Thursday, 1 February 2007

Heavens above - February 2007, by Dr Andrew McCrea

Last month the astronomical world was buzzing with news of a very bright comet – comet McNaught – discovered by Scotsman Robert McNaught on August 7th 2006 observing from Australia. From our latitudes, the comet hung very low above the western horizon during the opening weeks of the year and by all accounts could be seen with the naked eye and it sported a magnificent tail – but it was very difficult to see so low in the bright twilight sky. I searched in vain when the comet was reportedly at its best, but to no avail – cloud lingered in exactly the wrong spot, even when the rest of the sky was completely without obscuration.

The comet has now moved away to the southern sky where it has been staging a truly magnificent show. The tail and tail streamers are so stupendous they are visible even when the comet is well below the horizon – there are even reports of seeing them from Ireland. This comet came very close indeed to the Sun – inside the orbit of Mercury – and it was most probably a ‘first timer’ – that is it had never visited this part of the solar system before, so it was full of volatiles which produced the fantastic tail as the comet neared the Sun (see,-by-James-OFee.html).

Great comets such as this are rare indeed and comparisons have been drawn to the great comet, Ikeya Seki, of 1965. This was another comet which managed to slip past me but I well remember, as I am sure will many readers, comet Hale-Bopp which graced our skies for many weeks in 1997.

Turning to the starry heavens, February is an excellent month for astronomy with the beautiful star fields of Gemini, Taurus and Orion very evident even from the light polluted skies of Bangor. The sky is alive with interesting objects - even the smallest of telescopes will give fine views of the bright planets - Jupiter and Saturn as well as some of the winter showpieces.

The most dramatic of all is of course the 'Great Nebula in Orion'. Numbered as 42 in Messier's catalogue of deep sky objects, this misty patch of nebulosity hangs below Orion's distinctive belt in the region referred to as the sword. Under very dark, moonless skies it can be clearly seen as a misty patch with the unaided eye, rendered more extensive with binoculars. Even small telescopes will reveal the central star group - theta Orionis or the 'Trapezium' which powers the nebula, lighting it up ghostly grey. This cluster of four stars at the heart of the nebula illuminate the surrounding gas in what is one of the closest regions of star birth. The youngest of these Trapezium stars popped into existence just a few million years ago to begin their life as one of the inhabitants of our own star city - the Milky Way.

Evidence for the grip of winter's darkness easing comes with each new evening, as February's days stretch ever longer. Venus continues to startle in the west just before sunset, part of a group of planets huddling in that part of the sky. Mercury is below and to the left of Venus in the early part of the month but you will need a crystal clear, cloud free horizon to spot it. An interesting and rare event happens on the 18th February when the Moon occults the seventh planet Uranus. Uranus is around 6th magnitude which means that you will need binoculars to observe it as it disappears behind the lunar limb at around 17.50UT (5.50pm). It is a good month for occultations because the Moon will again occult the Pleiades (or Seven Sisters) on the 23-24th February. This event is less rare having just taken place at the end of January 2007, but it is fascinating to watch with a pair of 10x50 binoculars, as the Moon ploughs its way through the Seven Sisters open star cluster.

By mid-evening the heralds of spring, Cancer and Leo move into the south-eastern sky. Cancer is fairly indistinct as a group, although in dark skies the little 'Praesepe' star cluster might just be glimpsed as a fuzzy blob. The Praesepe is popularly referred to as 'the Beehive Cluster' and in binoculars it does resemble a swarm of 75 or more faint stars buzzing across an area three times larger than a full Moon. Leo is unmistakable due to the famous 'sickle' arrangement of its principal stars, marking out the lion's fine mane and head and in February it hosts one of the evening skies’ most superb delights – magnificent Saturn. Saturn is currently at its best and is visible all night long shining as a yellowish star just outside the sickle of Leo.

The ancients were well aware that Saturn's brightness varied markedly but they did not know the reason for this. It was not until astronomers, such as Galileo, turned their early telescopes to the heavens that they realised the true reason - the changing aspect of the magnificent ring system. This system is well on view at the moment, at wide open, giving Saturn a full magnitude of brightness over an occasion when the rings are at edge-on as viewed from Earth.

The Irish Astronomical Association (IAA) moves into February with a lecture on the 7th when two of our emerging local stars from the Queen’s University astrophysics department, Heather Thompson and Peter Farrell give separate talks on ‘Stellar Evolution’ and ‘Atomic Databases’ respectively. On the 21st February, the new Dean of the Astronomy and Astrophysics department at QUB, Professor Tom Millar, will give us a talk on his work entitled ‘Molecules in Space’.

Any (and very welcome!!) visitors to these meetings should note that they are held in Stranmillis College where meetings begin at 7.30 sharp in Lecture Room 5 of the main building. The venue has the significant advantage of ample free parking and entrance is through the Stranmillis Road roundabout main gate - I look forward to seeing you there.

Heavens Above is compiled the Green Spectator by Andrew McCrea, immediate past-President of the Irish Astronomical Association (IAA). I would be delighted to answer readers’ questions on matters astronomical, telescopes, binoculars and the IAA either by post to the Spectator office or by telephone on 028 9127 3584 or via email on or through my website

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