WADHURST ASTRONOMICAL SOCIETY

MAY NEWSLETTER 2006

INDEX: MEETINGS, OTHER NEWS, CONTACTS

MEETINGS

THE APRIL MEETING  

Instrumentation

Talk given by Ian King at the Society Meeting on Wednesday 19th April2006

    Ian King is a Society member, well known for his practical knowledge of Astronomical Instruments and his remarkable deep sky images.  He began by explaining that this talk was based on a presentation he uses in a lecture on Astronomical Imaging.

    Very important aids to the amateur astronomer are binoculars and Ian told the meeting that in many ways they are more useful than a telescope.  They are usually easier to transport and are immediately ready for observing.  Small roof prism binoculars have excellent optics and are very small and light.  Ian mentioned that 10 x 40 binoculars can be very useful and with apochromat composite lenses with different refractive indexes it is possible to considerably reduce chromatic aberration, although these are much more expensive.

    Larger binoculars still require some kind of solid support, although some binoculars now on the market use image stabilisation for even better observing.

    We turned to the various telescope mounts available, and Ian talked about various considerations such as payload, periodic error in tracking, backlash in the gearing and the use of "Goto" functions and PC connections.

    He began by introducing us to German Equatorial mounts.  These are versatile with a wide choice and can have accurate gears and built-in Polar Finders.  They can nearly always be broken down for transporting.  But they do suffer "meridian flip"where cables can get in the way during tracking, and also the telescope needs to have a counterweight balance.  Observing close to the polar axis can be very difficult.

    Ian described various makes starting at a few hundred pounds and going up to several thousand pounds.  We were shown pictures of the Vixen GP-DX mount, the Sphinx Goto mount and at the top end of the Vixen range, the Atlux, a much more solid mount but costing in the region of £3,000.

    The Skyscan EQ6 looked very professional at about £1,000 although the similar HEQ5 cost slightly less.

    Losmandy mounts starting with the GM8 German Equatorial looked a sturdy precision mount for smaller payloads.  The G11 has a payload of 65 lbs for telescope, extra equipment and counter balance weights.  At the top end is the Losmandy Titan, capable of an even greater payload, but also a lot more expensive.

    Ian showed us the Gemini G41 mount, a very impressive looking tracking platform and is in fact the one Ian says he uses, which, after seeing his deep sky results speaks for itself.

    At the top end of Ian's German mounts came the Astro Physics mount manufactured in the USA.  A mouth-watering mount with, as you would expect, the most stable and precise platform, but one's mouth dried as Ian told us that they cost about £8,000 and at present are taking 3 to 4 years to deliver!

    Another mount was the Bisque Paramount ME robotic mount, which can even be operated over the Internet.

    Fork Mounts came next which list amongst their advantages, the lack of meridian flip and more accessible mounts for a camera.  It is lighter than the German mounts.  The disadvantages include the fact that they are less versatile, less stable and are harder to counterbalance.  They are not quite as good when it comes to tracking.

    Ian now turned to telescopes themselves.  These days many very good telescopes are manufactured in the Far East, costing far less than those made in the West.  Refractor telescopes have the advantage of good flat fields, easy to focus and use, and are ideal for wide field observing.  There is a wide choice at all prices.  They are more expensive compared with reflector telescopes and have chromatic aberration although using APO lenses considerably reduces this disadvantage.

    Ian felt that there was a lot to be said for Russian optics, but particularly mentioned the Borg series of telescopes, which allow a modular approach where lenses can be easily changed.

    Over recent years there has been an exponential increase in the choice of eyepieces, which can now consist of as many as 8 or 9 lens elements with little loss in transmission, little astigmatism and good eye relief, - a particular advantage for observers wearing spectacles.

    Catadioptric telescopes use a front correcting lens, a main mirror and a spherical secondary mirror to reflect the image through a hole in the centre of the main mirror.  These instruments are very versatile with lots of available accessories and the moving main mirror enables plenty of back focus.  A disadvantage is the moderate off-axis performance.

    The Maksutov Cassegrain has a main mirror but a fairly thick front lens, which can result in some time needed for the telescope to cool ready for use.  These telescopes have good optical and mechanical performance and they have good off-axis results.  They are quite expensive and heavier.

    Ritchey Chretien Cassegrain instruments have a very wide field and inherently need a large secondary mirror.  They are ideal for CCD work but sensitive to collimation errors.

    Ian mentioned Newtonian telescopes as the least expensive and the one amateurs can make for themselves, including grinding the mirror.  They can have very fast f-numbers although they do suffer from lack of back focus.

    CCD cameras come in many sizes, but the pixel size and the effective noise are important factors to be considered.  They can come with filter wheels for use when making colour exposures allowing long luminance exposures for detail and short Red Green and Blue exposures to provide the colour.  Autoguiders took a lot of the effort out of accurately tracking during long exposures and are a good investment.

    Finally Ian showed a number of CCD Images starting with the Witches Broom in the Veil Nebula, which radiates in many different wavelengths so that using different filters produced startlingly different results.  He talked about narrow band filters used to considerably reduce the effects of light pollution and light from the moon.  We saw an incredible image of the Horse Head nebula using a hydrogen-beta filter to improve contrast with the background sky.

    He showed many other very sharp, clean images and one impressive image of M31, the Andromeda galaxy, with incredible detail and contrast.

    At coffee we had an opportunity of looking at the way Ian checked the performance of telescopes using a distant light source from the tip of a fibre-optic as an artificial star.  Racking the focus on the eyepiece we were able to witness the virtually perfect rings when defocused and over the whole field of view.

      An excellent and enjoyable talk.

MAY MEETING

    Wednesday 17th May 2006.  Dr. Robert Smith gives a talk with the alarming title, "Things that go Bang in the Night".

    The meeting will be held in the Upper Room of the Methodist Church, Wadhurst High Street and will commence at 7.30 pm.

FUTURE MEETINGS

      Wednesday 21st June 2006 is "The Solstice Telescope Evening" and will be an opportunity for members to bring along their telescopes and talk to newcomers, novices and the knowledgeable observers. The general public will be invited to join us. There is more than a modest number who would very much like to buy a 'scope if only they had the opportunity to talk to amateur astronomers like yourselves who can explain the pros and cons of the various instruments without any ulterior motive.  What better time than the 21st of June.

If any member would be interested in giving a short talk at this meeting they would be very welcome and should contact Phil Berry, Ian Reeves or myself, Geoff Rathbone.  The subject does not need to be pure astronomy as experiences and visits to locations can be just as interesting to members.

GO TO INDEX

OTHER NEWS

    There will be no meeting in August BUT Michael Harte and his wife are again kindly offering to hold an astro-barbecue evening on Saturday 26th August 2006.  Last year we had an excellent evening with three or four telescopes and binoculars, lots of astronomy chat and great hosts, but it would be good to see more members this year.

    The barbecue evening will be held at Greenham Farm, Wadhurst - on the south side of the B2099 immediately to the west on the railway bridge.  All Society members are invited and Michael suggests that members aim to arrive at 7.00 pm.

You need to bring your own food and drink, but everything else will be provided.

MAY NIGHT SKY

      At any one time there are a number of comets in the night sky but are so difficult to find that really dedicated observers will have a better idea where to find them than I.  But during May there is one comet worth mentioning.  It has a period of about 5.43 years and is 73P/Schwassmann-Wachmann, first discovered in 1930 by two German astronomers.

      This comet has never been easy to find but it is noted because in 1995 it brightened to magnitude +6 and it was discovered that the head had split into several pieces.  This year two pieces pass through the Summer Triangle of Deneb, Vega and Altair in mid May although they are well over ten degrees apart.  The brightest piece passes less than a degree from M57, the Ring Nebula in Lyra on 9th May.  Using a pair of 10x binoculars it should be in the field of view just south of Vega.  There is a good article on the comet in the May edition of "Sky at Night" and they recommend fairly low power binoculars to find it and see the tail.  It is thought that the comet could be a naked-eye object, despite the Moon.  There is a website at: http://aerith.net/comet/catalog/0073P/2006.html

NASA SPACE PLACE  

Who wants to be a Daredevil?

By Patrick L. Barry and Dr. Tony Phillips  

    When exploring space, NASA naturally wants to use all the newest and coolest technologies-artificial intelligence, solar sails, onboard supercomputers, exotic materials. 

    But "new" also means unproven and risky, and that could be a problem.  Remember HAL in the movie "2001: A Space Odyssey"?  The rebellious computer clearly needed some pre-flight testing. 

    Testing advanced technologies in space is the mission of the New Millennium Program (NMP), created by NASA's Science Mission Directorate in 1995 and run by JPL.  Like the daredevil test pilots of the 1950s who would fly the latest jet technology, NMP flies new technologies in space to see if they're ready for prime time.  That way, future missions can use the technologies with much less risk.

    Example:  In 1999, the program's Deep Space 1 probe tested a system called "AutoNav," short for Autonomous Navigation.  AutoNav used artificial intelligence to steer the spacecraft without human intervention.  It worked so well that elements of AutoNav were installed on a real mission, Deep Impact, which famously blasted a crater in Comet Tempel 1 on July 4, 2005.  Without AutoNav, the projectile would have completely missed the comet.

    Some NMP technologies "allow us to do things that we literally could not do before," says Jack Stocky, Chief Technologist for NMP.  Dozens of innovative technologies tested by NMP will lead to satellites and space probes that are smaller, lighter, more capable and even cheaper than those of today.

    Another example: An NMP test mission called Space Technology 9, which is still in the planning phase, may test-fly a solar sail.  Solar sails use the slight pressure of sunlight itself, instead of heavy fuels, to propel a spacecraft.  Two proposed NASA missions would be possible only with dependable solar sails-L1 Diamond and Solar Polar Imager-both of which would use solar sails to fly spacecraft that would study the Sun.

    "The technologies that we validate have future missions that need them," Stocky says.  "We try to target [missions] that are about 15 to 20 years out."

    A menagerie of other cool NMP technologies include ion thrusters, hyperspectral imagers, and miniaturized electronics for spacecraft navigation and control.  NMP focuses on technologies that have been proven in the laboratory but must be tested in the extreme cold, vacuum, and high radiation environment of space, which can't be fully recreated in the lab.

    New NMP missions fly every year and one-half to two years, taking tomorrow's space technology for a daredevil test drive.

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

GO TO INDEX

CONTACTS

Any material for inclusion in the June Newsletter should be with the Editor by May 28th 2006

GO TO INDEX