Amateur astronomer discovers first interstellar comet
It is two years since astronomers in Hawaii discovered the first object known to have approached the Sun from beyond our solar system. Given the Hawaiian name of ʻOumuamua, this appeared to be a reddish and elongated slab-shaped body of about the size of a skyscraper that passed 38 million km from the Sun before sweeping within 24 million km of the Earth. It came from roughly the current direction of the star Vega and headed away towards the Square of Pegasus, though it may take 20,000 years to leave the solar system completely.
Its small size meant that it was followed only faintly and for barely a month. Astronomers were surprised to notice no sign of cometary activity – no surrounding fuzzy coma and no tail – while suggestions that it was an alien probe prompted unsuccessful scans for any artificial radio emissions.
Now the second-known interstellar intruder has been sighted, and this one appears larger, brighter and is surely a comet. It was discovered photographically on 29 August from an observatory in Crimea by the amateur astronomer Gennady Borisov using a telescope he built himself. Initially called C/2019 Q4 (Borisov), or Comet Borisov for short, it was clearly speeding along a strongly hyperbolic path past the Sun, very unlike the elliptical or nearly parabolic orbits followed by all previous comets. Now it has been awarded the official interstellar designation of 2I/Borisov.
The comet was travelling at about 33 km per second as it entered the solar system from the direction of the constellation Cassiopeia, fast enough to cover the 4-light-years distance of the nearest star in under 40,000 years. Perihelion, its closest point to the Sun, occurs at 303 million km on 8 December, putting it still beyond the orbit of Mars, and it reaches its closest to the Earth at 293 million km twenty days later.
It is still faint, no better than magnitude 17, but may attain magnitude 14 near perihelion and, while it will never reach naked-eye or binocular visibility, is likely to be within telescopic range until at least the middle of next year. This gives plenty of time for astronomers to study a comet that probably formed elsewhere in the Milky Way galaxy at a different time and with possibly a different composition than those that formed alongside the Sun and Earth. October has Comet Borisov travelling south-eastwards to the west of the Sickle of Leo and passing within a Moon’s-breadth east of the star Regulus on the 24th.
Leo’s Sickle rises in the north-east in the early morning and stands some 30° high in the east before dawn as our southern sky is dominated by the glorious constellation of Orion. The pre-dawn also gives us a chance to spot Mars as it emerges from the Sun’s far side. The planet rises in the east one hour before the Sun on the 1st and two hours before sunrise on the 31st. Moving east-south-eastwards in Virgo, it shines only at magnitude 1.8 and lies 8° below the slender earthlit Moon on the 26th.
As the Sun tracks southwards by 11° during October, the sky at nightfall is changing only slowly. The Summer Triangle is still high in the south as darkness falls, although its three stars, Vega in Lyra, Deneb in Cygnus and Altair in Aquila, have shifted into the west by our star map times. By then, Pegasus, the upside-down flying horse with his nose near Delphinus the Dolphin, stands high in the south.
The sunrise/sunset times for Edinburgh change this month from 07:15/18:49 BST (06:15/17:49 GMT) on the 1st to 07:17/16:35 GMT on the 31st, following Summer Time’s end on the 27th. The Moon reaches first quarter on the 5th, full phase on the 13th, last quarter on the 21st and new on the 28th.
Like Mars, Venus is also coming into view from beyond the Sun, but this time into our evening twilight in the west-south-west. Although brilliant at magnitude -3.9, it stands a mere 3° high at sunset for Edinburgh and sets at present only 30 minutes later, so we need good weather and a clear horizon to catch it. On the 29th, look for it 2.8° below the sliver of the earthlit young Moon, only 3° illuminated. Mercury is fainter and even lower at sunset and not visible from Scotland.
Jupiter is well past its best as an evening object although it remains obvious low in the south-west at nightfall, sinking to set at Edinburgh’s south-western horizon at 21:14 BST on the 1st and as early as 18:34 GMT by the 31st. At magnitude -2.0 to -1.9 and 36 to 33 arcseconds in diameter, it lies close to the Moon on the 3rd and 31st.
Saturn, one tenth as bright at magnitude 0.5 to 0.6, lies some 25° to the left of Jupiter. When it is close to the first quarter Moon on the 5th, its disk and rings span 17 and 38 arcseconds respectively. It is in Sagittarius low in the south at nightfall and sets in the south-west soon after our map times.
Neptune and Uranus are binocular brightness object of magnitudes 7.8 and 5.7 in Aquarius and Pisces respectively. There is little hope of locating them using our chart, but a web search, such as “Where is Uranus?”, should bring up information and a finder chart. Uranus, in fact, reaches opposition at a distance of 2,817 million km on the 28th when it stands directly opposite the Sun and appears as a tiny 3.7 arcseconds blue-green disk through a telescope.
Our Diary, below, records the peak dates for two of the October’s meteor showers, the Draconids on the 8th and the Orionids on the 22nd. Neither is among the year’s top showers, though both can yield rates of 20 or more meteors per hour under ideal conditions. The Draconids are active from the 6th to the 10th with slow meteors that diverge from a radiant near the Head of Draco, the quadrilateral of stars below and left of the D of DRACO on our north map. Unfortunately, the light of the bright gibbous Moon will hinder observations before the Moon sets in the early morning.
The Orionids, like May’s Eta Aquarids shower, are caused by meteoroid debris from Comet Halley. They last throughout the month and into early November but are expected to be most prolific on the nights of the 22nd and 23rd when their fast meteors diverge from a point that lies around 10° north-east (above-right) of Betelgeuse at Orion’s shoulder. That point passes high in the south before dawn but is just rising in the east-north-east at our map times, so no Orionids appear before then. As with those other swift meteors, the Perseids of August, many of the brighter Orionids leave glowing trains in their wake.
Diary for 2019 October
Times are BST until the 27th and GMT thereafter.
3rd 21h Moon 1.9° N of Jupiter
5th 18h First quarter
5th 22h Moon 0.3° S of Saturn
8th 07h Peak of Draconids meteor shower
13th 22h Full moon
17th 23h Moon 2.9° N of Aldebaran
20th 05h Mercury furthest E of Sun (25°)
21st 14h Last quarter
22nd Peak of Orionids meteor shower
22nd 06h Moon 1.0° N of Praesepe
23rd 19h Moon 3° N of Regulus
26th 18h Moon 5° N of Mars
27th 02h BST = 01h GMT End of British Summer Time
28th 04h New moon
28th 08h Uranus at opposition at distance of 2,817 million km
29th 14h Moon 4° N of Venus
30th 08h Mercury 2.7° S of Venus
31st 14h Moon 1.3° N of Jupiter
This is an extended version, with added diary, of Alan’s article published in The Scotsman on September 30th 2019, with thanks to the newspaper for permission to republish here.
Jupiter’s conspicuous opposition in the Balance
Jupiter is at its brightest and best in the constellation of Libra, the Weighing Scales or Balance, this month. Its opposition, when it stands directly opposite the Sun, occurs on the morning of the 9th but it is prominent every night as it transits low across the south from the south-east at nightfall to the south-west before dawn.
Venus, however, outshines it in the western evening sky and both Saturn and the increasingly striking Mars follow Jupiter into the southern morning sky.
The Sun climbs another 7° northwards during May as Edinburgh’s sunrise/sunset times change from 05:29/20:52 BST on the 1st to 04:36/21:45 on the 31st. Because twilight is also lengthening, official darkness in the middle of the night lasts for under one hour by May’s end.
The Moon is at last quarter on the 8th, new on the 15th, at first quarter on the 22nd and full on the 29th.
Venus stands 20° high in the west at sunset, sinking to set in the north-west by 23:40 on the 1st and one hour later by the 31st. Brilliant at magnitude -3.9, it begins the month 6° above-right of Taurus’ brightest star, Aldebaran, and tracks east-north-eastwards between the Bull’s horns to end May in mid-Gemini, below Castor and Pollux.
The young earthlit Moon makes an impressive sight almost 6° below-left of the planet on the evening of the 17th. Three days later, as Venus joins the region of sky covered by our chart, it passes 1.0° (two Moon-diameters) above-right of the star cluster M35 whose brightest stars may be glimpsed through binoculars from their distance of some 2,800 light years. Still on the far side of its orbit, Venus approaches from 217 million to 190 million km this month as its almost-full disk swells to 13 arcseconds in diameter.
After dominating our winter nights, Orion ducks below our western horizon as the evening twilight fades at present. The Plough is overhead and Leo high in the south with its main star Regulus which has a close encounter with the first quarter Moon on the night of 21st/22nd.
By our map times, Leo sis inking in the west and Jupiter is easily the most conspicuous object in the south though it stands barely 18° high for Edinburgh. Moving westwards in Libra, it lies close to the Moon on the 27th. Its motion takes it from 4° east (left) of the well-known double star Zubenelgenubi at present to lie just 1.0° north-east of the star on the 31st.
Jupiter is 658 million km away at opposition, shines at magnitude -2.5 and shows a 45 arcseconds wide disk through a telescope. Its two main darker cloud bands, its northern and southern equatorial belts, straddle a lighter equatorial zone. The famous Great Red Spot is gradually losing its status, however, being less than half as wide as it was a century ago and currently more salmon-pink in hue than red. It sits in a bay at the southern edge of the south equatorial belt and, like the many other Jovian cloud features, is carried smartly across the disk as the planet spins in just under ten hours.
Steadily-held binoculars show the four main moons of Jupiter, Io, Europa, Ganymede and Callisto which change their configuration to the east and west of Jupiter from night to night, sometimes disappearing as they hide behind Jupiter or cross the disk, along with their shadows.
If Jupiter’s low elevation makes telescopic views less than sharp, this is even more the case with Saturn which rises in the south-east at our map times and is 6° lower in the sky than Jupiter as it reaches the meridian just before dawn. Saturn improves from magnitude 0.4 to 0.2 as it creeps westwards above the Teapot asterism in Sagittarius. It lies 1,392 million km away at mid-month when its oblate globe is 18 arcseconds across set within 40 by 17 arcseconds rings that have their north face inclined at 26° to our view. Look for it 4° right of the Moon on the morning of the 5th.
Less than 2° below Saturn is the globular star cluster M22, a ball of thousands of stars that lies about 10,600 light years away and formed some 12 billion years ago. At about magnitude 5.1 and visible as a hazy glow through binoculars, it was the first globular to be discovered and is brighter than M13 in Hercules, the best globular in the northern sky.
Mars lies almost 15° east of Saturn at present and rises at Edinburgh’s south-eastern horizon at 02:46 on the 1st. As it more than doubles in brightness, from magnitude -0.4 to -1.2, it also speeds 12° eastwards from Sagittarius to Capricornus so that by the 31st it rises at 01:31 and its fiery glow is unmistakable above the south-south-eastern horizon before dawn.
Catch Mars below the Moon on the morning of the 6th. Telescopically, its disk swells from 11 to 15 arcseconds as its distance falls from 126 million to 92 million km. Its approach opens the optimum window for sending probes to the planet and NASA’s InSight lander to study “marsquakes” and the Martian interior is due for launch between 5 May and 8 June.
Meteors of the Eta-Aquarids shower, debris from Comet Halley, appear until the 20th as they radiate from a point that lies low in the east for an hour or so before dawn over Scotland. The shower peaks with some moonlight interference on the 6th and brings a fine shower for watchers further south but only a handful of meteors for us.
Diary for 2018 May
Times are BST
3rd 18h Venus 7° N of Aldebaran
4th 21h Moon 1.7° N of Saturn
5th – 6th Peak of Eta Aquarids meteor shower
6th 08h Moon 2.7° N of Mars
8th 03h Last quarter
9th 02h Jupiter at opposition at distance of 658 million km
15th 13h New moon
17th 19h Moon 5° S of Venus
22nd 03h Moon 1.5° N of Regulus
22nd 05h First quarter
27th 19h Moon 4° N of Jupiter
29th 15h Full moon
This is a slightly revised version, with added diary, of Alan’s article published in The Scotsman on April 30th 2018, with thanks to the newspaper for permission to republish here.
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.
Ice giants lurk in our southern sky
Our October nights are some of the finest for stargazing in the entire year. The temperatures have yet to plumb the bone-chilling depths of winter, but the constellations visible between dusk and dawn include all the highlights of our summer and winter skies. It is just a shame that most of the bright planets are poorly placed at present.
The nights begin with the Summer Triangle high in the south. Formed by the prominent stars Vega in Lyra, Altair in Aquila and Deneb in Cygnus, its stands just to the west of the meridian at nightfall, but tumbles into the west by the star map times. In a dark sky, the diffuse band of the Milky Way flows through it is it arches overhead through Cepheus and Cassiopeia.
Look up in the south at our map times for the large, and largely empty, Square of Pegasus, and very low in the south, less than 5° high for Edinburgh, to find Fomalhaut in Pisces Austrinus, the Southern Fish. A young star only 25 light years away, it is surrounded by disks of dust and probably orbited by two or more planets.
Only two planets are visible at our map times as they lurk to the south of the Square. Uranus and Neptune are plotted on our chart in Pisces and Aquarius respectively, but they are binocular-brightness at magnitude 5.7 and 7.8 and demand more detailed charts, perhaps from the Internet, to identify them. They show tiny bluish disks through a telescope, with Uranus only 3.7 arcseconds wide when it comes to opposition at a distance of 2,845 million km on the 7th, while Neptune is currently 2.3 arcseconds and 1,500 million km further away. Both have ring systems, invisible under normal circumstances, and a plethora of moons.
For decades, these distant worlds have been classed among the gas giants to distinguish them from the smaller rocky planets closer to the Sun. Both are of similar size, some four times wider than Earth, with Uranus being 51,118 km in equatorial diameter and Neptune only 1,600 km smaller. Unlike Jupiter and Saturn, though, they contain a much smaller proportion of raw hydrogen and helium and instead are predominantly composed of the ices of water, methane and ammonia. Indeed, they are more often now classed as ice giants.
Taurus, climbing in the east, is the forerunner of the spectacular constellations of winter centred around Orion. The latter rises below Taurus over the following two hours and is unmistakable in the south before dawn as Sirius, the brightest star, twinkles furiously in the south-south-east.
In northern Orion, 10° to the north-east of Betelgeuse at Orion’s shoulder, lies the radiant point for the Orionids meteor shower which is active in the mornings from the 16th to the 30th. Fast meteors diverge from the point, particularly around the 22nd when numbers may approach 25 per hour under dark moonless skies. The meteoroids were released by Comet Halley.
The Sun sinks another 11° southwards during October as sunrise/sunset times for Edinburgh change from 07:15/18:48 BST (06:15/17:48 GMT) on the 1st to 07:17/16:35 GMT on the 31st. British Summer Time ends at 02:00 BST on the 26th when clocks are set back one hour to 01:00 GMT. Nautical twilight at dawn and dusk persists for a little over 80 minutes.
The Moon is at first quarter on the 1st and full on the 8th when observers around the Pacific, including N America, see a total lunar eclipse. Last quarter occurs on the 15th with new moon on the 23rd which brings a partial solar eclipse visible over most of N America and the north-eastern Pacific. First quarter comes round again on the 31st.
The solitary conspicuous planet is Jupiter but we must wait until the morning hours to see it. The largest of the gas giants shines at magnitude -1.9 as it rises in the east-north-east at about 02:00 BST at present and before 23:30 at the month’s end, climbing high into the south-east and even the south before dawn later in the period. Mid-October sees it slip from Cancer into Leo and by the 31st it has drawn to within 10° of Leo’s main star Regulus. The Moon stands 6° below Jupiter on the 18th when the planet is 35 arcseconds wide and 841 million km away.
Venus may be brilliant at magnitude -3.9 but it rises in the east only 40 minutes before sunrise on the 1st and is soon lost from view as it tracks towards superior conjunction on the Sun’s far side on the 25th. Mercury, though, slips through inferior on the Sun’s near side on the 16th and becomes a morning star during the final week of the month. By the 31st, it rises almost two hours before sunrise and shines at magnitude -0.4 low in the east-south-east.
Saturn and Mars are challenging evening planets just above the south-west horizon as darkness falls. Saturn, magnitude 0.6 in Libra, is lost from view later in the month as it is swallowed by the twilight, though experienced telescope users may be able to observe it being occulted by the young Moon in the late afternoon of the 25th. It is 11° high in Edinburgh’s south-west when it disappears behind the Moon’s eastern edge at 16:55 BST, though since they are 21° to the right of the Sun, caution is advised.
Mars, now well to the left of Saturn, dims from magnitude 0.8 to 0.9 as it tracks eastwards from 4° above Antares in Scorpius. Catch it 6° below the young Moon on the 28th.