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From: TerryMosel@aol.com
Date: 12 June 2006 19:38:53 BDT
Subject: IAA BBQ, NLCs, ISS all night, Blackrock Castle Obs

Hi all,

1. Irish Astronomical Association Midsummer BBQ: Don't forget the social
and gourmet (or should that be gluttony?) event of the year: the IAA's
annual midsummer barbecue, held in the lovely and historic grounds of
Armagh Observatory, courtesy of the Director, Professor Mark Bailey.   
We start at about 3 p.m., with some activities such as a tour of the
observatory, and we hope to have an astronomical treasure hunt as well,
with some worthwhile prizes. You can also see the amazing, unique,
'Human Orrery', and maybe the newly restored historic telescopes. And
although Armagh Planetarium won't be open to the public for another
month or two, you can admire the newly refurbished building from the
outside - it's a transformation.   We light the fire at about 5.0, with
cooking commencing about 5.30. The format is the same as usual: free
admission to members and guests (and if anyone else specially wants to
come, I don't think you'll be turned away!); you bring all your own
consumables, plates, cups, glasses, cutlery etc, and a folding chair or
rug to sit on. If you have your own BBQ tools (tongs, fork etc), bring
them too. We provide the cooking facility.    We have a large gazebo
just in case of rain, but we have been lucky with the weather every year
so far, and the long-range forecast is good. If it's clear, we'll have
some solar observing.    It's on SATURDAY 24 JUNE - don't miss it.

2. NLCs: The short summer nights bring few benefits for the amateur
astronomer, apart from the warmer temperatures of course.    But one is
that this is the best time of year to see Noctilucent Clouds, or NLCs
for short. 'Noctilucent' means 'night-shining', and these beautiful
high-altitude clouds do indeed 'shine at night', often being at their
best around local midnight, which in Ireland, allowing for Summer Time,
is usually around 01.20 - 01.40 on your watch. But they can be seen any
time from about 00.30 to 02.30, if the sky is dark enough, although very
near local midnight the Sun may be just too far below the horizon to
illuminate them all fully, especially for those living further South.   
Paul Evans(EAAS) from Larne got some lovely photos of them recently, and
one was featured on Spaceweather.com.    They are thought to be caused
by ice crystals condensing on meteoric dust, i.e. the very fine dust
left behind as meteors burn up on entry high up in the atmosphere, or
possibly even just extremely fine particles 'wafting in' from space.    
The reason that they can be seen is that they are so high up (about
80-85 km) that the Sun still illuminates them even when it is too far
below the local horizon to illuminate ordinary tropospheric clouds. And
this is the best time of year to see them because the Sun never dips
very far below the N horizon, even at local midnight, giving the best
conditions for seeing them. They can only be seen when the Sun is
between 6 and 16 degrees below the horizon.   They appear low down near
the N horizon, often in the vicinity of Capella, and appear as wispy
silvery or sometimes bluish streaks, often parallel to the horizon. Some
'curls' and 'billows' are also occasionally visible. They can be seen
anywhere in Ireland or Britain if you have a fairly clear N horizon, but
because they occur mainly at latitudes of 60 degrees to 80
degrees, those in the far South don't see them as well or as often.   
This year may have greater NLC activity than usual, because they are
seen more often around sunspot minimum, so do have a look on clear
evenings. They are quite easy to photograph, with exposures of 1" - 4"
on 400 ISO film (or 2" to 8" on ISO 200 film, etc); or just experiment
with your digital camera and see what you get with each trial.
Successive photos over a period of half an hour or so may show changes
in structure and motion.    Do not be fooled by ordinary wispy
cirrus-type clouds visible late on a summer evening: the sky needs to be
dark enough for you to see the first few brightest stars in order for
NLCs to be properly visible.

3. The ISS (International Space Station) is currently visible making a
series of 'morning' passes across Irish skies, but at this time of year,
as evening twilight merges into morning twilight, it will in fact
progress seamlessly into the next series of evening passes without a
break. This is because at this time of year the Sun will never be so far
below the horizon that it cannot illuminate the ISS as it passes over.
So we start seeing 'morning' passes getting earlier and earlier, and
then find both 'morning' and 'evening' passes occurring on the same
night.    Normally we can never see more than two orbital passes of the
ISS on any one night (evening or morning): since the orbital period is
about 95 minutes, the Sun would be too low below the horizon to
illuminate the ISS by the time it came over on its third orbit after the
sky got dark enough to see it (or for morning passes, the sky would be
too bright by the time of the third orbit). It still passes over of
course, but if it's in the Earth's shadow, or in daylight, we can't see
it.   However, with the Sun never getting too far below the horizon at
this time of year, we can sometimes see THREE orbital passes in the one
night. From the latitude of Belfast the first opportunity occurs on 16
June, with passes commencing at 00.20, 01.51 and 03.26. On 17/18 June we
have passes commencing at 23.28, 01.02, and 02.37. And on Solstice
night on 20/21 June, passes commence at 23.01, 00.35, and 02.10 (times
may change, and will vary slightly according to your location).   
Another bonus is that such passes are visible almost from horizon to
horizon! In other words, since the Earth's shadow is projected so low in
the sky, and towards the South, the ISS stays above it for almost all
the time it is above the horizon, and is thus illuminated, and visible.
   It takes about 5-6 minutes to cross the sky, roughly from West to
East, and can appear brighter than any star now visible, and sometimes
almost as bright as Jupiter. From Belfast the highest altitude it can
reach is about 46 degrees, in the Southern sky, but from South Cork it
can pass overhead. A 10" - 20" exposure on your camera will show its
motion very well, although beware of over-exposure of the twilight
background at this time of year!    Check the excellent and
free www.heavens-above.com for details for any location. If you are
entering your positional co-ordinates yourself, as opposed to picking a
town from the huge database, remember to select the 'UK + Ireland' time
zone, or it will give you the times in GMT all year round - rather than
in Summer Time at this time of year! That site also gives details of
lots of other things for your own location, such as Iridium flares,
other satellite passes, comets, etc.

4. Blackrock Castle Observatory, Cork: IAA members may recall an
excellent talk given by Dr Niall Smyth of CIT several years ago, when he
told us that plans had just been approved to restore Blackrock Castle,
on the entrance to Cork harbour (S side), featuring a new public/
research observatory facility there. I got an invitation from Paddy
Brennan, past Chairman of the Cork Astronomy Club (and IFAS treasurer),
to attend the special CAC event there last Saturday, just one week after
the official opening by Leo Enright.   The restoration has been done
very well, there's a nice restaurant in the grounds, and a separate bar
for other functions, and they will be adding extra car parking
spaces. And although it seems slightly incongruous, there is indeed a
dome containing a 16" Meade SCT telescope on top of the highest main
turret! This will be operated entirely robotically, and will link up
with CIT in Cork itself, and with other telescopes around the world,
with terabyte capacity. There will also be another telescope, and a
small radio telescope, although it is not in place yet. There is an
interactive hands-on science centre, a small conference room, a research
area, and of course there will be display and exhibition material.   
The tour of the castle and observatory by Niall Smith was followed by
various talks and telescope demonstrations by members of the Club - with
some very impressive equipment! - and there was a free lunch! All told,
a very enjoyable day - thanks again for the invitation! Congratulations
to Tom Bonner who did most of the organising, and the rest of the Club
for their efforts too, including the excellent catering.    And
congratulations to Niall Smith for bringing the project to fruition -
it's well worth a visit if you are ever in the area. It's not open to
the public just yet, but watch this space - I'll give further details as
they become available.

Clear Skies,

Terry Moseley.


Last Revised: 2006 June 13th
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