ophiuchus, 6° north of the red supergiant star Antares in Scorpius. Antares is around magnitude 1.0 while Saturn is almost twice as bright at 0.4. Saturn stands above Antares low in the south-south-west as tonight’s twilight fades but are outshone by the Red Planet, Mars, which lies 10° to their right and is three times brighter than Saturn at magnitude -0.8.
Mars, though, is moving eastwards (to the left) at almost a Moon’s-breadth each day and passes between Antares and Saturn, and 1.8° above Antares, on the 24th. Even though Mars dims to magnitude -0.4 by then, it remains much brighter than Antares even though the star’s name comes from the Ancient Greek for “equal to Mars”. Both appear reddish, of course, but for very different reasons – Antares has a bloated “cool” gaseous surface that glows red at about 3,100°C while Mars has a rocky surface which is rich in iron oxide, better known as rust.
The Moon stands above-right of Mars and to the left of Saturn on the 11th when Mars appears only 12 arcseconds wide if viewed through a telescope. Saturn is 17 arcseconds across while its rings span 39 arcseconds and have their north face tipped 26° towards us. By the 31st, Mars has faded further to magnitude -0.3 and lies 4° above-left of Antares.
Observers at our northern latitudes must work hard to spot any other bright planet this month although anyone in the southern hemisphere can enjoy a spectacular trio of them low in the west at nightfall. Seen from Scotland, though, the brilliant (magnitude -3.9) evening star Venus stands barely 5° above our western horizon at sunset and sets itself less than 40 minutes later. We need a pristine western outlook to see it, and quite possibly binoculars to glimpse it against the twilight.
Fainter (magnitude -1.7) is Jupiter which stands currently 27° to the left of Venus and 5° higher so that it sets more than 70 minutes after the Sun. Between them, and considerably fainter, is Mercury which stands furthest from the Sun (27°) on the 16th and, perhaps surprisingly, is enjoying its best evening apparition of the year as seen from the southern hemisphere.
Jupiter sinks lower with each evening and meets Venus on the 27th when Venus passes less than 5 arcminutes north of Jupiter. This is the closest planetary conjunction of the year and would be spectacular were the two not so twilight-bound. As it is, binoculars might show Jupiter 9 arcminutes below and left of Venus on that evening.
This is a slightly-revised version of Alan’s article published in The Scotsman on August 1st 2016, with thanks to the newspaper for permission to republish here.
Juno to begin hazardous mission at Jupiter
The Sun is edging southwards again but our night-long summer twilight subsides only slowly and, given that we also have bright moonlight through mid-July, we must wait until the month’s final week to enjoy a truly dark midnight sky.
From a good vantage point, we may then see the Milky Way as it arches high across our eastern sky, culminating close to the star Deneb in Cygnus. Deneb occupies the top-left corner of the Summer Triangle which remains a feature of our high southern night sky until the autumn. The Triangle was so named by our much-missed Sir Patrick Moore and has its other corners marked by Vega in Lyra and Altair in Aquila.
Sunrise/sunset times for Edinburgh change from 04:32/22:01 BST on the 1st to 05:16/21:21 on the 31st, by which date nautical twilight persists for two hours before dawn and after dusk. The Moon is new on the 4th, at first quarter on the 12th, full on the 19th and at last quarter on the 26th.
As the twilight fades at present, the giant planet Jupiter shines brightly low in the west and Mars, only a little fainter but distinctly reddish in hue, hovers at much the same altitude in the south-south-west. Our third naked-eye planet, Saturn, stands 18° to the east (left) of Mars and is creeping westwards in the southern reaches of the constellation Ophiuchus as Mars begins to accelerate eastwards in Libra.
Jupiter is nearing the end of its apparition as it sinks lower in our evening sky on its way to conjunction on the Sun’s far side in September. Its altitude above Edinburgh’s western horizon one hour after sunset falls from 11° on the 1st to less than 2° on the 31st. By then it will be difficult to spot in the bright twilight, and we will not see it again in our evening sky for another six months.
Moving eastwards in southern Leo, Jupiter remains brighter than any star, though it does fade slightly from magnitude -1.9 to -1.7 as its distance grows between 862 million and 919 million km. Viewed telescopically, its disk appears 34 arcseconds across when it stands 6° to the right of the crescent Moon on the 9th.
Although Jupiter is well past its best for telescopic study, we can expect some of our sharpest views after NASA’s Juno probe enters a highly-eccentric orbit over the planet’s poles early on July 5th UK time – the engine firing to do so is due to last for 35 minutes and end at 04:53 BST on that day. Launched in 2011, and with the benefit of a gravity assist flyby of the Earth in 2013, Juno will have travelled for 2,800 million km to reach Jupiter, not far shy of the distance between the Sun and Uranus.
Juno’s initial orbit is to carry it around Jupiter in 53.5 days, but this is to be reduced by mid-October to one of 14 days that takes within 4,200 to 4,900 km of the equatorial cloud-tops. That path plunges through Jupiter’s hazardous radiation belts and, while it avoids their most deadly regions, Juno’s sensitive electronics need to be located in a first-of-its-kind radiation-shielded vault.
Jupiter owns some of the most interesting moons we know of, but Juno is focused firmly on learning as much as possible about Jupiter’s origins and structure, from its intense magnetosphere all the way down to its core. The probe’s trio of 9-metres long solar panels provide 500 watts of power, making it the first craft to rely on solar power so far from the Sun. If it survives, the plan calls for Juno to dive to a fiery destruction in Jupiter’s atmosphere in February, 2018.
Venus, brilliant at magnitude -3.9, stands closer to the Sun in our evening twilight than Jupiter and is unlikely to be seen from our latitudes. Mercury, much fainter, enters the same area of sky following its superior conjunction on the Sun’s far side on the 7th and is even less likely to be seen.
Mars dims from magnitude -1.4 to -0.8 this month as its distance grows from 86 million to 106 million km and its diameter shrinks from 16 to 13 arcseconds. Telescopes still show some detail on its rusty surface, but it, too, stands lower each evening and by the month’s end it sets before midnight BST. Look for Mars 7° below the gibbous Moon on the evening of the 14th.
The opposing motions of Mars and Saturn mean that their separation in the sky decreases to 11°, with Saturn fainter at magnitude 0.2 to 0.4 and noticeably above-left of Mars by the month’s end. The red supergiant star Antares in Scorpius lies 6° below Saturn while the Moon stands 5° above-right of Saturn on the 15th and 9° to the planet’s left on the 16th.
Viewed telescopically, Saturn appears 18 arcseconds wide at mid-month with the north face of the rings inclined 26° towards us and 40 arcseconds from side to side. Saturn’s main moon, Titan, shines at magnitude 8.5 and is best seen through a telescope as it orbits every16 days. Catch it 3 arcminutes west of Saturn on the 4th and 20th, and a similar distance east on the 11th and 27th.
It happens that my previous note was timely in its warning about noctilucent clouds. The first good displays were sighted within a couple of days, appearing as electric-blue cirrus-like banks low above the north-western horizon after dusk and shifting round into the north-east before dawn. Composed of ice-crystals some 82 km above the ground, we should expect further shows until mid-August.
This is a slightly-revised version of Alan’s article published in The Scotsman on July 1st 2016, with thanks to the newspaper for permission to republish here.
Saturn at its best as summer begins
The Sun reaches its most northerly place in the sky at the summer solstice on the 20th, regarded by many as the start of summer in our northern hemisphere. Contradictorily, though, the days around then are also classed as midsummer though the actual days of any midsummer celebrations vary from country to country. More sensibly, in my view, the Met Office defines summer to span the months of June to August which would place the middle of summer in mid-July and, consequently, means that summer begins on June 1.
The solstice occurs late on the 20th, at 23:34 BST, while sunrise/sunset times for Edinburgh change from 04:35/21:47 on the 1st, to 04:26/22:03 on the 20th and 04:31/22:02 on the 30th. Scotland’s nights remain twilight throughout, with little hope of spotting the fainter stars and, from the north of the country, only the brighter stars and planets may be seen.
One is the beautiful ringed world Saturn which stands opposite the Sun in the sky on June 3, only twelve days after Mars’ closest opposition since 2005. Both planets shine brightly in the south at our star map times as they track westwards across the sky. Unfortunately, Saturn climbs less than 14° above Edinburgh’s horizon and Mars is a degree or so lower still so telescopic views are hindered by their low altitudes.
Having stood at its closest (75 million km) on May 30, Mars fades from magnitude -2.0 to -1.5 as it recedes to 86 million km while telescopes show it contracting from almost 19 to 16 arcseconds in diameter, still large enough to show some detail on the disk. It tracks 5° westwards into the heart of Libra this month, its motion slowing to a halt on the 30th before resuming as an easterly progress that will persist for the next two years.
Saturn’s disk is similar in size, 18 arcseconds at opposition, but its rings are 42 arcseconds wide and have their north face tipped 26° towards us. Not since 2003 have the rings been so wide open to inspection. It dims slightly, from magnitude 0.0 to 0.2 as it creeps westwards in southern Ophiuchus about 7° above-left of Antares in Scorpius.
Third but not least in our planetary line-up, Jupiter is prominent at magnitude -2.0 in the south-west as the sky darkens at present, but sinks lower with each day and sets in the west a little more than one hour after our map times. Now moving eastwards below the main figure of Leo, it passes within 0.1° south of the magnitude 4.6 double star Chi Leonis on the 10th and dims a shade to magnitude -1.9 by the 30th.
Of the other naked-eye planets, Mercury stands 24° west of the Sun on the 4th and, while well placed for observers south of the equator, is swamped in our predawn twilight. Venus reaches superior conjunction on the Sun’s far side on the 6th and is not visible either.
The Moon is new on the 5th, close to Jupiter on the 11th, at first quarter on the 12th, above Spica in Virgo on the 14th, above-right of Mars on the 17th, close to Saturn on the 18th, full in the 20th and at last quarter on the 26th.
Our star charts show the stars of the Summer Triangle, Vega, Deneb and Altair, climbing in the east to south-east as the Plough stands high in the north-west. The curve of the Plough’s handle extends to the brightest star visible at our map times, Arcturus in Bootes. Look some 20° above and to the left of Arcturus for the pretty arc of stars that make up Corona Borealis, the Northern Crown, which, because it is incomplete, should perhaps be called the Northern Tiara.
Corona’s leading star has the dual names of Gemma, for an obvious reason, and Alphecca which derives from the Arabic for “the bright of the broken ring”. At magnitude 2.2, though, it was surpassed briefly and unexpectedly exactly 150 years ago, in 1866, by the appearance of a nova (“new star”) just beyond the crown’s south-eastern edge.
Now called T Coronae Borealis (or T CrB), this reached magnitude 2.0 but plunged below naked eye visibility after only eight days to became slightly variable in brightness as a telescopic object just fainter than the tenth magnitude. To much surprise it burst into prominence again in 1946 though this time it was already fading at magnitude 3.2 when it was first spotted.
T CrB thus earned its nickname as the Blaze Star and became the brightest known of ten such recurrent novae in the sky. Studies over the past year show it slightly brighter and bluer than usual and hint that a new outburst may occur at any time, so this is one to check regularly.
Another variable star, R CrB, is usually near the sixth magnitude and the brightest star within the crown. However, normally for a few weeks or months every few years, it fades to become a dim telescopic object when, so it is thought, clouds of soot form in its atmosphere and block its light. Strangely, it has yet to recover following a record-breaking fade in 2007 and was still near the 14th magnitude a few days ago.
Despite our summer twilight, Scotland is best placed to see noctilucent or “night-shining” clouds which may appear cirrus-like and often bluish low down between the north-west after sunset and the north-east before dawn. Formed by layers of ice-crystals near 82 km in height, these are Earth’s highest clouds and able to shine in the sunlight long after our normal clouds have dimmed to darkness.
This is a slightly-revised version of Alan’s article published in The Scotsman on June 1st 2016, with thanks to the newspaper for permission to republish here.
Mercury to transit face of Sun on 9th
May is seldom an outstanding month for astronomy for observers at Scotland’s latitudes. The Sun’s northwards progress, welcome as it is, leads to later and briefer nights and, as the month ends, twilight begins to persist throughout the night even over the south of the country.
Two astronomical events occur this May, though, that should arouse our interest. The first is the transit by Mercury across the Sun’s face on the 9th which, if the weather holds, should be our best opportunity until 2049 to view its inky silhouette against the Sun. The month also sees Mars approach closer to us and appear brighter than at any time since 2005.
I must repeat the usual serious warning about the dangers of observing the Sun. To prevent permanent damage to your eyes, never look directly at the Sun through a telescope or binoculars, or even stare at it with the unaided eyes. We may project the solar image onto a shaded white card using a pinhole, binoculars or a small telescope, but note that using a large telescope for this may damage its eyepiece.
Sadly, Mercury’s outline will be too small to view by pinhole-projection, and nor will we see it using so-called eclipse glasses. In my opinion, though, it is best to equip your telescope with a certified solar filter to cover the objective (“big”) end of your instrument and block all the harmful radiation.
The precise times we experience the transit can vary by a couple of minutes across the Earth. For Scotland, Mercury begins to encroach on the eastern (left) edge of the solar disk at 12:12 BST and it takes a little more than three minutes before its outline is complete against the Sun. After crawling across the southern half of the Sun it finally leaves at the south-western (lower-right) edge at 19:41.
At a mere 12 arcseconds in diameter, though, it appears only 1/150th as wide as the Sun and a fifth as wide as did Venus during its transit in 2012. Whereas there are more than a dozen transits of Mercury each century, the next one by Venus is not until 2117 and we must be patient until 2125 for the next to be observable from Scotland.
The Sun climbs 7° northwards during May as sunrise/sunset times for Edinburgh change from 05:28/20:53 BST on the 1st to 04:36/21:46 on the 31st. The Moon is new on the 6th, at first quarter on the 13th, full on the 21st and at last quarter on the 29th.
Other than during its transit, Mercury is not visible for us at all this month, and neither is Venus which is lost in the glare on the Sun’s far side.
Jupiter, though, remains prominent in the heart of our southern sky at nightfall where it is slow moving in southern Leo and reaches a stationary point on the 10th before edging eastwards again. May has it dimming slightly from magnitude -2.3 to -2.0 as it recedes from 723 million to 791 million km and its disk shrinks from 41 to 37 arcseconds in diameter. Catch it near the Moon on the 14th and 15th.
By our star chart times, Leo and Jupiter are sinking into the west and our southern sky is dominated by the bright star Arcturus, the equally bright planet Saturn and, most conspicuous of all, the Red Planet, Mars. The Plough is tumbling westwards from the zenith as the Summer Triangle formed by the bright stars Vega in Lyra, Deneb in Cygnus and Altair in Aquila, occupies our lower eastern sky.
Mars rises in the south-east at 23:14 BST on the 1st and at sunset on the 22nd, the day it stands directly opposite the Sun in the sky at opposition. Our chart plots it low down in the south-south-east about one hour before it reaches its highest point, albeit less than 13° above Edinburgh’s southern horizon.
It lies 5° above the red supergiant star Antares in Scorpius at present but is retrograding, or moving westwards, against the stars and enters Libra towards the end of the period as it brightens from magnitude -1.5 to rival Jupiter at magnitude -2.0 at opposition. Because it is on the inwards leg of its somewhat eccentric orbit, it is actually closest to us at 75,280,00 km on the 30th, almost a million km closer than on the day of opposition.
Mars’ low altitude means that views of its reddish disk, only 18 arcseconds wide at opposition, may be less sharp (under “poorer seeing”) than if it stood high in the sky. Even so, telescopes should show the small northern polar cap, tipped 10° towards us, and other surface features as they drift slowly to the right across the disk. Those features return to almost the same position from one night to the next since Mars’ day is 40 minutes longer than that of the Earth. Mars comes 17 million km closer during its next opposition in 2018, but will be 4° lower still in our sky so we should make the most of any chance to view it this time around.
Shining to the east (left) of Mars is Saturn which this month brightens from magnitude 0.2 to 0.0 as it creeps westwards in southern Ophiuchus. It always rewards us with stunning telescopic views, its disk being (like Mars) 18 arcseconds wide but set within a glorious ring system that spans 41 arcseconds and has its north face inclined towards us at 26°. Look for the Moon above Mars late on the 21st and closer still to Saturn on the next night.