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Scotland’s Sky in January, 2019
Rise early for a total lunar eclipse on the 21st
The maps show the sky at 21:00 GMT on the 1st, 20:00 on the 16th and 19:00 on the 31st. An arrow depicts the motion of Mars. (Click on map to enlarge)
Any month that has the glorious constellation of Orion in our southern evening sky is a good one for night sky aficionados. Add one of the best meteor showers of the year, a total eclipse of the Moon, a meeting between the two brightest planets and a brace of space exploration firsts and we should have a month to remember
Orion rises in the east as darkness falls and climbs well into view in the south-east by our star map times. Its two leading stars are the blue-white supergiant Rigel at Orion’s knee and the contrasting red supergiant Betelgeuse at his opposite shoulder – both are much more massive and larger than our Sun and around 100,000 times more luminous.
Below the middle of the three stars of Orion’s Belt hangs his Sword where the famous and fuzzy Orion Nebula may be spied by the naked eye on a good night and is usually easy to see through binoculars. One of the most-studied objects in the entire sky, it lies 1,350 light years away and consists of a glowing region of gas and dust in which new stars and planets are coalescing under gravity.
The Belt slant up towards Taurus with the bright orange giant Aldebaran and the Pleiades cluster as the latter stands 58° high on Edinburgh’s meridian. Carry the line of the Belt downwards to Orion’s main dog, Canis Major, with Sirius, the brightest star in the night sky. His other dog, Canis Minor, lies to the east of Orion and is led by Procyon which forms an almost-equilateral triangle with Sirius and Betelgeuse – our so-called Winter Triangle.
The Moon stands about 15° above Procyon when it is eclipsed during the morning hours of the 21st. The event begins at 02:36 when the Moon lies high in our south-western sky, to the left of Castor and Pollux in Gemini, and its left edge starts to enter the lighter outer shadow of the Earth, the penumbra.
Little darkening may be noticeable until a few minutes before it encounters the darker umbra at 03:34. Between 04:41 and 05:46 the Moon is in total eclipse within the northern half of the umbra and may glow with a reddish hue as it is lit by sunlight refracting through the Earth’s atmosphere. The Moon finally leaves the umbra at 06:51 and the penumbra at 07:48, by which time the Moon is only 5° high above our west-north-western horizon in the morning twilight.
This eclipse occurs with the Moon near its perigee or closest point to the Earth so it appears slightly larger in the sky than usual and may be dubbed a supermoon. Because the Moon becomes reddish during totality, there is a recent fad for calling it a Blood Moon, a term which has even less of an astronomical pedigree than supermoon. Combine the two to get the frankly ridiculous description of this as a Super Blood Moon.
Sunrise/sunset times for Edinburgh change from 08:44/15:49 on the 1st to 08:10/16:43 on the 31st. New moon early on the 6th, UK time, brings a partial solar eclipse for areas around the northern Pacific. First quarter on the 14th is followed by full moon and the lunar eclipse on the 21st and last quarter on the 27th.
The Quadrantids meteor shower is active until the 12th but is expected to peak sharply at about 03:00 on the 4th. Its meteors, the brighter ones leaving trains in their wake, diverge from a radiant point that lies low in the north during the evening but follows the Plough high into our eastern sky before dawn. With no moonlight to hinder observations this year, as many as 80 or more meteors per hour might be counted under ideal conditions.
Mars continues as our only bright evening planet though it fades from magnitude 0.5 to 0.9 as it recedes. Tracking through Pisces and well up in the south at nightfall, it stands above the Moon on the 12th. Our maps show it sinking in the south-west and it sets in the west before midnight.
Venus, its brilliance dimming only slightly from magnitude -4.5 to -4.3, stands furthest west of the Sun (47°) on the 6th and is low down (and getting lower) in our south-eastern predawn sky. Look for it below and left of the waning Moon on the 1st with the second-brightest planet, Jupiter at magnitude -1.8, 18° below and to Venus’s left. As Venus tracks east-south-eastwards against the stars, it sweeps 2.4° north of Jupiter in an impressive conjunction on the morning of the 22nd while the 31st finds it 8° left of Jupiter with the earthlit Moon directly between them.
Saturn, magnitude 0.6, might be glimpsed at the month’s end when it rises in the south-east 70 minutes before sunrise but Mercury is lost from sight is it heads towards superior conjunction on the Sun’s far side on the 30th.
China hopes that its Chang’e 4 spacecraft will be the first to touch down on the Moon’s far side, possibly on the 3rd. Launched on December 7 and named for the Chinese goddess of the Moon, it needs a relay satellite positioned beyond the Moon to communicate with Earth.
Meantime, NASA’s New Horizons mission is due to fly within 3,500 km of a small object a record 6.5 billion km away when our New Year is barely six hours old. Little is known about its target, dubbed Ultima Thule, other than that it is around 30 km wide and takes almost 300 years to orbit the Sun in the Kuiper Belt of icy worlds in the distant reaches of our Solar System.
Diary for 2019 January
1st 06h New Horizons flyby of Ultima Thule
1st 22h Moon 1.3° N of Venus
2nd 06h Saturn in conjunction with Sun
3rd 05h Earth closest to Sun (147,100,000 km)
3rd 08h Moon 3° N of Jupiter
4th 03h Peak of Quadrantids meteor shower
6th 01h New moon and partial solar eclipse
6th 05h Venus furthest W of Sun (47°)
12th 20h Moon 5° S of Mars
14th 07h First quarter
17th 19h Moon 1.6° N of Aldebaran
21st 05h Full moon and total lunar eclipse
21st 16h Moon 0.3° S of Praesepe
22nd 06h Venus 2.4° N of Jupiter
23rd 02h Moon 2.5° N of Regulus
27th 21h Last quarter
30th 03h Mercury in superior conjunction
31st 00h Moon 2.8° N of Jupiter
31st 18h Moon 0.1° N of Venus
Alan Pickup
This is a slightly revised version, with added diary, of Alan’s article published in The Scotsman on December 31st 2018, with thanks to the newspaper for permission to republish here.
Scotland’s Sky in November, 2016
Nights begin with Venus and end at Jupiter
The maps show the sky at 21:00 GMT on the 1st, 20:00 on the 16th and 19:00 on the 30th. An arrow depicts the motion of Mars after the first week of the month. (Click on map to enlarge)
The end of British Summer Time means that we now enjoy six hours of official darkness before midnight, though I appreciate that this may not be welcomed by everyone. The starry sky as darkness falls, however, sees only a small shift since a month ago, with the Summer Triangle, formed by the bright stars Vega, Deneb and Altair, now just west of the meridian and toppling into the middle of the western sky by our star map times.
Those maps show the Square of Pegasus high in the south. The star at its top-left, Alpheratz, actually belongs to Andromeda whose other main stars, Mirach and Almach, are nearly equal in brightness and stand level to its left. A spur of two stars above Mirach leads to the oval glow of the Andromeda Galaxy, M31, which is larger than our Milky Way and, at 2.5 million light years, is the most distant object visible to the unaided eye. It is also approaching us at 225 km per second and due to collide with the Milky Way in some 4 billion years’ time.
Binoculars show M31 easily and you will also need them to glimpse more than a handful of stars inside the boundaries of the Square of Pegasus, even under the darkest of skies. In fact, there are only four such stars brighter than the fifth magnitude and another nine to the sixth magnitude, close to the naked eye limit under good conditions. How many can you count?
Mars is the easiest of three bright planets to spot in tonight’s evening sky. As seen from Edinburgh, it stands 11° high in the south as the twilight fades, shining with its customary reddish hue at a magnitude of 0.4, and appearing about half as bright as the star Altair in Aquila, 32° directly above it.
Now moving east-north-eastwards (to the left), Mars is 5° below-right of the Moon on the 6th and crosses from Sagittarius into Capricornus two days later. Soon after this, it enters the region covered by our southern star map, its motion being shown by the arrow. By the 30th, Mars has dimmed slightly to magnitude 0.6 but is almost 6° higher in the south at nightfall, moving to set in the west-south-west at 21:00. It is a disappointingly small telescopic sight, though, its disk shrinking from only 7.5 to 6.5 arcseconds in diameter as it recedes from 188 million to 215 million km.
We need a clear south-western horizon to spy Venus and Saturn, both low down in our early evening twilight. Venus, by far the brighter at magnitude -4.0, is less than 4° high in the south-west thirty minutes after sunset, while Saturn is 4° above and to its right, very much fainter at magnitude 0.6 and only visible through binoculars. The young earthlit Moon may help to locate them – it stands 3° above-right of Saturn on the 2nd and 8° above-left of Venus on the 3rd.
Mercury is out of sight in the evening twilight and Saturn will soon join it as it tracks towards the Sun’s far side. However, Venus’ altitude thirty minutes after sunset improves to 9° by the 30th when it sets for Edinburgh at 18:30 and is a little brighter at magnitude -4.1. Viewed telescopically, Venus shows a dazzling gibbous disk that swells from 14 to 17 arcseconds as its distance falls from 178 million to 149 million km.
Sunrise/sunset times for Edinburgh change from 07:20/16:31 on the 1st to 08:18/15:44 on the 30th. The Moon reaches first quarter on the 7th, full on the 14th, last quarter on the 21 and new on the 28th.
The full moon on the 14th occurs only three hours after the Moon reaches its perigee, the closest point to the Earth in its monthly orbit. As such, this is classed as a supermoon because the full moon appears slightly (7%) wider than it does on average. By my reckoning, this particular lunar perigee, at a distance of 356,509 km, is the closest since 1948 when it also coincided with a supermoon.
Of the other planets, Neptune and Uranus continue as binocular-brightness objects in Aquarius and Pisces respectively in our southern evening sky, while Jupiter, second only to Venus in brightness, is now obvious in the pre-dawn.
Jupiter rises at Edinburgh’s eastern horizon at 04:28 on the 1st and stands more than 15° high in the south-east as morning twilight floods the sky. It outshines every star as it improves from magnitude -1.7 to -1.8 by the 30th when it rises at 03:07 and is almost twice as high in the south-south-east before dawn.
Currently close to the famous double star Porrima in Virgo, Jupiter is 13° above-right of Virgo’s leader Spica and draws 5° closer during the period. Catch it less than 3° to the right of the waning earthlit Moon on the 25th. Jupiter’s distance falls from 944 million to 898 million km during November while its cloud-banded disk is some 32 arcseconds across.
The annual Leonids meteor shower has produced some stunning storms of super-swift meteors in the past, but probably not this year. Active from the 15th to 20th, it is expected to peak at 04:00 on the 17th but with no more than 20 meteors per hour under a dark sky. In fact, the bright moonlight is likely to swamp all but the brightest of these this year. Leonids diverge from a radiant point that lies within the Sickle of Leo which climbs from low in the east-north-east at midnight to pass high in the south before dawn.
Alan Pickup
This is a slightly-revised version of Alan’s article published in The Scotsman on November 1st 2016, with thanks to the newspaper for permission to republish here.
Scotland’s Sky in September, 2015
Total eclipse of the harvest supermoon on the 28th
The maps show the sky at 23:00 BST on the 1st, 22:00 on the 16th and 21.00 on the 30th. (Click on map to englarge)
There is no shortage of stellar interest in our September evening sky but anyone willing and able to observe later in the night may see the largest full moon of the year turn dull and red as it is totally eclipsed on the morning of the 28th. There is also a nice grouping of planets in the east before dawn.
Our chart depicts the sky in our late evening at present and shows the star Deneb in Cygnus almost at the zenith as the Summer Triangle it forms with Vega and Altair begins to topple westwards. The Square of Pegasus is climbing in the south-east in a rather sparsely populated region of the sky.
The Pleiades in Taurus glimmer low in the east-north-east as they begin their climb to the high meridian by dawn. They stand above the Moon on the Friday night of the 5th/6th as the Moon draws closer to Aldebaran, the leading star of Taurus, eventually to occult the star during the morning twilight. As seen from Edinburgh the star winks out as it disappears behind the sunlit eastern edge of the Moon at 05:51 BST on Saturday, 6th.
Our sole bright evening planet, Saturn, hovers only 10° above Edinburgh’s south-western horizon as darkness falls and sinks a little lower each evening as it creeps eastwards against the stars of eastern Libra. Telescopically, its disk appears 16 arcseconds broad while the rings are 37 arcseconds across with their north face inclined at 24°, but it is past its best as a target and, since it sets 30 minutes before our map times, we need to be quick to catch it. Look for it to the left of the young Moon on the 18th.
The Sun slips southwards over the celestial equator at 09:21 BST on the 23rd, marking the autumnal equinox in our northern hemisphere. Meanwhile, sunrise/sunset times for Edinburgh change from 06:16/20:08 BST on the 1st to 07:13/18:52 to the 30th as the duration of nautical twilight at dawn and dusk shrinks from 89 to 80 minutes.
The Moon is at last quarter on the 5th and new on the 13th when a partial solar eclipse is visible from southern Africa and Antarctica. Following first quarter on the 21st, the full moon on the 28th is a much more intriguing event because not only is it totally eclipsed, but it coincides with the Moon’s closest approach to the Earth (at perigee) in the whole of 2015. As a result, the Moon appears 7% wider than it does on average and, while the enlargement is not startlingly obvious to the casual observer, it has led to near-perigee full moons being called supermoons.
As the full moon closest to the equinox, this is also the harvest moon, a title that comes from the fact that, for several nights in a row, the bright Moon hangs low in our eastern sky as the night begins and extends the period by which the harvest may be gathered. The illusion that makes the Moon appear larger than usual when it stands low in the sky is also pronounced around this time and can only be enhanced by the supermoon circumstance.
The eclipse on the morning of the 28th, though, begins at 01:12 BST with the Moon well up in our southern sky, in the constellation Pisces and below the Square of Pegasus. The Moon meets the outer edge of the Earth’s penumbral shadow at that time, but little darkening may be noticed for another 30 minutes or more.
The dark shadow of the umbra beings to invade the lunar disk at 02:07, while from 03:11 until 04:23 the Moon is totally eclipsed as it crosses the southern part of the umbra. Here the Moon is only illuminated, usually with a reddish hue, by light scattered around the edge of the Earth. Varying atmospheric conditions, clouds and volcanic dust, on our home world mean that the appearance and brightness of the eclipsed Moon is always of interest. The Moon leaves the umbra behind at 05:27 and stands only 7° above Edinburgh’s western horizon when it exits the last of the penumbra at 06:23.
Venus, already a spectacular morning star, rises at Edinburgh’s east-north-eastern horizon 100 minutes before the Sun on the 1st and more than four hours before sunrise at the month’s end. Improving from magnitude -4.4 to -4.5, it shows a slender but dazzling crescent through binoculars though it shrinks in diameter from 51 to 43 arcseconds as it recedes from 48 million to 76 million km.
The giant planet Jupiter lags some 20° below-left of Venus and emerges from the Sun’s far side by mid-month to shine at magnitude -1.7, just brighter than Sirius which is low in the south-east at the time.
Our third morning planet, Mars, is much fainter at magnitude 1.8 and stands 9° above-left of Venus on the 1st. Also still on the far side of its orbit, it slips down and to the left in the direction of Jupiter and passes 0.8° north of Leo’s leading star Regulus on the 24th. The blue-white of Regulus outshines the orange tinted Mars and the contrasting pair make an interesting sight roughly half-way between Venus and Jupiter for a few mornings around that day.
The little innermost planet, Mercury, stands furthest east of the Sun (27°) on the 4th but is much too low in our western evening twilight to be seen this month. After sweeping around the Sun’s near side on the 30th, it is due to make its best appearance of the year as a morning star in October.
Alan Pickup
This is a slightly-revised version of Alan’s article published in The Scotsman on September 1st 2015, with thanks to the newspaper for permission to republish here.
Scotland’s Sky in September, 2014
Mars greets a rival and two new orbiters
The maps show the sky at 23:00 BST on the 1st, 22:00 on the 16th and 21.00 on the 30th. (Click on map to enlarge)
The Summer Triangle, formed by the bright stars Vega, Deneb and Altair, still has pride of place high in our southern sky at nightfall. Mars and Saturn are visible on our September evenings, too, but we must look low in the south-west to catch them. Both are well past their best and less interesting telescopic targets than Jupiter which is now resplendent in the east before dawn.
Having swept 3°, or six Moon-widths, to the south of Saturn on 27 August, Mars has a trio of further notable encounters later in September. Two new spacecraft, NASA’s MAVEN and India’s MOM or Mangalyaan, are on course to enter orbit around Mars on the 21st and 24th respectively while the planet is due to pass 3° north of the enormous red supergiant star Antares in Scorpius on the 27th. The name Antares comes from the Ancient Greek for “rival to Mars” and, while they may indeed be similar in brightness by the month’s end, it will be fascinating to see how their colours compare.
Meanwhile, Mars, or rather the spacecraft in orbit around it, are due for a more challenging encounter when the icy nucleus of comet C/2013 A1 Siding Spring sweeps within some 130,000 km of the planet on 19 October. The operators of NASA’s Mars Reconnaissance Orbiter and Mars Odyssey, and of Europe’s Mars Express, are arranging to shield their craft from the worst of the dust storm that is likely to be accompanying the comet, and similar precautions may be needed for MAVEN and MOM.
In other space news, Europe’s Rosetta craft is now studying five potential landing sites for its Philae lander on the nucleus of Comet Churyumov-Gerasimenko. The landing is not due until November, but it is planned to choose a primary and a backup site this month as Rosetta closes to with 30 km of the nucleus.
By our star map times, the Summer Triangle lies just west of our meridian as it gives way to the stars of autumn led by the topsy-turvy winged horse Pegasus whose nose is marked by the star Enif. Use binoculars to look 4° north-west of Enif for the star cluster M15 which appears as a fuzzy blob less than half as wide as the Moon. In fact, it is one of the finest globular clusters in the sky and contains more than 100,000 stars at a distance in excess of 30,000 light years.
The Sun tracks 11.5° southwards in the sky during September and crosses the equator at 03:29 BST on the 23rd, the time of this year’s autumnal equinox. Sunrise/sunset times for Edinburgh change from 06:17/20:07 on the 1st to 07:13/18:51 on the 30th as the duration of nautical twilight at dawn and dusk falls from 89 to 80 minutes.
The Moon is at first quarter on the 2nd, full on the 9th, at last quarter on the 16th and new on the 24th. As the full moon nearest to the equinox, the one on the 9th is also our Harvest Moon and, since it comes less than a day after the Moon is closest to the Earth, it is yet another supermoon.
Saturn stands about 11° high in the south-west and only 0.3° above the northern tip of the crescent Moon as the evening twilight fades on 31 August, with Mars another 4° below and to their left.
On 27 September, the young Moon returns to lie 6° to the right of Saturn which, by then, is 4° lower in the sky and becoming hard to spot in the twilight. Both planets begin the period at magnitude 0.6, but Mars dims slightly to magnitude 0.8 by the 29th when it stands 5° below the Moon and 3° above Antares. It is also 20° to the left of Saturn and drops below Edinburgh’s horizon at 20:51 BST. Viewed through a telescope, Mars is only 6 arcseconds in diameter at midmonth, while Saturn is 16 arcseconds wide within rings that span 36 arcseconds and have their north face tilted 22° towards us.
After Mars and Saturn set, the sky is devoid of bright planets until Jupiter rises more than five hours later. True, Neptune and Uranus are binocular objects at magnitudes of 7.8 and 5.7 in Aquarius and Pisces respectively, but we need better charts to identify them.
There is no mistaking Jupiter, though. The conspicuous giant planet rises at Edinburgh’s east-north-eastern horizon at 03:29 on the 1st and by 02:07 on the 30th. climbing well clear of the eastern to south-eastern horizon by dawn. As it brightens slightly from magnitude -1.8 to -1.9, it also tracks 6° eastwards, below and away from the Praesepe or Beehive star cluster in Cancer. Look for the waning earthlit Moon 6° below and right of Jupiter before dawn on the 20th. Viewed through a telescope on that morning, the cloud-banded Jovian disk is 33 arcseconds across.
Venus is also a morning object and, although it remains brilliant at magnitude -3.9, it is sinking deeper into the twilight as it approaches conjunction on the Sun’s far side in October. On the 1st, it rises 87 minutes before the Sun and stands 14° below and left of Jupiter as it climbs 12° above our eastern horizon by sunrise. Jupiter soon leaves it behind, though, so by the 30th it rises 32 minutes before the Sun and is only 6° high at sunrise. Viewed telescopically, its almost full disk is only 10 arcseconds across.
The other inner planet, Mercury, moves to lie 26° east of the Sun on the 21st, but hugs the western horizon at sunset and is not observable from our latitudes.
Alan Pickup
This is a slightly-revised version of Alan’s article published in The Scotsman on August 29th 2014, with thanks to the newspaper for permission to republish here.
Scotland’s Sky in August, 2014
Two brightest planets in closest meeting for 14 years
The maps show the sky at 00:00 BST on the 1st, 23:00 on the 16th and 22:00 on 31st. (Click on map to enlarge)
Our usual highlight for August is the return of the prolific and reliable Perseids meteor shower. Unfortunately, meteor-watchers have to contend with moonlight this year and it is just as well that we have other highlights as compensation. Foremost among them is the closest conjunction between Venus and Jupiter, the two brightest planets, since 2000 though they are low down in our morning twilight. Mars and Saturn rendezvous, too, and we have our best supermoon of the year.
Sunrise/sunset times for Edinburgh change from 05:17/21:20 BST on the 1st to 06:15/20:10 on the 31st. The spell of nautical twilight at dusk and dawn shrinks from 121 to 89 minutes. The Moon is at first quarter on the 4th, full on the 10th (see below), at last quarter on the 17th and new on the 25th.
The term supermoon has gained currency in recent years to describe a full moon that occurs when the Moon is near its closest in its monthly orbit. At such times, it can appear 7% wider and 15% brighter than an average full moon. In my view, the enhancement is barely perceptible to the eye and is less impressive than the illusion that always makes the Moon appear larger when it is near the horizon. As the media have discovered, though, supermoons provide a good excuse to feature attractive images of the Moon against a variety of landscapes, and if this encourages more people into astrophotography, so much the better.
This month, the Moon is full at 19:10 BST on the 10th, less than 30 minutes after its closest point (perigee) for the whole of 2014. On that evening, the supermoon is already 4° high in the east-south-east as the Sun sets for Edinburgh, so judge (and photograph?) for yourself.
Venus is brilliant at magnitude -3.9 as a morning star. Rising at Edinburgh’s north-eastern horizon at 03:10 BST on the 1st, it stands 15° high in the east-north-east at sunrise. By the 31st, it rises at 04:42 and is 12° high at sunrise. Between these dates it is caught and passed by Jupiter which emerges from the twilight below and to Venus’ left on about the 7th and stands only 0.2° below Venus before dawn on the 18th.
Jupiter is magnitude -1.8, one seventh as bright as Venus, but still outshines every star so the conjunction is a spectacular one, albeit at an inconvenient time of the night. In fact, the event occurs less than a degree south-west of the Praesepe or Beehive star cluster in Cancer, but this may be hard to spot in the twilight. Before dawn on the 23rd, the two planets lie to the left of the waning and brightly earthlit Moon. By the month’s end, Jupiter rises by 03:25 and stands 13° above-right of Venus.
Mars and Saturn have set by the map times but stand low in the south-west as our evening twilight fades. On the 1st, Mars is magnitude 0.4 and lies 10° to the left of Spica in Virgo. Saturn, only a little dimmer at magnitude 0.5 in Libra, is 13° to Mars’ left, and slightly higher. Look for the Moon to the right of Mars on the 2nd, between Mars and Saturn on the 3rd and to the left of Saturn on the 4th. Mars, meanwhile, tracks eastwards to cross from Virgo to Libra on the 10th and pass 3.5° below Saturn on the 24th. By the 31st, both planets have faded to magnitude 0.6, and Mars lies 5° below-left of Saturn with the Moon between them again and very close to Saturn.
After passing around the Sun’s far side on the 8th, Mercury is too low to be seen in our evening twilight.
Our chart depicts the bright stars Deneb, Vega and Altair high in our southern sky where they form the Summer Triangle. The centre of our Milky Way galaxy lies in Sagittarius on the south-south-western horizon but the Milky Way itself flows northwards through Aquila and Cygnus before tumbling down through Cepheus, Cassiopeia and Perseus in the north-north-east.
Use binoculars to seek out the star Mu Cephei high above familiar “W” of Cassiopeia. Dubbed the Garnet star by Sir William Herschel, Mu is one of the reddest stars we know and pulsates semi-regularly between magnitude 3.4 and 5.1. Some 6,000 light years away, it is so large that it would extend beyond the orbit of Saturn if it replaced the Sun and is sure to explode as a supernova within a few million years.
The Perseids are due to peak in the middle of the night on 12-13th August when we might have been able to glimpse more than 80 meteors per hour under ideal conditions. As it is, bright moonlight will ensure that meteor counts are well down, though we can still expect some impressive bright meteors that leave persistent glowing streaks, called trains, in their wake.
Decent rates may be seen from perhaps 10-15th August and, in fact, the shower is already underway as the Earth takes from 23 July to 20 August to traverse the stream of Perseid meteoroid particles laid down by Comet Swift-Tuttle. It is only appropriate that the resulting meteors are swift, too, as they disintegrate in the upper atmosphere at 59 km per second. Although they move in parallel through space, perspective means that they appear to diverge from a radiant point in Perseus, plotted on our northern star map below Cassiopeia. That point climbs through the north-east overnight to approach the zenith by dawn, but remember that the meteors can appear in any part of the sky and not just towards the radiant.
Alan Pickup
The Astronomical Society of Edinburgh Journal 