MEETINGS

APRIL MEETING

        Phil Berry opened the meeting by saying we now have a new general email address to contact the Committee at: wadhurstastro@gmail.com

        Should any member have any queries or suggestions to make to the Committee as a whole, then this address should be used.

        Further to his attempts to look into light pollution around Wadhurst, Phil has found that the greatest light pollution is coming from Uplands College across the road from our venue.  He has been in contact with the college and they have listened sympathetically to what he has to say, and they are looking into improving the situation providing the money can be made available.

        Last month, John Wayte gave us another of his interesting snippets from the world of science and one of them was about the largest known star.  We had just had a very informative talk about Large Mass stars by Ben Richie who showed reserve when asked by John to confirm his giant star.  Afterwards, Ben told Phil Berry that in fact an even larger star is thought to have been discovered, but it still has to be finally confirmed before the findings are published.  So in a way, John managed to inadvertently extract some information of a possible new discovery; we wait to hear more…

        Next Phil introduced our speaker who had come through heavy rain from near Wiston in West Sussex.

Making Every Photon Count

By Steve Richards

        Steve has had a life long interest in photography but in 2004 he began to specialise in Astro-photography and now writes for Sky at Night magazine, often as their technical guru.  He has also written a book with the same title as this talk.

        He began by saying if you are able to satisfy 6 “F” words; Find, Focus, Frame, Follow, Film, Finish then you are well on the way to taking successful Astro-photographs.

        FIND.  Steve said that finding the object you want to photograph in the night sky can be exceedingly difficult.  Not only is the object usually too faint to line up on but counteracting the Earth’s movement requires special techniques.

        It was demonstrated that making a number of short exposures using an alt-azimuth mount, and then stacking the results gave a blurred image because the telescope turns relative to the area being imaged.  It is better to use an equatorial mount with a Right Ascension drive.  An equatorial wedge provided a good solution, although as in all equatorial mounts, it is important to polar-align first.  Steve showed a long exposure of the celestial pole he had taken himself and this clearly showed that Polaris is not exactly at the axis point, and this difference needs to be taken into account for precision.

        Setting circles are regarded as a bit hit-and-miss and Steve uses a go-to scope using a planetarium computer programme.

        FOCUS.  Having got close to the area to be imaged, Steve finds a bright star near by to use to obtain focus.  With a Newtonian telescope, the spider holding the secondary mirror causes diffraction spikes.  Focus has been achieved when the spikes become a single set of lines crossing each other at one single point.

        Although a refractor, Schmidt-Cassegrain or Maksutov telescope does not have a spider because there is no need to support a secondary mirror, though it can be simulated using cross wires in front of the aperture, crossing at the centre.

        A good aid to achieving focus is a device called a Bahtinov Mask that sits in front of the front of the telescope.

      

        Here, as focus is adjusted, one of the diffraction lines moves across the intersection where the other lines meet.  Focus has been achieved when this line sits exactly across the centre point.

        The mask can be bought, but Steve has made his own out of cardboard and using a craft knife.  A template can be down loaded from the internet and scaled to the size of the telescope’s aperture:

        FRAME.  Once looking in the desired location, Steve takes a number of 6-second exposures and then looks at the result to make sure he is framing the image correctly.  He then makes small adjustments to get the final framing exactly as he wants it.

        FOLLOW:  With the mount accurately aligned, manufacturing tolerances can still cause “Periodic Errors” causing even very slight star trails after very long exposure times.  To reduce this error as far as possible, “guiding” helps enormously.

        Auto-guiding is where a second telescope and CCD camera are attached to the same mount as the imaging telescope.  This second telescope is directed to a “guide” star close to the area being imaged and the output drift error used to correct the movement of the mount via computer to compensate for any tracking error that may occur.

        Another method that gets round having a second telescope is to use an off-axis guider.  A very small amount of light is reflected by a prism that sits in the light path but looks at a wider field to include the guide star.  The movement of the guide star is picked up by a separate CCD and errors used for corrections.  The problem here is that the guide star needs to be very close to the field being imaged.

        FILM.  Steve said that he used this word because it began with “F” to fit in with the other headings.  Really what he was looking at was to compare DSLR cameras with Astro-imaging CCD cameras.

        DSLRs have large sensors, are self-contained and are reasonably priced, but they have an infrared filter in front of the sensor which removes wavelengths such as hydrogen-alpha emitted by emission nebulae.  It is expensive to have removed and cannot be replaced making the camera difficult, but not impossible to use in normal photography with colour correction.

        An astro-imaging CCD camera is much more expensive and it is essential to have a computer.  It does not use an IR filter but does use a Peltier device to cool the sensor, so reducing sensor noise.  Steve said these were ideal for deep sky imaging and very long exposures.

        The two main types are either colour or black and white with colour filters.  Colour CCDs give results straight away while B&W CCDs need separate exposures using different colour filters.  These separate exposures are then combined to give the final colour result.  Ultimately, the B&W CCD and filters give higher resolution.

        Steve uses a filter wheel and apart from colour filters he also includes Hα, IR, Olll, S and Hβ filters.  We were shown several images taken using different filters to enhance certain features of different objects and the effectiveness was very noticeable.

        FINISH:  Once a set of frames of an image have been stored, processing can begin and as Steve says, this can take as long as it takes to capture the images in the first place.

        A set of additional frames need to be taken showing the camera’s characteristics, such as shading, pixel sensitivity and “dust bunnies” (dust in the optical path).

        A Dark frame with the telescope aperture covered reveals inevitable shading on the sensor.  A Bias frame is made up of a series of short exposures with the lens covered and these images stacked.  This reveals dark pixel offsets of the sensor.  A Flat frame is taken with the telescope looking towards an evenly illuminated white screen.  This frame will show differences in pixel sensitivity.  All these frames are used to subtract mathematically from the final image so that errors can be greatly reduced and even eliminated

        Steve ended by showing a number of his very impressive images many taken from his Chanctonbury Observatory near Wiston in West Susex.

        He has written a book with the same title as his talk and he has a website.

        Here are many more of his images with descriptions and well worth a visit.

Snippets from the Scientific World

John Wayte

This month, John’s first note was from Stephen Hawking who said that if the rate of expansion one second after the Big Bang had been smaller by even 1 part in a hundred thousand million million (1 part in  1016) the Universe would have collapsed and no intelligent life could have evolved!

But as John said, if he’s right, we are here and if he’s wrong, then we are still here!

In the second of his notes, John had read that Jeff Bezos, founder of Amazon, financed an expedition that has located the five F-1 engines used to power the Apollo 11 spacecraft to the moon.  Despite these engines being 4.3 kilometres below the surface of the Atlantic Ocean he wants to bring at least one of them up.

Basic Astronomy – The Earth

Brian Mills

Our Director of Observations felt he had covered Constellation Recognition for some time and for a change he is going to introduce a series of talks aimed at the beginner and as he said, what better place to start than with the Earth.

Seventy per cent of the surface of the Earth is salt water and has a pole-to-pole diameter of 12,712 Km but because of its spin has an equatorial diameter of 12,756 Km.

The planet comprises the crust holding the sea, land and mountains on Tectonic Plates.  Below this is the plastic Upper and Lower Mantle and then below this is the core which is divided into the Upper Core which is liquid iron and the Lower Core which is solid iron.

Brian then looked at the surface, beginning with the bottom of the Oceans down to about 11,000 metres and then at the atmosphere.

The lowest 20 Km is called the Troposphere and contains 80% of our atmosphere with a temperature at the top of approximately -60o C.  Next comes the Stratosphere where the temperature increases at the top to about 0o C.  Above this is the Mesosphere where meteors burn up and the temperature here falls to about -100o C.

Above this is the Thermosphere where temperatures can reach an incredible 1,500o C.  Brian said this is the layer in which the International Space Station orbits at an altitude of about 350 Km.  The Aurora occurs in the lower levels.

Above the Thermosphere is the Exosphere, the upper limit of our atmosphere which now mainly consists of rarefied hydrogen and helium.

Brian turned to how the Earth was formed from the primordial soup of gas and dust orbiting the Sun where particles collected together to form larger planetesimals and planets in an elliptical orbit.

Finally Brian looked at the tilt of the Earth’s rotation relative the plane of its orbit causing the seasons; so important for life.

MAY MEETING

        Wednesday 16th May 2012 – Our Director of Observations, Brian Mills will be giving a talk entitled “Astronomy – Its Relevance and its Women”.

        Meetings begin at 1930 although members are invited to arrive anytime after 1900 as this is a good time to exchange ideas and discuss problems and also relax before the meeting.

        The venue as always is held in the Upper Room of the Methodist Church at the east end of Wadhurst Lower High Street, opposite the entrance to Uplands College.  (For those with SatNav – the post code is TN5  6AT)

        Anyone is welcome but non-members are asked if they wouldn’t mind contributing £2 towards costs.

FUTURE  MEETINGS

        Wednesday 20th June 2012 – The Society’s “Open Evening” when there will be short talks and demonstrations of equipment and software.  The meeting is open to anyone with an interest in astronomy and there is an invitation to bring along telescopes and discuss their set-up and use.

        For non-members we ask if they would not mind paying £2 towards coffee and biscuits etc.

        Wednesday 18th July 2012 – John Strachan talks about “Amateur Astronomical Spectroscopy”.  This is fast growing area of astronomy amateurs are becoming interested in.

OTHER NOTES AND INFORMATION

The Observatory Science Centre Herstmonceux

Brian Mills

        On Saturday April 21st two members of WAS attended the above centre to take part in the CCD imaging course being run by our own Ian King, along with Nik Szymanek. They are two of the foremost CCD imagers working in the UK today and were involved in the very early days of this type of photography.

        The course, which took place in the dome of the 36” Yapp reflector (see photo) covered all aspects of imaging including choosing the best equipment, acquiring the data and then finally processing it. This final stage included a tutorial on using Photoshop to manipulate the data and bring out hidden depths in images that formally had been invisible. If you want to find out more about imaging, or want to hone your skills a little more, then this is the course for you. I’m sure Ian and Nik will be running it again although you will need to speak to Ian for details and locations.

   

CCD Imaging Course held at Herstmonceux

A Visit to see Patrick Moore

At the end of February three WAS members were fortunate to be able to visit Patrick Moore at his home in Selsey, Sussex . With them was Steve Collingwood who is a well known and respected optics engineer who is Service Manager for Telescope House at Lingfield in Surrey. Steve was responsible for refurbishing some of Patrick’s telescopes, including his first ever ‘scope (a three inch brass f/12 refractor) that is now magnificently restored as shown in the December 2011 edition of “ Astronomy Now”.

Patrick was, as always, a very genial and generous host, so after helping him to sample a bottle of his favourite Whisky that we had brought with us, an Indian take-away was ordered.

      

Patrick Moore’ and Guests

The picture, with Patrick centre stage, shows from left to right Phil Berry, Brian Mills and Ian King.

SKY NOTES FOR MAY

Planets

Mercury is a morning object after reaching western elongation on the 18th of last month, but due to the angle of the ecliptic at this time it only rises 24 minutes before the Sun on May 1st and is effectively unobservable.

Venus sets 4 hours after the Sun at the start of the month, but by the end this has reduced to just under 1 hour, although it will be lost in the twilight glare before then. The planet is, of course, making its way towards its most interesting inferior conjunction for more than a century when it will appear in transit across the face of the Sun on June 5th/6th.

        In the early part of the month it can still be seen as a brilliant object just slightly north of west at magnitude -4.2 with an apparent diameter of 45 arc seconds as the phase becomes a thinner crescent. In fact it is so bright that at the time of writing (end of April) I was able to project it onto the inside of the observatory roof and see the crescent quite clearly. If you have a small telescope or binoculars, have a look to see if you can make out the phase because although the portion illuminated is getting less, the apparent size of the planet is increasing.

Mars at magnitude +0.2 is now moving direct (west to east) in Leo after reaching its second stationary point last month. Its apparent size is decreasing rapidly from 9.9” (arc seconds) to 8.1” during this month as the Earth moves away from Mars. Its position is shown on the map.

Jupiter sets just 40 minutes after the Sun on the 1st of the month prior to its conjunction on the 13th when it will appear to pass invisibly below the Sun by approximately one solar diameter. It then moves west of our parent star although it will not be on view as a morning object until late June or early July from these latitudes.

Saturn still lies in the constellation of Virgo at magnitude +0.4 and is on the meridian at 23.00hrs mid month. The rings are well displayed and can be seen even in a small telescope although if you are taking a telescope outside from a warm house you should leave it to cool down for at least an hour, if not more before you use it. This gives a chance for the optics and the tube to cool to the outside temperature thus avoiding a lot of atmospheric turbulence that would ruin the image. Its position is shown on the “Mars” map.

Lunar Occultations

        Unfortunately there is only one reasonably bright occultation that occurs before midnight this month although there are many others that are either of fainter stars or take place at more unsociable hours.  DD = disappearance at the dark limb Time is in BST.

May

Time

Star

Mag

Ph

Alt °

%

illu

28th

22.39

SAO 118347

6.6

DD

24

51

Occultation of M67

        On the evening of 26th May the crescent Moon occults the open cluster M67 in Cancer. The blue circle in diagram shows roughly the apparent boundry of the cluster and you can see from this it is around the same size as a full Moon. M67 contains mainly faint stars with brightness’s from 7th magnitude through to 10th but if the sky is clear it could be worthwhile watching as twilight deepens. The event begins around 21.30 hrs BST. Incidentally the other dots you can see both within the grey area showing the Moon’s passage and outside it are all stars.

Phases of the Moon for May

Full

Last ¼

New

First ¼

6th

12th

20th

28th

ISS

        There are no evening passes of the ISS visible from Wadhurst this month.

Iridium Flares

        The flares that I’ve listed are magnitude -3 or brighter although there are a lot more that are fainter, occur after midnight or at a lower altitude. If you wish to see a complete list, or obtain timings for somewhere other than Wadhurst, go to www.heavens-above.com

        Remember that when one of these events is due it is sometimes possible to see the satellite in advance of the “flare”, although of course it will be much fainter at that time. There are several events that reach magnitude -8 which is as bright as these flares ever get, making them worthy of a look. Times are in BST.

May

Time

Mag

Alt°

Az.

2nd

22.32

-3

34

NE

6th

22.17

-8

40

NE

10th

22.02

-3

47

NE

11th

21.56

-5

47

NE

12th

23.14

-5

11

NNE

15th

23.06

-3

18

NNE

17th

23.03

-4

22

NNE

21st

21.14

-4

64

ENE

21st

22.49

-4

29

NE

25th

22.34

-7

36

NE

29th

22.20

-8

42

NE

31st

22.12

-4

46

NE

The Night Sky in May (Written for 22.00hrs BST mid month)

        In the north the Plough is on the meridian and just a few degrees from the zenith. Being on the opposite side of the pole, Cassiopeia is also on the meridian but is only 20° above the horizon. Cygnus, the winged horse, has now risen whilst one of the other members of the Summer Triangle (Vega) lies slightly higher and to the east.

        Looking east the spring constellations of Hercules and Corona Borealis are now on view as well as the large and rather featureless areas around Ophiuchus and Serpens.

To the south Virgo and Leo are either side of the meridian. Passing below both of them is Hydra, the water snake, with the small star groups of Crater and Corvus riding on its back.

In the west Gemini is the sole survivor from the winter constellations, although Capella in Auriga is still prominent. Just east of Gemini is the faint collection of stars that makes up Cancer, with the head of Hydra just below it.

Advanced Warning for June

        June 5th/6th - the last chance you have to see a transit of Venus. The Sun will be low and only the very end will be seen in the UK . Sunrise is at 04.46 hrs BST with last contact occurring at 05.49 hrs BST. The diagram shows graphically the path of Venus across the Sun, but be aware the times in the lower right hand corner are GMT. More details in the next newsletter.

Advance Warning for July

July 15th - grazing occultation of Jupiter and its moons.

Brian Mills

NASA’S SPACE PLACE

NASA Helps Europe Study a Comet–Up Close and Personal

By Dr. Tony Phillips

Europe’s Rosetta spacecraft is on its way to intercept comet 67P/Churyumov-Gerasimenko. Comets have been intercepted before, but this mission is different. Rosetta aims to make history by landing a probe on the comet’s surface while the mother ship orbits overhead.

“Rosetta is the European equivalent of a NASA flagship mission,” explains Claudia Alexander, project scientist for the U.S. Rosetta Project at NASA's Jet Propulsion Laboratory. “It will conduct the most comprehensive study of a comet ever performed.”

Rosetta’s payload contains 21 instruments (11 on the orbiter, 10 on the lander) designed to study almost every aspect of the comet’s chemistry, structure, and dynamics. Three of the sensors were contributed by the U.S. : Alice (an ultraviolet spectrometer), IES (an ion and electron sensor), and MIRO (a microwave sounder).

The main event of the mission will likely be the landing. The 100-kg lander, which looks a bit like a cross between NASA’s old Viking Mars landers and a modern microsatellite, will spend two weeks fastened to the comet’s icy surface. The European-built probe will collect samples for analysis by onboard microscopes and take stunning panoramic images from ground level.

“First the lander will study the surface from close range to establish a baseline before the comet becomes active,” explains Alexander. “Then the orbiter will investigate the flow of gas and dust around the comet's active, venting nucleus.”

Rosetta’s sensors will perform the experiments that reveal how the chemicals present interact with one another and with the solar wind. Alice and MIRO detect uncharged atoms and molecules, while IES detects the ions and electrons as the solar wind buffets the nucleus.

One problem that often vexes astronomers when they try to study comets is visibility. It’s hard to see through the dusty veil of gas billowing away from the heated nucleus. The microwaves MIRO detects can penetrate the dust, so MIRO can see and measure its target molecules even when other instruments can’t.

MIRO is one of several experiments focused on the comet’s structural properties. It will determine the comet’s dielectric constant, emissivity, and thermal conductivity to determine whether it is made of a powdery loose material, has a detectable layer of loose material, or is hard as rock.

“We want to find out whether comets have retained material from when the solar system formed,” says Alexander. “If the ancient materials are still there, we can get an idea of what conditions were like at the dawn of the solar system.”

Rosetta enters orbit in 2014. Stay tuned for updates!

Check out “Comet Quest,” the new, free iPhone/iPad game that has you operating the Rosetta spacecraft yourself. Get the link at spaceplace.nasa.gov/comet-quest.

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

  Description: rosetta2

Rosetta’s lander Philae will eject from the spacecraft, touch down on the comet’s nucleus, and immediately fire a harpoon into the surface to anchor itself so it won’t drift off in the weak gravity.

CONTACTS

General email address to contact the Committee

                                                      wadhurstastro@gmail.com

Chairman                                    John Vale-Taylor

Secretary & Events                 Phil Berry            

Treasurer                                   Mike Wyles  

Editor                                           Geoff Rathbone

Director of Observations       Brian Mills

Paul Treadaway                      

Wadhurst Astronomical Society website:

                                                      www.wadhurst.info/was/

SAGAS web-site                        www.sagasonline.org.uk

Any material for inclusion in the June 2012 Newsletter should be with the Editor by May 28th 2012