The GranTeCan

Talk given by Ian King at the Society's February meeting

After a quick commercial for the newly mastered Star Trek series Ian started a fascinating journey through the observatories at La Palma in the Canaries following a recent visit.

The first digital photograph was of the new Gran Telescopio Canarias segmented 10-metre telescope, currently the largest optical telescope in the world.  More familiarly know as GranTeCan and abbreviated to GTC.  The dome is one amongst several on the site at the top of a mountain whose shape has been formed from a caldera.

The adaptive optics main mirror is composed of 36 hexagonal mirrors, each about 1.9 metres across and separately controlled by a main computer, which amongst other things uses a laser guider to produce a guide star from which the computer calculates information to counteract atmospheric aberrations. (see later in the Newsletter)

The GranTeCan observatory is a joint financial venture between Spain, Mexico and the USA.

Ian King was actually invited to visit the interior of the observatory and showed a video of the inside of the dome and of the telescope itself.  Each of the hexagonal mirrors is just 3 mm away from the next providing an almost continuous surface.

Previously, the largest telescope on the 8,000 foot high mountain was the 4.2 Metre William Herschel telescope f2.5.  Ian said that most of the work was done using the true prime focus of the telescope.

Another observatory that Ian visited was the 2.5 metre Isaac Newton telescope.  This telescope had previously been housed in the Isaac Newton dome at Herstmonceux in East Sussex but had been moved because of light pollution.  The picture Ian showed us showed the telescope using a Cryostat cooler for the CCD imaging device, reducing the temperature to around -120 degrees to reduce image noise to a minimum.

The Jacobus Kapteyn telescope was next.  This is a 1-metre telescope in a dome where the whole observatory rotates.

We also saw a picture of the 1 metre Mercator Belgium telescope, which is semi robotic.

Yet another telescope Ian showed was the Swedish Solar telescope, well know for its high-resolution solar images.

The whole of the area has its own power supply and is free from relying on any external electric power.

We were shown several useful time-lapse videos Ian had made, which illustrated how most of the clouds formed and remained thousands of feet below the telescopes, leaving near ideal conditions for ground-based telescopes.  It was close to the domes that he set up his telescopes for some first rate observing.

From this point on Ian related his fascinating experiences with the Ritchie Chretien telescopes he was having made by Franco, a telescope maker in Italy.

The Ritchie Chretien telescope is much favoured by professional astronomers because of is superior optical properties.  Both the primary and secondary mirrors are hyperbolic which makes the telescope difficult to manufacture but is coma free.  Coma is the distortion that can occur towards the outer edge of the field of view in most amateur telescopes.

Ian was finding that it was taking a long time to take delivery of his orders so he decided that it was best to visit the workshops in southern Italy where the temperature was a staggering 42 degrees.  But this also gave the opportunity to look at some of the problems such as the mirror mountings, which needed to be made more stable.

Franco was a very good mirror maker but another of the problems was that in Italy there appears to be only one aluminiser, which meant that time was being used up waiting for the mirrors to be returned after coating.

We saw a number of photographs of Franco's workshop and the wonderful Italian town in which it was situated.

The result is that Ian has now improved his delivery times of this excellent telescope.

Finally, we were treated to some of Ian's deep sky images of the Crescent in Aquila, the Crab Nebula in Ha and a remarkable image of the Horsehead Nebula.


Wednesday 21st March 2007  Our guest speaker will be Dr. Stephen Serjeant and his talk is called "The Big Questions in Cosmology". 

The meeting commences at 1930 and will be held in the Upper Room of the Methodist Church, entrance to the left of the church and up the stairs, avoiding the Weight Watcher's meeting downstairs!

The church is at the eastern end of Wadhurst High Street, opposite the gates to Upland College.


Wednesday 18th April 2007 Jerry Workman will return to update the Society with the progress of Mars Express.

Wednesday 16th May 2007   Nik Symanec will be talking about important basic facts in an introduction to CCD imaging.  He calls his talk "Pixel Magic".

Wednesday 20th June 2007   This will be an open Telescope Evening.  A number of telescopes will be at the meeting for discussion and demonstration.

Wednesday 18th July 2007   George Satterthwaite will be giving a talk about "George Airy and His Contribution to Positional Astronomy"




I must confess that I didn't really know much about laser guiders, so I did a little reading on the subject, and I hope what follows will be of interest to anyone else who feels the same.

Unlike space telescopes, ground based telescopes can be very large but suffer from atmospheric instability.  This is now being overcome by the use of Adaptive Optics where each of the individual segments of the main mirror is controlled separately by a computer that receives information about the way the atmosphere is distorting what the telescope is looking at.

This information is derived from an artificial guide star created by firing a dye laser with a power of about 15-watts close to where the telescope is looking.  The "dye" is chosen to tune the laser so that it excites the sodium atoms in a naturally occurring layer 90 km above the earth's surface.  This produces an artificial star and using the information calculated by the computer to correct the atmospheric distortion, the adaptive optics of the main mirror can be made to "see" distant images with vastly improved clarity.

To prevent the possibility of the laser beam entering the eyes of those in a passing aircraft, there is a safety device that cuts the laser off immediately if a moving object is detected anywhere near the beam.  One hopes it is 100 % effective.


Subscriptions for the coming year became due on the 1st of January 2007.  Subscriptions remain the same as previous years at 15 per member and 20 for two members within the same family.  Cheques should be made payable to "Wadhurst Astronomical Society" and can be presented to the Treasurer, Mike Wyles at the next meeting or can be sent to him by post if that is more convenient.  Mike's address is: Mr. M. Wyles, 31 Rowan Tree Road, Tunbridge Wells, Kent.  TN2  5PZ.


At present there is a petition running on the Downing Street website, asking "to ensure that all exterior lights are shaded to direct their light downwards, so as to prevent light pollution obscuring the beauty of the night sky".  If you feel strongly about this issue you can add your name to the petition, which runs until 29th of May 2007.

More information can be found on the website at:


If you do sign up, you will be sent an email which asks for your confirmation by "clicking" on a link in the email.


Don't forget that BST starts on Sunday 25th March at 02.00.


Mercury moves into the morning sky but is very low and unfavourably placed for observation.

Venus is becoming a more prominent object in the evening sky as its apparent diameter and magnitude increase. It is easily visible in the southwest after sunset.

Mars is a morning object in the constellation of Capricornus (the sea goat) at magnitude 4.7. Unfortunately it is difficult to observe this month.

Jupiter is a bright morning object in the constellation of Ophiuchus (the serpent bearer) despite being only some 15 above the horizon when it culminates. At magnitude -2.2 it is the brightest object by far in the south west before dawn. Its four brightest moons are easily visible in a small telescope.

Saturn is ideally placed for observation as it is visible for most of the night. It lies in the constellation of Leo (the lion) not far from the star Regulus at a magnitude of +0.1. It's rings continue to close up as viewed from Earth.

Lunar Eclipse

On March 3rd/4th there is a total eclipse of the moon. The eclipse begins at 21.30 and ends at 01.11, with the total phase lasting from 22.44 until 23.57. A lunar eclipse occurs when the Moon moves into the Earths shadow as cast by the Sun. When this happens it is normally still possible to see the moon although it often takes on a "copper" hue depending on the current state of the Earth's upper atmosphere. Recent volcanic events can significantly affect the moon's appearance, and on occasions (presumably when the Earth's atmosphere is unusually free from contaminants) it has been reported to have disappeared completely.


Interestingly there are some lunar occultations that take place during the eclipse but these are stars of magnitudes between 7 and 10. If you would like any information about these please let me know. (01732 832691)

Sadly there are no lunar occultations in March of stars brighter that magnitude 6 that occur before midnight. However, if you are an early riser there are 2 other interesting events to observe.

Firstly, Saturn is occulted by an almost full Moon on Friday 2nd March at 02.45.

Secondly, the brightest star in Leo (Regulus) at magnitude 1.4 is occulted by a gibbous Moon on 30th March. It disappears at 03.30 (04.30 BST) and reappears on the bright limb at 04.19 (05.19 BST). For those who are a little further west the Moon will appear to "graze" along the limb of the Moon.


Unfortunately all the easily observed passes by the ISS in March occur in the early morning.

Lunar Occultations

I said last month that I would talk about lunar occultations in a little more depth. Exact timings of these events are used to determine the position of the Moon in space.

By far the easiest type of occultation to observe is the disappearance, especially when the Moon is between new and first quarter. Normally this is the time when you can see a thin crescent as well as the "dark" portion of the Moon illuminated by earthshine. Viewed through a telescope you can easily see the faintly illuminated portion of the Moon approaching the star so it is easy to tell when the light from the star will be extinguished. Once the Moon has reached first quarter it's not as easy to see any earthshine, so predicting when the star will disappear is trickier and means you have to stay at the eyepiece as the predicted time approaches.

More difficult to observe is the re-appearance. These generally occur when the Moon is waning. In these cases the star will have earlier disappeared behind the bright limb, unseen by us because the light from the star will have been drowned out by the light from the Moon. It will then suddenly appear from behind the dark limb. With this type of observation you need to know exactly where to look around the limb of the Moon (the position angle in degrees) to be able to accurately record the time of the event.

A type of occultation event that is a combination of both the above is the "graze". This occurs when a star as seen from Earth just makes contact with the Moon's limb. When this occurs it is possible, with some fairly simple equipment, to time the star as it disappears and reappears in between the mountains and valleys of the Moon. These events are visible over a very narrow track on the Earth's surface and often group observations are arranged with observers in positions perpendicular to the track. This information is used to build up an accurate profile of that area of the Moon through which the star appeared to pass.

I hope that brief insight into occultations might encourage some of you to try this particular type of astronomy. If you would like any more information please ask.

Brian Mills


Even Solar Sails Need a Mast

by Patrick L. Barry

Like the explorers of centuries past who set sail for new lands, humans may someday sail across deep space to visit other stars.  Only it won't be wind pushing their sails, but the slight pressure of sunlight.

Solar sails, as they're called, hold great promise for providing propulsion in space without the need for heavy propellant.  But building a solar sail will be hard; to make the most of sunlight's tiny push, the sail must be as large as several football fields, yet weigh next to nothing.  Creating a super-lightweight material for the sail itself is tricky enough, but how do you build a "mast" for that sail that's equally light and strong?

Enter SAILMAST, a program to build and test-fly a mast light enough for future solar sails.  With support from NASA's In-Space Propulsion Program to mature the technology and perform ground demonstrator tests, SAILMAST's engineers were ready to produce a truss suitable for validation in space that's 40 meters (about 130 feet) long, yet weighs only 1.4 kilograms (about 3 pounds)!

In spite of its light weight, this truss is surprisingly rigid. "It's a revelation when people come in and actually play with one of the demo versions-it's  like, whoa, this is really strong!" says Michael McEachen, principal investigator for SAILMAST at ATK Space Systems in Goleta, California.

SAILMAST will fly aboard NASA's Space Technology 8 (ST8) mission, scheduled to launch in February 2009.  The mission is part of NASA's New Millennium Program, which flight tests cutting-edge technologies so that they can be used reliably for future space exploration.  While actually flying to nearby stars is probably decades away, solar sails may come in handy close to home.  Engineers are eyeing this technology for "solar sentinels," spacecraft that orbit the Sun to provide early warning of solar flares.

Once in space, ST8 will slowly deploy SAILMAST by uncoiling it.  The truss consists of three very thin, 40-meter-long rods connected by short cross-members.  The engineers used high-strength graphite for these structural members so that they could make them very thin and light.

The key question is how straight SAILMAST will be after it deploys in space.  The smaller the curve of the mast the more load it can support.  "That's really why we need to fly it in space, to see how straight it is when it's floating weightlessly," McEachen says.

It's an important step toward building a sail for the space-mariners of the future.

Find out more about SAILMAST at nmp.nasa.gov/st8.  Kids can visit spaceplace.nasa.gov/en/kids/st8/sailmast to see how SAILMAST is like a Slinky(r) toy in space.

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



Chairman   John Vale-Taylor  pjvalet@tiscali.co.uk

Phil Berry  01892 783544 phil.berry@tiscali.co.uk

Treasurer  Mike Wyles  01892 542863 mikewyles@globalnet.co.uk

Publicity & Website  Michael Harte  01892 783292 michael@greenman.demon.co.uk

Newsletter Editor  Geoff Rathbone  01959 524727 Geoff@rathbone007.fsnet.co.uk

Any material for inclusion in the April Newsletter should be with the Editor by March 28th  2007