WADHURST ASTRONOMICAL SOCIETY
FEBRUARY NEWSLETTER 2006
INDEX: MEETINGS, OTHER NEWS, CONTACTS
History of the Telescope
given at the Society's meeting on Wednesday 18th January 2006 by Dr John
John Lawrence began his talk by taking us through the most common problem
with lenses; chromatic aberration where not all colours come into focus at the
same point producing coloured edges to images, and spherical aberration where a
lens cannot produce perfect focus over the whole image.
Then he went far back to the Egyptians around 1500 BC who knew how to
make glass but didn't understand the optical properties it possessed.
Between 1285 and 1300 various lenses were being used by spectacle makers
and it may have been during this time that various spectacle lenses had been
used to magnify distant objects. It
wasn't until the early 16th century that there is recorded use of the telescope
to study the solar system and the stars.
Leonard Digges and Dr. Dee made new discoveries in the combination of
lenses to detect distant objects and worked on the perspective lens around 1575.
In 1585 Giovanni Battista della Porta did further work with single convex
John went on to tell us that in 1608 the children of Lippershey, a
spectacle maker in Middleburg, held up two of his lenses and found that they
could magnify the weathervane on top of the church.
Lippershey then went on to make telescopes for military purposes.
Galileo heard of this and went on to develop his first telescope in 1609
using existing lenses.
With his telescopes he began to map the night sky and was able to see the
surface of the moon in greater detail than it had ever been seen up to that
time. Galileo also discovered that
the Milk Way was in fact made up of billions of faint individual stars. He was
also able to clearly identify the four brightest moons of Jupiter.
The phases of Venus lead him to suggest that the Sun was at the centre of
the Solar System, for which he almost lost his head!
He found that the surface of the Sun had blemishes on it called Sun Spots
and these showed that the Sun was rotating, and for this he found himself in
deep trouble for even suggesting that the Sun wasn't perfect.
Kepler did research on the human eye and found that the surface of the
lens was hyperbolic and not spherical, something De Scartes went on to proved
Early telescopes were very long, as much as 150 feet and this meant that
the tubes were difficult to handle and were prone to bend under the weight,
although this was addressed by having an eye piece and the object lens held
separately at the appropriate the distance with no tube to support in between.
Because there is no refraction in the reflecting telescope, apart from
the eye-piece, John pointed out that some of the problems were overcome,
although here it was found that although mirrors were more easily produce with a
spherical profile, they needed to be parabolic which was more difficult to
produce in the early days of making reflecting telescopes. Robert Hooke and Christopher Wren
worked together to develop the reflecting telescope.
John related a horrific account of how Isaac Newton inserted a bodkin
between his eye and eye-socket in his search for the workings of the human eye.
He also stared at the Sun for as long as he could in another experiment;
something we are always warning against! But
Newton did a lot of work on colour and refraction.
James Short experimented with quicksilver-coated mirrors and could
produce magnifications of between 8 and 20 times.
In 1773, William Herschel ground many of his own lenses and mirrors
whilst living in the city of Bath and before he moved to Slough where he managed
to make a telescope with a 48-inch mirror.
Herschel also discovered infrared radiation by chance whilst using a
In an attempt to reduce chromatic aberration, Chester Moor Hall combined
lenses and is credited with inventing the achromatic lens in 1729.
John and Peter Dolland experimented with these lenses and produced lens
combinations with almost no chromatic aberration and with lenses with a diameter
of as much as 5-inches.
In 1892 John told the meeting that the first of the mountain-based
telescopes began to be erected by George Ellery Hale.
He constructed the 40-inch refracting telescope near Lake Geneva,
Chicago. Hale was also responsible for the 60-inch mirror telescope at
Mount Wilson Observatory and the 200-inch telescope on Mount Palomar, financed
by the Rockefeller Foundation and opened in 1948.
Between 1920 and 1923 Edwin Hubble catalogued many nebulae and estimated
the distance of the Andromeda Galaxy as one million light years.
(Now known to be about 2.2 million light years)
In 1929 Hubble and Milton Humason measured the red shift of many stars
and distant galaxies and calculated the rate of the expanding Universe,
something already proposed in 1927.
John showed a number of slides of various observatory telescopes and finally ended showing the up-to-date 95-inch Hubble Space Telescope yet saying that new ground-based telescopes and techniques were now able to exceed its results.
Wednesday 15th February 2006. The
Society meeting will take place as usual in the Upper Room of Wadhurst Methodist
Church at the lower end of the High Street and opposite the entrance the Uplands
College and begins at 7.30 pm.
There will be a talk given by Dr. Martin Heath with the intriguing
entitled of "Habitability of Red Planets"
Wednesday 15th March 2006 Martin
Frey talks about "Great Astronomical Blunders"
Wednesday 19th April 2006 Our
own Ian King tells us about "Instrumentation".
Wednesday 17th May 2006 Dr.
Robert Smith gives a talk with the alarming title of "Things that go Bang
in the Night"
Wednesday 21st June 2006 We
are to have a Members evening called "Summer Solstice Telescope
Evening" when members are invited to bring their telescopes and any other
astronomical equipment and when we get the chance to discuss our interests.
If any member would be interested in giving a short talk, they would be
very welcome and should contact either Phil Berry, Ian Reeves or Geoff Rathbone.
Wednesday 19th July 2006 Gilbert
Satterthwaite FRAS will be talking to us about "Sir George Airy's
Contribution to Positional Astronomy".
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Security does of course concern all members and our need to be aware of
Safety as we conduct our meetings. I
think we already adopt a number of so called common sense procedures.
Anxiety does not normally stretch to the dangers lurking in operating an
observatory as far as Wadhurst is concerned until we have a gather-round at
Tim's or Michael's! However we need
to be aware of the risks posed by the equipment introduced by the Society and by
visiting speakers. The obvious
concern is for the use of extension cables that supply power to projectors
during meetings. Our early reaction
has been to order a cable protection shield.
Most members are well aware of the dangers surrounding the outdoor use of
telescopes, not only from tripods and trailing cables at nighttime but from the
added ones during daytime events.
Subscriptions became due on 1st November 2005 and any outstanding
payments will be gladly received by our Treasurer Mike Wyles either by post or
at the next Society meeting. £15 for members and £20 for joint members within a family.
The opportunity exists for everyone find Mercury this month, as it
reaches greatest elongation on 24th February when it can be found soon after
sunset when Mercury's altitude is 15 degrees and azimuth 248 degrees, slightly
south of due West. The apparent magnitude will be -0.3 but if looking for it be
sure the sun has set for safety reasons. This
should one of the best times in the year to find Mercury with binoculars or
Saturn's rings are beginning to close but are still worth observing.
Recently the planet occulted a 7.9 magnitude star.
Cloud prevented me from seeing the star pass behind the rings although I
was able to see it emerge from beneath the planet. I hope other members had better luck.
High in the night sky at this time of year is Castor and Pollux, above
and to the east of Orion. The pair are distinguished by their contrasting colours.
Castor is the white star of magnitude 1.58 and at a distance of 51 light
years from us. Four and a
half degrees to the south is Pollux, a decidedly red star of magnitude 1.15 but
considerably nearer at 33 light years away.
The colours become even more noticeable if you rack out of focus slightly
looking through a pair of binoculars.
The Whirlpool galaxy, M51, about 3 degrees to the right of Alkaid the end
star of The Plough is worth observing even through a small telescope, but its
companion galaxy NGC 5195 may be seen on a good night using a larger telescope.
on Pluto by Dr. Tony Phillips
There's a nip in the air. Outside it's beginning to snow, the first fall
of winter. A few delicate flakes
tumble from the sky, innocently enough, but this is no mere flurry.
Soon the air is choked with snow, falling so fast and hard it seems to
pull the sky down with it. Indeed, that's what happens. Weeks later when the
storm finally ends the entire atmosphere is gone.
Every molecule of air on your planet has frozen and fallen to the ground.
That was a snowstorm-on Pluto!
Once every year on Pluto (1 Pluto-year = 248 Earth-years), around the
beginning of winter, it gets so cold that the atmosphere freezes. Air on Pluto
is made mainly of nitrogen with a smattering of methane and other compounds.
When the temperature dips to about 32 K (-240 C), these molecules
crystallize and the atmosphere comes down.
"The collapse can happen quite suddenly," says Alan Stern of
the Southwest Research Institute. "Snow begins to fall, the surface
reflects more sunlight, forcing quicker cooling, accelerating the snowfall. It
can all be over in a few weeks or months."
Researchers believe this will happen sometime during the next 10 to 20
years. Pluto is receding from the
warmth of the Sun, carried outward by its 25% elliptical orbit. Winter is
So is New Horizons. Stern is
lead scientist for the robotic probe, which left Earth in January bound for
Pluto. In 2015 New Horizons will become the first spacecraft to
visit that distant planet. The
question is, will it arrive before the snowstorm?
"We hope so," says Stern. The spacecraft is bristling with
instruments designed to study Pluto's atmosphere and surface.
"But we can't study the atmosphere if it's not there."
Furthermore, a layer of snow on the ground ("probably a few centimetres
deep," estimates Stern) could hide the underlying surface from New
Horizon's remote sensors.
Stern isn't too concerned: "Pluto's atmosphere was discovered in
1988 when astronomers watched the planet pass in front of a distant star-a
stellar occultation." The star, instead of vanishing abruptly at Pluto's solid
edge, faded slowly. Pluto was
"fuzzy;" it had air. "Similar
occultations observed since then (most recently in 2002) reveal no sign of
[impending] collapse," says Stern. On
the contrary, the atmosphere appears to be expanding, puffed up by lingering
heat from Pluto's waning summer.
Nevertheless, it's a good thing New Horizons is fast, hurtling toward
Pluto at 30,000 mph. Winter. New
Horizons. Only one can be first. The
race is on....
Find out more about the New Horizons mission at pluto.jhuapl.edu
. Kids can learn amazing facts
about Pluto at spaceplace.nasa.gov/en/kids/pluto.
article was provided by the Jet Propulsion Laboratory, California Institute of
Technology, under a contract with the National Aeronautics and Space
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Secretary Phil Berry 01892 783544
Any material for inclusion in the March Newsletter should be with the Editor by February 28th 2006
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