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From: TerryMoselaol.com
Date: Sat, 18 Mar 2006 20:26:54 EST
Subject: Equinox, TV, 2 lectures
Hi all,
1. The Spring Equinox will be 20 March at 18h 26m, when the Sun will cross
the equator going Northwards. From then on, we are told, days will be longer
than nights, in the N Hemisphere.
But even on 19 March the Sun will be above our horizon for more than 12
hours! Tables of sunrise and sunset usually give sunrise as the moment when
the top of the Sun's disc first appears above the horizon, and sunset as when
the top of the disc disappears below the horizon. But even if one takes the
rising and setting of the centre of the Sun's disc, it still appears above
our horizon for over 12h 2 minutes on 19 March! How come? Because of the
refraction effects of the Earth's atmosphere. When we see the centre of the Sun on
the horizon, it has actually already 'set', but the atmosphere bends its
light just enough for us to still see it.
In fact, under most conditions, when the bottom of the Sun's disc appears
to touch the horizon, the whole of the Sun has actually set!
It's the refraction effect which often makes the Sun's disc appear
noticeably flattened when it's near the horizon.
So the 'observed' Spring equinox actually occurs a few days before the
theoretical date. And of course the observed Autumn Equinox occurs a few days
late for the same reason.
TV:
2. Sun, 19 March, 9.40am, RTE1 TV: Leo Enright's Space Odyssey
3. Sun 19 March, 5.35pm, BBC1 TV: John Daly visits Armagh Observatory.
4. Sun 19 March, 8.00pm BBC4 TV: TIME - Michio Kaku discusses cosmic
possibilities (4/4).
5. Mon, 20 Mar, 7.00pm, BBC4 TV: The Sky at Night - Patrick Moore looks
back over five decades.
6. Mon, 20 Mar, 11.05pm, BBC1 TV: John Daly visits Armagh Observatory
(repeat).
7. Tue, 21 Mar, 9.00pm, BBC4 TV: TIME - Michio Kaku discusses cosmic
possibilities (4/4).
LECTURES:
8. The Irish Astronomical Society lecture: "Worlds that Never Were" (Curious
Episodes in the History of Astronomy) to be given by the indomitable Mr John
Flannery, March 20th in Ely House, Ely Place, Dublin, at 8 p.m. Details on
www.irishastrosoc.org.
9. Talking of the Sun, don't forget:
IAA Public Lecture, by Dr Miruna Popescu: "The Solar Wind: from Explosions
on the Sun to Us", Wed 22 March, 7.30 p.m., Stranmillis College, Belfast, as
already notified.
Clear skies,
Terry Moseley
aol.com Date: Sat, 18 Mar 2006 20:26:54 EST Subject: Equinox, TV, 2 lectures Hi all, 1. The Spring Equinox will be 20 March at 18h 26m, when the Sun will cross the equator going Northwards. From then on, we are told, days will be longer than nights, in the N Hemisphere. But even on 19 March the Sun will be above our horizon for more than 12 hours! Tables of sunrise and sunset usually give sunrise as the moment when the top of the Sun's disc first appears above the horizon, and sunset as when the top of the disc disappears below the horizon. But even if one takes the rising and setting of the centre of the Sun's disc, it still appears above our horizon for over 12h 2 minutes on 19 March! How come? Because of the refraction effects of the Earth's atmosphere. When we see the centre of the Sun on the horizon, it has actually already 'set', but the atmosphere bends its light just enough for us to still see it. In fact, under most conditions, when the bottom of the Sun's disc appears to touch the horizon, the whole of the Sun has actually set! It's the refraction effect which often makes the Sun's disc appear noticeably flattened when it's near the horizon. So the 'observed' Spring equinox actually occurs a few days before the theoretical date. And of course the observed Autumn Equinox occurs a few days late for the same reason. TV: 2. Sun, 19 March, 9.40am, RTE1 TV: Leo Enright's Space Odyssey 3. Sun 19 March, 5.35pm, BBC1 TV: John Daly visits Armagh Observatory. 4. Sun 19 March, 8.00pm BBC4 TV: TIME - Michio Kaku discusses cosmic possibilities (4/4). 5. Mon, 20 Mar, 7.00pm, BBC4 TV: The Sky at Night - Patrick Moore looks back over five decades. 6. Mon, 20 Mar, 11.05pm, BBC1 TV: John Daly visits Armagh Observatory (repeat). 7. Tue, 21 Mar, 9.00pm, BBC4 TV: TIME - Michio Kaku discusses cosmic possibilities (4/4). LECTURES: 8. The Irish Astronomical Society lecture: "Worlds that Never Were" (Curious Episodes in the History of Astronomy) to be given by the indomitable Mr John Flannery, March 20th in Ely House, Ely Place, Dublin, at 8 p.m. Details on www.irishastrosoc.org. 9. Talking of the Sun, don't forget: IAA Public Lecture, by Dr Miruna Popescu: "The Solar Wind: from Explosions on the Sun to Us", Wed 22 March, 7.30 p.m., Stranmillis College, Belfast, as already notified. Clear skies, Terry Moseley
