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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.
Moon between Venus and Mars on the 2nd
The new year opens with the Moon as a slim crescent in our evening sky, its light insufficient to hinder observations of the Quadrantids meteor shower.
Lasting from the 1st to the 6th, the shower is due to reach its maximum at about 15:00 GMT on the 3rd. Perhaps because of the cold weather, or a lingering hangover from Hogmanay, this may be the least appreciated of the year’s top three showers. It can, though, yield more than 80 meteors per hour under the best conditions, with some blue and yellow and all of medium speed. It can also produce some spectacular events – I still recall a Quadrantids fireball many years ago that flared to magnitude -8, many times brighter than Venus.
Although Quadrantids appear in all parts of the sky, perspective means that their paths stream away from a radiant point in northern Bootes. Plotted on our north map, this glides from left to right low across our northern sky during the evening and trails the Plough as it climbs through the north-east later in the night. The shower’s peak is quite narrow so the optimum times for meteor-spotting are before dawn on the 3rd, when the radiant stands high in the east, and during the evening of that day when Quadrantids may follow long trails from north to south across our sky.
Mars and Venus continue as evening objects, improving in altitude in our south-south-western sky at nightfall and, in the case of Venus, becoming still more spectacular as it brightens from magnitude -4.3 to -4.6. Mars, more than one hundred times fainter, dims from magnitude 0.9 to 1.1 but is obvious above and to Venus’ left, their separation falling from 12° to 5° during the month as they track eastwards and northwards from Aquarius to Pisces.
On the evening of the 1st, Mars stands only 18 arcminutes, just over half a Moon’s breadth, above-left of the farthest planet Neptune though, since the latter shines at magnitude 7.9, we will need binoculars if not a telescope to glimpse it. At the time, Neptune, 4,556 million km away, is a mere 2.2 arcseconds wide if viewed telescopically and Mars appears 5.7 arcseconds across from a range of 246 million km. On that evening, the young Moon lies 8° below and right of Venus, while on the 2nd the Moon stands directly between Mars and Venus. The pair lie close to the Moon again on the 31st.
As its distance falls from 115 million to 81 million km this month, Venus swells from 22 to 31 arcseconds in diameter and its disk changes from 56% to 40% sunlit. In theory, dichotomy, the moment when it is 50% illuminated like the Moon at first quarter, occurs on the 14th. However, the way sunlight scatters in its dazzling clouds means that Venus usually appears to reach this state a few days early when it is an evening star – a phenomenon Sir Patrick Moore named the Schröter effect after the German astronomer who first reported it. Venus stands at its furthest to the east of the Sun, 47°, on the 12th.
The Sun climbs 6° northwards during January and stands closer to the Earth in early January than at any other time of the year. At the Earth’s perihelion at 14:00 GMT on the 4th the two are 147,100,998 km apart, almost 5 million km less than at aphelion on 3 July. Obviously, it is not the Sun’s distance that dictates our seasons, but rather the Earth’s axial tilt away from the Sun during winter and towards it in summer.
Sunrise/sunset times for Edinburgh change from 08:43/15:49 on the 1st to 08:09/16:44 on the 31st. The Moon is at first quarter on the 5th, full on the 12th, at last quarter on the 19th and new on the 28th.
The Moon lies below the Pleiades on the evening of the 8th and to the left of Aldebaran in Taurus on the next night. Below and left of Aldebaran is the magnificent constellation of Orion with the bright red supergiant star Betelgeuse at his shoulder. Soon in astronomical terms, but perhaps not for 100,000 years, Betelgeuse will disintegrate in a supernova explosion.
The relics of a supernova witnessed by Chinese observers in AD 1054 lies 15° further north and just 1.1° north-west of Zeta Tauri, the star at the tip of Taurus’ southern horn. The 8th magnitude oval smudge we call the Crab Nebula contains a pulsar, a 20km wide neutron star that spins 30 times each second.
The conspicuous planet in our morning sky is Jupiter which rises at Edinburgh’s eastern horizon at 01:27 on the 1st and at 23:37 on the 31st. Creeping eastwards 4° north of Spica in Virgo, it brightens from magnitude -1.9 to -2.1 and is unmistakable in the lower half of our southern sky before dawn. Catch it just below the Moon on the 19th when a telescope shows its cloud-banded disk to be 37 arcseconds broad at a distance of 786 million km. We need just decent binoculars to check out the changing positions of its four main moons.
Saturn, respectable at magnitude 0.5, stands low in our south-east before dawn, its altitude one hour before sunrise improving from 3° to 8° during the month. Look to its left and slightly down from the 6th onwards to glimpse Mercury. This reaches 24° west of the Sun on the 19th and brightens from magnitude 0.9 on the 6th to -0.2 on the 24th when the waning earthlit Moon stands 3° above Saturn.
This is a slightly-revised version of Alan’s article published in The Scotsman on December 31st 2016, with thanks to the newspaper for permission to republish here.
Mercury crosses Sun as bright planets converge in evening sky
With all the planets in view and a sky brimming with interest from dusk to dawn, November is a rewarding month for stargazers, particularly since temperatures have yet to plumb their wintry lows. Our astro-highlight of the month, if not the year, though, comes in daylight on the 11th when Mercury appears as a small inky dot crossing the Sun’s face.
Perhaps one puzzle is why such transits of Mercury are not more frequent. After all, Mercury orbits the Sun every 88 days and, as we see it, passes around the Sun’s near side at its so-called inferior conjunction every 116 days on average.
The reason we don’t enjoy around three transits each year is that the orbits of Mercury and the Earth are tipped at 7° in relation to each other. For a transit to occur, we need Mercury to reach inferior conjunction near the place where its orbit crosses the orbital plane of the Earth, and currently this can occur only during brief windows each May and November. This condition restricts us to around one transit of Mercury every seven years on average but there are wide variations. Indeed, our last transit occurred as recently as May 2016 while we need to wait until November 2032 for the next. We must hang around even longer, and travel beyond Europe, for the next transit of Venus in 2117.
This month’s transit begins at 12:35 on the 11th when the tiny disk of Mercury, only 10 arcseconds wide, begins to enter the eastern (left) edge of the Sun. The Sun stands 16° high in Edinburgh’s southern sky at that time but it falls to 5° high in the south-west by 15:20 when Mercury is at mid-transit, only one twenty-fifth of the Sun’s diameter above the centre of the solar disk. The Sun sets for Edinburgh at 16:13 so we miss the remainder of the transit which lasts until 18:04.
The usual warnings about solar observation apply so that, if you value your eyesight, you must never observe the Sun directly. Solar glasses that you might have used for an eclipse will be no help since Mercury is too small to see seen without magnification. Instead, use binoculars or, better, a telescope which has been equipped securely with an approved solar filter.
A few days after its transit, Mercury begins its best morning apparition of the year. Between the 23rd and 30th, it rises more than two hours before the Sun and shines brightly at magnitude -0.1 to -0.5 while 7° high in the south-east one hour before sunrise. Higher but fainter in the south-east before dawn is Mars (magnitude 1.7) which tracks south-eastwards in Virgo to pass 3° north of Spica on the 8th and end the period 11° above-right of Mercury. Catch it below the waning Moon on the 24th.
The Sun’s southwards progress leads to sunrise/sunset time for Edinburgh changing from 07:19/16:33 GMT on the 1st to 08:17/15:45 on the 30th. The Moon is at first quarter on the 4th, full on the 12th, at last quarter on the 19th and new on the 26th.
Three bright planets vie for attention in our early evening sky but the brightest, Venus, is currently also the first to drop below the horizon as the twilight fades. Blazing at magnitude -3.9, it stands less than 4° high in the south-west at Edinburgh’s sunset on the 1st and sets itself only 38 minutes later.
Second in brightness comes Jupiter, magnitude -1.9, which lies some 24° to the left of Venus on the 1st and sets two hours after sunset. Then we have magnitude 0.6 Saturn which lies another 22° to Jupiter’s left so that it is about 10° high in the south-south-west as darkness falls tonight and sets about 50 minutes before our map times.
Venus tracks quickly eastwards to pass 1.4° south of Jupiter on the 24th when it stands 6° high at sunset as it embarks on an evening spectacular that lasts until May. The young Moon lies 7° below-right of Saturn on the 1st, makes a stunning sight between Jupiter and Venus on the 28th and is nearing again Saturn on the 29th.
Vega, the leader of the Summer Triangle, blazes just south-west of overhead at nightfall at present but is sinking near the middle of our western sky by our map times. Well up in the south by then is the Square of Pegasus whose top-left star, Alpheratz, leads the three main stars of Andromeda, lined up to its left. A spur of two fainter stars above the middle of these, Mirach, points the way to the oval glow of the Milky Way’s largest neighbouring galaxy, the famous Andromeda Galaxy, M31.
Below the Square is the dim expanse of Pisces that lies between the distant binocular-brightness planets Neptune and Uranus, in Aquarius and Aries respectively.
Orion, the centerpiece of our winter’s sky, is rising in the east at our map times and takes six hours, until the small hours of the morning, to reach its highpoint in the south. Preceding Orion is Taurus and the Pleiades while on his heals comes Sirius in Canis Major which twinkles its way across our southern sky before dawn.
The morning hours, particularly on the 19th, are also optimum for glimpsing members of the Leonids meteor shower. Arriving between the 6th and 30th, but with a sharp peak expected late on the 18th, these swift meteors diverge from Leo’s Sickle which rises in the north-east before midnight and climbs to stand in the south before dawn. Fewer than 15 meteors per hour may be sighted this year, far below the storm-force levels witnessed around the turn of the century.
Diary for 2019 November
2nd 07h Moon 0.6° S of Saturn
4th 10h First quarter
8th 15h Mars 3° N of Spica
11th 15h Mercury transits Sun at inferior conjunction
12th 14h Full moon
14th 04h Moon 3.0° N of Aldebaran
18th 11h Moon 1.2° N of Praesepe
18th 23h Peak of Leonids meteor shower
19th 21h Last quarter
20th 00h Moon 4° N of Regulus
24th 09h Moon 4° N of Mars
24th 14h Venus 1.4° S of Jupiter
25th 03h Moon 1.9° N of Mercury
26th 15h New moon
28th 10h Mercury furthest W of Sun (20°)
28th 11h Moon 0.7° N of Jupiter
28th 19h Moon 1.9° N of Venus
29th 21h Moon 0.9° S of Saturn
This is an extended version, with added diary, of Alan’s article published in The Scotsman on October 31st 2019, with thanks to the newspaper for permission to republish here.
Amateur astronomer discovers first interstellar comet
It is two years since astronomers in Hawaii discovered the first object known to have approached the Sun from beyond our solar system. Given the Hawaiian name of ʻOumuamua, this appeared to be a reddish and elongated slab-shaped body of about the size of a skyscraper that passed 38 million km from the Sun before sweeping within 24 million km of the Earth. It came from roughly the current direction of the star Vega and headed away towards the Square of Pegasus, though it may take 20,000 years to leave the solar system completely.
Its small size meant that it was followed only faintly and for barely a month. Astronomers were surprised to notice no sign of cometary activity – no surrounding fuzzy coma and no tail – while suggestions that it was an alien probe prompted unsuccessful scans for any artificial radio emissions.
Now the second-known interstellar intruder has been sighted, and this one appears larger, brighter and is surely a comet. It was discovered photographically on 29 August from an observatory in Crimea by the amateur astronomer Gennady Borisov using a telescope he built himself. Initially called C/2019 Q4 (Borisov), or Comet Borisov for short, it was clearly speeding along a strongly hyperbolic path past the Sun, very unlike the elliptical or nearly parabolic orbits followed by all previous comets. Now it has been awarded the official interstellar designation of 2I/Borisov.
The comet was travelling at about 33 km per second as it entered the solar system from the direction of the constellation Cassiopeia, fast enough to cover the 4-light-years distance of the nearest star in under 40,000 years. Perihelion, its closest point to the Sun, occurs at 303 million km on 8 December, putting it still beyond the orbit of Mars, and it reaches its closest to the Earth at 293 million km twenty days later.
It is still faint, no better than magnitude 17, but may attain magnitude 14 near perihelion and, while it will never reach naked-eye or binocular visibility, is likely to be within telescopic range until at least the middle of next year. This gives plenty of time for astronomers to study a comet that probably formed elsewhere in the Milky Way galaxy at a different time and with possibly a different composition than those that formed alongside the Sun and Earth. October has Comet Borisov travelling south-eastwards to the west of the Sickle of Leo and passing within a Moon’s-breadth east of the star Regulus on the 24th.
Leo’s Sickle rises in the north-east in the early morning and stands some 30° high in the east before dawn as our southern sky is dominated by the glorious constellation of Orion. The pre-dawn also gives us a chance to spot Mars as it emerges from the Sun’s far side. The planet rises in the east one hour before the Sun on the 1st and two hours before sunrise on the 31st. Moving east-south-eastwards in Virgo, it shines only at magnitude 1.8 and lies 8° below the slender earthlit Moon on the 26th.
As the Sun tracks southwards by 11° during October, the sky at nightfall is changing only slowly. The Summer Triangle is still high in the south as darkness falls, although its three stars, Vega in Lyra, Deneb in Cygnus and Altair in Aquila, have shifted into the west by our star map times. By then, Pegasus, the upside-down flying horse with his nose near Delphinus the Dolphin, stands high in the south.
The sunrise/sunset times for Edinburgh change this month from 07:15/18:49 BST (06:15/17:49 GMT) on the 1st to 07:17/16:35 GMT on the 31st, following Summer Time’s end on the 27th. The Moon reaches first quarter on the 5th, full phase on the 13th, last quarter on the 21st and new on the 28th.
Like Mars, Venus is also coming into view from beyond the Sun, but this time into our evening twilight in the west-south-west. Although brilliant at magnitude -3.9, it stands a mere 3° high at sunset for Edinburgh and sets at present only 30 minutes later, so we need good weather and a clear horizon to catch it. On the 29th, look for it 2.8° below the sliver of the earthlit young Moon, only 3° illuminated. Mercury is fainter and even lower at sunset and not visible from Scotland.
Jupiter is well past its best as an evening object although it remains obvious low in the south-west at nightfall, sinking to set at Edinburgh’s south-western horizon at 21:14 BST on the 1st and as early as 18:34 GMT by the 31st. At magnitude -2.0 to -1.9 and 36 to 33 arcseconds in diameter, it lies close to the Moon on the 3rd and 31st.
Saturn, one tenth as bright at magnitude 0.5 to 0.6, lies some 25° to the left of Jupiter. When it is close to the first quarter Moon on the 5th, its disk and rings span 17 and 38 arcseconds respectively. It is in Sagittarius low in the south at nightfall and sets in the south-west soon after our map times.
Neptune and Uranus are binocular brightness object of magnitudes 7.8 and 5.7 in Aquarius and Pisces respectively. There is little hope of locating them using our chart, but a web search, such as “Where is Uranus?”, should bring up information and a finder chart. Uranus, in fact, reaches opposition at a distance of 2,817 million km on the 28th when it stands directly opposite the Sun and appears as a tiny 3.7 arcseconds blue-green disk through a telescope.
Our Diary, below, records the peak dates for two of the October’s meteor showers, the Draconids on the 8th and the Orionids on the 22nd. Neither is among the year’s top showers, though both can yield rates of 20 or more meteors per hour under ideal conditions. The Draconids are active from the 6th to the 10th with slow meteors that diverge from a radiant near the Head of Draco, the quadrilateral of stars below and left of the D of DRACO on our north map. Unfortunately, the light of the bright gibbous Moon will hinder observations before the Moon sets in the early morning.
The Orionids, like May’s Eta Aquarids shower, are caused by meteoroid debris from Comet Halley. They last throughout the month and into early November but are expected to be most prolific on the nights of the 22nd and 23rd when their fast meteors diverge from a point that lies around 10° north-east (above-right) of Betelgeuse at Orion’s shoulder. That point passes high in the south before dawn but is just rising in the east-north-east at our map times, so no Orionids appear before then. As with those other swift meteors, the Perseids of August, many of the brighter Orionids leave glowing trains in their wake.
Diary for 2019 October
Times are BST until the 27th and GMT thereafter.
3rd 21h Moon 1.9° N of Jupiter
5th 18h First quarter
5th 22h Moon 0.3° S of Saturn
8th 07h Peak of Draconids meteor shower
13th 22h Full moon
17th 23h Moon 2.9° N of Aldebaran
20th 05h Mercury furthest E of Sun (25°)
21st 14h Last quarter
22nd Peak of Orionids meteor shower
22nd 06h Moon 1.0° N of Praesepe
23rd 19h Moon 3° N of Regulus
26th 18h Moon 5° N of Mars
27th 02h BST = 01h GMT End of British Summer Time
28th 04h New moon
28th 08h Uranus at opposition at distance of 2,817 million km
29th 14h Moon 4° N of Venus
30th 08h Mercury 2.7° S of Venus
31st 14h Moon 1.3° N of Jupiter
This is an extended version, with added diary, of Alan’s article published in The Scotsman on September 30th 2019, with thanks to the newspaper for permission to republish here.
Friendly Delphinus the Dolphin wins a place among the stars
The Sun’s southwards motion carries it across the sky’s equator at 08:50 BST on the 23rd, marking our autumnal equinox when days and nights are about equal around the Earth. It also means that our nights are lengthening at their fastest pace of the year.
The Summer Triangle (Vega, Deneb and Altair) remains in prime position high in the south at nightfall with the Milky Way flowing through it as it arches across the east from south to north. The brighter stars of Ursa Major, the Great Bear, form the familiar pattern of the Plough which stands in the north-west at nightfall as it begins to swing below the Pole Star, Polaris, in the north.
By our map times, the relatively empty expanse of the Square of Pegasus is climbing in the south-east while below it is the lengthy but dim constellation of Pisces, neatly book-ended by the Sun’s most distant planets Neptune and Uranus. Over the following few hours, though, this same region is invaded by the glorious form of Orion and his entourage of sparkling winter constellations
Last month I mentioned that Vega’s constellation, Lyra, was named for a lyre, but how that musical instrument came to be up there is associated with a myth that also involves Delphinus the Dolphin, a small but distinctive constellation that lies just to the left of the Summer Triangle.
That myth concerns Arion, a (real) poet and musician of ancient Greece. It has him returning by sea following lucrative performances in Sicily, only to be robbed and cast overboard before being rescued by a dolphin and delivered safely to shore. In gratitude, Apollo subsequently elevated the dolphin and Arion’s instrument, a lyre, to their places among the stars.
The four stars that represent the Dolphin’s head form a diamond or kite while telescope reveal that one of these, Gamma (see chart), is a superb double consisting of two stars of contrasting colours that appear only 9 arcseconds apart – in fact, they are separated by 330 times the Earth-Sun distance and take 3,200 years to orbit each other.
How two of the other stars in the diamond, Rotanev and Sualocin, came to be named was a mystery after they first appeared in a star catalogue issued by the Palermo Observatory in 1814. Then it was realised that spelled backwards they became Nicolaus Venator, the Latin equivalent of Niccolò Cacciatore which just happened to be the name of the assistant astronomer at the observatory. While his ruse succeeded, it is worth remembering that the modern craze for “buying” star names has no official standing and the names are not recognised by astronomers worldwide.
The prominent planet Jupiter is already past its best as the sky darkens and sinks from almost 10° high in the south-south-west to set in the south-west by our map times. Still brighter than any star, it dims slightly from magnitude -2.2 to -2.0 this month as it edges eastwards in southern Ophiuchus. The first quarter Moon stands 6° right of Jupiter on the 5th when a telescope shows it to be 38 arcseconds wide at its range of 767 million km.
Telescopes and good binoculars show Jupiter’s four main moons, Io, Europa, Ganymede and Callisto. Europa, with its ice-covered surface and likely sub-surface ocean, is of particular interest and the main target of a just-confirmed NASA mission, the Europa Clipper, which may launch as early as 2023 with arrival in 2026. This would see it beat the European Space Agency’s Jupiter Icy Moons Explorer (or JUICE) probe which is scheduled to launch in 2022 but only arrive at Jupiter in 2029. JUICE will explore all the main moons apart from Io, the volcanic innermost moon which appears to have less water than any other object in the solar system.
Saturn, our only other easy naked eye planet, is at its best at nightfall, albeit barely 12° high in the south and just below the so-called Teaspoon of Sagittarius. Non-twinkling and fading slightly this month between magnitude 0.3 and 0.5, Saturn moves to set in the south-west two hours after the map times. Catch it right of the Moon on the 8th when it appears 17 arcseconds wide with rings spanning 39 arcseconds and tipped 25° to our view.
Sunrise/sunset times for Edinburgh change from 06:16/20:08 BST on the 1st to 07:13/18:52 on the 30th. The Moon is at first quarter near Jupiter on the 6th, full near Neptune on the 14th, at last quarter above Orion on the 22nd and new on the 28th. On the 29th, the Moon’s sliver stands 6° high in the west-south-west at sunset and 3° above the evening star Venus. We have only the slimmest of chances of spotting the pair from our latitudes but binoculars may help – just don’t use them until the Sun is safely below the horizon.
We do need binoculars, at least, to see either Neptune and Uranus which shine at magnitudes of 7.8 and 5.7 respectively. Neptune lies in eastern Aquarius where it tracks 0.8° westwards during the month to pass a mere 13 arcsecond south of the naked-eye star Phi Aquarii (magnitude 4.2) on the 6th. At that time, just four days before it reaches opposition, Neptune lies 4,328 million km away and appears as a tiny 2.3 arcsecond bluish disk. Being seven times brighter, Uranus would be easier to recognise were it not in a star-sparse region in south-western Aries.
Of the other planets, Mars is in conjunction on the Sun’s far side on the 2nd, as is Mercury two days later, while both remain hidden in the Sun’s glare.
Diary for 2019 September
Times are BST
2nd 12h Mars in conjunction with Sun
4th 03h Mercury in superior conjunction
6th 04h First quarter
6th 08h Moon 2.3° N of Jupiter
8th 15h Moon 0.04° S of Saturn
10th 08h Neptune at opposition at distance of 4,328 million km
14th 06h Full moon
18th 07h Saturn stationary (motion reverses from W to E)
20th 18h Moon 2.7° N of Aldebaran
22nd 04h Last quarter
23rd 08:50 Autumnal equinox
24th 23h Moon 0.7° N of Praesepe
26th 10h Moon 3° N of Regulus
28th 02h Moon 4° N of Mars
28th 19h New moon
29th 23h Moon 6° N of Mercury
This is a slightly revised version, with added diary, of Alan’s article published in The Scotsman on August 31st 2019, with thanks to the newspaper for permission to republish here.
Giant planets hang low in evenings as Perseid meteors fly
Recent weeks have seen the Earth pass between the Sun and its two largest planets, the gas giants Jupiter and Saturn. Now they hang low in our evening sky, with Jupiter brighter than any star but less than 12° high in the south-south-west at nightfall as it sinks to set in the south-west one hour after our star map times. Saturn, one tenth as bright, trails 30° behind Jupiter and crosses our meridian a few minutes before the map times.
With the exception of Mercury, these are our only naked eye planets. Both Venus and Mars are hidden on the Sun’s far side where Venus reaches its superior conjunction on the 14th. Mars stands at the far-point in its orbit of the Sun on the 26th and, by my reckoning, is further from the Earth on the 28th (400 million km) than it has been for 32 years.
The Summer Triangle of bright stars, Deneb, Vega and Altair, fills the high southern sky at our map times as the Plough stands in the north-west and “W” of Cassiopeia climbs high in the north-east. Below Cassiopeia is Perseus and the Perseids radiant, the point from which meteors of the annual Perseids shower appear to diverge as they disintegrate in the upper atmosphere at 59 km per second.
The meteoroids, debris from Comet Swift-Tuttle, encounter the Earth between about 17 July and 24 August but arrive in their greatest numbers around the shower’s maximum, expected at about 08:00 BST on the 13th. Sadly, the bright moonlight around that date means that we may see only a fraction of the 80-plus meteors that an observer might count under ideal moonless conditions. It is just as well that Perseids include a high proportion of bright meteors prone to leaving glowing trains in their wake. Our best night is likely to be the 12th-13th as the radiant climbs to stand around 70° high in the east as the morning twilight takes hold.
The Sun drops almost 10° lower in our midday sky during August as the sunrise/sunset times for Edinburgh change from 05:16/21:21 BST on the 1st to 06:14/20:10 BST on the 31st. New moon on the 1st is followed by first quarter on the 7th, full moon on the 15th, last quarter on the 23rd and new moon again on the 30th.
In a month that sees Jupiter dim slightly from magnitude -2.4 to -2.2 and its distance increase from 691 million to 756 million km, its westerly motion in southern Ophiuchus slows to a halt and reverses at a so-called stationary point on the 11th. Its cloud-banded disk, around 41 arcseconds wide, remains a fascinating telescopic sight, particularly given the recent disruption to its Great Red Spot.
Saturn recedes from 1,362 million to 1,409 million km and dims from magnitude 0.2 to 0.3 as it creeps westwards below the Teaspoon, a companion asterism to the Teapot of Sagittarius. Through a telescope, Saturn’s disk appears 18 arcseconds wide while the rings span 41 arcseconds and have their north face tipped at 25° towards the Earth.
Catch the Moon close to Jupiter on the 9th and to the left of Saturn as the Perseids peak on the 12th-13th.
Mercury stands between 2.5° and 5° high in the east-north-east one hour before Edinburgh’s sunrise from the 5th and 22nd. It becomes easier to spot later in this period as it brightens from magnitude 1.0 to -1.2, though we need a clear horizon and probably binoculars to spot it. It is furthest from the Sun, 19°, on the 10th.
The only constellation named for a musical instrument, Lyra the Lyre, stands high on the meridian as darkness falls. Its leading star, the white star Vega, is more than twice as massive as the Sun and 40 times more luminous, making it the second brightest star in our summer night sky (after Arcturus) at its distance of 25 light years (ly). Infrared studies show that Vega is surrounded by disks of dust, but whether this hints at planets coalescing or asteroids smashing together is a matter of controversy – perhaps a mixture of the two.
Some 162 ly away and three Moon-breadths above-left of Vega is the interesting multiple star Epsilon, the Double Double. Binoculars show two almost-equal stars, but telescopes reveal that each of these is itself double. One of the four has its own dim companion and the whole system is locked together gravitationally, though the orbital motions are so slow that little change in their relative positions is noticeable over a lifetime.
The more dynamic system, Beta Lyrae (see map), lies almost 1,000 ly away and has two main component stars that almost touch as they whip around each other in only 12.9 days. Tides distort both stars and, as they eclipse each other, Beta’s total brightness varies continuously between magnitudes of 3.2 and 4.4 – sometimes it can rival its neighbour Gamma while at others it can be less than half as bright.
At a distance of 2,570 ly and 40% of the way from Beta to Gamma is the dim Ring Nebula or M57. At magnitude 8.8 and appearing through a telescope like a small smoke ring around one arcminute across, it surrounds a much fainter white dwarf star which is what remains of a Sun-like star that puffed away its atmosphere towards the end of its life. The Dumbbell Nebula, M27, lies further to the southeast in Vulpecula, some 3° north of the arrowhead of Sagitta the Arrow. At 1,230 ly, its origin is identical to that of the Ring though it is larger and brighter and readily visible through binoculars.
Diary for 2019 August
Times are BST
1st 04h New moon
7th 19h First quarter
10th 00h Mercury furthest W of Sun (19°)
10th 00h Moon 2.5° N of Jupiter
11th 17h Jupiter stationary (motion reverses from W to E)
12th 11h Moon 0.04° S of Saturn
13th 08h Peak of Perseids meteor shower
14th 07h Venus in superior conjunction
15th 13h Full moon
17th 11h Mercury 0.9° S of Praesepe
23rd 16h Last quarter
24th 11h Moon 2.4° N of Aldebaran
26th 02h Mars farthest from Sun (249m km)
28th 13h Moon 0.6° N of Praesepe
30th 12h New moon
This is a slightly revised version, with added diary, of Alan’s article published in The Scotsman on July 31st 2019, with thanks to the newspaper for permission to republish here.
A partial eclipse of the Moon next to Saturn on the 16th
July brings a slow return to darker and longer nights as the Sun’s trek southwards continues in the wake of our summer solstice. Until the 12th, the Sun dips no more than 12° below Edinburgh’s northern horizon so that twilight persists through every night. By the month’s end, though, we enjoy almost four hours of effective darkness and, with the Moon out of the way, the fainter stars are once again on show.
The 50th anniversary of Apollo 11’s pioneering lunar landing occurs on the 20th while, for stargazers and the weather permitting, the highlight may be the partial eclipse of the Moon which comes four days earlier on the evening of the 16th, though the Moon rises, and the Sun sets, while the eclipse is already underway.
The event begins at 19:44 BST when the Moon begins to encroach of the edge of the outer shadow of the Earth, the penumbra. Between 21:02 and midnight, part of the Moon lies within the central dark umbra where, in the absence of any direct sunlight, it is illuminated in only a dim reddish glow by sunlight refracting around the edge of the Earth. The Moon rises above Edinburgh’s south-eastern horizon at 21:44 and greatest eclipse occurs at 22:31 when the Moon stands only 8° high in the twilight with its northern 65% covered by the umbra. The eclipse ends when disk exits the penumbra at 01:18.
Sunrise/sunset times for Edinburgh change from 04:31/22:01 on the 1st to 05:14/21:23 on the 31st. New moon on the 2nd brings a total eclipse of the Sun visible along a track that crosses the south-eastern Pacific to Chile and Argentina. Surrounding areas, but not Europe, enjoy a partial eclipse. The Moon reaches first quarter on the 9th, is full at the lunar eclipse on the 16th and at last quarter on the 25th.
Saturn, the fainter of the two bright planets low down in our southern night sky, lies 8° to the right of the Moon and a little higher on the evening of the lunar eclipse. One week earlier, on the 9th, it reaches opposition in the constellation Sagittarius when it lies directly opposite the Sun so that it rises at sunset and is highest in the south in the middle of the night, albeit at an elevation of only 12°. It is also closest to us, 1,351 million km, and at its brightest at magnitude 0.1.
A telescope shows Saturn’s disk to be 18 arcseconds wide while its rings extend across 42 arcseconds and have their northern face tipped Earthwards at 24 degrees. Saturn’s globe is blanketed with clouds of ammonia crystals whose shade varies in bands running parallel to its equator. They appear much less prominent than the equivalent bands on Jupiter and there are few noticeable spots.
Jupiter, itself, lies in southern Ophiuchus some 31° to the right of Saturn and far outshines its neighbour even though it dims slightly in July from magnitude -2.6 to -2.4 as its distance grows from 649 million to 691 million km. It lies just below the bright Moon on evening of the 13th when a telescope shows its disk to be 44 arcseconds wide.
The previous evening, the 12th, would be an opportune time to check out Jupiter’s Red Spot which, as I mentioned last time, appears to have been spooling some of its reddish material into its adjacent cloud belt. It is certainly measurably smaller than it was just a few weeks ago but there are also signs that the disturbance may have subsided.
The other naked eye planets are poorly placed. The brightest, magnitude -3.9 Venus, rises 50 minutes before the Sun and stands less than 5° high in the north-east at sunrise. Mercury stands 4° to the left of Mars in the west-north-west during the hour after sunset on the 1st but both are too dim, at magnitudes of 1.2 and 1.8 respectively, to be glimpsed in our bright twilight.
Mars is edging towards the Sun’s far side and reappears before dawn in October. Mercury reaches inferior conjunction between the Sun and the Earth on the 21st when it passes 5° south of the Sun on its way to our morning sky in August. When Mercury next reaches inferior conjunction, on 11 November, it passes almost centrally across the Sun’s disk in a transit that we hope to witness from Scotland.
Our charts show Jupiter and Saturn low down in our southern sky while the star Vega, only slightly brighter than Saturn, crosses the meridian high above them. Vega, of course, forms the Summer Triangle with Deneb in Cygnus, high in the east, and Altair, lower in Aquila. Our map projection squashes the Triangle somewhat – in fact, Deneb and Vega are closer together in the sky than is either star to Altair. An even larger triangle, this one almost equilateral, fills our south-western sky and has its corners at Vega, Jupiter and Arcturus, which lies due west as the leading star of Bootes.
Capella in Auriga stands at its lowest below Polaris in the north and often features in images of noctilucent clouds or NLCs. Little did I realise when I mentioned these silvery-blue “night-shining” clouds last time that 2019 was to unleash some of our best NLC displays in decades. Formed by ice condensing on high-altitude dust particles, some perhaps debris from meteors, they catch the sunlight when our usual lower-level clouds are in darkness during the middle hours of our nights. Researchers are investigating why this should be such a special year for NLCs but expect the bonanza to continue into August.
Diary for 2019 July
Times are BST
2nd 20h New moon and total solar eclipse
4th 23h Earth farthest from Sun (152,100,000 km)
6th 04h Moon 3° N of Regulus
7th 15h Mercury 4° S of Mars
9th 12h First quarter
9th 18h Saturn at opposition at distance of 1,351 million km
13th 21h Moon 2.3° N of Jupiter
16th 08h Moon 0.2° S of Saturn
16th 23h Full moon and partial lunar eclipse
20th 21h 50th anniversary of first manned lunar landing
21st 14h Mercury in inferior conjunction
24th 00h Mercury furthest E of Sun (25°)
25th 02h Last quarter
28th 02h Moon 2.3° N of Aldebaran
This is a slightly revised version, with added diary, of Alan’s article published in The Scotsman on June 29th 2019, with thanks to the newspaper for permission to republish here.
Is Jupiter’s Great Red Spot unfurling before our eyes?
The Sun reaches its most northerly point at 16:54 BST on the 21st, marking the summer solstice in our northern hemisphere. Between its setting in the north-west and its rising in the north-east, it follows only a shallow arc below Edinburgh’s horizon and stands, at most, 10.6° below Edinburgh’s due-north horizon at 01:14 BST. As a result, twilight persists throughout our June nights and we must stay up late to glimpse even the brighter stars and planets.
The sunrise/sunset times for Edinburgh change from 04:36/21:46 BST on the 1st, to 04:26/22:03 on the 21st and 04:30/22:02 on the 30th. The Moon is new on the 3rd, at first quarter on the 10th, full on the 17th and at last quarter on the 25th.
At times like these, some stargazers forsake their hobby for a couple of months while others switch to observing the Sun, or, perhaps, noctilucent clouds. This June, though, the giant planet Jupiter is well worth a look as it comes to opposition on the 10th. It is then closest to us (641 million km) and stands directly opposite the Sun, so that it rises in the south-east at sunset and passes (for Edinburgh) less than 12° high in the south in the middle of the night.
Conspicuous at magnitude -2.6 as it creeps westwards against the stars of southern Ophiuchus, Jupiter outshines every other object in our night sky except for the Moon which lies close to it on the night of the 16th-17th. A small telescope or good steadily-held binoculars reveal its four main moons, the Galilean moons, as they orbit from east to west of the planet in periods that range from 1.8 days for Io to 16.7 days for Callisto. Jupiter has more moons, 79 at the latest count, than any other planet, with Saturn’s tally of 62 coming second. Jupiter’s 75 lesser moons, though, are too small and dim to be spotted using any but the largest telescopes.
Jupiter’s globe is shrouded in clouds, mainly of ammonia crystals but tinted red and brown by other compounds which may include hydrocarbons. Telescopes show bands of darker cloud and a plethora of streaks and spots that transit smartly across the disk as the planet rotates in its sub-ten-hour day.
The most famous feature, the Great Red Spot, is an anticyclonic storm that may be more than 300 years old and was once larger than three Earths. It has shrunk significantly over the last century but observations over the past two weeks suggest something startling may be afoot and even that the spot may be disintegrating. It appears that 10,000-km-long streamers of reddish gas, perhaps methane-rich, are peeling away from the spot into the adjacent cloud band, the South Equatorial Belt, that circles the planet. Likened by some to the spot unfurling, nothing on this scale has been seen before so it is just as well that NASA’s Juno probe has a ring-side view as it orbits Jupiter.
Some 30° to the east of Jupiter, below the so-called Teaspoon of Sagittarius, is our Sun’s other gas giant planet, Saturn. Rising in the south-east about one hour before our map times, it brightens slightly from magnitude 0.3 to 0.1 to rival the two brightest stars on our south map – Vega in Lyra which stands very high in the east-south-east and Arcturus in Bootes in the middle of our south-western sky. When Saturn lies just left of the Moon on the night of the 18th, it lies 1,361 million km away and a telescope shows its disk and rings to span 18 and 41 arcseconds respectively.
The constellations of Ophiuchus and Hercules sprawl across the meridian at the map times, though our twilight means that this is not the best month for spotting M13, the Great Globular Cluster in Hercules (see map). Discovered by Edmond Halley of comet fame in 1714, this ball of hundreds of thousands of stars is some 160 light years across, 22,200 light years away and is thought to have formed 11.65 billion years ago. Under the best conditions, binoculars show it as a fuzzy circular patch around two-thirds as wide as the Moon.
Although Venus is brilliant at magnitude -3.9, it rises in the north-east around 40 minutes before the Sun and is unlikely to be noticed in Scotland’s dawn twilight. Mars is now as dim as magnitude 1.8 and becoming much harder to spot low down in our north-western evening twilight. Tracking eastwards in Gemini to pass below Castor and Pollux, it sets for Edinburgh at 00:05 BST on the 5th when it is 4° to the right of the slender young earthlit Moon. Mercury, much easier at magnitude -0.7, lies 11° below-right of Mars at that time and is 4° above the horizon one hour after sunset between the 5th and 19th. Mercury passes 0.2° above Mars on the 18th and stands furthest east of the Sun (25°) on the 24th.
Scotland’s noctilucent cloud season is just beginning and we can look forward to occasional displays of these “night-shining” clouds until August. Often with a bluish-white sheen, they may appear as wisps, streaks and whirls and merge into banks with cirrus-like herring-bone patterns. The clouds are formed when ice crystallises on dust particles in a narrow range of altitudes near 82 km. Here they are high enough to catch the sun’s light when our more typical lower-level terrestrial clouds are in darkness, from, say, one hour after sunset until one hour before sunrise. They rarely reach more than 20° above the horizon and favour directions towards the north-west at nightfall shifting to the north-east before dawn.
Diary for 2019 June
Times are BST
3rd 11h New moon
4th 17h Moon 4° S of Mercury
5th 16h Moon 1.6° S of Mars
7th 09h Moon 0.5° N of Praesepe
8th 21h Moon 3° N of Regulus
10th 07h First quarter
10th 16h Jupiter at opposition at distance of 641 million km
16th 20h Moon 2.0° N of Jupiter
17th 10h Full moon
18th 16h Mercury 0.2° N of Mars
19th 05h Moon 0.4° S of Saturn
21st 16:54 Summer solstice
24th 00h Mercury furthest E of Sun (25°)
25th 11h Last quarter
30th 17h Moon 2.3° N of Aldebaran
This is a slightly revised version, with added diary, of Alan’s article published in The Scotsman on May 31st 2019, with thanks to the newspaper for permission to republish here.
Giant world Jupiter becoming obvious in May’s twilit nights
With its lengthening days and increasingly twilit nights, May is hardly a vintage month for stargazing from Scotland’s latitudes. Official (nautical) darkness for Edinburgh lasts for more than five hours around midnight as the month begins but dwindles to nothing by the start of June and does not return until 12 July
Edinburgh’s sunrise/sunset times change from 05:30/20:51 on the 1st to 04:37/21:45 on the 31st, while the Moon is new on the 4th, at first quarter on the 12th, full on the 18th and at last quarter on the 26th.
Our charts show Leo diving westwards as the Summer Triangle formed by Vega, Altair and Deneb is climbing in the east. After the Moon, our most obvious nighttime object is the planet Jupiter which rises in the south-east 30 minutes before our map times and reaches less than 12° high in the south before dawn. In fact, look for the Moon above-right of Jupiter on the night of the 19th and closer to the planet’s left on the 20th.
The giant world is now edging westwards against the stars of southern Ophiuchus and brightens from magnitude -2.4 to -2.6 as its distance falls from 678 million to 644 million km. The Jovian globe spans 45 arcseconds in mid-May and telescopes show that it is crossed by bands of cloud that lie parallel to its equator. The four principal moons of Jupiter are also easy targets, though sometimes one or more hide from view as they pass in front of, or behind, the disk or are eclipsed in Jupiter’s shadow.
Saturn trails almost two hours behind Jupiter but is fainter at magnitude 0.5 to 0.3. It lies in Sagittarius, below the Teaspoon asterism, where it stands above the Moon but low down in the south-south-east before dawn on the 23rd. Always an impressive sight through a telescope, though not helped by its low altitude, its disk appears 18 arcseconds wide at mid-month, circled by rings that measure 40 by 16 arcseconds.
Mercury and Venus are too deep in the morning twilight to be seen at present, though Mercury slips around the Sun’s far side on the 21st. The morning twilight also hinders views of the Eta-Aquarids meteor shower which peaks around the 6th-7th and brings swift meteors that stream from a point which hovers low in our east-south-eastern sky for two hours before sunrise.
Mars sets a few minutes before our star map times and may be hard to spot low down in our west-north-western evening sky. It stands between the horns of Taurus on the 1st and shines at magnitude 1.6 to rival the star Elnath, which lies 5° above Mars and marks the tip of the Bull’s northern horn.
Mars’ pinkish-orange hue is best appreciated through binoculars as the planet dims further to magnitude 1.8 and speeds 20° eastwards during May, crossing into Gemini at mid-month and sweeping only 0.2° north of the star cluster M35 (use binoculars) on the 19th. It recedes from 335 million to 363 million km during May but, at a mere 4 arcseconds in diameter, is too small to be of telescopic interest. Catch Mars above the slim earthlit Moon on the 7th.
NASA’s InSight lander used its sensitive French-built seismometer to detect its first likely marsquake on 6 April. The faint vibrations are now being studied for clues as to Mars’ interior. Another instrument, a German heat probe designed to drill up to five metres into the surface, seems to have encountered a rock and is currently stalled well short of its target depth.
The Plough looms directly overhead at nightfall and stands high in the west by our map times. If we extend a curving line along its handle, we reach the prominent star Arcturus which, at magnitude -0.05, is the brightest of all the stars in the sky’s northern hemisphere and, after Sirius, the second brightest (nighttime) star visible from Scotland, although both Vega and Capella come close.
Classed officially as a red giant star, though more yellow-orange in hue, Arcturus is slightly more massive than our Sun and perhaps 50% older. As such, it has depleted the hydrogen used to power its core through nuclear fusion, progressed to fusing helium instead and inflated to 25 times the Sun’s radius and 170 times its luminosity. Eventually, after shedding its outer layers, it will settle down as a dim white dwarf star comparable in size to the Earth.
At present, though, we admire it as the leading star in the constellation of Bootes which has been likened to a pale imitation of Orion or even an ice-cream cone. Bootes takes its name from the Greek for herdsman or plowman, apparently in relation to the seven stars of the Plough which were also known as the “Seven Oxen” in early times.
Arcturus’ own name comes from the Greek for “guardian of the bear”, another reference to its role in following Ursa Major across the sky. In truth, it is something of a temporary guardian since it is rushing past our solar system at 122 km per second at a distance of 36.7 light years and will likely fade from naked-eye view within (only) half a million years as it tracks south-westwards in the direction of Virgo and the bright star Spica.
It is in the north of Virgo, and roughly coincident with the “D” of the label for Denebola on our south star map, that we find the galaxy M87, the owner of the supermassive black hole whose image was released a few weeks ago. M87 is 54 million light years away and visible as a smudge in small telescopes.
Diary for 2019 May
Times are BST
5th 00h New moon
6th 15h Peak of Eta-Aquarids meteor shower
6th 23h Moon 2.3° N of Aldebaran
8th 01h Moon 3° S of Mars
11th 03h Moon 0.3° N of Praesepe
12th 02h First quarter
12th 16h Moon 3° N of Regulus
18th 22h Full moon
19th 18h Mars 0.2° N of star cluster M35 in Gemini
20th 18h Moon 1.7° N of Jupiter
21st 14h Mercury in superior conjunction
22nd 23h Moon 0.5° S of Saturn
26th 18h Last quarter
This is a slightly revised version, with added diary, of Alan’s article published in The Scotsman on April 30th 2019, with thanks to the newspaper for permission to republish here.
Galaxy clusters of interest in April’s southern evening sky
Orion stands in the south-west at nightfall as the sparkling skies of winter give way to the less flamboyant constellations of spring, led by Leo and Virgo. By our map times, Orion has mostly set the west and the Milky Way arcs only some 30° above Edinburgh’s north-western horizon as it flows between Auriga and the “W” formation of Cassiopeia.
The Milky Way, of course, marks the plane of our disk-shaped galaxy, itself dubbed the Milky Way, around which our Sun orbits every 240 million years. If we look along it, we encounter numerous distant stars but countless more are forever hidden from sight behind intervening clouds of gas and dust – the raw material from which new stars and planets may eventually coalesce. If we gaze in directions away from the plane of the Milky Way, though, the star numbers fall away and there is negligible gas and dust to hide our view of galaxies far beyond our own.
It follows that we might expect our best view of the distant universe to be in directions at right angles to the plane, towards the galactic poles. Regions around the North Galactic Pole are ideally placed in our April evening sky and host some of the most interesting clusters of galaxies in the entire sky.
The pole itself lies in the less-than-startling Coma Berenices which is approaching the high meridian at our map times. As the only modern constellation named for a historic person, this celebrates Queen Berenice II of Egypt who is said to have sacrificed her long hair as an offering to Aphrodite. Her tresses are represented by a cascade of stars that spill southwards through the “M” of “COMA” on the chart. These make up a dispersed but nearby star cluster at a distance of about 280 light years – the second closest star cluster after the Hyades in Taurus.
Roughly coincident with the “C” of “COMA” is another cluster, but this one of more than 1,000 galaxies at a distance of some 320 million light years. The Coma Cluster’s brightest galaxies are only around the twelfth magnitude and, as such, a challenge for many amateur telescopes. It was by studying this cluster that the Swiss astronomer Fritz Zwicky uncovered evidence as long ago as 1933 for the existence of what we now call dark matter. He found its galaxies were simply moving too fast to be held together unless addition material was present to supply an extra gravitational pull. Now we suspect that up to 90% of the Coma Cluster consists of this still-mysterious dark matter.
Lying south of Coma Berenices, and about 9° to the east (left) of Leo’s star Denebola, is the closer Virgo Cluster of galaxies. This sprawls across 8° of sky and holds about 1,500 galaxies at a distance of 54 million light years or so. Small telescopes show several, though we’d struggle to locate them without a better chart than I can supply here. In fact, The Virgo Cluster lies at the heart of a much larger family of galaxies and galaxy clusters dubbed the Virgo Supercluster which includes the so-called Local Group of galaxies in which the Milky Way is a major player. The Coma Cluster rules another supercluster.
Edinburgh’s sunrise/sunset times change from 06:44/19:50 BST on the 1st to 05:32/20:49 on the 30th as the Moon stands at new on the 5th, first quarter on the 12th, full on the 19th and last quarter on the 26th. As I mentioned last time, satellites may now be spotted at any time of night though the current spell of evening passes by the International Space Station ends on or about the 5th.
Mars stands some 30° high and alongside the Pleiades in our western sky as our nights begin at present. The planet, though, is tracking east-north-eastwards against the stars and passes north of Taurus’ main star, Aldebaran, to lie between the Bull’s horns later in the month. The young earthlit Moon is an impressive sight 9° below Mars on the 8th and stands above Aldebaran and to the left of Mars on the 9th.
Mars no longer glares like an orange beacon in our sky and is now only half as bright as Aldebaran. As its distance grows from 302 million to 335 million km in April, it dims a little more from magnitude 1.5 to 1.6. Even large telescopes reveal little detail on its small ochre disk, less than 5 arcseconds in diameter, and viewing conditions can only deteriorate as it sinks towards the north-western horizon where it sets in the middle of the night.
There are two brighter planets in our predawn sky, both of them low in the south to south-east as the Summer Triangle formed by Vega, Deneb and Altair climbs through the east.
Jupiter, conspicuous at magnitude -2.2 to -2.5, rises in the south-east less than three hours after our map times and stands 11° above Edinburgh’s southern horizon before dawn. Slow-moving in southern Ophiuchus, it reaches a stationary point on the 10th when its motion appears to reverse from easterly to westerly as it begins to be overtaken by the Earth. Saturn, rather fainter at magnitude 0.6 to 0.5 and at its own stationary point on the 30th, lies in Sagittarius some 25° to Jupiter’s left. Catch the Moon near Jupiter on the 23rd and Saturn on the 25th.
Although Venus is brilliant at magnitude -4.0, it rises in the east less than 38 minutes before sunrise and is unlikely to be noticed. Mercury is furthest west of the Sun (28°) on the 11th but is much fainter and lower still in the morning twilight.
Diary for 2019 April
Times are BST
2nd 05h Moon 2.7° S of Venus
3rd 00h Moon 4° S of Mercury
5th 10h New moon
9th 08h Moon 5° S of Mars
9th 17h Moon 2.1° N of Aldebaran
10th 18h Jupiter stationary (motion reverses from E to W)
11th 21h Mercury furthest W of Sun (28°)
12th 20h First quarter
13th 22h Moon 0.1° N of Praesepe
15th 10h Moon 2.8° N of Regulus
16th 23h Mars 7° N of Aldebaran
19th 12h Full moon
23rd 00h Uranus in conjunction with Sun
23rd 13h Moon 1.6° N of Jupiter
25th 15h Moon 0.4° S of Saturn
26th 23h Last quarter
30th 03h Saturn stationary (motion reverses from E to W)