3rd May 2017
Andrew said that next week we have Astronomer’s Question Time.
He also said that the Evening Echo had advertised a spoof event for us (CPAC) for this Friday. Mike said he would talk to them as we need a denial publishing.
Peter said Jupiter is still good and you could Google when the GRS was visible. Comet 2015V2 Johnson was near the handle of the Plough.
The Jim Heycroft School need some expert help for an event to be held on a Friday.
Ed said he had placed a load of goodies on the top table for us to take away.
Mike introduced Andy for his talk:
The HR Diagram Part 2
Andy said the top scale on the chart was about Temperature, Spectral Class and Colour Index.
The Spectral Class is divided into seven classes O, B, A, F, G, K and M each of which can be split into ten sub divisions
Andy spoke about Absorption Lines in a spectrum; they show what specific elements are present. There are three types: - Lyman Series, Balmer Series and Paschen Series.
He showed us a fascinating chart showing loads of star characteristics including spectral class, size, luminosity and life expectancy plus lots more.
Andy said that the temperature of a star can be got from the Colour Index, this treats stars as if they were black bodies. The radiation curves of black bodies have a distinctive shape.
Most stars radiate as black bodies our Sun is a close fit to a black body with a temperature of 57770.
He showed us a chart indicating the relationship of colour to temperature. When we talk about magnitude 1 is brighter than 2 and very bright stars have negative values.
He told us about Cecilia Payne-Gaposchkin, a British born American astronomer, who discovered that stars are made mainly of hydrogen and helium and established that they could be classified according to their temperatures.
Andy spoke about Luminosity Class; some stars with similar temperature have different luminosity where they have different surface areas. This can affect stars in the super giant, main sequence or white dwarfs. Thus we have a plot of temperature against luminosity.
He finished with the news that Part 3 will be about how the chart is used.
10th May 2017
Andrew said that next week we have Dr Louise Alexander with a talk about the history of the Solar System using lunar samples. Plus the internet links are now on our website.
Gerald said that he would be here at 19.00 with our solar scope to have a look at the Sun.
Andrew got us started with tonight's entertainment which is:
Astronomers´ Question Time
Ted started us off with a question about whether increased solar activity meant there would be an auroral display. Peter said there were a number of good sites that gave quite accurate information on the phenomena. He also took the opportunity to talk about Noctiluscent Clouds which can be visible in the Northern skies well after sunset in summer.
Jack said he had acquired a set of Vixen 2.1 X 42 low power wide field bins - he said they were great for looking at the Milky Way. He said the literature described them as using Galilean Optics - What were they? It was explained by Ron that this was a simple system that used convex and concave lens to provide an erect image and low magnification. Jack said they were listed at £259 he got his second hand for £150.
Peter said that because he had poor vision in one eye and found most bins impossible to use. Other also reported the same problem. I reported that a friend had a pair of German bins that did not require focusing perhaps they would resolve the matter. Ken said he had Glaucoma and that the test for driving which was to read a number plate at 25 yards did not apply any more he had to get examined by an optician.
Gord asked a tongue-in-cheek question - Why do we need to focus at all and continually readjust? There was a general discussion about how temperature can affect focus but that the atmosphere was the main cause. Larger professional scopes use adaptive optics to continually adjust the focus and gain that precise image. It was also mentioned that long focus refractors are less affected so it would appear to be a depth of field issue.
Jack asked why the collimation of his spectroscope changes. Possibly because of temperature changes as it had an aluminium tube.
The HST although it had its own very serious focusing issues at first it does not suffer from this problem as it is above the atmosphere. When the James Webb scope gets going it will be placed at the Earth´s Le Grange point behind the Earth relative to the Sun.
Gord asked why would the ISS ever have to be finished - surely it is of immense value to humanity. If/when its useful life comes to an end although it can be kept in position quite cheaply there would be an ongoing risk that something would happen and it might come down out of control and cause a disaster.
Cosmin asked how he should take astronomical images - he was specifically concerned as he had heard talk at the club that a camera needed to be modified. It was quickly established that any camera or phone could take an image through a scope without modification. The removal of the red filter in expensive cameras was to allow long exposures to be made of deep sky objects. Ordinary cameras that had manual controls of exposure were perfectly capable of taking excellent images.
Emma´s assistant asked where he should look for the source of the Big Bang. The strange answer is everywhere.
He also wanted to know you cannot hear in space. This is simply because there is no air to carry the sound wave.
Cosmin said he understood we only see the Universe because light reaches us from it. The strange thing is we now know the universe is expanding at an ever increasing rate so we must anticipate that eventually the stars will go out or be too far away for the light to reach us their speed increases.
Always amazing how the discussion flows with a gathering of intelligent folk pondering apparently simple questions.
31st May 2017
Andrew said that next week we have an outside speaker with the return of Nick James with an update on Comet 67P.
Ted said the Village Fayre was on July 15th – unfortunately he and other regulars will be away so some volunteers are needed.
Andrew introduced Ed for his talk:
Me and My Scope
Ed told us it was a 10inch Dob. He said it was a very simple instrument that was actually a Newtonian Reflector with a simple mount that allowed it to be rotated and elevated. The idea and hence its name came from John Dobson who was an American monk with an interest in astronomy and needed a device to interest the public in astronomy so invented this ‘Sidewalk‘ telescope.
Ed told us about the lightpath with the aid of a diagram. He demonstrated that set up time was minimal just place the tube assembly onto the base - job-done.
He said he had modified it to increase ground clearance. He said this was necessary if setting up on rough ground. He simply added three feet and took the opportunity to extend the base a little at the same time. He also drilled holes in the base of the mirror cell to improve the ventilation so the mirror reaches ambient temperature more easily.
He also added a brake to help the scope maintain position when he had his heavier eyepieces in use. This took the form of two pads of Teflon that were in contact with the mounting disc and the effect was adjustable.
He also said the main cover for the tube was too flimsy so he used an actual shower cap. You would never guess as he turned it inside out to hide the Donald Duck Motif.
He also added a handle at the top end to enable easier adjustment. He also found the focuser a tad jerky so he modified it with a Teflon pad – now excellent.
Ed said he preferred visual astronomy and was very happy with the Moon and the Planets with a bit of deep sky. He said that he had recently seen Stephan’s Quintet which is a cluster of galaxies close to 7331 but rather harder to see. We saw one of his drawings of Stephan’s Quintet – he said it was one moon diameter away from 7331. Ed said the Quintet was actually discovered in 1877!
To finish Ed treated us to a stunning pic of the group he said they were 300lya - to help us understand this distance he said that when the light that we see now left the Earth only had one land mass – Pangaea.
Andrew said that he was doing the second part of the evening with a talk:
How Long is a Day?
He said that although we all know it is 24 hours long this is actually a simplistic view.
A Solar Day is the time it takes for the Sun to return to its highest point in the sky.
He saw us a chart showing how day length varied dependent upon the latitude.
The Earth rotates from West to East and is tilted at 23.40.
With the help of a chart he explained how the seasons work.
He told us about leap years which are required because the year is actually 365 days 6 hours long.
We saw pictures of a clock and a sundial. With a sundial the Noon to Noon time varies. Noon is when the Sun crosses the Meridian but this varies with the individual location.
He said that 1O was equivalent to 4minutes and 15O was 1 hour.
Way back there were lots of Meridians this eventually got sorted so now we have the Greenwich Meridian also known as the Prime Meridian.
He showed us a chart indicating Time Zones and the International Date Line.
We are 0.6O East of Greenwich so we are 0.6 X 4 or minus 2.4 minutes earlier.
There are a few days a year when there is no difference between a sundial and a clock. These are April 15th, June 14th, Sept 2nd and Dec 25th.
We saw a chart showing the error in a sundial and a graph of how a sundial goes slow and fast periodically. The Equation of Time is used to show the differences of sundial to clock.
Andrew said this was caused by the eccentricity of our orbit. This means the the Earth’s speed along its track varies from 29.291 Km/sec to 30.287 Km/sec.
Andrew also said that the Obliquity of the Ecliptic which is the inclination of Earth’s equator with respect to the ecliptic. This means the Sun is not always at its highest at Noon.
We saw a remarkable photo that showed the pattern of the Sun’s position at Noon over a year and it traces out a large figure 8 shape.
Andrew finished with the fact that there are 86,400seconds in 24 hours, a Solar Day was 86,400.002s econds and a Sidereal Day was 23 hours 56 mins 4.0916 seconds. A Sidereal Day which uses the background stars is shorter because the Earth moves further around its orbit.