From: TerryMoselat signaol.com

Date: 20 June 2010 15:43:23 GMT+01:00

Subject: Superb IAA/UAS event; Solstice; BBC broadcast on the solstice


Hi all,

 

I BALLYNOE EVENT: The joint IAA/UAS/NIEA event at Ballynoe Stone Circle yesterday was a great success. There were many more members from both astronomical & archaeological backgrounds than we expected, and we had a glorious day, with a cool Northerly breeze to stop us overheating in the Sun.

   Liam McQuillan from NIEA gave a comprehensive description of this large, impressive & complex site, and noted that it may be one of the oldest Stone Circles in Ireland, almost as old as Newgrange in his opinion. He described the various stages of development, which may have occurred over a period of hundreds of years. He noted that much more research on the site needs to be done.

   I then gave an account of the possible astronomical alignment with the winter solstice sunset in the very prominent 'notch' in the distant Mourne Mountains, between Slieve Donard and Slieve Commedagh.

  But nothing is clear cut at this site, which has several orientations, not all of them astronomical (as far as we can see). One of the complications is the large number of outlier stones (at least 16 are known, only one of which has an obvious astronomical alignment, lying due East). Much more research needs to be done on the astronomical aspect too.

   We then adjourned to nearby Minerstown beach, which has car access, so we had a 'Barbie on the Beach', in best Ozzie style! I even went in for a swim, but it was cut short when I found I was surrounded by a swarm of jellyfish!

  Thanks to Liam for his input, and to all who attended. Photos should be on the IAA website soon: www.irishastro.org.

 

SUMMER SOLSTICE: The Sun will reach its most Northerly point in its annual journey around the ecliptic on 21 June, at 11h 28m UT (12h 28m BST). This is close enough to local noon to make 21 June almost as long a day as it's possible to have at our latitude.

  Believe it or not, at my house in Glengormley, there will be an interval of 17h 17m 50s between 'sunrise' and sunset' on 21 June. If you think that's longer than theoretically possible, you are almost right!

  The extra time over the purely theoretical length of the day is due to two factors:

(1) 'Sunrise' is defined as the moment when the upper limb (or edge) of the Sun comes above the theoretical horizon (i.e. no hills etc in the way), and 'Sunset' is the time when the upper limb of the Sun disappears below the horizon at sunset. Since the Sun has a diameter of over half a degree, this adds quite a few minutes to the time compared with taking the times for the centre of the Sun.

(2) The Earth's atmosphere refracts or bends the light from the Sun so that we see it even when it is theoretically below the horizon! This amounts to over half a degree as well, at both sunrise and sunset. (When we see the lower edge of the Sun touch the horizon at sunset, the WHOLE Sun is actually really below the horizon!)

  So when you combine these two effects, and also factor in the fact that the Sun approaches the horizon at a very oblique angle at both sunrise and sunset at this time of year at our latitude, the total effect is quite considerable!

  Then when you add in the effects of twilight, in effect we hardly get true 'night' at all at this time of year in the N half of the island!

 

3. BBC Good Morning Ulster will be doing a feature on the solstice tomorrow morning (21st), at about 08.50 - 08.55. They will have contributions from a Druid, and an 'astronomer'; the latter being me, although I have often fancied trying a bit of 'Druidism' myself, if that's the correct word!  The attractions of Mead vs Meade, I suppose you could say....

 

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Clear skies,

 

Terry Moseley