Castle Point Astronomy Club
Castle Point Astronomy Club Diary
April 2017 by Dave Stratton
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5th April 2017

Peter said that Mercury was in the evening sky now sunset is at 19.30 and at 20.00 Mercury will be above where the Sun set. Jupiter is also looking good.

Comet 41P is overhead at mag 4.5 at the end of Ursa Minor. There is another Lovejoy comet imminent. See the in-the-sky website.

Mike spoke about the Open Night last Saturday saying that it went very well and how proud he was of the club and thanked everybody for their help.

Mike introduced Andy T for his talk:

The Hertzsprung Russell Diagram Part 1

He explained what the scales were.

He said he thought it very pretty and made no apologies for showing it so many times.

He said the top right of the diagram was the home of the very large stars and the lower left was for the very small.

It relates stars relative to the Sun which is pretty much in the middle.

He referred to the Hipparchus satellite.

Gaia will look at 1000,000,000 stars.

He spoke of Ejnar Hertzsprung and Henry Norris Russell. They both had craters named after them - Ejnar´s is 600km diameter on the far side of the moon and Henry´s is 120km diameter and on Mars.

However he said they were not the first to have the idea of having a diagram that compared temperature against luminosity of stars that was Schwarzschild and Rosenberg.

Andy said that a scatter diagram was an excellent way of presenting data - he showed us a page of 'meaningless' numbers in columns and then a scatter diagram of the same info and it was ‘CPAC‚ -simple. So a picture really is worth a thousand words.

He showed us HR diagrams of the Hyades and Pleiades circa 1910.

He asked - what is luminosity? It can be measured using the whole electromagnetic spectrum or just in visual light.

Luminosity is actually difficult to measure - we really measure the brightness.

He spoke of Hipparchus who came up with a way of talking about magnitude. He had 5 magnitudes with a factor of 2 between each - such that mag 2 was twice as bright as mag 3, so that mag 1 was 100 times as bright as mag 5.

Sir Norman Pogrom developed a slightly different system called Pogrom´s ratio where the difference is 2.512. This is better and still in use today.

Andy said that luminosity is diluted by distance so we need to compare not a star's magnitude but its absolute magnitude. This is what its magnitude would be if viewed at 10 Parsecs. If viewed at this distance our Sun would be 4.83 mag. (quite unassuming).

We look forward to parts 2 and 3.

12th April 2017

Our usual scibe was away so here is a brief summary of the evening:

Andrew started by mentioning that the Club had been invited to have a free stand at the Weald Park Country Show on 30th April and 1st May. He asked that anyone interested in going let him know.

Peter then mentioned that there were currently three comets in the sky that were visible with binoculars. Two were virtually overhead and visible all night and the other coudl be seen at 4am in the mornings.

We then went on to the main talk for the evening which was Mike Culley on Meteorites.

Mike started by definig what a meteorite was. It is any kind of natural meterial that did not originate on Earth. In other words, it falls to the ground from space. He then went through the history of their study. It was originally believed that rocks coudl not fall from space so they must be from hale or lightening storms. Scientists eventually proved they were from space.

He then went through the different types which are stoney, iron and a mixture of the two. He explained how each are formed and their origins. The most common are stoney and come from collsions of object in the asteroid belt throwing off small chunks of rocl which eventually make their way to earth. Iron meteorites come from the cores of asteroids which have been destroyed or broken up by collision. They are much rarer. Meteorites which are a mixture of iron and stone are even less commom and come from the boundary layer of an object´s core and it's outer layers. The most rare types are pieces of the Moon and Mars which have found their way to Earth.

Mike then discussed some large impact craters and events both in prehistoric times and in recent history. Some of them have been spectacular.

He finished by passing round some samples of the various meteorite types in his possession.

A very interesting talk.

Mike finished by saying that next week there would be an evening on people´s favourite astronomy websites. He asked that people email the URL of their favourite site to him or bring along a screen grab of it.

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