Monthly Archives: November 2013
Comet ISON – probably not the Comet Of The Century
Comet ISON swept through its perihelion within 1,165,000 km of the Sun’s surface at about 18:38 GMT on 28 November, but did it even make it that far in one piece? There have been signs that its brightening was halting again and perhaps that its icy nucleus might be breaking up even before it encountered the extreme heat and tidal forces of perihelion. In my view, sensationalist claims that ISON would be the Comet Of The Century, visible in broad daylight and an unmistakable spectacle in our night sky, are about to be proved wrong. While I am duty-bound to speculate on its appearance as it emerges from the Sun’s glare, no-one knows exactly what if anything we will see.
After a disappointing few months, a sudden surge in ISON’s activity and brightness began on 13 November. I glimpsed it through binoculars three days later and it continued to brighten as it dived lower in our south-eastern pre-dawn sky, first passing the star Spica in Virgo and then Mercury, by which time it was near the fourth magnitude and disappearing into the twilight. Since then we have relied mainly on observations from spacecraft. Claims that it may have stopped brightening as the production of gas and dust from its nucleus fell dramatically, and even that the nucleus was already disintegrating, painted a pessimistic picture. However, the mood changed when ISON appeared to be remarkably healthy and intact in the final hours before perihelion.
Even if the nucleus does shatter, it may not spell the end of ISON as an interesting object. Its gas and dust has to go somewhere, and that may lead to the comet’s tail remaining visible, and possibly brightly so. Don’t miss any opportunity to look for it stretching almost vertically above our east-south-eastern horizon before dawn over the coming few days, perhaps beginning as early as 1 December. It may also be glimpsed reaching up and to the right from our western horizon after sunset.
The comet’s head and nucleus, assuming it survives, tracks almost due northwards in the sky, climbing steeply in the east before dawn and heading to a position halfway between the bright stars Vega and Arcturus on the 21st. Our “Looking North” chart picks up ISON at this point and depicts its progress onwards and upwards into Draco by the year’s end. It is closest to the Earth, 64 million km, on the 26th but will it still be visible at Christmas?
Even if ISON fails miserably, our December nights are a treat to behold. They begin with Venus blazing low down between the south and south-west as it sinks from about 10° high at sunset. The planet is at its brilliant best, magnitude -4.7, as it stands 7° below-left of the young Moon on the 5th and 12° below-right of the Moon on the 6th. By Hogmanay it sets 105 minutes after the Sun as seen from Edinburgh and is 59 arcseconds in diameter, near enough (42 million km) and large enough for its slender 4% illuminated crescent to be recognised easily through binoculars, and perhaps by the keenest naked eyes.
Our second prominent planet, Jupiter, rises at Edinburgh’s north-eastern horizon at 18:21 GMT on the 1st and only 16 minutes after sunset by the 31st. Conspicuous in the east at our map times, it passes high in the south six hours later and is sinking in the west before dawn. Jupiter lies some 9° below and right of Castor and Pollux in Gemini and is slowly retrograding (tracking westwards) to pass only 0.25° north of the third magnitude star Wasat or Delta Geminorum on the 10th. Telescopically, the Jovian globe swells from 45 to 47 arcseconds as the planet approaches opposition in early January.
Orion, stands to the south of east at our map times, and is impressive as it climbs to cross the meridian during the midnight hours. A line upwards along Orion’s Belt extends to Aldebaran and the Pleiades in Taurus. Look for the Moon close to Aldebaran on the night of the 15th and near Jupiter on the 18th.
Mars rises in the east at 01:00 on the 1st and 30 minutes earlier on the 31st. Tracking eastwards against the stars of Virgo, it improves from magnitude 1.2 to 0.8 this month as its disk swells from 5.6 to 6.8 arcseconds in diameter – still too small for surface detail to be seen easily through a telescope. Look for Mars above the Moon on Boxing Day morning. Our second morning planet, Saturn, lies in Libra and rises in the east-south-east at about 06:00 at present. By year’s end, though, it rises at 04:20 and shines at magnitude 0.6, making it the brightest object low in the south-east to south before dawn. Catch it above-right of the waning Moon on the 29th.
Only a few days before the end of its best apparition of 2013, Mercury shines brightly at magnitude -0.7 and stands almost 5° high in the south-east forty minutes before sunrise tomorrow.
The annual Geminids meteor shower is active from the 8th to the 17th and is expected to peak in the predawn hours on the 14th. The bright moonlight for most of the night may still allow several slow bright Geminids meteors to be seen as they stream away from a radiant point close to Castor, roughly where the M of GEMINI lies on our north star map.
The Sun reaches its most southerly point in our sky at 17:11 GMT on the 31st, marking the winter solstice. Sunrise/sunset times for Edinburgh vary from 08:19/15:44 on the 1st to 08:42/15:40 on the 21st and 08:44/15:48 on the 31st. Nautical twilight persists for about 95 minutes at dawn and dusk. The Moon is new on the 3rd, at first quarter on the 9th, full on the 17th and last quarter on the 25th.
This is a slightly-revised version of Alan’s article published in The Scotsman on November 29th 2013, with thanks to the newspaper for permission to republish here.
Peter and I concluded this must be our fourth evening at the Royal Botanic Garden John Hope Gateway Centre. But this time it was not an astronomy event per se, but a coming together of art and science, and a preview of the Sea Change exhibition on 2013-11-07.
As on previous occasions, we would set up on the terrace outside the restaurant. Graham Rule had taken large binoculars and tripod on the bus, while Peter Mulholland and I brought very similar small refractors on identical mounts. And John Wood had just got hold of the ASE’s 250 mm Schmidt-Cassegrain that he still needed to get used to.
The day had been clear and sunny, but after dark it turned cloudy and rainy. While Graham was already checking the Balmoral Hotel clock through the binoculars, we reluctantly set up the scopes – under the roof where they would stay the whole three hours due to regular spells of rain. Some time into the event we could identify Auriga, Cygnus and Vega. Peter trained his goto computer and later kept tracking the clouds in front of the Pleiades. We did see the star cluster in binoculars and toward the end also as star map on an Android screen.
Not many people therefore ventured out into the dark and cold; mostly we could only show some leaves on trees across the pond through two telescopes. Some interesting conversations were had, but the weather made this an almost complete washout. Having fulfilled our duty we packed up at 22:00. Last was the SCT with tripod and tube already detached. When Jupiter not only split the cloud but also found a gap between the trees. While John and Graham still tightened the bolts that keep the scope on the tripod I swung the tube to acquire the giant planet in the finder and in three minutes we were looking at the Galilean moons and Jovian cloud bands. A few of the guests and staff were also still around to get a view during gaps in the cloud.
It is of course common for planned observing meetings to be clouded out, whether that be ASE members meeting in a park or an outreach event like this. At least there is good company and the effort is appreciated by the hosts and budding observers.
Comet ISON sweeps close to the Sun on the 28th
A brace of comets and the year’s best apparition by Mercury might be enough to tempt us outside during the chill predawn hours this month.
Let us start with the evening, though, where Venus remains poorly placed for our northern latitudes. Although it blazes brilliantly at magnitude -4.4, it stands less than 6° above Edinburgh’s south-south-western horizon at sunset on the 1st and sinks to set in the south-west only 91 minutes later. It is also at its greatest angle of 47° to the east of the Sun. On the 6th, it is 8° below and left of the young Moon and at a more southerly declination (celestial latitude) than at any time since 1930. Turning northwards again, it is 9° high in the south at sunset on the 30th, when it remains visible for 157 minutes and is brighter still at magnitude -4.6.
Our charts show the stars of the Summer Triangle, Vega, Altair and Deneb, tumbling into the west as the Square of Pegasus crosses the meridian. To the south of Pegasus are Pisces and Aquarius where the two most distant planets, Uranus and Neptune, shine dimly as binocular objects of magnitude 5.7 and 7.9 respectively.
The winter constellations are beginning to climb in the east, with their centrepiece, Orion, just rising below Taurus and the Pleiades. Jupiter, magnitude -2.4 and brighter than any star, rises 35 minutes before our map times and climbs to pass 56° high in the S before dawn. By the month’s end it has improved to magnitude -2.6 but has hardly shifted in position in Gemini, below and to the right of Castor and Pollux. The Moon is nearby on the night of the 21st/22nd when Jupiter’s cloud-banded disk appears 44 arcseconds wide if viewed telescopically.
Mars rises in the east at 01:17 on the 2nd and shines at magnitude 1.5 well up in the south-east, 10° below and left of Regulus in Leo, before dawn. Speeding eastwards into Virgo, it brightens to magnitude 1.3 by the 30th when it rises only 16 minutes later. Catch it below the Moon on the 27th.
Comet ISON is on track to graze within 1,100,000 km of the Sun’s surface when it reaches perihelion at 18:35 GMT on the 28th. However, whether it will survive the encounter is anyone’s guess. Sadly, hopes that it would blossom into the Comet of the Century have been dimming by the day as its performance has fallen further and further below what most comet experts were predicting after its discovery more than a year ago. Even this summer, the expectations were that it would be an easy binocular object by now and that it would surpass Venus at perihelion. As it is, it has still not been sighted through binoculars and it is even being suggested that it may never be visible to the unaided eye.
Claims earlier in October that the comet was already on the brink of disintegrating were soon countered by Hubble telescope observations showing it still to be intact. Images show a greenish head or coma surrounding ISON’s nucleus, with a tail pointing away from the Sun and narrowing along its length. It is brightening, but only by as much as can be explained by the intensifying sunlight and there are few signs that it is actually growing larger and more active.
Plunging sunwards, Comet ISON crosses the Earth’s orbital distance today and may be a telescopic object near magnitude 8.5 some 8° below-left of Mars in the south-east before dawn on the 2nd. It may be as much as a magnitude brighter and Moon’s breadth right of the star Beta Virginis before dawn on the 7th and perhaps near the sixth magnitude, and visible through binoculars, when it lies 0.7° below-left of Virgo’s brightest star, Spica, on the 18th.
Mercury, meantime, is emerging from the Sun’s glare to become conspicuous low down in the morning twilight in the south-east. Between the 10th and 29th, it rises more than 100 minutes before the Sun, climbs to stand between 8° and 11° high 30 minutes before sunrise, and brightens from magnitude 0.6 to -0.7. It is joined before dawn by Saturn (magnitude 0.6) which stands just 0.5° above Mercury on the 26th.
We can use Mercury to locate ISON later in the period. The comet may yet become a naked-eye object with its tail slanting back towards Spica as it sinks from 7° to the right of Mercury on the 21st to lie 5° below-right of Mercury three days later. That may be our final view of it until after perihelion. Comet Encke, a much more predictable and reliable binocular fuzz-ball at about the fifth magnitude, sinks from 6° above-right of Mercury on the 13th to pass 1.5° right of Mercury on the 18th before we lose it in the twilight.
With Comet ISON no longer expected to excel at perihelion, and because of the serious danger to our eyesight, do not attempt to observe it close to the Sun. If its tail does unfurl spectacularly, though, it may climb steeply from our south-eastern horizon before dawn on the 29th and 30th.
As the Sun tracks southwards, sunrise/sunset times for Edinburgh change from 07:20/16:32 on the 1st to 08:18/15:45 on the 30th. New moon on the 3rd is followed by first quarter on the 10th, full on the 17th and last quarter on the 25th. The new moon brings a solar eclipse on the 3rd which begins as an annular or ring eclipse over the western Atlantic but soon evolves to a total eclipse whose narrow path tracks eastwards to cross equatorial Africa from Gabon to Somalia. Surrounding areas, but not Britain, see a partial eclipse.