Monthly Meeting 5th November 2007 - The Sun, an exciting Introductionby Dr Miruna Popescu
The third meeting of the season was held, as usual, in the lecture theatre of Ballyclare High School and was attended by over forty EAAS members and guests. As everyone entered the theatre they were each given a pair of 3D spectacles, giving everyone an indication that this was not going to be a standard lecture.
The meeting was opened and the Chairman introduced a special edition to the meeting, Dr David Asher of Armagh Observatory. Dr Asher is a world leading authority on ‘Near Earth Objects’ and was asked, at short notice, would he be able to give us a short talk on what has been the most exciting astronomical event for some time, the outburst of Comet 17P Holmes.
Dr Asher began by noting that while this is a very unusual event, such events have been observed before on other comets, and in fact, the same happened to this comet in 1892. The comet is, at present, approx 100,000 times brighter than normal, although it will get fainter fairly quickly in the coming weeks.
What we are seeing is material expanding away from the comet, but what we are not seeing is the nucleus itself, which is far too small to be seen at the comet's current distance, which is well beyond the orbit of Mars. Rather, the object which most people think is the nucleus, i.e. the tiny central dot, is merely concentrated material being thrown off the nucleus. The comet is a mixture of ice and dust, and as the ice expands and is thrown away from the nucleus, it drags the dust with it. This forms the coma, and the increase in brightness of the comet is caused by the very large area of this ice/dust mixture that is reflecting sunlight.
Dr Asher then considered possible reasons for why this outburst has occurred. Although many have speculated that it may have occurred as a result of a collision with an asteroid, it is more likely that the outburst is associated with some internal mechanism within the comet itself. The fact that the 1892 outburst happened in a different part of its orbit supports this view. He noted that up to 1% of the total mass of the comet has been lost in this outburst which will add to the comet's relatively short life of about 10,000 years..
After a few questions it was time for the main lecture of the evening, ‘The Sun – an exciting introduction’ by Dr Miruna Popescu of Armagh Observatory. Dr Popescu had not been present during Dr Asher’s short talk and the reason for this soon became clear. As she was introduced she entered the theatre attired elegantly in Victorian dress.
Dr Popescu opened her talk, to the surprise of her audience, by thanking the Royal Astronomical Society for allowing her to be the first woman to address a meeting in this year of 1892. She also thanked Dr Dreyer, director of Armagh Observatory, for allowing her to use the Observatory’s magnificent 10” Grubb refractor to observe the sun during the day, while he slept after a busy nights observing and recording for his ‘New General Catalogue’. Dr Popescu then mentioned some of the more bizarre thoughts about the sun from 1892 and before, as how some had believed that sunspots were holes inhabited by aliens and that comets orbited the sun providing it with fuel so it could keep burning.
Dr Popescu then told how one morning she had woken up, after a good nights sleep, to find herself in 2007. She then began by telling how much more is known about the sun in 2007 compared to 1892, she gave a short explanation of the structure of the sun and it composition, from its elemental breakdown to the various layers within the sun from the Core to the Corona. Check out the EAAS Solar feature page for info on our nearest star http://www.eaas.co.uk/news/solar_features.html
Dr Popescu then compared some images taken by ground based and space based solar observatories to drawings from the 18th and 19th century. The similarities were amazing, the details recorded in the drawings matching remarkably the details shown in modern day photos - of note were the drawings of sunspots which were especially detailed. When describing sunspots, Dr Popescu used movies from the SOHO (Solar and Heliospheric Observatory) to show the development and path of these spots across the sun, though she did lament that 2007 was solar minimum and the sun had been devoid of interesting sunspots for some time.
Dr Popescu also used images and movies from the SOHO mission and the STEREO mission to illustrate other aspects and phenomena of the sun such as Prominences, Filaments, Coronal Holes, Coronal Mass Ejections and Flares. The images and movies from STEREO were very interesting as many were in 3D, (hence the glasses on entry).
The lecture was wrapped up with some advice on how to observe the sun safely by either projecting an image of it on a card or using a ‘white light’ filter to observe sunspots, or using a Hydrogen Alpha filter or scope to view prominences and surface detail. It was stressed that one must never use the ‘naked eye’ to look at the sun as this will do irreparable damage to one’s eyesight. Read are EAAS article on, "How to observe the Sun safely".
Dr Popescu then opened the floor for some questions, which she answered with her usual aplomb. This lecture was one of the most unusual and interesting ever given to the EAAS and Dr Popescu’s novel approach and delivery was very much appreciated by all present. After the lecture some of those presence took the opportunity to observe Comet 17P Holmes through binoculars, while others took the opportunity to talk to both Dr Popescu and Dr Asher.
Dr Miruna Popescu is a graduate of Bucharest University in Romania; she studied at Turin Astronomical Observatory, and subsequently worked as a research assistant at the Astronomical Institute of the Romanian Academy in Bucharest and at the National Solar Observatory at Kitt's Peak, Arizona. She completed her PhD in Solar Physics at Queen's University Belfast with her thesis "Searching for The Origins of The Fast Solar Wind". She now holds a post-doctoral research fellowship at Armagh Observatory, where she is also heavily involved in outreach work for the Observatory.
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