1st March 2017
Mike gave the sad news about Ed´s wife Ann with details of the arrangements.
Andrew said the BBC wanted to interview a bunch of astronomers about an invention that they would like to see. Let him know if you are interested.
Peter said that MikeB had asked if there are any more candidates for our next camp.
Also he said there was a coronal hole on the Sun so perhaps we will get some aurora.
Plus we should look out for Jupiter as it is rising at 21.30.
Mike introduced Gord Falconer for his talk:
The Why (and some Ys) of Eclipses
Gord put up a slide immediately to explain his strange title - History, Observability, Geometry, Frequency and Predictability (each ends in a Y).
He began by explaining Bessel´s Method of eclipse prediction according to Roberdeau Buchanan.
The basic concept is that Besselian elements describe the movement of the shadow cast by the occulting body - for solar eclipses this is the shadow of the Moon - on a specifically chosen plane, called the fundamental plane. This is the geocentric, normal plane of the shadow axis. In other words, it is the plane through the Earth´s center that is perpendicular to the line through the centers of the occulting and the occulted bodies. One advantage, among others, of choosing this plane is that the outline of the shadow on it is always a circle, and there is no perspective distortion.
We got a bit of history next from the 3rd Millennium BC. Apparently if the king got an eclipse that he was not expecting the court philosopher stood a fair chance of getting paying the ultimate price. Gord said that Thales of Miletus predicted an eclipse for 28th May 585 BCE. However there is some doubt that he had the ability at the time.
Gord said that eclipses ran in cycles. It is important to recognize that it is not how often they occur but how often they can be seen.
Lunar eclipses can be seen from anywhere by everyone. Solar eclipses happen just as often but the path of totality is very narrow. A partial eclipse can happen without being noticed. Even with a total eclipse the changes are minimal until totality is almost reached.
In Southend dduring the 20th century there were 42 eclipses at some level, of these, none were total and only four managed 90%. There were 166 lunar eclipses of which 60 were total.
Gord mentioned the Saros Cycle: The periodicity and recurrence of eclipses is governed by the Saros cycle, a period of 6,585.3 days (18 years 11 days 8 hours). It was known to the Chaldeans as a period when lunar eclipses seemed to repeat themselves, but the cycle is applicable to solar eclipses as well.
Gord explained with the aid of some diagrams that the Moon´s orbit is not co-planer. It is tilted by 5.1450 which means it crosses the plane of the ecliptic (where the Sun is) twice each month. We can only get an eclipse when the Moon is crossing the ecliptic. Gord said the Sun moves by almost 10 per day. There is a period of 34 days centred about the node when the paths of Sun and Moon are close enough for an eclipse to occur.
The line of nodes precesses westward by 190 per year whilst the Sun is moving 10 per day eastwards. This means the sun can reach the next node after 173.3 days (less than 180).
There are always two eclipse seasons in a year, there can be two eclipses per season and often four counting both solar and lunar.
The actual delay from season to season is 173.3 - 34 equals 139 days.
Successive eclipse will always be very different - see paragraph on Saros Cycle above.
The period of time it takes for the Moon to complete an orbit from one node to the same node is known as the ‘Draconitic Month’. The Draconitic month is slightly shorter than the Synodic month. The main reason for this is that during the time that the Moon has completed an orbit around the Earth, the Earth (and Moon) have completed about 1/13th of their orbit around the Sun.
Gord mentioned that the Saros Cycle means that after the 6,585.3 days the cycles will repeat. He also mentioned there is the Exeligmos cycle which is three Saros Cycles but suggested that was best left to another talk!
Gord showed us four slides depicting the tracks of solar eclipses from 1999, 2017, 2035 and 2053. They are all across the US. (In fact the event in 2017 is the much acclaimed August 21st one that several club members are going to attend). They have very similar tracks and are 18 years apart and demonstrating the Saros Cycle.
At any time there are about 40 Saros Cycles in progress.
Gord finished with some pretty pics starting with a stunning Hybrid Eclipse, this is when an eclipse is annular at one location and total at another. We saw two images of the same eclipse taken 3000km apart. Stunning images - Gord said we get typically six hybrids per century. Also another of an annular as it was setting and finally one more annular taken in Argentina on 26th February 2017 (a few days ago).
8th March 2017
Andrew reminded us about the ‘Outreach’ thing he is interested in.
Ted said he had organised some flowers for Ann.
MikeB said the club camp in two weeks was now sorted.
Andrew introduced Jim for his talk:
My 10 inch Travel Scope
Jim said that on a trip to Oz some time ago he realised the advantages of a scope designed for travel.
So he made one - a Dob. He had brought it along for us to see. It is very nicely presented being very squat with eight struts to make it rigid and the boxes are made of wood painted red.
He said that a Dob is actually a Newtonian Reflector, with the aid of diagrams and the scope he explained how they work in principle.
He used UK Astro buy and sell to get the mirror. He said it is similar to EBay but it specialises in astro stuff so it is easier to trust it. He got a GSO mirror (made in Taiwan) for £100 which he tested and is pleased with.
With the aid of a diagram he explained how he tested the mirror and said that a rolled edge was a problem but a defect in the middle did not matter as that part is not used as the secondary mirror covers it. He used a beam splitter so that the laser illuminated the whole of the mirror.
Jim showed an image of a mirror through a Rounchigrame grid (I think) showing the pattern of lines.
He described how a Dob works and said the sliding surfaces used bumpy Formica sheets and Teflon/PTFE pads which give a good slide without friction.
He explained that the modern Dobs were much squatter than the earlier models. The scope was open sided to reduce weight but they need a shroud to cut out glare if there are nearby lights.
He explained the design of the rocker box and we saw a pic of his set-up in his garden to establish the actual focal length and establish the length of his truss poles. He ended up with eight to improve the rigidity.
He uses a Red Dot finder.
His initial design used bungee cords to prevent the scope from falling over, but these got replaced by a rather neat spring system.
His structure is made of wood which works fine but will cause a problem if it goes to Australia as they do not allow wood to be imported.
He showed sketches of his new project which is a Schmitt Cassegraine and then a 24inch Dob. (He is struggling with a 20inch at present!).
Andrew introduced MikeB for his talk:
Recognizing The Night Skies
Mike by saying that due to the Earth´s spinning the sky appears to rotate each 24 hours and it also changes with the seasons. He took us quickly through how this works.
He also explained what sidereal time was. Briefly sidereal time is a time scale that is based on Earth´s rate of rotation measured relative to the fixed stars rather than the Sun.
Polaris is almost at the celestial pole and is a major help in orientating the sky.
He loaded Stellarium and set it to show the sky rotating and the constellations moving.
He explained that we can find stuff by using a system similar to latitude and longitude called RA and Dec. He said that RA was in fact time and Dec was the angle from the Equator.
We often use the term ‘object’ in astronomy - this is anything in the sky.
He mentioned star catalogues of which there are several: The Messier has 110 objects, Caldwell has 109, NGC has 8000 and IC has 4000 in addition to NGC.
There are 88 constellations and they do not look like their names.
Mike said it was important to learn the sky. He found a simple Planisphere very useful and there are many sky programmes available - including Stellarium - which is free. He used to just pick a constellation and study it - what was in it? He found the Phillips Night Sky Atlas to be very good and the Cambridge Star Atlas.
He gave a demo on his tablet which was connecting to our projector via Bluetooth so he could hold the tablet up to the ceiling and on the screen was what the tablet was ‘seeing’.
He described in principle how imaging was done with the aid of an iOptron Sky Tracker. It is a device that can carry a camera and follow the sky. An AstroTrac will do similar.
He mentioned that red dot finders were a great aid to pointing the scope correctly.
He said that getting the focus correct was hard so he suggested using the Moon or Venus to set focus was good. He also said The Bahtinov mask is a device used to focus small astronomical telescopes accurately. It was invented by Russian amateur astrophotographer Pavel Bahtinov in 2005.
He gave us some nice images of stuff he has done including star trails, ISS, meteor showers, Milky Way, Earthshine, North American and Pelican Nebulae, Orion´s belt plus M42, Barnard´s Loop, Flame and Horsehead Nebulae, Heart and Soul Nebulae, M41, M31 and M13.
Wonderful - If that was a ‘Frantic-Fill-In’ we should have them more often.
15th March 2017
Barrie said he was raising money for a charity and had a box of stuff for all to consider.
Ed was having a clear out and had a miscellany of mainly computer stuff including a colour printer and loads of recordable CDs, books etc. and it was all free.
Andrew said we were having a: Stikfest
Jim was up first with IC1396A the Elephant´s Trunk nebula is a concentration of interstellar gas and dust. We saw a stunning image of the nebula which is 3 - 4 moons across. The two bright stars, close together, are causing a shock wave. This was the result of 20hours of imaging as it´s very faint.
Then he had a nice crescent image of Venus. As Venus is an inferior planet, inside our orbit, it always shows a phase. It is currently getting closer, in line of sight, to the Sun and we will shortly be treated to the phenomena that it will be both an evening ‘star’ and a morning one at the same time. Jim finished with a single channel image of 1396.
Peter had an image of Comet 21P - Giacobini-Zinner it is a periodic comet with a circular orbit at Jupiter-like distance. It has variable brightness. Peter said he had imaged it over 3 months - on 19th August it was very faint but by 22nd it was much brighter. It is thought that this is caused by an outburst of material from within which results in the brightness increasing.
Peter explained that he uses a system that compares the brightness of known stars nearby to that of the comet and judges the subject object from them.
Jack had some stuff on his phone that a bunch of clever folk were needed to get the phone to communicate with the laptop. Which despite their doubts they managed to do!
He began with images of the 10.4 m (34 ft) Great Canary Telescope, dedicated 24 July 2009. Both general views and from within and explained what we were looking at. He also had a video that involved turning the phone he had connected to our projector to show it, being held on its side to get the picture the right way up!
He also had pics of the Meridian line at Stratford. He said if you wanted your picture taken there it was a much better bet than Greenwich where you had to pay for the privilege. However it should be noted that the actual meridian is not there anymore it is actually 102 meters to the East! But it´s still history.
Jack also had a pic of a set of Brandon eyepieces that he considered buying at AstroFest. We also saw a pic of a ‘dead’ lamppost (lying on its side) - I failed to record why! And he showed a pic of a Celestron 130 scope complete that was at the Rayleigh community tip! He finished with some images of Einstein´s papers collection.
Interesting and different.
22nd March 2017
Mike reminded us that the Open Night was on 1st April from 8 until 10 but we should be there from 7pm. Mike explained briefly what the event was for the benefit of new members and guests. Emphasizing that it was at Hadleigh Country Park not Hadleigh Castle. He encouraged people to let him know if they could make it and said that many a new member in the past had spent their first time behind a scope showing something to members of the public!
Ted said that the Dark Site routine was due to change in that instead of keys we would have a zapper that allowed entry through an automatic gate. This would be operational on 1st June. Peter said that the last time he went the gate was missing so access was easy.
Peter said that recent skies have been good and the forecast for the coming weekend for our Club Astro Camp was good. He added that Jupiter was good from 10pm and that he had seen it through a 10inch refractor, one of only three in the UK, the Northern Belt was good but the Southern poor.
He said that Comet 41P has been close to M97 and M108, it would continue to improve up to mid April when it would be in the Plough and possibly naked eye. Comet 2015V2 Johnson would be closest to the Sun at the end of April - it has a good tail.
Mike got us started on the business of the evening which was:
Astronomers´ Question Time
This is where members of the audience ask questions and members of the audience answer them.
The first question was from Gord who wanted to know who had seen the youngest new Moon. He had seen two very young moons of 23hours 58minutes and 31hours, Mike had seen one at 24 hours and another at 18 hours. Apparently the shortest possible is circa 7.5 hours. Gord said the best time to capture one was at the equinox, but timing was very critical as the Moon is always going to be close to the Sun.
Martine asked why do scientists think that Dark Matter is particle related. Apparently there was a good item about it in the ‘Infinite Monkey Cage’ programme in January. Much spirited discussion followed but the truth is the phrase has been coined to describe the fact that the universe is much heavier than we can see and study. So the phrase says just that. There are many schools of thought, but the strong possibility is we may never now for sure. We may have to rewrite the physics. Jack said he would put a link that may be helpful around the group.
Emma wanted to know why we use the term lunar to describe the Moon. The name Luna was a Latin name for the Moon. The Moon takes roughly a month to orbit and the word for month was moonth.
Roger said that a bunch of folk in New Zealand were going to charter a plane tomorrow to fly across the International Date Line and back in the hope of seeing an auroral display!! There followed a lively discussion about places to see them like Iceland and Scotland.
Somehow we got to talking about geostationary satellites - Peter said it is possible to see them with a scope. They are of course not stationary but they remain over the same spot on the Earth - so if you find one and turn off the scope drives the satellite will remain in the scope but the stars will whizz past.
Mike said the early British satellite Prospero is still up there and he imaged it recently.
Mike asked if we had favourite constellations. Gord said we should consider whether we are talking about constellations or asterisms. The fact is a constellation is one of 88 specific areas of the sky whilst an asterism is a pattern of stars within a constellation - The Plough is an asterism within the constellation of Ursa Major. However he admitted that his favourite was Crux. Mike said his was Cygnus.
Ed said that whilst camping on one occasion he had a patch of sky visible through the tree canopy and he could just about see the Summer Triangle - so he made do with that and very much enjoyed it.
Mike said he enjoyed Scorpio.
MikeB liked Cassiopeia and Persius.
Gord said that if we were to go to Alpha Centauri and look at the Sun we would see that Cassiopeia had acquired an extra V!
Martine pondered why some objects had such misleading names - such as planetary nebula.
This prompted a discussion about what we would change if it were possible - the first suggestion was perhaps we should turn-off the Moon!
Perhaps we should reinstate Pluto - NO it´s science progress.
Jack asked if there was a naming system for Exoplanets. Apparently there is one.
There was a short discussion about tides - the Sun and the Moon affect tides, when they both pull in the same direction we get larger tides - at full and new Moon. And they are lower at the half Moon stage. Also North-South oceans have larger tides and East-West ones smaller - the Med. has very small tidal changes. A final fact is that the land experiences tides as well as the sea!
29th March 2017
Mike spoke about our Open Night this coming Saturday and passed round a paper so we could add our names.
He also said the club astro camp went well and we saw several pics from the event including a nice sun pillar. Plus Ron fixing a scope mount.
Mike introduced Andrew for the second part of his talk:
How the Sky Works Part 2
This was an explanation of how the Moon and planets move though the sky. If you would like a copy of the presentation, please contact us.