WADHURST ASTRONOMICAL SOCIETY

FEBRUARY NEWSLETTER 2006

INDEX: MEETINGS, OTHER NEWS, CONTACTS

MEETINGS

THE JANUARY MEETING

The History of the Telescope

Talk given at the Society's meeting on Wednesday 18th January 2006 by Dr John Lawrence

      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 lenses.

      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 mathematically.

      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 prism.

      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.

FEBRUARY MEETING

      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"

FUTURE MEETINGS

      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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OTHER NEWS

HEALTH AND SAFETY

      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.

Ian Reeves

SUBSCRIPTIONS

      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.

FEBRUARY NIGHT SKY

      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 telescopes.

      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.

NASA SPACE PLACE

Snowstorm 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 coming.

      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.

This article was provided by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.

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CONTACTS

Chairman          Tim Bance                   01732 832745

                                   timbance@hotmail.com

Secretary         Ian Reeves                        01892 784255

Secretary        Phil Berry                        01892 783544

Treasurer         Mike Wyles                   01892 542863

                                    mikewyles@globalnet.co.uk

  Publicity         Michael Harte                       01892 783292

& Web site                    michael@greenman.demon.co.uk

  Editor            Geoff Rathbone                01959 524727

                  Geoff@rathbone007.fsnet.co.uk

Any material for inclusion in the March Newsletter should be with the Editor by February 28th  2006

 

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