Geminid meteors sparkle during long December nights
December brings us spectacular night skies and arguably the richest meteor shower of the year, the Geminids. We still have the Summer Triangle of bright stars, Vega in Lyra, Deneb in Cygnus and Altair in Aquila, high in the south-west at nightfall while the unmistakable figure of Orion dominates the midnight hours, surrounded by his cohort of familiar winter constellations. By the predawn, the Plough sails overhead and the night’s only conspicuous planets shine to the south of east.
Our longest nights, of course, occur around the winter solstice when the Sun reaches its most southerly point in its annual trek around the sky. This occurs at 16:28 GMT on the 21st when Edinburgh’s night, measured from sunset to sunrise, lasts for 17 hours and 3 minutes, which no less than 10 hours and 39 minutes longer than at June’s summer solstice.
Sunrise/sunset times for Edinburgh during December vary from 08:19/15:44 on the 1st to 08:42/15:40 on the 21st and 08:44/15:48 on the 31st. The Moon is full on the 3rd, at last quarter on the 10th, new on the 18th and at first quarter on the 26th,
By our map times, the Summer Triangle has toppled low into the west and is being followed by the less impressive Square of Pegasus. The Square’s top-left star, Alpheratz, belongs to Andromeda whose other main stars, Mirach and Almach, line up to its left. A spur of fainter stars above Mirach leads us to the Andromeda Galaxy, whose oval glow reaches us from 2.5 million light years away.
Orion is in the east-south-east, his Belt pointing up Aldebaran and the Pleiades in Taurus and down to where the brightest nighttime star, Sirius in Canis Major, rises less than one hour later.
The Moon lies to the right of Aldebaran and below the Pleiades on the night of 2nd-3rd, to the left of Aldebaran a day later and comes around again to occult the star in the early hours of the 31st. We need a telescope to see Aldebaran wink out at the Moon’s limb at 01:01 and reappear at 01:57 as seen from Edinburgh.
It is from a radiant point near Castor in Gemini, north-east of Orion, that meteors from the Geminids shower diverge between the 8th and 17th although, of course, the meteors fly in all parts of the sky. With negligible moonlight this year, and given decent weather, we are in for a stunning display of sparkling long-trailed meteors whose paths point back to the radiant. Rates for an observer under an ideal dark sky could peak at more than 100 per hour at the shower’s peak on the night of the 13th-14th, though most of us may glimpse only a fraction of these.
Although most meteors originate as cometary debris, the Geminids appear to be rocky splinters from the 5 km-wide asteroid, Phaethon, which dives within 21 million km of the Sun every 523 days. In what is its closest approach to the Earth since its discovery in 1983, Phaethon sweeps only 10.3 million km from the Earth on the 16th when a telescope might show it as a tenth magnitude speck speeding past Alpheratz.
December’s second shower, the Ursids, derives from Comet Tuttle and is active between the 17th and 25th, peaking on the 23rd. Typically it yields fewer than ten meteors per hour so I rarely mention it here – I believe my last time was 37 years ago – but very occasionally it rivals the Geminids in intensity, if only for a few hours. The radiant point lies near the star Kochab in Ursa Minor and is plotted on our northern chart.
The unprecedented interstellar asteroid, discovered using a telescope in Hawaii and featured here hast time, has now been called 1I/’Oumuamua. This indicates that it is our first known interstellar visitor and employs the Hawaiian word ’Oumuamua to reflect its supposed status as a scout from the distant past. Further observations imply that it is remarkably elongated, being at least five times longer than it is wide.
Venus shines brilliantly at magnitude -3.9 very low in the south-east as the night ends, but is soon lost from view as it dives towards the Sun’s far side. It leaves Jupiter as our most prominent (magnitude -1.7 to -1.8) morning object. The giant world rises at Edinburgh’s east-south-eastern horizon at 05:31 on the 1st and 04:07 on the 31st, climbing southwards in the sky to stand some 15° high before dawn. Tracking eastwards in Libra, it passes 0.7° north of the celebrated double star Zubenelgenubi on the 21st.
Mars, fainter at magnitude 1.7 to 1.5, lies 16° above-right of Jupiter on the 1st when it is also about half as bright as Virgo’s star Spica, 3° below and to its right. As Mars tracks east-south-eastwards from Virgo to Libra it almost keeps pace with the Sun, so that it rises at around 03:50 throughout the month. By the 31st, it stands 3° from Jupiter, with Zubenelgenubi below and to Mars’ left in the same binocular field of view. The waning Moon forms a nice triangle with Mars and Spica on the 13th and with Mars and Jupiter on the 14th.
Saturn sets in our bright evening twilight as it heads towards conjunction beyond the Sun on the 21st. Mercury slips around the Sun’s near side on the 13th to become best placed as a morning star between Christmas and New Year. Between the 21st and 31st it brightens between magnitude 0.8 and -0.3, rises 100 or more minutes before Edinburgh’s sunrise and stands around 8° high in the south-east thirty minutes before sunrise.
This is a slightly revised version of Alan’s article published in The Scotsman on November 30th 2017, with thanks to the newspaper for permission to republish here.
At the recent Member’s Evening on 3 November 2017, Mark Phillips gave a presentation about his experience of astro imaging.
Here is a link to the Prezi presentation (use the arrows at the bottom of the screen to navigate):
Astro imaging is a large topic so the presentation covers, at a general level, the sorts of imaging that I do with my own equipment. It describes the techniques, software and equipment I use, and shows some of the results. I hope it will be an encouragement to others to try astro imaging maybe for the first time or maybe to get back into it again.
You can see more of my images and projects on my astronomy website: http://www.forthimage.co.uk/
Here are some links to the software mentioned in the presentation:
- Cartes du Ciel: https://www.ap-i.net/skychart/en/start
- EQMOD: http://eq-mod.sourceforge.net/
- Astrophotography Tool (APT): https://www.ideiki.com/astro/Default.aspx
- PHD Guiding 2: https://openphdguiding.org/
- ASCOM: https://ascom-standards.org/
- FireCapture: http://www.firecapture.de/
- Deep Sky Stacker: http://deepskystacker.free.fr/english/index.html
- Autostakkert: https://www.autostakkert.com/
- Registax: http://www.astronomie.be/registax/
- Microsoft ICE: https://www.microsoft.com/en-us/research/product/computational-photography-applications/image-composite-editor/
Mark has been a member of the ASE for just over a year, having found us through his love of astro imaging.
Astronomers spot a mystery interstellar visitor
Comets have always been of particular interest. Appearing without warning, and sometimes with impressive tails, it was not surprising that they were regarded as portents of battles to be won or lost and of the passing of kings.
It was in 1705 that Edmond Halley first published the orbit of the comet that now bears his name. This, and the more than 5,000 comets that have been studied since, have all proved to be members of our solar system.
Some, like Halley, follow closed elongated orbits, returning to perihelion in the Sun’s vicinity every few years. Many more, though, trace almost parabolic paths as they dive towards the Sun from the Oort cloud, a spherical reservoir of icy worlds at the edge of the Sun’s influence – if they ever return to perihelion it may not be for millions of years. A handful, though, receive a sufficient gravitational boost as they pass a planet that they are flung beyond the Oort cloud into interstellar space, never to return.
Now astronomers have sighted a faint object which appears to have originated far beyond the Oort cloud, perhaps as an escapee from another star. Discovered by the Pan-STARRS 1 telescope in Hawaii on 18 October, it had already reached its perihelion within 38 million km of the Sun nine days before and passed 24 million km from the Earth on the 14th. Dubbed at first Comet/2017 U1 (PanSTARRS) because of its highly eccentric comet-like orbit, its name was changed to A/2017 U1 on 25 October when observers failed to detect any trace of a tail or hazy coma surrounding its small nucleus, probably less than 200 metres wide. So, for the moment, it is classed as an asteroid.
Its path though is certainly hyperbolic, having entered the solar system at a relative speed of 26 km per second from a direction close to the bright star Vega in the constellation Lyra. This is also close to the direction that our solar system is moving at 20 km per second with regard to the stars around us, so it may be expected that interstellar intruders, be they comets or asteroids, are most likely to appear from this region. As our first known visitor from interstellar space, frantic efforts are underway to investigate its spectrum and nature before it recedes forever from view in the direction of the Square of Pegasus.
Vega, itself, is the brightest object very high in the south-west at nightfall, falling into the west by our star chart times as Pegasus and Andromeda occupy our high meridian. Orion is rising in the east below Taurus whose brightest star, Aldebaran, is occulted by the bright Moon on the morning of the 6th. Use a telescope to watch it slip behind the Moon’s lower-left limb between 02:27 and 03:26 as seen from Edinburgh
Our sole bright evening planet, Saturn at magnitude 0.5, is easy to miss as it hangs low in the south-west at nightfall, sinking to Edinburgh’s horizon at 18:40 on the 1st and by 16:58 on the 30th. We may need binoculars to spy it in the twilight 5° left of the young earthlit Moon on the 20th and 8° below-right of the Moon a day later. Mercury stands 22° east of the Sun on the 24th but is unlikely to be visible from our latitudes.
The other naked-eye planets are all in our predawn sky. Mars rises in the east just before 04:00 throughout November, climbing to stand 15° to 20° high in the south-east before its magnitude 1.8 pinprick is swallowed by the twilight. This month, it tracks 19° east-south-eastwards in Virgo to pass 3° north of Virgo’s leading star Spica on the 28th. Mars stands to the right of the waning Moon on the 15th when a telescope show it as only 4 arcseconds wide – too small to see any detail.
Venus continues as a brilliant morning star of magnitude -3.9, but it stands lower each morning as it approaches the Sun’s far side. Currently above and left of Spica but speeding east-south-eastwards into Libra, it rises a little more than two hours before the Sun on the 1st and one hour before sunrise by the 30th.
Jupiter, about to emerge from the Sun’s glare below-left of Venus, climbs to pass a mere 16 arcminutes, or half the Moon’s diameter, below-right of Venus on the 13th. Conspicuous at magnitude -1.7, the Jovian disk appears 31 arcseconds wide as compared with only 10 arcseconds for Venus. On the 17th, the incredibly slim earthlit Moon lies above-left of Venus and to the left of Jupiter while the later stands 18° above-right of Venus by the 30th.
Sunrise/sunset times for Edinburgh change from 07:20/16:32 on the 1st to 08:18/15:45 on the 30th. The Moon is full on the 4th, at last quarter on the 10th, new on the 18th and at first quarter on the 26.
The annual Leonids meteor shower lasts from the 15th to the 20th and peaks on the night of the 17th-18th. Its meteors, all of them very fast and many leaving glowing trains in their wake, emanate from the Sickle, the reversed question-mark of stars above Regulus in Leo. This rises in the north-east at 22:00, with most Leonids visible during the predawn hours as it climbs through our eastern sky. The shower has given some spectacular meteor storms in the past, notably in 1966 and 1999, but the parent comet, Comet Tempel-Tuttle, is now near the farthest point of its orbit and rates may be around a dozen meteors per hour. For once, though, moonlight is no hindrance.
This is a slightly revised version of Alan’s article published in The Scotsman on October 31st 2017, with thanks to the newspaper for permission to republish here.
Saturn at full tilt as Comet Halley’s meteors fly
Our charts capture the sky in transition between the stars of summer, led by the Summer Triangle of Deneb, Vega and Altair in the west, and the sparkling winter groups heralded by Taurus and the Pleiades star cluster climbing in the east. Indeed, if we look out before dawn, as Venus blazes in the east, we see a southern sky centred on Orion that mirrors that of our spectacular February evenings. October also brings our second opportunity this year to spot debris from Comet Halley.
As the ashes of the Cassini spacecraft settle into Saturn, the planet reaches a milestone in its 29-years orbit of the Sun when its northern hemisphere and rings are tilted towards us at their maximum angle of 27.0° this month. In practice, our view of the rings’ splendour is compromised at present by its low altitude.
Although it shines at magnitude 0.5 and is the brightest object in its part of the sky, Saturn hovers very low in the south-west at nightfall and sets around 80 minutes before our map times. The rings span 36 arcseconds at mid-month while its noticeably rotation-flattened disk measures 16 arcseconds across the equator and 14 arcseconds pole-to-pole. Catch it below and to the right of the young crescent Moon on the 24th.
The Sun moves 11° further south of the equator this month as sunrise/sunset times for Edinburgh change from 07:16/18:48 BST (06:16/17:48 GMT) on the 1st to 07:18/16:34 GMT on the 31st, after we set our clocks back on the 29th.
Jupiter is now lost in our evening twilight as it nears the Sun’s far side on the 26th. Saturn is not alone as an evening planet, though, for both Neptune and Uranus are well placed. They are plotted on our southern chart in Aquarius and Pisces respectively but we can obtain more detailed and helpful diagrams of their position via a Web search for a Neptune or Uranus “finder chart” – simply asking for a “chart” is more likely to lead you to astrological nonsense.
Neptune, dimly visible through binoculars at magnitude 7.8, lies only 0.6° south-east (below-left) of the star Lambda Aquarii at present and tracks slowly westwards to sit a similar distance south of Lambda by the 31st. It lies 4,346 million km away on the 1st and its bluish disk is a mere 2.3 arcseconds wide.
Uranus reaches opposition on the 19th when it stands directly opposite the Sun and 2,830 million km from Earth. At magnitude 5.7 it is just visible to the unaided eye in a good dark sky, and easy through binoculars. Currently 1.3° north-west of the star Omicron Piscium and also edging westwards, it shows a bluish-green 3.7 arcseconds disk if viewed telescopically.
North of Aquarius and Pisces are Pegasus and Andromeda, the former being famous for its relatively barren Square while the fuzzy smudge of the Andromeda Galaxy, M31, lies 2.5 million light years away and is easy to glimpse through binoculars if not always with the naked eye.
Mercury slips through superior conjunction on the Sun’s far side on the 8th and is out of sight. Venus remains resplendent at magnitude -3.9 in the east before dawn though it does rise later and stand lower each morning. On the 1st, it rises for Edinburgh at 04:44 BST (03:44 GMT) and climbs to stand 20° high at sunrise. By the month’s end, it rises at 05:30 GMT and is 13° high at sunrise. Against the background stars, it speeds from Leo to lie 5° above Virgo’s star Spica by the 31st.
Mars is another morning object, though almost 200 times dimmer at magnitude 1.8 as it moves from 2.6° below-left of Venus on the 1st to 16° above-right of Venus on the 31st. The pair pass within a Moon’s breadth of each other on the 5th and 6th when Venus appears 11 arcseconds in diameter and 91% sunlit and Mars (like Uranus) is a mere 3.7 arcseconds wide.
Comet Halley was last closest to the Sun in 1986 and will not return again until 2061. Twice each year, though, the Earth cuts through Halley’s orbit around the Sun and encounters some of the dusty debris it has released into its path over past millennia. The resulting pair of meteor showers are the Eta Aquarids in early-May and the Orionids later this month. Although the former is a fine shower for watchers in the southern hemisphere, it yields only the occasional meteor in Scotland’s morning twilight.
The Orionids are best seen in the morning sky, too, and produce fewer than half the meteors of our main annual displays. This time the very young Moon offers no interference during the shower’s broad peak between the 21st and 23rd. In fact, Orionids appear throughout the latter half of October as they diverge from a radiant point in the region to the north and east of the bright red supergiant star Betelgeuse in Orion’s shoulder and close to the feet of Gemini. Note that they streak in all parts of the sky, not just around the radiant.
Orionids begin to appear when the radiant rises in the east-north-east at our map times, building in number until it passes around 50° high in the south before dawn. Under ideal conditions, with the radiant overhead in a black sky, as many as 25 fast meteors might be counted in one hour with many leave glowing trains in their wake. Rates were considerably higher than this between 2006 and 2009, so there is the potential for another pleasant surprise.
This is a slightly revised version of Alan’s article published in The Scotsman on September 30th 2017, with thanks to the newspaper for permission to republish here.
Cassini’s scheduled suicide at Saturn
The heroic Cassini mission to Saturn is set to reach its dramatic conclusion on 15 September. After a seven-year journey from Earth, the probe has been studying the planet, its glorious rings and its fascinating moons for the past thirteen years. Now, with its fuel running low, it is time for the NASA probe to plunge into the Saturnian atmosphere where, in the interest of so-called planetary protection, it will disintegrate and vaporise.
To leave it in orbit around the planet would run the risk of it colliding with the rings or one of the moons, with the outside possibility of contaminating them with microbes from the Earth. This was of little concern when Cassini’s mission was planned, and it carried and delivered the European-built Huygens probe which parachuted to the surface of Saturn’s largest moon, Titan. It touched down on a world in which rivers of liquid hydrocarbons, chiefly methane, flow into lakes in a landscape dominated by water-ice mountains.
Now, though, we realise that despite Saturn’s remoteness from the Sun, the possibility of alien life there cannot be discounted. Indeed, it seems clear that its small moon Enceladus has a subsurface watery ocean and there has been talk of sending a mission to search for organic compounds in the plumes of water erupting from geysers on its surface.
Recent orbits of Saturn have seen Cassini piercing the gap between Saturn and its rings, and even skimming the planet’s outer atmosphere. It will continue to collect data as it begins its final suicidal dive into Saturn’s atmosphere on the 15th, but its signal will be lost at around 13:00 BST as aerodynamic forces cause it to tumble and, eventually, break apart and burn up.
The Sun crosses southwards over the equator at 21:02 BST on the 22nd, the moment of our autumnal equinox. Sunrise/sunset times for Edinburgh change from 06:17/20:07 BST on the 1st to 07:14/18:50 on the 30th. The Moon is full on the 6th, at last quarter on the 13th, new on the 20th and at first quarter on the 28th.
Now that Scotland’s persistent summer twilight is behind us, our nights offer views of the Milky Way as it arches directly overhead from the south-west to the north-east at our chart times, carving through the Summer Triangle formed by Deneb, Altair and Vega which now lies just west of the high meridian.
To the east of the Triangle is the distinctive form of the celestial dolphin, Delphinus, where the celebrated English amateur astronomer George Alcock discovered a famous and unusual naked-eye nova fifty summers ago in 1967. I remember watching the stellar outburst as it took five months to reach its peak brightness at magnitude 3.5. Now assigned the variable-star tag HR Delphini, the star is still visible as a twelfth magnitude object through telescopes.
Another 13° east of Delphinus is the globular star cluster Messier 15, 4° north-west of Pegasus’s brightest star, Enif. A tightly packed globe of perhaps 100,000 stars, all very much older than our Sun, M15 lies around 34,000 light years away and looks like a fuzzy star through binoculars.
Saturn is the sole bright planet to appear on our star maps. Look for it as the brightest object low down in the south-south-west at nightfall and even lower in the south-west by our map times, only thirty minutes before it sets. Edging eastwards in Ophiuchus, it shines 4° below-left of the Moon on the 26th.
Jupiter is bright at magnitude -1.7 but hard to see very low in the west-south-west just after sunset. By mid-month it is likely to be lost in the twilight.
Our charts plot the two outer planets, the ice giant world Uranus in Pisces and its near-twin Neptune in Aquarius, though we probably need more detailed charts to identify them through binoculars or telescopes. At magnitude 5.7, Uranus is at the verge of naked-eye visibility, while Neptune reaches opposition on the 5th and is dimmer at magnitude 7.8.
The other planets are about to join Venus low down in our eastern sky at the end of the night. The brilliant morning star shines at magnitude -4.0 when it rises in the north-east at 03:04 for Edinburgh on 1 September, and climbs 25° high into the east by sunrise. Catch it through binoculars before the twilight intervenes on that day and look 1.2° to its left for the Praesepe or Beehive cluster of stars in Cancer. Leaving the cluster behind, Venus tracks east-south-eastwards into Leo to pass 0.5° (a Moon’s breadth) north of the star Regulus on the 20th.
Mercury emerges from the Sun’s glare to stand 18° west of the Sun and 11° below-left of Venus on the 12th. Between the 6th and 23rd it rises more than 80 minutes before sunrise and brightens eightfold from magnitude 1.1 to -1.1. On the 6th, in fact, Mercury lies 2.5° to the right of Regulus which, in turn, is 0.8° to the right of the fainter magnitude 1.8 planet Mars. As Regulus climbs above them, the two planets then converge to lie less than 0.5° apart on the 16th and 17th.
Early risers are in for a special treat when the waning earthlit Moon joins the party on the 17th. On that morning, Venus stands 10° below-left of the Moon and almost 4° above-right of Regulus, with the Mars-Mercury conjunction another 8° below and to the left. On the 18th, the line-up is even more compact as the Moon shifts to lie 0.7° below Regulus. By the 30th, Venus rises in the east-north-east at 04:41 and is 3° above-right of Mars.
This is a slightly-revised version of Alan’s article published in The Scotsman on August 31st 2017, with thanks to the newspaper for permission to republish here.
Countdown to the Great American Eclipse
With two eclipses and a major meteor display, August is 2017’s most interesting month for sky-watchers. Admittedly, Scotland is on the fringe of visibility for both eclipses while the annual Perseids meteor shower suffers moonlight interference.
The undoubted highlight is the so-called Great American Eclipse on the 21st. This eclipse of the Sun is total along a path, no more than 115km wide, that sweeps across the USA from Oregon at 18:17 BST (10:17 PDT) to South Carolina at 19:48 BST (14:48 EDT) – the first such coast-to-coast eclipse for 99 years.
Totality is visible only from within this path as the Moon hides completely the dazzling solar surface, allowing ruddy flame-like prominences to be glimpsed at the solar limb and the pearly corona, the Sun’s outer atmosphere, to be admired at it reaches out into space. At its longest, though, totality lasts for only 2 minutes and 40 seconds so many of those people fiddling with their gadgets to take selfies and the like may be in danger of missing the spectacle altogether.
The surrounding area from which a partial eclipse is visible even extends as far as Scotland. From Edinburgh, this lasts from 19:38 to 20:18 BST but, at most, only the lower 2% of the Sun is hidden at 19:58 as it hangs a mere 4° high in the west. Need I add that the danger of eye damage means that we must never look directly at the Sun – instead project the Sun through a pinhole, binoculars or a small ‘scope, or use an appropriate filter or “eclipse glasses”.
A partial lunar eclipse occurs over the Indian Ocean on the 7th as the southern quarter of the Moon passes through the edge of the Earth’s central dark umbral shadow between 18:23 and 20:18 BST. By the time the Moon rises for Edinburgh at 20:57, it is on its way to leaving the lighter penumbral shadow and I doubt whether we will see any dimming, It exits the penumbra at 21:51.
Our charts show the two halves of the sky around midnight at present. In the north-west is the familiar shape of the Plough while the bright stars Deneb in Cygnus and Vega in Lyra lie to the south-east and south-west of the zenith respectively. These, together with Altair in Aquila in the middle of our southern sky, make up the Summer Triangle. The Milky Way flows through the Triangle as it arches overhead from the south-west to the north-east where Capella in Auriga rivals Vega in brightness.
Of course, many of us have to contend with light pollution which swamps all trace of the Milky Way and we are not helped by moonlight which peaks when the Moon is full on the 7th and only subsides as last quarter approaches on the 15th. New moon comes on the 21st and first quarter on the 29th. The Sun, meantime, slips another 8° southwards during the month as sunrise/sunset times for Edinburgh change from 05:17/21:20 BST on the 1st to 06:15/20:09 on the 31st.
Meteors of the annual Perseids shower, the tears of St Lawrence, are already arriving in low numbers. They stream away from a radiant point in the northern Perseus which stands in the north-east at our map times, between Capella and the W-pattern of Cassiopeia. We spot Perseids in all parts of the sky, though, and not just around Perseus.
Meteor numbers are expected to swell to a peak on the evening of the 12th when upwards of 80 per hour might be counted under ideal conditions. Even though moonlight will depress the numbers seen this time, we can expect the brighter ones still to impress as they disintegrate in the upper atmosphere at 59 km per second, many leaving glowing trains in their wake. The meteoroids concerned come from Comet Swift-Tuttle which last approached the Sun in 1992.
Although Neptune is dimly visible through binoculars at magnitude 7.8 some 2° east of the star Lambda Aquarii, the only naked-eye planet at our map times is Saturn. The latter shines at magnitude 0.3 to 0.4 low down in the south-west as it sinks to set less than two hours later. It is a little higher towards the south at nightfall, though, where it lies below-left of the Moon on the 2nd when a telescope shows its disk to be 18 arcseconds wide and its stunning wide-open rings to span 40 arcseconds. Saturn is near the Moon again on the 29th.
Jupiter is bright (magnitude -1.9 to -1.7) but very low in our western evening sky, its altitude one hour after sunset sinking from 6° on the 1st to only 1° by the month’s end as it disappears into the twilight. Catch it just below and right of the young Moon on the 25th.
Venus is brilliant at magnitude -4.0 in the east before dawn. Rising in the north-east a little after 02:00 BST at present, and an hour later by the 31st, it climbs to stand 25° high at sunrise. Viewed through a telescope, its disk shrinks from 15 to 12 arcseconds in diameter as it recedes from 172 million to 200 million km and its gibbous phase changes from 74% to 83% sunlit.
As Venus tracks eastwards through Gemini, it passes below-right of the star cluster M35 (use binoculars) on the 2nd and 3rd, stands above-left of the waning earthlit Moon on the 19th and around 10° below Castor and Pollux as it enters Cancer a few days later. On the 31st it stands 2° to the right of another cluster, M44, which is also known as Praesepe or the Beehive.
This is a slightly-revised version of Alan’s article published in The Scotsman on July 31st 2017, with thanks to the newspaper for permission to republish here.
Pole stars of the future in the Summer Triangle
The Sun’s southerly motion since the solstice on 21 June has yet to gain speed and not until 12 July does it lie sufficiently far south for Edinburgh to enjoy any so-called nautical darkness, with the Sun more than 12° below the northern horizon in the middle of the night. Even then, moonlight is troublesome for a few more days to delay our first views of a dark summer night sky.
If there is one star-pattern that dominates our skies over the summer, it is the Summer Triangle. Formed by the bright stars Vega in the constellation Lyra, Deneb in Cygnus and Altair in Aquila, it occupies the upper part of our south star map, though its outline is not depicted. In fact, the projection used means that the Triangle’s proportions are squashed, because Vega and Deneb are significantly closer together in the sky than either are to Altair.
The leader and brightest of the Triangle’s stars is Vega which moves from high in the east at nightfall to stand even higher in the south at our map times. Blazing at magnitude 0.0 from a distance of 25 light years, it is a white star, twice as massive as our Sun but very much younger. Excess heat revealed by infrared astronomy indicates that Vega is encircled by a disk of dust which may be evidence that a planetary system is forming around it.
Set your time machine for about AD 13,700 and you will be able to glimpse Vega close to where we currently find Polaris, our current Pole Star. This is because the Earth’s axis is slowly toppling in space, taking 26,000 years to complete a 47° circle in the sky and carrying the axis to within 4° of Vega. Polaris happens to lie within 0.8° of the axis at present so that, as the Earth rotates once each day, it stays almost fixed in our sky and the other stars appear to circle counterclockwise around it
Altair is the second brightest of the Triangle’s stars and one of the closest bright stars at “only” 16.7 light years. Shining at magnitude 0.8, half as bright as Vega, it is 80% more massive than our Sun but, remarkably, spins on its axis in about nine hours as compared with the more leisurely 25 days taken by the Sun. As a result, it is noticeably oblate, measuring 20% wider across its equator than it does pole-to-pole.
Deneb’s magnitude of 1.2 makes it the dimmest of the Triangle’s corner stars but it is also one of the most luminous stars in our Milky Way Galaxy. Because its distance may be around 2,600 light years, it very difficult to measure the minuscule shift in its position when viewed from opposite sides of the Earth’s orbit around the Sun – the parallax technique that gives us accurate distances to Vega and Altair. Indeed, estimates of Deneb’s distance differ by well over 1,000 light years.
White-hot and shining at some 200,000 Sun-power, Deneb is large enough to engulf the Earth were it to swap places with the Sun. It is also burning its nuclear fuel at such a rate that it seems destined to disintegrate in a supernova within a few million years, although it should survive to be another of our future pole stars as it comes as close as 5° to the pole in AD 9,800.
The Sun eventually tracks 5° southwards during July as Edinburgh’s sunrise/sunset times change from 04:32/22:01 BST on the 1st to 05:15/21:22 on the 31st. The Moon is at first quarter on the 1st, full on the 9th, at last quarter on the 16th, new on the 23rd and returns to first quarter on the 30th.
At magnitude -2.0, Jupiter remains our brightest evening planet though it stands lower in the south-west to west as it sinks to set in the west just before our star map times. Above and to the right of the star Spica in Virgo, it lies to the right of the Moon in the south-west as the sky darkens on the 1st and is just below the Moon and much lower in the west-south-west on the 28th. The cloud-banded Jovian disk appear 39 arcseconds wide at mid-month if viewed telescopically, while binoculars allow glimpses of its four main moons.
Saturn is less conspicuous at magnitude 0.1 to 0.3 but continues as the brightest object low in our southern night sky. Creeping westwards against the stars of southern Ophiuchus, it crosses Edinburgh’s meridian at an altitude of 12° one hour before our map times and may be spotted 3° below-left of the Moon on the 6th. Binoculars show it as more than a round dot, while small telescopes reveal the beauty of ring system which is tilted wide open to our view and spans 41 arcseconds in mid-July.
Venus is brilliant at magnitude -4.1 in the east before dawn. After rising in the north-east at about 02:15 BST throughout the month. it climbs to stand 17° high at sunrise as the month begins and higher still by its end. Seen through a telescope, it is 16 arcseconds across and 70% illuminated when it lies to the left of waning (15% sunlit) and earthlit Moon on the 20th. Against the background stars of Taurus, the planet moves from 8° below-right of the Pleiades tomorrow to pass 3° above-left of Aldebaran on the 14th.
Of the other bright planets, Mars is out of sight as it reaches conjunction on the Sun’s far side on the 27th, while Mercury stands furthest east of the Sun (27°) on the 30th but is unlikely to be seen near our west-north-western horizon in the bright evening twilight.
This is a slightly-revised version of Alan’s article published in The Scotsman on June 30th 2017, with thanks to the newspaper for permission to republish here.
In 1961, Professor Frank Drake attempted to estimate the number of extra-terrestrial civilizations in the Milky Way with which we might come into contact by making several assumptions. The Drake equation  states that:
N = R* x Fp x Ne x Fl x Fi x Fc x L
N = the number of civilizations in our galaxy with which communication might be possible;
R* = the average rate of star formation per year in our galaxy
Fp = the fraction of those stars that have planets
Ne = the average number of planets that can potentially support life per star that has planets
Fl = the fraction of the above that actually go on to develop life at some point
Fi = the fraction of the above that actually go on to develop intelligent life
Fc = the fraction of civilizations that develop a technology that releases detectable signs of their existence into space
L = the length of time such civilizations release detectable signals into space.
Drake gave each parameter the following values:
R* = 10/year (10 stars formed per year, on average over the life of the galaxy)
Fp = 0.5 (half of all stars formed will have planets)
Ne= 2 (stars with planets will have 2 planets capable of supporting life)
Fl = 1 (100% of these planets will develop life)
Fi = 0.01 (1% of which will be intelligent life)
Fc = 0.01 (1% of which will be able to communicate)
L = 10,000 years (which will last 10,000 years).
So that N = 10 × 0.5 × 2 × 1 × 0.01 × 0.01 × 10,000 = 10.
Recently, Professor Paul Davies has made a different estimate with a range of different values in the Equation . His N is between 1 and a billion!
I find Drake’s approach strange. A more logical approach might be to ask how many stars there are in the Galaxy. If there are between 100 and 400 billion stars, if half of all stars have planets, if there is life on only one planet in each system, but if only one in a million of those planets develops intelligent life, then there are between 50,000 and 200,000 planets with intelligent life.
Of course the values chosen for the Equation are highly questionable; they are merely wild guesses. However, one can question some more than others. The guess that, where stars have planets, two of them will harbour life is hardly justified from the example of the Solar System, where, as far as we know, only one planet (Earth) carries life. Even that change could halve Drake’s estimate to five. More importantly, these estimates seem to overlook the circumstances in which intelligent life has emerged on Earth. In particular, the value given to Fi (that intelligent life emerges on only one in a hundred planets where life has developed) is questionable.
It is easy to assume that because we exist, intelligent life is common (see the popular belief in aliens). However, we should consider the peculiar circumstances that have allowed us to evolve. Although life appeared very early on Earth (at least only 500 million years after the planet’s birth), multicellular life did not emerge until about 600 million years ago (MYA), fish only 500 MYA, reptiles only 300 MYA and our species only about 500,000 years ago. So it may be that modern humans have existed for only about 0.1 per cent of the life of the planet and it is certain that our modern technological civilization has existed for only about 200 years (~0.00004% of the life of planet Earth). That is a chance of only 1 in 2.5 billion that anyone looking for an advanced technological civilization (ATC) on Earth between the planet’s birth and now would be successful. What does that say for our chance of finding another ATC now?
Then consider the possibility that such a civilization will destroy itself. Nuclear war could have destroyed our civilization in 1962, before we even began looking for signals from another Galactic civilization (although not before our radio, TV and radar signals leaked out). This could lead to the conclusion that the chance of finding another ATC at this time is vanishingly small (Paul Davies allows for fi to be zero).
The Equation does not appear to have made allowance for the fact that we owe our existence to the demise of the dinosaurs 65 MYA. It should not be assumed that such destruction does not threaten other planets, or that it does. Without that event, the dinosaurs, who had ruled for 180 million years would probably still rule the Earth. If life on other planets follows such a path, do we have to assume some equivalent calamity before intelligent life can emerge? If so, what odds do we put on it?
Another important factor is our Moon, which is unusual in being so large and influential. We already believe that the Moon’s birth was the result of a catastrophic collision been the proto-Earth and another planetismal the size of Mars. How typical would such a collision be and what odds do we put on it occurring in a planetary system? If the result is a moon such as ours and such a large moon is unusual, then perhaps such collisions themselves are unusual. But does that mean that we owe our existence, inter alia, to the Moon?
Professor Neil F. Comins asked himself what the implications would be if the Moon did not exist . There would have been many differences, including a shorter rotation period and a different chemical composition, but those that might influence the development of life include the possibility of a different tilt axis and instability of that axis. The Moon, besides gradually slowing Earth’s rotation, also stabilizes Earth’s axis. The lack of the Moon would mean smaller ocean tides, perhaps making the transfer of life from the oceans to land more difficult. It may also have meant more bombardment of Earth by asteroids and/or comets (the Moon has shielded Earth to some extent). This may have interfered with the development of life. Comins also thought that a Moon-less Earth (he called it ‘Solon’) would have a different atmosphere, with such a large amount of carbon dioxide that ‘life as we know it may never have been feasible’.
It has already been observed that our civilization has developed in a balmy interglacial, but Professor James Hansen has recently drawn attention to the fact that (unusually) sea levels have been remarkable stable for the last 7000 years (the climate kept an ice sheet from forming in Canada but kept stable ice sheets in Greenland and Antarctica). He pointed out that, because our major civilizations have mostly developed on coasts, especially on river deltas, this may have contributed to the development of civilization. Repeated changes in sea level would have inhibited the development of civilization .
Most anthropologists agree that bipedal hairless apes (humans) evolved out of many other varieties of hominins due to fortuitous climatic changes. Some believe that these forced our ancestors out of the trees onto the African savannah (the ‘Tarzan hypothesis’) and some believe that we evolved our special characteristics, not least of all our large brains, in an aquatic environmental excursion (hardly a normal evolutionary experience) . Either way, we appear to owe our emergence to random climatic fluctuations. How typical would that be of life on other planets?
Some point to the explosion of the super-volcano Toba (Indonesia) about 70,000 years ago, which may have led to the extinction of many rival hominins and severely reduced our own numbers and created a bottle neck in our evolution. This catastrophe may also have been the trigger for our migration out of Africa, which itself may have led to the development of civilization. It is fortunate for us that no other super-volcano has erupted since (the next one to do so may be the end of civilization).
Does it not seem that we have been lucky ? Or rather that we owe our existence to a series of fortuitous chance events that must be rare in themselves never mind in combination? If that is true, then we probably are a very rare phenomenon: an intelligent species that has developed advanced technology, even now venturing into space. My guess is that the chance of another such species emerging elsewhere in our Galaxy is almost nil and we may indeed be alone, even in the whole universe.
- See http://en.wikipedia.org/wiki/Drake_equation
- The Eerie Silence: Are We Alone in the Universe? by Paul Davies (2010, Allen Lane).
- ‘The Earth Without the Moon’, Astronomy 19:2 (Feb 1991); later in What if the Moon didn’t exist? by Neil F. Comins (1993, Harper Collins, New York).
- Storms of My Grandchildren by James E. Hansen (Bloomsbury, 2009).
- The Aquatic Ape Hypothesis by Elaine Morgan (1997, Souvenir Press).
- Lucky Planet – Why Earth is Exceptional – and What that Means for Life in the Universe by David Waltham (Icon Books, 2014).
Steuart is a science writer, a member of the ASE and a regular contributor to the Journal.
Saturn at its best as noctilucent clouds gleam
The first day of June marks the start of our meteorological summer, though some would argue that summer begins on 21 June when (at 05:25 BST) the Sun reaches its most northerly point at the summer solstice.
Sunrise/sunset times for Edinburgh vary surprisingly little from 04:35/21:47 BST on the 1st, to 04:26/22:03 at the solstice and 04:31/22:02 on the 30th. The Moon is at first quarter on the 1st, full on the 9th, at last quarter on the 17th and new on the 24th.
The Sun is already so far north that our nights remain bathed in twilight and it will be mid-July before Edinburgh sees its next (officially) dark and moonless sky. This is a pity, for the twilight swamps the fainter stars and, from northern Scotland, only the brightest stars and planets are in view.
If we travel south, though, the nights grow longer and darker, and the spectacular Milky Way star fields in Sagittarius and Scorpius climb higher in the south. From London at the solstice, for example, official darkness, with the Sun more than 12° below the horizon, lasts for three hours, while both Barcelona and Rome rejoice in more than six hours.
It is in this same area of sky, low in the south in the middle of the night, that we find the glorious ringed planet Saturn. This stands just below the full moon on the 9th and is at opposition, directly opposite the Sun, on the 15th when it is 1,353 million km away and shines at magnitude 0.0, comparable with the stars Arcturus in Bootes and Vega in Lyra. The latter shines high in the east-north-east at our map times and, together with Altair in Aquila and Deneb in Cygnus, forms the Summer Triangle which is a familiar feature of our nights until late-autumn.
Viewed telescopically, Saturn’s globe appears 18 arcseconds wide at opposition while its rings have their north face tipped 27° towards us and span 41 arcseconds. Sadly, Saturn’s low altitude, no more than 12° for Edinburgh, means that we miss the sharpest views although it should still be possible to spy the inky arc of the Cassini division which separates the outermost of the obvious rings, the A ring, from its neighbouring and brighter B ring.
Other gaps in the rings may be hard to spot from our latitudes – we can only envy the view for observers in the southern hemisphere who have Saturn near the zenith in the middle of their winter’s night. For us, Saturn is less than a Moon’s breadth further south over our next two summers, while the ring-tilt begins to decrease again.
On the other hand, we can sympathize with those southern observers for most of them never see noctilucent clouds, a phenomenon for which we in Scotland are ideally placed. Formed by ice condensing on dust motes, their intricate cirrus-like patterns float at about 82 km, high enough to shine with an electric-blue or pearly hue as they reflect the sunlight after any run-of-the-mill clouds are in darkness. Because of the geometry involving the Sun’s position below our horizon, they are often best seen low in the north-north-west an hour to two after sunset, shifting towards the north-north-east before dawn – along roughly the path taken by the bright star Capella in Auriga during the night.
Jupiter dims slightly from magnitude -2.2 to -2.0 but (after the Moon) remains the most conspicuous object in the sky for most of the night. Indeed, the Moon lies close to the planet on the 3rd – 4th and again on the 30th. As the sky darkens at present, it stands some 30° high and just to the west of the meridian, though by the month’s end it is only half as high and well over in the SW. Our star maps plot it in the west-south-west as it sinks closer to the western horizon where it sets two hours later.
The giant planet is slow-moving in Virgo, about 11° above-right of the star Spica and 3° below-left of the double star Porrima. As its distance grows from 724 million to 789 million km, its disk shrinks from 41 to 37 arcseconds in diameter but remains a favourite target for observers.
The early science results from NASA’s Juno mission to Jupiter were released on 25 May. They reveal the atmosphere to be even more turbulent than was thought, with the polar regions peppered by 1,000 km-wide cyclones that are apparently jostling together chaotically. This is in stark contrast to the meteorology at lower latitudes, where organized parallel bands of cloud dominate in our telescopic views. In addition, the planet’s magnetic field is stronger and more lumpy than was expected. Juno last skimmed 3,500 km above the Jovian clouds on 19 May and is continuing to make close passes every 53 days.
Both Mars and Mercury are hidden in the Sun’s glare this month, the latter reaching superior conjunction on the Sun’s far side on the 21st.
Venus, brilliant at magnitude -4.3 to -4.1, is low above our eastern horizon before dawn. It stands at its furthest west of the Sun in the sky, 46°, on 3 June but it rises only 78 minutes before the Sun and stands 10° high at sunrise as seen from Edinburgh. By the 30th, it climbs to 16° high at sunrise, having risen more than two hours earlier. Between these days, it shrinks in diameter from 24 to 18 arcseconds and changes in phase from 49% to 62% illuminated. It lies left of the waning crescent Moon on the 20th and above the Moon on the following morning.
This is a slightly-revised version of Alan’s article published in The Scotsman on May 31st 2017, with thanks to the newspaper for permission to republish here.
Cassini begins Grand Finale at Saturn
This month brings the final truly dark night skies for Scotland until mid-July or later. Our dwindling nights are dominated by Jupiter, bright and unmistakable as it passes about 30° high in our southern evening sky and sinks to the western horizon before dawn. Venus is brighter still but easily overlooked as it hovers low in our brightening eastern dawn twilight. Saturn is also best as a morning planet, though it rises at our south-eastern horizon a few minutes before our May star map times.
Saturn creeps westwards from the constellation Sagittarius into Ophiuchus this month and brightens a little from magnitude 0.3 to 0.1, making it comparable with the brightest stars visible at our map times – Arcturus, Capella and Vega. The ringed planet, though, climbs to only 12° high in the south by the time morning twilight floods our sky, which is too low for crisp telescopic views of its stunning rings. On the morning of the 14th, as Saturn stands only 3° below-right of the Moon, its rotation-squashed globe measures 18 arcseconds in diameter while its rings stretch across 41 arcseconds and have their northern face tipped at 26° to our view.
Saturn’s main moon, Titan, takes 16 days to orbit the planet and is an easy telescopic target on the ninth magnitude. It stands furthest west of the disk (3 arcminutes) on the 3rd and 19th and furthest east on the 11th and 27th.
The Cassini probe is now into the final chapter, its so-called Grand Finale, of its epic exploration of the Saturn system. On 22 April, it made its 127th and last flyby of Titan, while on 26 April it dived for the first time through the gap between the planet and its visible rings, successfully returning data from a region it has never dared to explore before. Cassini’s new orbit sees it make another 21 weekly dives until, come 15 September, its almost-20 years mission ends with a fiery plunge into the Saturnian atmosphere.
The Sun’s northwards progress during May, to within only 1.4° of its most northerly point at the summer solstice, changes the sunrise/sunset times for Edinburgh from 05:29/20:52 BST on the 1st to 04:36/21:46 on the 31st. The Moon reaches first quarter on the 3rd, full on the 10th, last quarter on the 19th and new on the 25th.
This crescent Moon on the 1st lies in the west, between the stars Pollux in Gemini and Procyon in Canis Minor, lower to its left, while on the 2nd it is 4° below-left of the Praesepe star cluster in Cancer, best viewed through binoculars. It lies near Regulus in Leo on the 3rd and 4th, and appears only 1.2° above the conspicuous Jupiter on the 7th.
The giant planet lies 10° above-right of Virgo’s leading star Spica and edges 2° to the west-north-west this month, drawing closer to the celebrated double star Porrima whose two equal stars orbit each other every 169 years but appear so close together at present that we need a good telescope to divide them.
Following its opposition on 7 April, Jupiter recedes from 678 million to 724 million km during May, dimming slightly from magnitude -2.4 to -2.2 as its diameter shrinks from 43 to 41 arcseconds. Any telescope should show its changing cloud-banded surface while its four main moons may be glimpsed through binoculars, although sometimes one or more disappear as they transit in front of the disk or are hidden behind it or in its shadow.
Some 30° above and to the left of Jupiter is the orange-red giant star Arcturus in Bootes the Herdsman. At magnitude -0.05, this is (just) the brightest star in the northern celestial hemisphere ahead of Capella in Auriga, low in the north-north-west at our map times, and Vega in Lyra, climbing in the east. It is also one of the closer stars to the Sun, but it is only a temporary neighbour for it is speeding by the solar system at 122 km per second at a distance of 36.7 light years. Even so, it takes 800 years to move a Moon’s breadth across our sky. It is also a corner star of a rarely-heralded asterism dubbed the Spring Triangle – the other vertices being marked by Spica and Regulus.
A useful trick for finding Arcturus is to extend a curving line along the handle of the Plough which passes overhead during our spring evenings but is always visible somewhere in our northern sky. That line, still pending, leads to Arcturus and then onwards to Spica. The traditional mnemonic for this is “Arc to Arcturus, spike to Spica” but, given current circumstances, we might amend this to “Arc to Arcturus, jump to Jupiter”.
Venus rises 65 minutes before the Sun on the 1st and climbs to stand 9° high at sunrise. By the 31st, these figures change only a little to 75 minutes and 10°, so it is far from obvious as a morning star, even though it blazes at magnitude -4.5 to -4.3. Through a telescope, it shows a crescent whose sunlit portion increases from 27% to 48% while its diameter shrinks from 38 to 25 arcseconds. Early rises, or insomniacs, can see it left of the waning Moon on the 22nd.
Mercury stands below and left of Venus but remains swamped by our dawn twilight. It is furthest west of the Sun (26°) on the 18th. Still visible, but destined soon to disappear into our evening twilight, is Mars. Shining at a lowly magnitude 1.6, it lies 7° above-right of Aldebaran as the month begins and tracks between the Bull’s horns as Taurus sinks below our north-western horizon in the early evening.