Mars bright in evenings as ExoMars probe arrives
As we plunge into the final quarter of the year, our lengthening nights offer a procession of stellar views that stretch from the Summer Triangle in the evening to the stunning star-scapes around Orion during the morning hours. The brighter planets, though, are on show only low down around dusk and dawn.
The middle of the Summer Triangle stands some 60° high and due south as darkness falls tonight. Its brightest corner star, Vega in the constellation Lyra, lies just south-west of overhead, while Deneb in Cygnus is even higher in the south-east and Altair in Aquila lies below them on the meridian.
With no hindering moonlight over the next few evenings, now is a good time to spy the Milky Way as it arches almost overhead after dusk, climbing from Sagittarius on the south-south-western horizon and flowing through the heart of the Triangle on its way to Deneb and the “W” of Cassiopeia high in the north-east. Of course, unless we can find a dark site, away from the pollution of street lighting and the like, we may have trouble seeing the Milky Way or indeed any but the brighter stars on our chart.
Edinburgh’s sunrise/sunset times change this month from 07:16/18:47 BST (06:16/17:47 GMT) on the 1st to 07:18/16:34 GMT on the 31st after we set clocks back one hour with the end of BST on the morning of the 30th. The Moon is new on the 1st, at first quarter on the 9th, full on the 16th (the hunter’s moon), at last quarter on the 22nd and new again on the 30th.
Venus stands nearly 5° high in the south-west at sunset and sets itself only 43 minutes later on the 1st. By the 31st it is barely a degree higher in the south-south-west at sunset but remains visible for 73 minutes so is easier to spot if we enjoy an unobscured outlook. It blazes at magnitude -3.9 and stands 4° below-right of the slender earthlit Moon on the 3rd when its gibbous disk appears 12 arcseconds wide and 85% sunlit if viewed telescopically.
In the month that the first European-Russian ExoMars spacecraft reaches Mars, the planet is the brightest object low in the south-south-west as the twilight disappears. ExoMars consists of a Trace Gas Orbiter to study rare gases, and particularly methane, in Mars’ atmosphere and it also has the experimental Schiaparelli lander.
Mars fades slightly from magnitude 0.1 (almost equal to Vega) to 0.4 this month as it tracks 21° eastwards above the so-called Teapot of Sagittarius, clipping the top star of the Teapot’s lid (Kaus Borealis) on the 7th. The planet recedes from 160 million to 187 million km during October while its gibbous disk shrinks to 7.5 arcseconds in diameter which, with its low altitude, makes telescopic study all the more challenging. It lies below the Moon on the 8th.
A little fainter than Mars, and a little lower to Mars’ right in this evening’s sky, is the ringed planet Saturn. This shines at magnitude 0.6 in southern Ophiuchus and appears 16 arcseconds across, with its glorious rings spanning 36 arcseconds. Saturn lies to the left of the earthlit Moon on the 5th and dips lower with each evening until it is passed by Venus late in the month – catch Saturn 3° above Venus on the 29th.
By our map times, both Saturn and Mars have set and the Summer Triangle has toppled over into the west. High in the south is the Square of Pegasus, a line along its right-hand side pointing down to the southern bright star Fomalhaut in Piscis Austrinus the Southern Fish. Just to the right of this line, and 2° south-west (below-right) of the star Lambda Aquarii (magnitude 3.7), is the farthest of the Sun’s planets, Neptune. At magnitude 7.8 and a distance of 4,350 million km on the 1st, we need binoculars and a better chart to identify it, and probably a large telescope to glimpse its bluish disk only 2.3 arcseconds wide.
To the east of Aquarius lies the constellation of the two fish, Pisces, and the second most distant planet, Uranus, which stands directly opposite the Sun at opposition on the 15th at a distance of 2,835 million km. At magnitude 5.7 it is near the limit of naked-eye visibility under the darkest of skies, but is an easier binocular or telescope target with its diameter of 3.7 arcseconds.
Orion rises in the east less than two hours after our map times and strides across the meridian before dawn. To its north and east lies Gemini and between the two is the radiant point for the annual Orionids meteor shower. This is visible during our morning hours throughout the second half of the month and peaks at rates around 25 meteors per hour between the 21st and 24th. Its meteors are swift, with many leaving glowing trains in their wake, and represent the dusty debris laid down by Halley’s Comet.
The night ends with Mercury which is conspicuous at magnitude -0.7 and rises in the east 109 minutes before the Sun on the 1st, climbing to stand 9° high forty minutes before sunrise. By the 11th, as its favourable morning show draws to a close, it rises 76 minutes before sunrise. On that morning, the even brighter Jupiter lies only 0.7° below-right of Mercury as the giant planet climbs away from the Sun’s far side. By the 28th, Jupiter rises at about 05:40 BST and is an impressive sight 1.5° below the earthlit waning Moon.
This is a slightly-revised version of Alan’s article published in The Scotsman on October 1st 2016, with thanks to the newspaper for permission to republish here. Journal Editor’s apologies for the lateness of the article appearing here.
Harvest moon eclipsed on the 16th
Two eclipses and a couple of notable space exploration milestones make September an interesting month for astronomers. I’ll postpone until the close of this note, though, my thoughts on the exciting news that Proxima Centauri, the closest star to our Sun, has a planet which is probably rocky, slightly larger than the Earth and in the star’s so-called habitable zone where liquid water might exist.
The first eclipse, an annular or “ring” eclipse of the Sun, occurs on the 1st with the Moon too distant to hide the Sun completely. Instead, a dazzling ring of sunlight remains visible along a narrow path that stretches across Central Southern Africa into the Indian Ocean. Surrounding areas enjoy a partial solar eclipse but nothing is seen as far north as Europe
Of greater interest for us is a penumbral eclipse of the Moon on the 16th during which the Moon passes through the southern outer part of the Earth’s shadow, the penumbra. The event lasts from 17:55 to 21:54 BST although, as seen from Edinburgh, the Moon only rises in the east at 19:29. Maximum eclipse occurs 25 minutes later, at 19:54, when all but the southern 9% of the Moon is within the penumbra. Little darkening of the disk may be noticeable, except near the northern edge which is closest to the Earth’s umbra where all direct sunlight is extinguished.
Since this full moon is the one closest to the autumnal equinox, due at 15:21 BST on the 22nd, it is also called the harvest moon. The tradition is that the bright moon stands at a similar altitude in the eastern sky over several evenings at this time, so permitting the harvesting hours to be extended.
The Sun tracks 11.5° southwards during September to cross the celestial equator at the equinox when day and night have approximately equal lengths around the Earth. Sunrise/sunset times for Edinburgh change from 06:18/20:06 BST on the 1st to 07:14/18:50 on the 30th. The moon is new on the 1st, at first quarter on the 9th, full on the 16th, at last quarter on the 23rd and new again on 1 October.
Jupiter is now lost from view as it nears conjunction on the Sun’s far side on the 26th. It leaves Venus as an evening star, but even though Venus is brilliant at magnitude -3.9 it stands less than 5° above Edinburgh’s horizon at sunset and sets itself within the next 45 minutes. Catch it, if you can, in the west as September begins, shifting to the south-west by the month’s end.
Mars, Saturn and the star Antares in Scorpius form a triangle low in the south-west as darkness falls at present, with Saturn above Antares and Mars a few degrees to their left. Saturn is magnitude 0.5 while Mars is brighter and noticeably reddish, though it fades from magnitude -0.3 to 0.1 as it speeds 18° eastwards and further away. By month’s end, its motion brings it onto our chart and close to the so-called Teapot of Sagittarius, just setting in the south-west.
Look for the Moon close to Saturn on the 9th and above Mars on the 10th when, if viewed telescopically, the two planets appear 16 and 10 arcseconds wide respectively, with Saturn’s wide-open rings spanning 37 arcseconds.
Mercury begins its best morning appearance of the year late in the month. From the 24th onwards, it rises in the east more than 95 minutes before the Sun and reaches more than 8° high forty minutes before sunrise. It is furthest west of the Sun (18°) on the 28th and is magnitude -0.5 when it lies alongside the slender earthlit Moon on the 29th.
Just a day later, on the 30th, Europe’s Rosetta spacecraft is destined to end its mission when it collides with Comet Churyumov-Gerasimenko, the rubber-duck shaped body it has been orbiting and investigating since August 2014. The collision will be gentle but radio contact and data-collection is likely to be lost as the craft settles on the comet’s surface.
Earlier in the month, during a month-long launch window beginning on the 8th, NASA’s OSIRIS-REx spacecraft is due to embark on its seven-years mission to collect and return samples from the surface of Bennu, a small asteroid which has been given an outside chance of having a catastrophic impact with the Earth late in the next century.
Proxima Centauri lies at a distance of only 4.25 light years but is much too dim to be seen without a telescope, A small red dwarf star, it is less than 15% as massive and wide as our Sun and has less than 0.2% of the Sun’s energy output. Also called Alpha Centauri C, it was discovered in 1915 by the Edinburgh-born astronomer Robert Innes and lies 15° to the east of the Southern Cross in a part of the sky we never see from Britain. It is thought to form a triple star system with Alpha Centauri A and B, a tight binary of more Sun-like stars that lie 2° away in the sky.
The newly discovered world has been dubbed Proxima b but it is something of a stretch to call it Earth-like. It orbits its star in a year of 11.2 Earth-days at a distance of less than 8 million km where it is blasted by X-rays from dramatic flares that we see erupting on Proxima’s surface – far from ideal for life. It is also probably tidally locked – keeping its same face towards the star – and we do not even know (yet!) that it has water, never mind life.
This is a slightly-revised version of Alan’s article published in The Scotsman on September 1st 2016, with thanks to the newspaper for permission to republish here.
Perseids rain as Mars approaches his rival
Every year at this time the Earth sweeps through the stream of meteoroids released by Comet 109P/Swift-Tuttle which passed just inside the Earth’s orbit in 1992 and is not due to return until 2126. And every year at this time, some of those meteoroids plunge into our upper atmosphere at 59 km per second, producing a rich display of bright meteors, many leaving glowing trains in their wake. According to some claims, this year’s meteor spectacle could be even better than usual.
The meteors appear in all parts of the sky but, since they are moving in parallel, perspective causes their paths to point away from a so-called radiant point in the constellation Perseus. It has already been active for a week, but it is expected to peak at about 13:00 BST on the 12th when, typically, an observer beneath the radiant and with a perfect dark sky might count 80 or more Perseids per hour. Of course, this year’s peak occurs in daylight for Scotland, but we should still enjoy high rates on our nights of 11/12th and 12/13th.
The radiant, plotted on our north star map, stands in the north-east at nightfall and climbs to lie just east of overhead before dawn. As the radiant climbs, so we face more directly into the Perseids stream and meteor rates climb in sympathy. This means that our morning hours are favoured and we have the extra advantage that the Moon sets in the middle of the night on the critical nights, though moonlight will hinder evening watches. Another bonus is that the nights are much less cold than they are for the year’s other two major showers which occur in the depths of winter.
The suggestions that the Perseids might be particularly active in 2016, with perhaps twice as many meteors as usual, derive from the fact that Jupiter approaches the Perseids stream every 12 years and its gravity might be diverting a segment of the stream closer to the Earth on each encounter. Indeed, there does seem to be a 12-years periodicity in enhanced Perseids displays with the last one in 2004, so we may be due for another special show this month.
Sunrise/sunset times for Edinburgh change from 05:17/21:19 BST on the 1st to 06:16/20:09 on the 31st. The Moon is new on the 2nd, at first quarter on the 10th, full on the 18th and at last quarter on the 25th.
Our chart depicts the Summer Triangle, formed by Deneb, Vega and Altair, high on the meridian as the Plough sinks in the north-west and the “W” of Cassiopeia climbs in the north-east, above the Perseids radiant. The large but rather empty Square of Pegasus balances on a corner in the east-south-east while the Teapot of Sagittarius is toppling westwards on our southern horizon. To its right, and very low in the south-west, is Saturn, the only bright planet visible at our map times.
Saturn hardly moves this month, being stationary against the stars on the 13th when it reverses from westerly to easterly in motion. It lies in Ophiuchus, 6° north of the red supergiant star Antares in Scorpius. Antares is around magnitude 1.0 while Saturn is almost twice as bright at 0.4. Saturn stands above Antares low in the south-south-west as tonight’s twilight fades but are outshone by the Red Planet, Mars, which lies 10° to their right and is three times brighter than Saturn at magnitude -0.8.
Mars, though, is moving eastwards (to the left) at almost a Moon’s-breadth each day and passes between Antares and Saturn, and 1.8° above Antares, on the 24th. Even though Mars dims to magnitude -0.4 by then, it remains much brighter than Antares even though the star’s name comes from the Ancient Greek for “equal to Mars”. Both appear reddish, of course, but for very different reasons – Antares has a bloated “cool” gaseous surface that glows red at about 3,100°C while Mars has a rocky surface which is rich in iron oxide, better known as rust.
The Moon stands above-right of Mars and to the left of Saturn on the 11th when Mars appears only 12 arcseconds wide if viewed through a telescope. Saturn is 17 arcseconds across while its rings span 39 arcseconds and have their north face tipped 26° towards us. By the 31st, Mars has faded further to magnitude -0.3 and lies 4° above-left of Antares.
Observers at our northern latitudes must work hard to spot any other bright planet this month although anyone in the southern hemisphere can enjoy a spectacular trio of them low in the west at nightfall. Seen from Scotland, though, the brilliant (magnitude -3.9) evening star Venus stands barely 5° above our western horizon at sunset and sets itself less than 40 minutes later. We need a pristine western outlook to see it, and quite possibly binoculars to glimpse it against the twilight.
Fainter (magnitude -1.7) is Jupiter which stands currently 27° to the left of Venus and 5° higher so that it sets more than 70 minutes after the Sun. Between them, and considerably fainter, is Mercury which stands furthest from the Sun (27°) on the 16th and, perhaps surprisingly, is enjoying its best evening apparition of the year as seen from the southern hemisphere.
Jupiter sinks lower with each evening and meets Venus on the 27th when Venus passes less than 5 arcminutes north of Jupiter. This is the closest planetary conjunction of the year and would be spectacular were the two not so twilight-bound. As it is, binoculars might show Jupiter 9 arcminutes below and left of Venus on that evening.
This is a slightly-revised version of Alan’s article published in The Scotsman on August 1st 2016, with thanks to the newspaper for permission to republish here.
Juno to begin hazardous mission at Jupiter
The Sun is edging southwards again but our night-long summer twilight subsides only slowly and, given that we also have bright moonlight through mid-July, we must wait until the month’s final week to enjoy a truly dark midnight sky.
From a good vantage point, we may then see the Milky Way as it arches high across our eastern sky, culminating close to the star Deneb in Cygnus. Deneb occupies the top-left corner of the Summer Triangle which remains a feature of our high southern night sky until the autumn. The Triangle was so named by our much-missed Sir Patrick Moore and has its other corners marked by Vega in Lyra and Altair in Aquila.
Sunrise/sunset times for Edinburgh change from 04:32/22:01 BST on the 1st to 05:16/21:21 on the 31st, by which date nautical twilight persists for two hours before dawn and after dusk. The Moon is new on the 4th, at first quarter on the 12th, full on the 19th and at last quarter on the 26th.
As the twilight fades at present, the giant planet Jupiter shines brightly low in the west and Mars, only a little fainter but distinctly reddish in hue, hovers at much the same altitude in the south-south-west. Our third naked-eye planet, Saturn, stands 18° to the east (left) of Mars and is creeping westwards in the southern reaches of the constellation Ophiuchus as Mars begins to accelerate eastwards in Libra.
Jupiter is nearing the end of its apparition as it sinks lower in our evening sky on its way to conjunction on the Sun’s far side in September. Its altitude above Edinburgh’s western horizon one hour after sunset falls from 11° on the 1st to less than 2° on the 31st. By then it will be difficult to spot in the bright twilight, and we will not see it again in our evening sky for another six months.
Moving eastwards in southern Leo, Jupiter remains brighter than any star, though it does fade slightly from magnitude -1.9 to -1.7 as its distance grows between 862 million and 919 million km. Viewed telescopically, its disk appears 34 arcseconds across when it stands 6° to the right of the crescent Moon on the 9th.
Although Jupiter is well past its best for telescopic study, we can expect some of our sharpest views after NASA’s Juno probe enters a highly-eccentric orbit over the planet’s poles early on July 5th UK time – the engine firing to do so is due to last for 35 minutes and end at 04:53 BST on that day. Launched in 2011, and with the benefit of a gravity assist flyby of the Earth in 2013, Juno will have travelled for 2,800 million km to reach Jupiter, not far shy of the distance between the Sun and Uranus.
Juno’s initial orbit is to carry it around Jupiter in 53.5 days, but this is to be reduced by mid-October to one of 14 days that takes within 4,200 to 4,900 km of the equatorial cloud-tops. That path plunges through Jupiter’s hazardous radiation belts and, while it avoids their most deadly regions, Juno’s sensitive electronics need to be located in a first-of-its-kind radiation-shielded vault.
Jupiter owns some of the most interesting moons we know of, but Juno is focused firmly on learning as much as possible about Jupiter’s origins and structure, from its intense magnetosphere all the way down to its core. The probe’s trio of 9-metres long solar panels provide 500 watts of power, making it the first craft to rely on solar power so far from the Sun. If it survives, the plan calls for Juno to dive to a fiery destruction in Jupiter’s atmosphere in February, 2018.
Venus, brilliant at magnitude -3.9, stands closer to the Sun in our evening twilight than Jupiter and is unlikely to be seen from our latitudes. Mercury, much fainter, enters the same area of sky following its superior conjunction on the Sun’s far side on the 7th and is even less likely to be seen.
Mars dims from magnitude -1.4 to -0.8 this month as its distance grows from 86 million to 106 million km and its diameter shrinks from 16 to 13 arcseconds. Telescopes still show some detail on its rusty surface, but it, too, stands lower each evening and by the month’s end it sets before midnight BST. Look for Mars 7° below the gibbous Moon on the evening of the 14th.
The opposing motions of Mars and Saturn mean that their separation in the sky decreases to 11°, with Saturn fainter at magnitude 0.2 to 0.4 and noticeably above-left of Mars by the month’s end. The red supergiant star Antares in Scorpius lies 6° below Saturn while the Moon stands 5° above-right of Saturn on the 15th and 9° to the planet’s left on the 16th.
Viewed telescopically, Saturn appears 18 arcseconds wide at mid-month with the north face of the rings inclined 26° towards us and 40 arcseconds from side to side. Saturn’s main moon, Titan, shines at magnitude 8.5 and is best seen through a telescope as it orbits every16 days. Catch it 3 arcminutes west of Saturn on the 4th and 20th, and a similar distance east on the 11th and 27th.
It happens that my previous note was timely in its warning about noctilucent clouds. The first good displays were sighted within a couple of days, appearing as electric-blue cirrus-like banks low above the north-western horizon after dusk and shifting round into the north-east before dawn. Composed of ice-crystals some 82 km above the ground, we should expect further shows until mid-August.
This is a slightly-revised version of Alan’s article published in The Scotsman on July 1st 2016, with thanks to the newspaper for permission to republish here.
Saturn at its best as summer begins
The Sun reaches its most northerly place in the sky at the summer solstice on the 20th, regarded by many as the start of summer in our northern hemisphere. Contradictorily, though, the days around then are also classed as midsummer though the actual days of any midsummer celebrations vary from country to country. More sensibly, in my view, the Met Office defines summer to span the months of June to August which would place the middle of summer in mid-July and, consequently, means that summer begins on June 1.
The solstice occurs late on the 20th, at 23:34 BST, while sunrise/sunset times for Edinburgh change from 04:35/21:47 on the 1st, to 04:26/22:03 on the 20th and 04:31/22:02 on the 30th. Scotland’s nights remain twilight throughout, with little hope of spotting the fainter stars and, from the north of the country, only the brighter stars and planets may be seen.
One is the beautiful ringed world Saturn which stands opposite the Sun in the sky on June 3, only twelve days after Mars’ closest opposition since 2005. Both planets shine brightly in the south at our star map times as they track westwards across the sky. Unfortunately, Saturn climbs less than 14° above Edinburgh’s horizon and Mars is a degree or so lower still so telescopic views are hindered by their low altitudes.
Having stood at its closest (75 million km) on May 30, Mars fades from magnitude -2.0 to -1.5 as it recedes to 86 million km while telescopes show it contracting from almost 19 to 16 arcseconds in diameter, still large enough to show some detail on the disk. It tracks 5° westwards into the heart of Libra this month, its motion slowing to a halt on the 30th before resuming as an easterly progress that will persist for the next two years.
Saturn’s disk is similar in size, 18 arcseconds at opposition, but its rings are 42 arcseconds wide and have their north face tipped 26° towards us. Not since 2003 have the rings been so wide open to inspection. It dims slightly, from magnitude 0.0 to 0.2 as it creeps westwards in southern Ophiuchus about 7° above-left of Antares in Scorpius.
Third but not least in our planetary line-up, Jupiter is prominent at magnitude -2.0 in the south-west as the sky darkens at present, but sinks lower with each day and sets in the west a little more than one hour after our map times. Now moving eastwards below the main figure of Leo, it passes within 0.1° south of the magnitude 4.6 double star Chi Leonis on the 10th and dims a shade to magnitude -1.9 by the 30th.
Of the other naked-eye planets, Mercury stands 24° west of the Sun on the 4th and, while well placed for observers south of the equator, is swamped in our predawn twilight. Venus reaches superior conjunction on the Sun’s far side on the 6th and is not visible either.
The Moon is new on the 5th, close to Jupiter on the 11th, at first quarter on the 12th, above Spica in Virgo on the 14th, above-right of Mars on the 17th, close to Saturn on the 18th, full in the 20th and at last quarter on the 26th.
Our star charts show the stars of the Summer Triangle, Vega, Deneb and Altair, climbing in the east to south-east as the Plough stands high in the north-west. The curve of the Plough’s handle extends to the brightest star visible at our map times, Arcturus in Bootes. Look some 20° above and to the left of Arcturus for the pretty arc of stars that make up Corona Borealis, the Northern Crown, which, because it is incomplete, should perhaps be called the Northern Tiara.
Corona’s leading star has the dual names of Gemma, for an obvious reason, and Alphecca which derives from the Arabic for “the bright of the broken ring”. At magnitude 2.2, though, it was surpassed briefly and unexpectedly exactly 150 years ago, in 1866, by the appearance of a nova (“new star”) just beyond the crown’s south-eastern edge.
Now called T Coronae Borealis (or T CrB), this reached magnitude 2.0 but plunged below naked eye visibility after only eight days to became slightly variable in brightness as a telescopic object just fainter than the tenth magnitude. To much surprise it burst into prominence again in 1946 though this time it was already fading at magnitude 3.2 when it was first spotted.
T CrB thus earned its nickname as the Blaze Star and became the brightest known of ten such recurrent novae in the sky. Studies over the past year show it slightly brighter and bluer than usual and hint that a new outburst may occur at any time, so this is one to check regularly.
Another variable star, R CrB, is usually near the sixth magnitude and the brightest star within the crown. However, normally for a few weeks or months every few years, it fades to become a dim telescopic object when, so it is thought, clouds of soot form in its atmosphere and block its light. Strangely, it has yet to recover following a record-breaking fade in 2007 and was still near the 14th magnitude a few days ago.
Despite our summer twilight, Scotland is best placed to see noctilucent or “night-shining” clouds which may appear cirrus-like and often bluish low down between the north-west after sunset and the north-east before dawn. Formed by layers of ice-crystals near 82 km in height, these are Earth’s highest clouds and able to shine in the sunlight long after our normal clouds have dimmed to darkness.
This is a slightly-revised version of Alan’s article published in The Scotsman on June 1st 2016, with thanks to the newspaper for permission to republish here.
Mercury to transit face of Sun on 9th
May is seldom an outstanding month for astronomy for observers at Scotland’s latitudes. The Sun’s northwards progress, welcome as it is, leads to later and briefer nights and, as the month ends, twilight begins to persist throughout the night even over the south of the country.
Two astronomical events occur this May, though, that should arouse our interest. The first is the transit by Mercury across the Sun’s face on the 9th which, if the weather holds, should be our best opportunity until 2049 to view its inky silhouette against the Sun. The month also sees Mars approach closer to us and appear brighter than at any time since 2005.
I must repeat the usual serious warning about the dangers of observing the Sun. To prevent permanent damage to your eyes, never look directly at the Sun through a telescope or binoculars, or even stare at it with the unaided eyes. We may project the solar image onto a shaded white card using a pinhole, binoculars or a small telescope, but note that using a large telescope for this may damage its eyepiece.
Sadly, Mercury’s outline will be too small to view by pinhole-projection, and nor will we see it using so-called eclipse glasses. In my opinion, though, it is best to equip your telescope with a certified solar filter to cover the objective (“big”) end of your instrument and block all the harmful radiation.
The precise times we experience the transit can vary by a couple of minutes across the Earth. For Scotland, Mercury begins to encroach on the eastern (left) edge of the solar disk at 12:12 BST and it takes a little more than three minutes before its outline is complete against the Sun. After crawling across the southern half of the Sun it finally leaves at the south-western (lower-right) edge at 19:41.
At a mere 12 arcseconds in diameter, though, it appears only 1/150th as wide as the Sun and a fifth as wide as did Venus during its transit in 2012. Whereas there are more than a dozen transits of Mercury each century, the next one by Venus is not until 2117 and we must be patient until 2125 for the next to be observable from Scotland.
The Sun climbs 7° northwards during May as sunrise/sunset times for Edinburgh change from 05:28/20:53 BST on the 1st to 04:36/21:46 on the 31st. The Moon is new on the 6th, at first quarter on the 13th, full on the 21st and at last quarter on the 29th.
Other than during its transit, Mercury is not visible for us at all this month, and neither is Venus which is lost in the glare on the Sun’s far side.
Jupiter, though, remains prominent in the heart of our southern sky at nightfall where it is slow moving in southern Leo and reaches a stationary point on the 10th before edging eastwards again. May has it dimming slightly from magnitude -2.3 to -2.0 as it recedes from 723 million to 791 million km and its disk shrinks from 41 to 37 arcseconds in diameter. Catch it near the Moon on the 14th and 15th.
By our star chart times, Leo and Jupiter are sinking into the west and our southern sky is dominated by the bright star Arcturus, the equally bright planet Saturn and, most conspicuous of all, the Red Planet, Mars. The Plough is tumbling westwards from the zenith as the Summer Triangle formed by the bright stars Vega in Lyra, Deneb in Cygnus and Altair in Aquila, occupies our lower eastern sky.
Mars rises in the south-east at 23:14 BST on the 1st and at sunset on the 22nd, the day it stands directly opposite the Sun in the sky at opposition. Our chart plots it low down in the south-south-east about one hour before it reaches its highest point, albeit less than 13° above Edinburgh’s southern horizon.
It lies 5° above the red supergiant star Antares in Scorpius at present but is retrograding, or moving westwards, against the stars and enters Libra towards the end of the period as it brightens from magnitude -1.5 to rival Jupiter at magnitude -2.0 at opposition. Because it is on the inwards leg of its somewhat eccentric orbit, it is actually closest to us at 75,280,00 km on the 30th, almost a million km closer than on the day of opposition.
Mars’ low altitude means that views of its reddish disk, only 18 arcseconds wide at opposition, may be less sharp (under “poorer seeing”) than if it stood high in the sky. Even so, telescopes should show the small northern polar cap, tipped 10° towards us, and other surface features as they drift slowly to the right across the disk. Those features return to almost the same position from one night to the next since Mars’ day is 40 minutes longer than that of the Earth. Mars comes 17 million km closer during its next opposition in 2018, but will be 4° lower still in our sky so we should make the most of any chance to view it this time around.
Shining to the east (left) of Mars is Saturn which this month brightens from magnitude 0.2 to 0.0 as it creeps westwards in southern Ophiuchus. It always rewards us with stunning telescopic views, its disk being (like Mars) 18 arcseconds wide but set within a glorious ring system that spans 41 arcseconds and has its north face inclined towards us at 26°. Look for the Moon above Mars late on the 21st and closer still to Saturn on the next night.
This is a slightly-revised version of Alan’s article published in The Scotsman on April 30th 2016, with thanks to the newspaper for permission to republish here.
Smallest planet Mercury at its best for the year
It is surprising just how quickly our evening sky changes during April. If we look to the south-west as the twilight fades tonight, the foremost winter constellation of Orion stands well clear of the horizon, with Sirius sparkling to his left and Taurus and the Pleiades to the right, almost due west. By the month’s end, though, Orion has all-but-set as nautical twilight ends in the evening and only Betelgeuse at Orion’s shoulder remains (barely) in view, as shown by our monthly star chart. Taurus is setting, too, and Sirius has already gone.
Jupiter remains a striking object which is ideally placed for study in our evening sky as it slips westwards in the southern part of Leo, some 14° below and to the left of Regulus. Having stood at opposition, directly opposite the Sun, on March 8, the giant planet is unmistakable in the south-east at nightfall at present and passes 41° high in the S only thirty minutes before our map times.
Those maps have the Plough overhead, dragged out and distorted by the map projection used, while Virgo and the star Spica are nearing the meridian to the left of Jupiter. Spilling northwards from Virgo into the constellation of Coma Berenices is a region sometimes called the Realm of the Galaxies. This includes the Virgo cluster of well over 1,000 galaxies whose core lies some 54 million light years away and is roughly coincident with the “D” of “Denebola” on the chart.
More than a dozen of these Virgo galaxies are visible through medium-sizes telescopes and have entries in Charles Messier’s 18th century list of comet-like smudges in the sky. While it is impractical to plot their locations on our chart, a Web search and dark moonless skies over the next fortnight should allow some to be spotted.
The Sun climbs more than 10° northwards during April as sunrise/sunset times for Edinburgh change from 06:42/19:52 BST on the 1st to 05:30/20:51 on the 30th. New moon on the 7th is followed by first quarter on the 14th, full moon on the 22nd and last quarter on the 30th.
This month, Jupiter recedes from 676 million to 723 million km, dims only slightly from magnitude -2.4 to -2.3 and shrinks in diameter from 44 to 41 arcseconds. Binoculars show its four main moons and also show Jupiter passing only 7 arcminutes (one quarter of a Moon-breadth) above-left of the magnitude 4.6 star Chi Leonis on the 8th.
Jupiter loses its status as our sole evening planet this month. One of its usurpers is Mars which, as we’ll see, rises before midnight later in the period. The other is Mercury which emerges from the Sun’s glare over the coming week at the start of its best evening apparition of the year.
By the evening of the 8th, Mercury shines brightly at magnitude -0.9 and stands almost 8° high in the west-north-west 40 minutes after sunset. The very young crescent Moon, only 3% illuminated and brightly earthlit, lies 6° to its left but we will need a clear horizon, and perhaps even binoculars, to pick them out of the twilight. On the next evening, Mercury is 17° below-right of the still-spectacular earthlit Moon while, on the 10th, the Moon stands against the V-shaped Hyades star cluster in Taurus and sets as it draws close to the bright star Aldebaran.
As the Moon continues onwards, eventually to shine alongside Regulus on the 16th and Jupiter on the 17th, Mercury climbs to stand furthest east of the Sun (20°) on the 18th. By then, the innermost and smallest planet is 11° high 40 minutes after sunset and sets itself more than 90 minutes later still. It is fainter, though, at magnitude 0.2 and it dims further to magnitude 1.5 by the 25th when it is 2° lower and 7° below-right of the Pleiades. As Mercury dives towards the Sun’s near side, it is heading for a spectacular transit across the Sun’s face on May 9.
Mars is brightening rapidly as it draws closer to us on its way to opposition on May 22. It rises in the south-east about one hour after our chart times and from the 21st onwards rises before midnight as seen from Edinburgh. The best time to see it, though, is just before dawn when it reaches its highest point, admittedly only low down in the south. At magnitude -0.5 it is already the brightest object (after the Moon) down there, and by the month’s end it is more than twice as bright at magnitude -1.4.
Mars is currently in Scorpius, 6° north-north-west of the red supergiant star Antares, but it tracks 1.5° eastwards to a stationary point in Ophiuchus on the 17th before doubling back into Scorpius. Meantime, it approaches from 118 million to 87 million km and its disk swells from 12 to 16 arcseconds wide. Telescopes should reveal some markings on it desert surface, and perhaps its northern polar cap, but its low altitude is likely to make for poor observing conditions.
Not far to Mars’ left, and another victim of its low altitude, is the glorious ringed world Saturn. The second brightest object low in the south before dawn, it improves from magnitude 0.4 to 0.2 as it edges 1° westwards in Ophiuchus. Saturn lies almost 1,400 million km away in mid-April when its rotation-flattened disk is 18 arcseconds across and the rings span 40 arcseconds, their north face tipped 26° earthwards.
The Moon stands 4° above Mars before dawn on the 25th and a similar distance above-left of Saturn on the next morning.
This is a slightly-revised version of Alan’s article published in The Scotsman on April 1st 2016, with thanks to the newspaper for permission to republish here.
Jupiter conspicuous at opposition in Leo
The Sun, now climbing northwards at its fastest pace for the year, crosses the equator of the sky at 04:30 GMT on the 20th, the time of our vernal equinox. It then rises due east and sets due west, and days and night are equal in length around the globe.
The Sun’s progress means that our nights are falling rapidly later, an effect that appears to enjoy a step-change when we set our clocks forward to British Summer Time on the 27th, though, in this instance, the daylight we gain in the evening is lost in the morning. It is noticeable, too, that the stars at nightfall are shifting quickly to the west. Orion, for example, dominates in the south as darkness falls at present, but has tumbled well over into the south-west by the month’s end.
The Plough is nearing the zenith at our map times and it is the squat figure of Leo the Lion and the prominent planet Jupiter that dominate our southern sky. Jupiter is edging westwards beneath Leo’s hindquarters and passes just below the fourth magnitude star Sigma Leonis over the first few days of the month. Above and to its left is Denebola, the Lion’s tail, while further west (right) is Leo’s leading star Regulus in the handle of the Sickle. Algieba (see chart) appears as a glorious double star through a telescope.
Jupiter comes to opposition on the 8th when it stands opposite the Sun so that it rises in the east at sunset and is unmistakable as it climbs through our south-eastern evening sky to pass 40° high on Edinburgh’s meridian in the middle of the night. Eleven times wider than the Earth and yet with a day lasting under ten hours, it is 664 million km distant at opposition and shines at magnitude -2.5, more than twice as bright as any star other than the Sun.
View Jupiter through binoculars or a telescope, and the fun really begins. Binoculars show its four main moons, Io, Europa, Ganymede and Callisto, which change their relative positions to east and west of the planet’s disk from night to night as they orbit almost directly above the equator. Were it not for Jupiter’s glare, we could see all four of these with the naked eye.
With numerous sulphurous volcanoes, Io is the most geologically active body we know, while Europa is the only one of the four to be smaller than our Moon and is thought to harbour a deep ocean of water beneath its icy crust. This makes it so irresistible as a potential home for life that the US Congress has urged NASA to add a lander craft to a planned mission to Europa over the next decade.
The Jovian disk appears 44 arcseconds wide when we view it through a telescope at present. Even a small telescope shows its main cloud belts but the smaller cloud features that indicate Jupiter’s rotation are more of a challenge. The famous Great Red Spot in the southern hemisphere is a storm that has raged for at least 185 years but is now shrinking noticeably.
By the time Jupiter is sinking in the west before dawn, the two brightest objects low in the south are Mars and Saturn. Mars stands 18° to the right of Saturn and is slightly the brighter of the two at present – their magnitudes being 0.3 and 0.5 respectively, with both of them outshining the red supergiant star Antares in Scorpius which lies more than 5° lower and between them. The Moon stands above-left of Mars on the 1st, above Saturn on the 2nd, and above and between them both on the 29th.
This month Saturn improves only slightly to magnitude 0.4 and hardly moves in southern Ophiuchus, being stationary in position on the 25th. Mars, tracking eastwards from Libra to Scorpius, more than doubles in brightness to magnitude -0.5 as it approaches from 161 million to 118 million km. It also swells in diameter from 9 to 12 arcseconds and telescopes are starting to show surface features, including its north polar cap. There is no comparison, though, with the beauty of Saturn whose superb rings have their north face tipped Earthwards at 26°, near their maximum tilt, and stretch across 38 arcseconds. Saturn’s disk is 17 arcseconds wide and has much more subdued cloud belts than Jupiter.
Although Venus is brilliant at magnitude -3.9, we have slim hopes of seeing it deep in our south-eastern twilight for just a few more mornings. Mercury, already lost from view, reaches superior conjunction on the Sun’s far side on the 23rd.
The sunrise/sunset times for Edinburgh change from 07:03/17:48 GMT on the 1st to 06:45/19:50 BST (05:45/18:50 GMT) on the 31st. The Moon is at last quarter on the 1st, new on the 9th, at first quarter on the 15th, full on the 23rd and at last quarter again on the 31st.
New moon on the 9th brings the first and best of this year’s four eclipses when a total eclipse of the Sun occurs along a path that travels eastwards across Indonesia before swinging north-eastwards over the Pacific to end to the north of Hawaii. Surrounding areas enjoy a partial eclipse but there is nothing to see from Europe. The Moon slims the outer and lighter shadow of the Earth during a penumbral lunar eclipse on the 23rd. Also best seen over the Pacific, it is partly visible from most of the Americas and eastern Asia, but only a minor fading of the southern part of the Moon may be expected.
This is a slightly-revised version of Alan’s article published in The Scotsman on March 1st 2016, with thanks to the newspaper for permission to republish here. Journal Editor’s apologies for the lateness of the article appearing here.
Almost every Christmas an astronomer attempts to explain the Star of Bethlehem. The Sky at Night team did so in their programme broadcast on 2015 Dec 30. They concluded that it was most likely to have been a comet and showed Giotto’s painting of the Nativity with a comet in the sky (see below). Other artists portraying the Nativity usually just showed a distant star.
I am a member of the ASE because I am interested in astronomy and cosmology. But I also have an abiding interest in the origin of Christianity and the life of Jesus. This is the result of a youth misspent as a Christian, a religion I abandoned a long time ago. This interest deepened until I found that I could write a book on the subject, which covers all aspects of the gospel story (see The Rise and Fall of Jesus, by Steuart Campbell). Necessarily the book examines Jesus’ birth and the story of the Star of Bethlehem.
The story comes only from Matthew’s Gospel, chapter 2, as follows (Authorised version):
Now when Jesus was born in Bethlehem of Judæa in the days of Herod the king, behold, there came wise men from the east to Jerusalem, saying, Where is he that is born King of the Jews? for we have seen his star in the east, and are come to worship him. When Herod the king had heard these things, he was troubled, and all Jerusalem with him. And when he had gathered all the chief priests and scribes of the people together, he demanded of them where Christ should be born. And they said unto him, In Bethlehem of Judæa: for thus it is written by the prophet,…Then Herod, when he had privily [secretly] called the wise men, enquired of them diligently what time the star appeared. And he sent them to Bethlehem, and said, Go and search diligently for the young child; and when ye have found him, bring me word again, that I may come and worship him also. When they had heard the king, they departed; and, lo, the star, which they saw in the east, went before them, till it came and stood over where the young child was.
Several things about this account should trouble astronomers. Does the account mean that the magi saw the ‘star’ in the east, i.e. rising, and followed it during a night as it travelled west? Or does it just mean that, being in the east themselves (Arabia?), they saw the ‘star’ in the west, over Palestine. If the latter, the ‘star’ would have set before they even came to Jerusalem. It is not clear.
The question of the time of the appearance of the ‘star’ is also obscure. No answer is given to this question and one wonders how it could be answered. Herod seems to have thought it significant, but we are not told why.
Most puzzling of all is the idea that the magi could follow the ‘star’ to identify a particular building in Bethlehem. Astronomers especially know that a celestial object or phenomenon cannot be identified with a particular location on the surface of the earth. Perhaps they are ignorant of this account or choose to ignore it as they search for any celestial phenomenon that might explain it. The entire confused account should alert astronomers to the possibility that it is unreliable and that they might not be looking for a real ‘star’.
It is important to understand that the two accounts of Jesus birth, one here in Matthew and another incompatible one in Luke’s Gospel are additions to the first Gospel, that of Mark. Both Matthew and Luke, took Mark as their basis and made additions to give Jesus an origin and background commensurate with his later deification and to elevate him the status of a Saviour God at least equal to contemporary such gods. The obvious comparison is with Mithras, the god of the Roman Army. Indeed, Matthew may have borrowed from the Mithraic books, which, it is reported, tell how, when Mithras was born, a star fell from the sky and was followed by Zoroastrian priests called ‘Magi’ on the way to worship him (by the way, Mithras birthday was Dec 25!).
Neither Mark’s nor John’s Gospel know anything about Jesus’ origin. Biblical scholars believe that the entire Birth Narratives of Matthew and Luke are inventions, for the purpose explained above.
Matthew in particular, writing for the Jewish community in Alexandria, was at pains to show fulfilment of Jewish prophecy, or at least to show links between Jesus’ origin and the Jewish Scriptures. Consequently he may have borrowed from a Jewish apocryphal book like The Testament of Levi (one of the Jewish patriarchs). In that book, in a description of the last days (18:3), one finds the statement that ‘his star shall arise in heaven as of a king. Lighting up the light of knowledge as the sun the day’. Also, in 24:1, the statement that ‘shall a star arise to you from Jacob in peace’. One can even see forecast of a star in Numbers 24:17 (‘There shall come a star out of Jacob’). In the Old Testament, the word ‘star’ often stood for the Messiah.
Jewish readers would easily see the connection and be persuaded that Jesus really was the Messiah, the point Matthew was trying to convey. I understand that The Talmud, a central text of Rabbinic Judaism, contains a statement that ‘when the Messiah is to be revealed a star will rise in the east…and seven other stars round it will fight on every side’.
It is common knowledge that ancient peoples saw celestial phenomena as signifying or celebrating some important event, such as the birth of a king, on Earth. It is not so obvious, but equally logical, that an important historical Earthly event must somehow have been reflected in the sky. Consequently, even though nothing appeared at the time, such an event was easily invented to convince people that the event described had great significance. Miraculous events were often invented to accompany the births or deaths of Roman Emperors. Such was the case here. Believing that Jesus was the expected Messiah, Matthew invented a celestial event to convince his readers of Jesus’ importance.
Astronomers even make a mistake about the date. Our year dating system was invented in 525 by a Scythian monk called Dionysius Exiguus. He based it on the assumed age of Jesus, by then thought to be in Heaven (we still keep to this system which was adopted by Bede in the 8th century). However, astronomers and many others are misled by the reference in Matthew’s account to king Herod. They assume that it must be Herod the Great, known for his cruelty and who died in 4 BCE. Consequently, they look for a celestial phenomenon prior to that date, perhaps 5 or 6 BCE and sometime they find one. However, ‘Herod’ was a family name and all of Herod the Great’s sons also carried the name. So merely calling a king ‘Herod’ was not sufficient identification and Dionysius’ calendar should not be accused of making a mistake. He almost certainly worked from Luke’s account of when John the Baptist began to preach (chapter 3). Note the reference to ‘Herod the Tetrarch’, whose name was actually ‘Antipas’:
1 Now in the fifteenth year of the reign of Tiberius Cæsar, Pontius Pilate being governor of Judæa, and Herod being tetrarch of Galilee, and his brother Philip tetrarch of Ituræa and of the region of Trachonitis, and Lysanias the tetrarch of Abilene
2 Annas and Caiaphas being the high priests, the word of God came unto John the son of Zacharias in the wilderness.
Also a statement about the age of Jesus:
23 And Jesus himself began to be about thirty years of age
Tiberias’ 15th year was the year we call, using Dionysius’ system, 28 CE. Making allowances for the period between the appearance of John and Jesus’ mission, his birth must be place in the year 1 BCE (there was no year zero). There is no reason to abandon Dionysius’ calendar and every reason to eschew the idea that he made a mistake. Consequently, even if there had been a celestial phenomenon at the time of Jesus’ birth, astronomers have been looking in the wrong time.
The mistake made by astronomers is a classic example of ‘the law of the instrument’ or over-reliance on a familiar tool. It means that astronomers have been looking at the biblical record only from their own point of view, ignorant of the fact that the record does not lie within their competence. There are other examples of experts in one discipline believing that they can explain something that lies in another discipline. In this case, astronomers have seen what appears to be an astronomical record and assumed that they would be able to explain it. But the star is imaginary. It never really existed.
Please remember this when you next hear, as you will, of an astronomer trying to explain The Star of Bethlehem.
This article is based on a talk given to the ASE by Steuart Campbell on the 8th of January 2016. Steuart has been a member of the ASE for many years and our thanks go to him for sharing with us his theory on the Star of Bethlehem.
An extra day of superb February evening skies
February brings our best evening skies of the year and, with this being a leap year, we have one extra day to enjoy them. Pride of place must go to Orion which marches across our southern sky from the south-east at nightfall tonight to stand in the south-south-west by our star map times.
We are all familiar with the Summer Triangle of bright stars (Vega, Deneb and Altair) which graces our summer nights, but less well known is the Winter Triangle that follows close behind Orion. Consisting of the stars Betelgeuse at Orion’s shoulder, Procyon in Canis Minor which stands level with Betelgeuse to its left, and Sirius in Canis Major, the Winter Triangle is brighter than its summer counterpart and much more isosceles in form.
Sirius, found by extending Orion’s belt down and to the left, is the brightest star in our night sky largely because it is one of the closest to us at 8.6 light years. Indeed, viewed from the same distance as Betelgeuse, some 500 light years, it would be too dim to see without binoculars.
Because they are so obviously placed in the sky in the shape of a man, it is easy to regard the main stars of Orion as lying at similar distances from us. Although they are all highly luminous and far away, they stand at very different distances so that Orion’s impressive outline would change beyond recognition if we could view it from a different direction. A striking example concerns the three stars of Orion’s belt which, in order from the left, are Alnitak, Alnilam and (slightly fainter) Mintaka. Alnitak and Mintaka are thought to stand around 700 light years from us, but some estimates put Alnilam as distant as 2,000 light years, more than twice as far.
The Sun climbs almost 10° northwards during February as sunrise/sunset times for Edinburgh change from 08:08/16:45 on the 1st to 07:06/17:46 on the 29th. The Moon is at last quarter on the 1st, new on the 8th, at first quarter on the 15th and full on the 22nd. Because its path is inclined steeply in the south-west at nightfall, there is an excellent opportunity to spot the very young and brightly earthlit Moon low in the west-south-west on the evening of the 9th. It should still be spectacular over the following few evenings.
No bright planets are visible until the conspicuous Jupiter begins its climb through our eastern and south-eastern sky as Orion crosses the meridian. It lies in south-eastern Leo, 22° below and left of Regulus, and is creeping westwards against the stars as it draws towards its opposition in March. This month it brightens from magnitude -2.4 to -2.5, approaches from 694 million to 665 million km and swells from 42 to 44 arcseconds in diameter.
Any telescope should show Jupiter’s two main dark cloud belts, appearing symmetrically and in parallel on either side of its pale equatorial zone. Spots and streaks in the clouds, including the famous Red Spot in its southern hemisphere, drift from east to west across the Jovian disk as the planet rotates in just under ten hours. Of course, we need only binoculars to spot Jupiter’s four main moons as they change their relative positions on either side of the disk.
The second bright planet of the night stands low in the south-east as Jupiter reaches the meridian some five hours after our map times. The reddish, or perhaps salmon-pink, Mars lies below the Moon and just above the double star Zubenelgenubi in Libra on the morning of the 1st.
Mars spends February sliding eastwards though Libra and brightening from magnitude 0.8 to 0.3 as it approaches from 205 million to 161 million km. Its small slightly-gibbous disk grows from 7 to 9 arcseconds and is starting to reveal detail through good telescopes, particularly if we catch it just before dawn as it passes less than 20° high in the south.
If we look before dawn and take a line from Jupiter, well over in the west-south-west, to Mars in the south and onwards to the left we reach the almost equally-bright Saturn (magnitude 0.6 to 0.5) which is slow-moving in southern Ophiuchus, 8° above-left of the red supergiant star Antares in Scorpius. The Moon stands above Antares and above-right of Saturn on the morning of the 3rd when Saturn’s disk appears 16 arcseconds wide, with its rings spanning 36 arcseconds and tipped 26° to our view – a stunning sight.
The line-up of Jupiter, Mars and Saturn may be extended to Venus and Mercury, hugging our south-eastern horizon, and has led to widespread claims of a spectacular planetary alignment in our morning sky. In fact, the term “planetary alignment” is more usually applied to those occasions when several planets collect together in the same region of sky. There was one such tight alignment of Venus, Mars and Jupiter before dawn in October and similar events have been preceded by apocalyptic pronouncements in the crackpot community.
The current alignment stretches over more than 100° of sky and is better appreciated by observers further south and particularly by those in the southern hemisphere. For Scotland, though, Venus is uncomfortably low in our bright predawn twilight and although it is brilliant at magnitude -4.0 it is sinking ever lower – its altitude at Edinburgh’s sunrise being 7° on the 1st and half that by the month’s end. Mercury, much fainter near magnitude 0.0 and farthest from the Sun on the 7th, is a few degrees to the lower-left of Venus and very difficult from our latitudes. Both stand below the slender waning Moon on the 6th.