WADHURST ASTRONOMICAL SOCIETY
AUGUST NEWSLETTER 2007
INDEX: MEETINGS, OTHER NEWS, CONTACTS
Contribution of Sir George Airy to Positional Astronomy
given by Gilbert Satterthwaite to the July Meeting of the Society
Satterthwaite had the distinction of being the last person at Greenwich to take
an observation using The Airy Transit Circle Telescope in 1954 before the
Observatory was eventually moved to Herstmonceux in East Sussex.
He had taken up his post at Greenwich straight from school in 1952 and
used instruments and books created by George Airy and so gained a great deal of
respect for the former Astronomer Royal; in fact Gilbert referred to himself as
a bit of a nut about Airy. Gilbert
is also Chairman of the Society for History of Astronomy and a member of the
International Astronomical Union.
began by looking at the problems associated with defining the positions of the
stars and planets in the heavens. Since
we observe from the surface of the earth and not at the centre, every observer
sees the night sky slightly differently and star positions need to be precisely
positioned in a way that is recognised by all.
explained definition of the Celestial Equator, the projection of the earth's
equator onto the background sky. The
ecliptic is the projection of the earth's orbit around the Sun and the point at
which they cross with the ecliptic rising is called the First Point of Aries and
defines zero hour on the sidereal clock.
observer has their own meridian, a line from due south, passing directly over
their head at its zenith and on to due north.
The Prime Meridian is the meridian at Greenwich Observatory as decided in
1884. The Alt-Azimuth system is used when considering the meridian
and since the horizon is not always clear, altitude readings are made from the
zenith at 90° this angle is known as the zenith distance.
position of a star is measured as it transits due south, when its zenith
distance is also measured and its precise azimuth determined.
look at the work done on Positional Astronomy, Gilbert introduced us first to
Friedrich Bessel, a German mathematician-astronomer who worked on the
observations made earlier by James Bradley, a former Astronomer Royal, to
produce precise positions of over 3,000 stars.
we were told about Stephen Groombridge, a business man and astronomer, born in
Goudhurst just 6 miles away from Wadhurst, who built a 3.5-inch aperture transit
telescope in an extension to his house on Blackheath close to Greenwich
observatory. From here he made some
very accurate observations, compiling his own star catalogue down to 9th
Biddell Airy came next. He was a
distinguished mathematician and astronomer at Cambridge and moved to Greenwich
in 1835 on being appointed Astronomer Royal.
When Groombridge suffered a stroke it was Airy who had had the work
completed. In fact Airy was very a
very exacting supervisor of calculations and also improved measurements made by
devising new instruments.
in Gilbert's list of important contributors to Positional Astronomy was Simon
Newcomb, born in Newfoundland in 1835. He
moved to the United States and worked in the US Naval Observatory where he
recalculated the positions of the planets and improved the astronomical
we returned to the huge contributions made by George Airy.
He reduced the effects of atmospheric distortion on his measurements by
using a wall mounted transit circle and by taking measurements using a bowl of
mercury and comparing them with direct measurements and thus was able to reduce
instrument devised by Airy made use of the fact that there is no atmospheric
distortion at or near the zenith. The
Reflex Zenith Tube worked by looking down onto the surface of mercury at the
reflection a star which was within 2 or 3 degrees of the zenith.
Measurements were made when the star crossed various wires in the light
path. the instrument was turned and
the reading taken again at 180 degrees. Dividing
this by 2 gave an exact position of the star.
These readings were required for the adjustment of the meridian
instruments and measurement of the variation of latitude.
Airy Transit Circle telescope was the last of the transit telescopes to be built
and used at Greenwich, and this is the instrument that Gilbert was so familiar
with. The observer listens to a clock mechanism and as the object
whose position was being measured crossed a series of wires in the optical path,
he would tap on a "Morse key". This
would produce an impulse on a drum chronograph that would be measured later with
an accuracy of 1/10 th of a second.
1915 accuracy was improved even more by the Impersonal Micrometer.
The observer tracked the star with a tracking wire.
As the tracking wire passed a fixed vertical wire, electrical contacts
within the eyepiece produced in impulse that was recorded on the barrel
chronograph, producing even more accurate results.
the same time, the altitude angle was measured by and assistant, reading a high
precision scale via one of a number of microscopes built through the side of the
telescope mount. Airy had also had
an additional channel incorporated through the mount to allow light to pass
through and illuminate the scale.
1939 a tickertape machine replaced the chronograph and resulted in readings
accurate to 1/1000 th of a second.
was retained as Astronomer Royal until he was 80!
He retired to a house just outside the walls of Greenwich Park and even
then continued as a consultant to the observatory and served on the Board of
Gilbert spoke of more recent methods of measuring transits using a development
of Airy's Zenith Tube utilising photographic techniques.
Using the PZT (Photographic Zenith Tube) extremely accurate results can
country of Copenhagen wanted a transit telescope at La Palma which was eventually
paid for by the Carlesberg lager company, and was called until recently the
"Carelsberg Automatic Meridian Telescope".
This is a fully computerised meridian telescope capable of very accurate
telescope was the first fully automatic telescope in the world.
At present it is used for Astrometry.
concluded his talk with a brief explanation of why the Global Positioning System
(GPS) places the worlds reference meridian about a hundred metres to the east of
Airy's Transit telescope and is marked by a litter bin.
In 1984 the World Geodetic System committee took the results of a number
of surveys from around the world, averaging them and also taking into account
the changes in gravity, plate movements and the oblateness of the earth's shape
to determined the present meridian reference position known as WGS84.
committee met in the Abergaveny Arms at Frant on Monday the 9th of July.
Treasurer announced that the currant account contained £490.85 and our Reserve
Account stood at £1,125.35. This
was considered to be healthy after the purchase of a slide projector and a new
digital projector often required by more recent speakers.
Berry spoke of a recent SAGAS (Southern Area Group of Astronomical Societies)
meeting he had attended at Chichester and one of the subjects they spoke of was
"The International Year of Astronomy".
This is to mark the 400th anniversary of Galileo and his telescope and
will take place in 2009.
number of events are being planned throughout the year such as Moon Week in July
to celebrate the first telescope observations of the Moon in 1609.
Committee discussed what our Society might do and it was felt that members may
have some suggestions. There is
plenty of time, but we would like to have some ideas before the next Committee
meeting this October.
As mentioned in previous Newsletters, there is no meeting of the Society
in August, but once again, we have been kindly invited to an Astro Barbecue
hosted by Michael Harte and his wife at Greenman Farm on Saturday 25th August
2007. In the past this has been one
of the Society's highlights of the year and promises to be again this year.
and his wife, Claire, live in a remarkable old farmhouse with extensive grounds
to the south. The sky is fairly
free from light pollution and apart from the occasional aircraft making its way
to or from Gatwick, observing can be very rewarding.
Farm, Wadhurst, is on the south side of the B2099 immediately to the west of the
railway over-bridge. All Society
members are invited and Michael suggests that members aim to arrive about 7.00
pm. The entrance to the farm is through two huge gates and there
is plenty of room inside for parking.
will only need to bring your own food and drink, as everything else will be
are invited to bring telescopes, binoculars and anything else of interest, but
MEETINGS & EVENTS
19th September 2007 George
Sallitt will be giving a talk about "Web cams", a subject that will
interest many members keen to get involved with this cheaper but surprisingly
satisfying method of imaging.
22nd September 2007 A visit to see
the largest private collection of clocks in the UK at Belmont House near
Faversham in Kent.
17th October 2007 Keith
Brackenborough will be giving a talk with the intriguing title "The
Calendar - A 5,000 year struggle to
Align the Clock to the Heavens".
Wednesday 21st November 2007 John Vale-Taylor is presenting "The Tim Bance Interview". Tim is a long-standing respected member of the Society and has a wealth of practical experience in the field of amateur astronomy.
Wednesday 12th December 2007 NOTE: THIS IS THE SECOND WEDNESDAY OF DECEMBER Society Member, Paul Treadaway is giving a talk he calls "Why are we Still Here?" - Food for thought...
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TO BELMONT HOUSE
Saturday the 22nd of September, The Society is visiting one of the finest
collections of clocks in Britain.
will need to find our own way there in our own transport.
rather interesting opportunity has arisen due to automatic methods used to
detect possible faint galaxies. In
New Mexico, Apache Point Observatory is carrying out a survey of a quarter of
the sky, searching for faint galaxies. They
already have over a million images, but are asking help in identifying the
Lintott, of Sky at Night programme fame, has helped to set up a website:
which you take a short training session, identifying different types of galaxies
and then are invited to look at the real images, identify them to see if they
are actual galaxies and then classifying them as edge on, right rotating, left
rotating, colliding, etcetera.
have spent a little while going through them and found it quite fascinating.
You will be looking at objects that no one else has ever seen until now
and so far I have found one that certainly deserved further study.
You are invited to send an email containing the identification number to
the observatory for further examination. Each
image is classified by 20 different assessors to help rationalise the results.
the debate about thoughtless lighting in the Wadhurst area, Phil Berry notes
that Wadhurst residential street lighting is now starting to be turned off after
midnight until 0500. Apparently the majority of residents have seen sense and
have voted to have it turned off.
will be a formal review in April 2008. If the benefits are good, it would be as
well to let the parish council know what we think ready for their review.
They are also looking at producing a lighting policy with a lighting
contractor to review the 159 streetlights that are in the parish with regard to
replacing the ones that are old and expensive to maintain.
will be writing to them to encourage them to put in as low wattage and as
"dark sky friendly" fittings as possible to meet the requirements.
Perhaps other members in the area would like to do the same.
Chairman of Highways & Lighting Committees is Anna Monaghan and The Wadhurst
Clerk to the Council is Philippa Hewes and she can be emailed with a view to
passing on comments via the email address:
is a morning object this month but will be low down and very difficult to spot.
also becomes a morning object later in August and might be seen in the east
before sunrise. It will present a thin crescent phase and will be magnitude
is in Taurus (the bull) and at magnitude 0.4 is growing in apparent diameter all
the time. By the end of the month Mars rises before midnight (BST) and can be
seen close to Aldebaran on the night of the 24th.
is in Ophiuchus (the serpent bearer) at magnitude -2.3. It is still a prominent
evening object in the south west but will soon be setting before midnight.
is not visible this month due to its conjunction on the 21st.
|Date||Time||Star (SAO Catalogue)||Constellation||Magnitude||Phase|
|Mon 20th Aug||2137||183485||Libra||7.5||DD|
|Thu 23rd Aug||2119||186444||Sagittarius||6.5||DD|
|Sun 26th Aug||2145||189986||Capricornus||4.9||DD|
|Mon 27th Aug||2248||164808||Aquarius||7.7||DD|
|Mon 27th Aug||2341||164809||Aquarius||7.6||DD|
|Tue 28th Aug||2344||146362||Aquarius||3.7||RD|
|Wed 29th Aug||2258||146862||Pisces||7.9||RD|
|Wed 29th Aug||2356||146885||Pisces||7.1||RD|
|Thu 30th Aug||2217||109282||Cetus||7.6||RD|
I said in the last Sky Notes, the Perseid meteor shower has its maximum this
month on the night of 12th to 13th which fortunately coincides perfectly with
new moon. Estimates of the ZHR (Zenithal Hourly Rate) vary but the average is
around 80 meteors per hour. This method of estimating meteors can be quite
confusing because it is a measure of the number that could be seen with a
perfect sky and with the radiant at the zenith where there would no loss of
seeing due to extinction.
I am quite happy to meteor watch simply for the enjoyment and relaxation that it
offers but I know others prefer to do something more tangible.
If you want too you can record what you see by noting the date, time,
magnitude estimate and the constellation where it was seen. Also if you have a
star map you can draw on the meteors you have seen and then follow the trails
back to show where the radiant is.
midnight the radiant lies in the north east but as the night progresses it moves
to the east and by dawn (if you've lasted till then) it is high in the
south/south east and the winter constellation of Orion will already be well
above the horizon.
on a sun lounger with the head end slightly raised and your feet pointing
towards the radiant is the best position. Don't watch too close to the radiant -
the best meteors are invariably seen further out over a wide field of view.
Don't forget that even during "summer" when daytime temperatures can
be high you will need a coat on if you watch for any period of time.
(International Space Station)
Below are just some of the best passes by the ISS this month. For more details log on to the web-site: - www.heavens-above.com All times are in BST.
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Chairman John Vale-Taylor firstname.lastname@example.org
Phil Berry 01892 783544 email@example.com
Mike Wyles 01892 542863
Website Michael Harte 01892 783292
Newsletter Editor Geoff Rathbone
Any material for inclusion in the September Newsletter should be with the Editor by August 28th 2007
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