InSight probe to land on bright evening planet Mars
The Summer Triangle, still high in the south at nightfall, shifts to the west by our map times as our glorious winter constellations climb in the east. Taurus with the Pleiades and its leading star Aldebaran (close to the Moon on the 23rd) stands well clear of the horizon while Orion is rising below and dominates our southern sky after midnight.
In the month that should see NASA’s InSight lander touch down on its surface, the planet Mars continues as a prominent object in the south at nightfall. Venus springs into view as a spectacular morning star but we must wait to see whether the Leonids meteor shower, which has produced some storm-force displays in the past, gives us any more than the expected few meteors this year.
InSight is due to land on the 26th on a broad plain called Elysium Planitia that straddles Mars’ equator. There it will place an ultra-sensitive seismometer directly onto the surface and cover it with a dome-like shell to shield it from the noise caused by wind and heat changes. This should be able of detect marsquakes and meteor impacts that occur all around Mars. Other InSight experiments will hammer a spike up to five metres into the ground to measure Mars’ heat flow, and further investigate the planet’s interior structure by using radio signals to track tiny wobbles in its rotation.
Until recently, Mars has remained low down as it performed a loop against the stars in the south-western corner of Capricornus. That loop, resulting entirely from our changing vantage point as the Earth overtook Mars and came within 58 million km on 31 July, took Mars more than 26° south of the sky’s equator and 3° further south than the Sun stands at our winter solstice.
Now, though, Mars is climbing east-north-eastwards on a track that will take it further north than the Sun ever gets by the time it disappears into Scotland’s night-long twilight next summer. One by-product of this motion is that Mars’ setting time is remarkably constant over the coming months, being (for Edinburgh) within 13 minutes of 23:42 GMT from now until next May.
This month sees Mars leave Capricornus for Aquarius and shrink as seen through a telescope from 12 to 9 arcseconds as it recedes from 118 million to 151 million km. Its path, indicated on our southern chart, carries it 0.5° (one Moon’s breadth) north of the multiple star Deneb Algedi, the goat’s tail, on the 5th. It almost halves in brightness, from magnitude -0.6 to 0.0, but its peak altitude above Edinburgh’s southern horizon early in the night improves from 16° to 25°, though by our map times it is sinking lower towards the south-west.
Mars is not our sole evening planet since Saturn shines at magnitude 0.6 low down in the south-west at nightfall. It is only a degree below-right of the young Moon on the 11th and sets more than 90 minutes before our map times. The two most distant planets, Neptune and Uranus, are also evening objects and may be glimpsed through binoculars at magnitudes 7.9 and 5.7 in Aquarius and Aries respectively.
Edinburgh’s sunrise/sunset times vary from 07:19/16:32 on the 1st to 08:17/15:45 on the 30th. The Moon is new on the 7th, at first quarter and below-right of Mars on the 15th, full on the 23rd and at last quarter on the 30th.
Jupiter is hidden in the solar glare as it approaches conjunction on the Sun’s far side on the 26th. Mercury stands furthest east of the Sun (23°) on the 6th but is also invisible from our northern latitudes.
Venus, though, emerges rapidly from the Sun’s near side into our morning twilight where it stands to the left of the star Spica in Virgo. Shining brilliantly at magnitude -4.1, the planet rises in the east-south-east only 29 minutes before the Sun on the 1st. By the 6th, though, it rises 80 minutes before sunrise and stands 8° below and right of the impressively earthlit waning Moon. Venus itself is 58 arcseconds wide and 4% illuminated on that morning, its slender crescent being visible through binoculars. By the 30th, Venus rises four hours before the Sun, climbs to stand 23° high in the south-south-east at sunrise and appears as a 41 arcseconds and 25% sunlit crescent.
It is just as well that my previous note led on the usually neglected Draconids meteor shower because observers, at least those under clear skies, were thrilled to see it provide perhaps the best meteor show of 2018. For just a few hours around midnight on 8-9th October, the sky became alive with slow meteors at rates of up to 100 meteors per hour or more.
Leonid meteors arrive this month between the 15th and 20th, with the shower expected to hit its usually-brief peak at around 01:00 on the 18th. Although they flash in all parts of the sky, they diverge from a radiant point in the so-called Sickle of Leo which rises in the north-east before midnight and climbs high into the south before dawn. No Leonids appear before the radiant rises, but even with the radiant high in a dark sky we may see fewer than 20 per hour – all of them very swift and many of the brighter ones leaving glowing trains in their wake.
Leonid meteoroids come from Comet Tempel-Tuttle which orbits the Sun every 33 years and was last in our vicinity in 1998. There has not been a Leonids meteor storm since 2002 and we may be a decade or more away from the next one, or are we?
Diary for 2018 November
2nd 05h Moon 2.1° N of Regulus
6th 16h Mercury furthest E of Sun (23°)
7th 16h New moon
11th 16h Moon 1.5° N of Saturn
15th 15h First quarter
16th 04h Moon 1.0° S of Mars
18th 01h Peak of Leonids meteor shower
23rd 06h Full moon
23rd 22h Moon 1.7° N of Aldebaran
26th 07h Jupiter in conjunction with Sun
26th 20h InSight probe to land on Mars
27th 09h Mercury in inferior conjunction on Sun’s near side
27th 21h Moon 0.4° S of Praesepe
30th 00h Last quarter
This is a slightly revised version, with added diary, of Alan’s article published in The Scotsman on October 31st 2018, with thanks to the newspaper for permission to republish here.
Draconid meteors glide away from the Dragon’s head
Mars dominates our southern evening sky but most of the other bright planets are poorly placed this month. Even so, our October nights are full of interest, from the Summer Triangle in the evening to the star-fest around Orion before dawn.
Although Mars dims from magnitude -1.3 to -0.6, its reddish light remains prominent as it moves from low in the south-south-east at nightfall to the south-south-west at our map times and onwards to set in the south-west a little before 01:00 BST (midnight GMT). As its distance grows from 89 million to 118 million km, and its diameter shrinks from 16 to 12 arcseconds, the planet speeds through Capricornus to climb 6° northwards and that much higher in our sky. Catch it to the left of the Moon on the 17th and below-right of the Moon on the 18th.
The Sun tracks 11° southwards as Edinburgh’s sunrise/sunset times change from 07:15/18:48 BST (06:15/17:48 GMT) on the 1st to 07:17/16:35 GMT on the 31st. The Moon is at last quarter on the 2nd, new on the 9th, at first quarter on the 16th, full (the Hunter’s Moon) on the 24th and back at last quarter on the 31st.
Our charts show the Plough in the north as it moves below Polaris, the Pole Star. Mizar, in the Plough’s handle, forms a famous double star with the fainter Alcor – the pair being separated by about one third the diameter of the Moon. Once held as a (not very rigorous) test of eyesight, they were dubbed “The Horse and Rider”.
Both lie 83 light years (ly) from us although we can’t be certain that they are tied together by gravity. In any case, we are not talking about just two stars, for Alcor has a faint companion and most telescopes show Mizar to be a binary star – the first to be discovered telescopically in the 17th century. Spectroscopes reveal that each of Mizar’s components is itself binary, so Mizar and Alcor, if they are truly associated, together form a sextuplet star system.
Mizar is the same brightness, magnitude 2.2, as Eltanin which lies 14° to the right of Vega and very high in the west at nightfall, falling into the north-west overnight. It is the brightest star in Draco and a member of a quadrilateral that marks the head of the Dragon whose body and tail twist to end between the Plough and Polaris. It lies 154 ly away but is approaching the Sun and will pass within 28 ly in another 1.5 million years to become the brightest star in Earth’s night sky.
Meteors from the Draconids shower diverge from a radiant point that lies close to Draco’s head (see our north map) between the 7th and 10th. Don’t expect a major display – perhaps no more than 10 meteors per hour, though all of them are very slow as they glide away from the radiant. The shower’s peak is due in a moonless sky around midnight on the 8th-9th and is worth checking because some years surprise us with strong displays and the shower’s parent comet, Comet Giacobini-Zinner, was visible through binoculars when it swept within 59 million km last month.
A better-known comet, Halley, is responsible for the meteors of the Orionids shower which lasts from the 16th to the 30th and has a broad but not very intense peak of fast meteors between the 21st and 24th. The radiant point, between Orion and Gemini, rises in the east-north-east soon after our map times and passes high in the south before dawn. Sadly, the peak coincides with the full moon, so don’t expect much of a show.
From high in the south at nightfall, the Summer Triangle (Vega, Deneb and Altair) tumbles into our western sky by the map times. By then, the less impressive and rather empty Square of Pegasus is in the south and Taurus and the Pleiades star cluster are climbing in the east. Orion rises below Taurus over the next two hours and crosses the meridian as the night ends.
Neptune and Uranus, now well placed in the evening, may be located through binoculars using better charts than I can provide here. A web search, for example for “Neptune finder chart”, should help. Neptune shines at magnitude 7.8 and lies in Aquarius at a distance of 4,342 million km on the 1st. Uranus is 2,824 million km away in Aries, near its border with Pisces, when it stands opposite the Sun in the sky (opposition) on the 24th. Although the full Moon stands close to it on that day, its magnitude of 5.7 makes it just visible to the unaided eye under a good dark and moonless sky.
October should see the launch of the European Space Agency’s BepiColombo mission to Mercury, but the planet itself is too low in our evening twilight to be seen. Venus sweeps around the Sun’s near side at inferior conjunction on the 26th and remains hidden in the Sun’s glare.
Jupiter is bright (magnitude -1.8) but less than 8° high in the south-west at sunset as the month begins. One of our last chances of spotting it in our bright evening twilight comes on the 11th when it lies 4° below-left of the young earthlit Moon.
Saturn, magnitude 0.5 and edging eastwards in Sagittarius, stands less than 10° high above Edinburgh’s south-south-western horizon as the sky darkens and sets in the south-west some 45 minutes before our map times. Look for it to the left of the Moon on the 14th.
Diary for 2018 October
Times are BST until the 28th
2nd 11h Last Quarter
9th 00h Peak of Draconids meteor shower
9th 05h New moon
11th 22h Moon 4° N of Jupiter
15th 04h Moon 1.8° N of Saturn
16th 19h First quarter
18th 14h Moon 1.9° N of Mars
21st – 24th Peak of Orionids meteor shower
24th 02h Uranus at opposition at distance of 2,824m km
24th 18h Full moon
26th 15h Venus in inferior conjunction on Sun’s near side
28th 02h BST = 01h GMT End of British Summer Time
31st 17h GMT Last quarter