Castle Point Astronomy Club
1969-2019 - 50th Anniversary Year
Castle Point Astronomy Club Diary
May 2019 by Dave Stratton

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Wednesday 1st May 2019

Tonight we had a May Day Astronomy Quiz. It was hosted by Andy T with Chairman Mike as score keeper and referee.

After four rounds of various astronomy questions, one team emerged victorious, much to their surprise.

Wednesday 7th May 2019

Mike said that our Open Day would be 2nd June.

Andrew said that next week we had an outside speaker - Chris Jones with Things that go Bang! In the Night.

Andrew said he was looking after us this evening with: Warp Drive - a Discussion

He began by saying that with our current technology our most distant probe was Voyager which had managed a meagre 1 light day in 40 years.

He explained very eloquently that he thought we should have a kind of thought experiment where we could travel anywhere at all with infinite speed and so be there instantly. So he wanted to know where we would go and why.

One of the things we should remember is that if say you went to an object that was 1 million light years away then when you arrived it would of course be ‘now’ and it may not be there anymore! However if you looked back at the solar system it would appear as it was 1 million years ago – before ‘us’!

Perhaps we should play safe and go to Titan – at least we could expect it still to be there.

Gord said he wanted to go to the far side of the Moon where it would be great for astronomy and very quite even from Earth’s radio emissions.

Andy wanted to go to a globular cluster and see what the Milky Way looks like from there, he surmised that if you went far enough you could see the solar system forming.

Mike imagined seeing Betelgeuse explode and being able to watch it do so repeatedly and if you got good enough at controlling your means of transport you could watch it in slow motion!

Cynthia wanted to land on a comet - although this has been done it was just a robot that experienced it.

Peter wanted to go to the edge of the Milky Way specifically to see how distance affected the way we see the star patterns.

Len wanted to have a look at an Exoplanet of similar size to the Earth.

Mike wondered how we might gauge life – years ago we used SETI now we can analyze a planet’s atmosphere using spectroscopy. We need to remember that Earth is the only safe place to live.

Trevor wanted to go to Mars and see what really happened to Beagle.

Mike fancied going to Cygnus X1 and having a good look at a black hole. We need to remember that communication with Earth would be impossible.

Paul wanted to go to the edge of the Universe and see if it looked the same.

Allan wanted to go to the furthest galaxy in the Hubble Deep Field and look from there.

Ken said he wanted to go somewhere where there were intelligent people who spoke English – this is of course a pipedream - we don’t even have that here.

Dave H said he wanted to go to a multiple star system to see what it looked like with lots of suns.

Mike wanted to get up-close to Omega Centauri – WOW! Also to swing by Stephan’s Quintet.

Andrew really wanted a good look at M51.

It is likely that objects such as the Ring Nebula would be too diffuse up close.

Cynthia wanted to get up close to Saturn particularly the ring system.

Gord said we should be very careful if we got to the edge of the Universe and there was nowhere else to go…………………………………………………

Scary but wonderful!

Wednesday 15th May 2019

Mike said that we have our Family Day on the Sunday after next.

Andrew said next week we have Astronomers’ Question Time which is excellent. He added that the week after that we had our very our Gord with the Eddington Eclipse – I’ve no idea - you need to come along and find out.

Jack announced that he wants a 4 inch refractor. He also said he had heard that there was a Supa Nova in NGC4353 at mag 13 and brightening. (After the meeting Dave Sm got an image of it!)

Peter introduced his long time friend Chris Jones who is Director of Risk Management and Compliance at Cory Environmental and keen astronomer for his talk: Things that go Bang! In the night

At this point Chris told us about various types of nova and supa nova where a pair of binary stars with one feeding matter off the other and getting to a critical size where its Hydrostatic Equilibrium between the gravity holding it together and the pressure of the internal reactions fails the pressure wins and – bang!

It was very fascinating but sadly I cannot reproduce it here.

Wednesday 22nd May 2019

Mike said that we have our Family Day on the Sunday after next 2nd June. Next week we have Gord with a talk: The Eddington Eclipse.

Martine still needs 2L fizzy drink bottles.

Ed said that last night was great for doubles.

Peter said the ISS was great for this evening and the next few days it’s overhead.

Mike said that this evening we were having: Astronomers’ Question Time

This is where we all can ask a question and we can all answer it.

Q. Martine got us started with: What are Globular Clusters and where they are? A globular cluster is a spherical collection of stars that orbit a galactic core, as a satellite. Globular clusters are very tightly bound by gravity, which gives them their spherical shapes, and relatively high stellar densities toward their centres.
Globular Clusters are in a halo around the galaxy some actually pass through the plane. Globular clusters contain some of the first stars to be produced in the galaxy; their origins and their role in galactic evolution are still unclear.

Q. Is there a halo of Dark Matter around our galaxy? This presupposes that Dark Matter exists. The stuff is to date undetectable so we have no idea where it is or even if it is!

Q. Peter said he had three pairs of binocular one of which was 11X80 they appeared to be the best but why - as the exit pupil size did not support that? Others in the room supported this view.
In optics, the exit pupil is a virtual aperture in an optical system. On a pair of binoculars it can be seen as the bright circle in the centre of each eyepiece when you hold them about 30cm away from your eyes and with the objective lenses pointed toward a bright light.
Another way to visualize the exit pupil is to first fully retract the eye-cups and focus the binoculars onto a bright area. Then hold a white card up to the eyepiece, this projects a disc of light onto the card. Now move the card closer to or further away from the eyepiece until you get the smallest possible diameter of the projected disc. The diameter of this bright disc is the diameter of the exit pupil.
Note: The exit pupil must always be circular and supply uniform brightness. If shadows are visible, this is an indicator of poor quality.

Q. Why is the Exit Pupil Important? It is important because the only light rays which pass through this virtual aperture can exit the system and enter your eyes. Therefore with all else being equal, the larger the exit pupil diameter, the more amount of light will be delivered to your eye. It is therefore an important aspect when comparing the theoretical brightness of two optical instruments and something to consider when choosing binoculars, especially for use in poor light conditions like at dawn or dusk or for astronomical observation.
We had a lively discussion about the way to measure pupil size, but we were missing our tame optician Andy – so it rests there. So when choosing bins you must look through them!

Q. Roger reported that something has been found in the Kuiper Belt with a ring! What is it? Perhaps it’s the result of a collision.

Q. Gary said he had read of a new Exoplanet being discovered in the Goldilocks zone of its star. Apparently it was discovered a while ago. Our known life is based on Carbon - Silicon while not as efficient as Carbon will still react with stuff.

Q. Natalie asked if there were any laws in space? Apparently there is a journal of space law - so yes.

Q. Mike asked who can launch when and where? Groups with the UN are involved as aircraft have to be kept clear of launches. Also there are rule preventing someone going somewhere and claiming it as theirs.

Q. Craig asked what the rings of Saturn were made from? Bits of rock in orbit around the planet.

Q. Martine asked what was the best way of projecting the Sun to see its features? This can be done with one half of a pair of bins, but be sure to leave the caps on the half not being used. Can also be done with a scope, but use a simple eyepiece not one with lots of elements that may get hot. Be especially careful if members of the public are involved as they may not understand the risks. Bada filters are recommended over the objective lens.

Q. Len asked what is a Quasar (quasi-stellar radio source)? An astronomical object of very high luminosity found in the centre of some galaxies and powered by gas spiraling at high velocity into an extremely large black hole. The brightest quasars can outshine all of the stars in the galaxies in which they reside, which makes them visible even at distances of billions of light-years. Quasars are among the most distant and luminous objects known.

Q. Len asked where was Saturn at the moment? Low in SE rising after midnight fairly close to Jupiter.

Peter announced that our Dengie Dark Site had been renewed so please use it.

Q. Mike asked what was the worst scope or gadget you had ever bought?
Many reported bad mounts and useless finder scopes. A report of buying a very expensive 6 inch refractor that he could not afford a mount for.
A pair of bins that always showed a double image.
A 70mm Celestron f9 that was only any good for very bright objects. Several reports of dodgy cheap refractors.
One report of a special device for setting correct focus to attach a camera to a scope that was very hard to use.

Very interesting.

Wednesday 29th May 2019

Ed said Pluto was close to Saturn and would help to spot it.

Andrew said that next week we have a Stikfest and the week after it’s Telescope Zoo and the week after that it’s Siân Cleaver – a junior member some time ago - on the 19th with a talk on: Airbus missions and Orion

Mike introduced our speaker for the evening Gordon with his talk: The Eddington Eclipse

In 1916, Albert Einstein published his general theory of relativity in full mathematical detail. That opened the window on a radically new framework for physics, abolishing established notions of space and time and replacing Newton’s formulation of the laws of gravity. Einstein’s revolution was to change the course of science; but in the years immediately after publication, there was no definitive observational evidence that his theory was correct.

Enter Arthur Stanley Eddington. An astronomer interested in Einstein’s theory because of its wide-ranging implications for astrophysics and cosmology, Eddington took on the task of proving it. By harnessing a total solar eclipse, he argued that the deflection, or bending, of light by the Sun’s gravity could be measured. This was a critical test, because Einstein’s theory predicted a deflection precisely twice the value obtained using Isaac Newton’s law of universal gravitation. The needed eclipse came 100 years ago, in 1919. Eddington is now forever associated with two expeditions to view it: from Sobral in northern Brazil, and the island of Príncipe off the coast of West Africa.

Einstein’s theory, eight years in the making, sprang from insights he had developed after he published his theory of special relativity in 1905. One of the effects predicted by the new theory was that light rays passing close to a massive body, such as a star, should be bent by its gravitational field. This effect had been predicted qualitatively using Newton’s theory of gravity. Tantalizingly, Newton himself had written in his 1704 opus Opticks: “Do not Bodies act upon Light at a distance, and by their action bend its Rays…?” But there is no evidence that he calculated the magnitude of the effect (the first full calculation was published by German mathematician Johann Georg von Soldner, in 1804).

Newton’s theory of gravity did not, of course, formulate gravity as a consequence of curved space. That was Einstein’s innovation. And when he calculated the effect, he confirmed that light is deflected (as in the Newtonian theory), but through curved space. It is this curvature that doubles the deflection.

Test conditions

Einstein first publicly aired the general theory of relativity to the Prussian Academy of Sciences in 1915. The First World War was by then well under way, in all its horror. The next year, despite wartime severance of communication channels, Eddington and fellow astronomer Frank Watson Dyson — then director of the Cambridge Observatory and Astronomer Royal, respectively — managed to obtain Einstein’s published papers. Dyson immediately realized that the total solar eclipse in 1919 would prove an ideal test.

During this eclipse, the Sun would sit in front of the Hyades, a cluster of bright stars in the constellation of Taurus. Thus, at totality, many stars would be visible near the eclipsed disk. (This was key because the light-bending effect predicted by Einstein is greatest for stars observed close to the Sun.) The stars’ positions relative to the Sun could be recorded and measured on photographic plates, and then compared with reference plates showing the stars when the Sun was nowhere near the field of view. Any apparent shifts, caused by the Sun’s gravitational field, could then be calculated. The more stars measured, the better the chance the observers would have of correcting for systematic errors and reducing random ones.

That was the idea, but there were many practical obstacles to surmount, both in the technicalities of making the observations, and in the expeditionary logistics. The eclipse’s path of totality passed from northern Brazil across the Atlantic to West Africa, making it impossible to mount an expedition from Britain until hostilities had ceased. The Armistice in November 1918 left just enough time to put the plan into action. Dyson, in overall charge of the expeditions, remained in England. Eddington travelled to Príncipe; Andrew Crommelin, who worked at the Royal Greenwich Observatory, London, went to Sobral.

The details of the dual expeditions are well served by No Shadow of a Doubt. Meticulously researched and vividly written, the account is sure to become the standard reference work on this fascinating example of ‘Big Science’. Eddington, Kennefick reveals, had terrible luck. Met by poor weather in Príncipe, he managed to make fewer measurements than he had hoped. Then, a proposed strike by a steamship company meant that he could not stay in Príncipe long enough to measure the star positions on his plates on site, and had instead to do the analysis after he had returned to England.

Crommelin had much better conditions in Brazil. Despite technical issues with equipment that left many plates badly blurred, his measurements were decisive, and were noticeably closer to the Einstein prediction than to the Newtonian. The results were announced collectively in November that year, at a special joint meeting of the Royal Society and Royal Astronomical Society in London. It made front-page news around the globe.

Questions and confirmation

That initial conclusion by Dyson, Eddington, Crommelin and their teams was subsequently confirmed by many further eclipse experiments. Yet Eddington has been accused by some of mishandling the eclipse measurements. Kennefick’s title, No Shadow of a Doubt, is thus both a pun and a declaration of intent to dispel these suspicions. Kennefick discusses the criticisms in some detail. I can add a couple of brief points.

One is that Eddington had to adopt a Plan B when analysing the Príncipe data, after misfortune had forced his hand; but, in my opinion, he did nothing unreasonable. All the 1919 eclipse measurements are tabulated (in F. W. Dyson et al. Philos. Trans. R. Soc. Lond. A 220, 291–333; 1920). It is straightforward, and also quite instructive, to analyse them using modern statistical techniques. I’ve done this, and found no evidence that Eddington ‘cooked the books’. It’s a huge misfortune that none of the original plates from either expedition survives: otherwise, it might have been possible to measure them using more sophisticated technology. Eddington’s plates were lost after he died in 1944 — his sister might have thrown them away when she was forced to move out of the Cambridge home they had shared. Crommelin’s plates seem to have disappeared in the course of successive reorganizations at the Royal Observatory.

Our Gord did a stunning job of conveying this brilliant story eloquently and humorously, but it was beyond me to capture it so above is the essence gathered from the internet

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