Wednesday 6th February 2019
Mike introduced our first guest speaker of the year Greg Smye-Rumsby for his talk: The History of Longitude at Greenwich
Greg is a regular contributor to the Astronomy Now magazine, a member of the Orpington Astronomy Society and a regular speaker at the Guildford Astronomy Society.
He said we take a lot of stuff for granted these days – such as our location on the planet. It’s so easy now we have gadgets in our pockets with maps and GPS.
In the not so distant past it was fairly easy to establish Latitude with a sextant – providing you could see the Sun at its highest point. But Lognitide was a different matter. The Earth spins once every 23hours 56minutes and 4.1seconds. Therefore the sun moves in the sky each day. We have 12hours on our clock faces due to the earlier use of sundials.
Greg explained how the seasons worked in the Northern hemisphere with the aid of a diagram. He said that we benefitted from the fact that the earth’s orbit is not circular and we are actually closer to the sun in the winter which keeps us warmer and further away in the summer that stops us getting too hot.
We saw an interesting graph that showed that clocks were behind in the early months then ahead in May, behind in July and August then ahead for the remainder of the year.
Greg told us about John Flamsteed FRS (19 August 1646 – 31 December 1719) was an English astronomer and the first Astronomer Royal in 1675. His principle task was to map the heavens.
He said the task of establishing longitude was far from new - Galilei Galileo was using the moons of Jupiter. Although this works it does require Jupiter to be in sight but there is another problem because the speed of light causes an error.
Another method was the Lunar Distance Method – this uses stars on the ecliptic that are occulted by the moon Such as Regulus and Spica. It fails because it is hard to see stars and the moon is not always up. Greg said the term Lunatic was coined for folk trying this method.
Sir Cloudesley Shovell, (1650–1707) was the Admiral of the Fleet when The Scilly naval disaster of 1707 saw the loss of four warships of a Royal Navy fleet off the Isles of Scilly in severe weather on 22 October 1707. Between 1,400 and 2,000 sailors lost their lives aboard the wrecked vessels, making the incident one of the worst maritime disasters in British naval history. The disaster has been attributed to a combination of factors such as the navigators' inability to accurately calculate their positions.
The Commissioners for the Discovery of the Longitude at Sea, or more popularly Board of Longitude, was a British government body formed in 1714 to administer a scheme of prizes intended to encourage innovators to solve the problem of finding longitude at sea.
The Board administered prizes for those who could demonstrate a working device or method. The main longitude prizes were:
Greg explained with the aid of a diagram that a nautical mile is a unit of measurement used in both air and marine navigation, and for the definition of territorial waters. Historically, it was defined as one minute of a degree of latitude. Today it is defined as 1,852 metres or 1.15miles the derived unit of speed is the knot, one nautical mile per hour.
Astronomer Royal Nevil Maskelyne 1791 favoured the Lunar Distance method.
'Cutty Sark' and ‘Thermopylae’ were rival clippers – both very fast sailing ships that travelled long distance routes and so needed accurate navigation.
John Harrison (3rd April 1693 – 24th March 1776) was a self-educated English carpenter and clockmaker who invented the marine chronometer, He decided to build a sea clock that would keep good time despite the unstable platform afforded by a sailing ship.
H1 his first attempt was very good and took 5years to make.
He went on to make H4 which was like a rather large pocket watch being 5inches in diameter. It was his best and proved to be invaluable.
Harrison’s clocks had a temperature correction feature in the form of a bimetal device that changed its curvature as the temperature varied. H4 even had a feature that the hands would stop prior to the spring running down by 30 minutes while the mechanism carried on so that no time was lost. Also no time was lost during winding.
Apparently he did not like H2 but thought H3 which had a reciprocating flywheel was better.
Captain James Cook took H4 on a trip and was very impressed.
In addition to inventing the bimetal strip John Harrison was responsible for the ball race.
The Board of Longitude remained reluctant to pay him out and only did so after George 3rd insisted. But only after another clockmaker, Larcum Kendall, was able to make one from John H’s plans.
Greg said that in the US when railways were first laid - to keep costs down they were single track which meant they had to be two-way. But because the country is so wide the problem of timing the trains was large. The issue was resolved by making four time zones and using the more accurate clocks and of course the telegraph.
At a conference in Washington in 1884 there was a meridian conference attended by 26 countries 22 of which chose to use Greenwich.
Chester Alan Arthur was an American attorney and politician who served as the 21st President of the United States from 1881 to 1885. He influenced the decision. He was much distrusted when he started but ended much respected.
Greg said the the Ordnance Survey maps that are so familiar today were actually made – as the name implies to allow the accurate placement of armaments for defence purposes.
A Leap Year occurs every four years if divisible by 4 unless it is divisible by 100. Those years are not Leap Years unless they are also divisible by 400. That is why 1900, 2100, 2200, 2300 are not Leap Years but 2000 and 2400 are Leap Years.
We also learnt that the time ball at Greenwich which falls at 13.00 each day was put in place in 1833 so sea captains could set their clocks prior to setting sale. Apparently the current one has dents as once when it blew down in a storm it was used as a football by some of the workmen.
The GPS system that is so familiar today was calibrated in 1969 using the George Airy Transit Circle telescope housed at Greenwich.
Absolutely wonderful. Probably the best talk and presentation we have ever had!
Wednesday 13th February 2019
We managed an observing night.
Ed has his Edmund AutoScan which is a rather strange looking Dobsonian with a spherical bottom that sits in a special base and can be pointed anywhere and will stay there. Ed really likes it and viewed Mars and Uranus (they’re close at the moment), the Beehive, M81 and M82 also the Pleiades.
Gerald had a mounted pair of binoculars and was looking at M42.
Abi had a very newly acquired 100mm SkyWatcher Schmitt Cassegraine with GPS and Bluetooth. It was second hand but virtually unused. The handset works the scope via Bluetooth so no wires. She was having some teething troubles getting it to set up with a single star line-up. If all else fails she might have to read the instructions! However it was working well under manual control.
Ron had a 10inch Dob and was looking at Polaris when I passed by.
Rob had a camera with telephoto lens on an AstroTrac mount and was imaging a comet and later M42 with some success.
Chris and his Dad had another binocular set up.
It was a good evening until the folk who were using the hall left and put up all the blinds letting the light out which they did not turn off – then Ed got involved.
It went well.
Wednesday 27th February 2019
To be added
Wednesday 27th February 2019
We managed another observing night.
Abi still appeared to be enjoying the struggle to get her newly acquired GPS equipped SkyWatcher to set up properly.
Andrew M had his ETX 70 Meade. He shared the rather surprising news that he had spent some time during the day lightly clad working in his new garden and was now well wrapped up for observing.
Charlie had his tripod mounted bins looking at M31.
Ken was pointing his Celestron 9.5 Schmidt Cassegraine at whatever he could find.
John Sm had the club’s 8inch Dob and looked very happy.
Ron had a pair of bins mounted on a super gadget attached to a tripod so as you changed the altitude they kept pointing the same way. (I wish I could think what it’s called).
Ed had his 10inch Dob and was looking at M35, M81, M82 and the Beehive.
Mike was pointing stuff out with his laser pointer.
New folk Christine and Allan came along for their first visit and were pretty much the last to leave. Caroline belongs to the Regents Park Astronomy Society who have been featured on Sky at Night.