Castle Point Astronomy Club
Castle Point Astronomy Club Diary
October 2017 by Dave Stratton
Castle Point Astronomy Club

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Wednesday 4th October 2017

Andrew said that last Saturday’s Open Night was clouded out but better luck next time.

He also said that they were writing the new programme and therefore speakers were required – hopefully there would be volunteers but if not ....................

Ron advised that the club has a grating and webcam to allow DIY spectroscopy.

Mike introduced Jack Martin for his talk:

Practical Stellar Spectroscopy

Jack started by showing us a slide of the spectrograph of Vega.

Jack explained that he had co-written a chapter in a book – Practical Amateur Spectroscopy and he wrote another – A Spectroscopic Atlas of Bright Stars (A pocket field guide).

He posed a question – Why do Spectroscopy?

It´s enjoyable, educational, inspiring, you make a contribution and it´s rewarding.

What is Spectroscopy?

It is the study of the light from an object that is passed through a prism such that the material contained within the object can be determined. Jack said that 85% of the knowledge we have of the universe comes through Spectroscopy.

He showed us a spectrograph of the Sun that was about 2.5m long that he had made himself and pointed out the absorption and emission lines that indicate the elements in the Sun.

What is Light?

Light is electromagnetic radiation within a certain portion of the electromagnetic spectrum. The word usually refers to visible light, which is visible to the human eye and is responsible for the sense of sight. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), between the infrared (with longer wavelengths) and the ultraviolet (with shorter wavelengths). Jack said we see only a tiny part of the whole spectrum.

What is a Spectrum?

It is the dispersion of light passed through a prism or refracted from a grating that is split into its component colours Red, Orange, Yellow, Blue, Indigo and Violet. The following mnemonic helps remember them - Richard Of York Gave Battle In Vain.

How are spectral lines formed?

A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies. Spectral lines are often used to identify atoms and molecules. These ‘fingerprints’ can be compared to the previously collected ‘fingerprints’ of atoms and molecules, and are thus used to identify the atomic and molecular components of stars and planets which would otherwise be impossible.

Jack showed us a HST picture of Betelgeuse – it was an approximately round blob – what can we learn from it? Not much.

He showed us spectrographs from a number of stars with of course loads of info – no contest.

What can we measure with spectroscopy?

Spectroscopy is the study of the interaction between matter and electromagnetic radiation. Historically, spectroscopy originated through the study of visible light dispersed according to its wavelength, by a prism. Later the concept was expanded greatly to include any interaction with radiative energy as a function of its wavelength or frequency. Spectroscopic data is often represented by an emission spectrum, a plot of the response of interest as a function of wavelength or frequency.

Jack showed us a spectrograph of a Type 1a Supa Nova SN2014J

He told us about William Huggins - Sir William Huggins, OM, KCB, PRS (7 February 1824 – 12 May 1910) was an English astronomer best known for his pioneering work in astronomical spectroscopy together with his wife Margaret Lindsay Huggins. Jack built his own spectrographic observatory in Rayleigh and named it after Sir W.

We saw a video clip of his observatory´s automatic sliding roof operating.

Jack showed us a video of his scope on its Paramount traversing. He added that his MX is very good and that it is a mistake to economise on the quality of the mount.

He said he does not use eyepieces everything is done on a screen. The LH one is for spectroscopy and the RH is his finder.

He has found that for spectroscopy the optics are not critical but aperture is important.

He explained how he had modified his spectroscopic mounting to make it easier to remove and refit.

He said he still uses Windows XP and finds it very good.

He explained with a diagram how a spectroscope works together with a detailed view of the optical train. He said the slit on his is 21microns wide (1micron is 0.001mm).

He is involved with a group of Pro/Am spectrographers that includes 200 amateurs.

We saw a slide showing all the current ongoing projects.

He showed us several spectrographs of well known stars – Sirius is a Standard Star and is useful to classify stars and remove contamination.

Jack is involved with four groups altogether.


Wednesday 11th October 2017

Andrew reminded us that he needs some speakers to give talks and other ideas for next year´s programme.

Rob said he was organising the club Christmas Meal on 7th Dec so talk to him.

Peter said that tomorrow a 20m rock will whizz past the Earth – we hope!

Andrew introduced Dave Smith for his talk:

Variable Stars

He began by posing the question:

What is a Variable Star?

Variable stars are stars that change brightness. The brightness changes of these stars can range from a thousandth of a magnitude to as much as twenty magnitudes over periods of a fraction of a second to years, depending on the type of variable star.

Why observe them?

There are a number of reasons why variable stars change their brightness. Pulsating variables, for example, swell and shrink due to internal forces. An eclipsing binary will dim when it is eclipsed by a faint companion, and then brighten when the occulting star moves out of the way.

Is it of any use?

Variable stars are stars whose light output, for some reason, varies. We often plot light curves showing the brightness (magnitude) of the star versus time, to see how the light output is changing.

Isn´t it like watching paint dry?

Dave explained that for him it all started with an email from Ed about Algol. He admitted that he was struggling with the concept but he imaged Algol and made a simple video which we saw this evening showing the change in brightness.

He showed us a chart of the when Algol is at its various mags. (2.1 to 3.4) over a 9.6hour duration.

We saw a chart showing Algol’s location in Persius.

Dave showed a pic of his kit and explained it – the mount is a NEQ6 he admitted that you do not need this level of quality stuff for variable stars but he has an automatic focuser, a focal reducer, filter wheel, CCD Camera he said he only had to buy one special filter.

He showed us his very first sequence for EG Cepheus.

He uses some free software – Muniwin to produce the graphs.

We saw his file for AD Andromeda.

He showed another chart of EG Cepheus and was pleased that his recorded mags. Were in line with the official data.

Dave showed us a with some software an animation of a typical variable star. He changed the parameters to demonstrate how this affected what we saw – fascinating.

We saw charts of All Aur, TZ Lyr, U Cep and AD And.

He also showed a pic of Roche Lobes and how material can transfer from one star to another thus changing their size.

Dave told us about detached binary stars, semi detached and contact binaries.

He told us about OV Boo which has a tiny period of 0.046days – his own chart showed the period to be about 1hour and over several days the mag changed from 11.5 to 13.8. It is possible that it is a neutron star with a white dwarf going around it.

The study of variable stars can be done with a DSLR.

There are two kinds of variable stars: intrinsic, in which variation is due to physical changes in the star or stellar system, and extrinsic, in which variability is due to the eclipse of one star by another or the effect of stellar rotation. Variable stars are frequently divided into five main classes: the intrinsic pulsating, cataclysmic, and eruptive variables, and the extrinsic eclipsing binary and rotating stars.

We also saw several supa novas and a number of people he worked with in the BAA. Plus the Pelican Nebula and the Elephants trunk Nebula.


Wednesday 25th October 2017

Andrew said that next week we are having a Stikfest and whilst progress is being made on the programme for 2018 we still need speakers.

Rob said he was still taking bookings for our Christmas Meal on 7th Dec.

Mike announced that as Peter was away he was covering for him with his talk:

The Autumn Skies October 2017

Mike began by saying that currently the planets are disappointing. Saturn is low in the West after sunset and Venus rises just before the Sun in the East. Mars rises a little earlier but is much harder to find. However Jupiter will soon be in the morning sky.

With the aid of a chart he pointed out the Autumn constellations including Cygnus to the West and Taurus in the East.

He spoke very entertainingly about the ancient Greek Mythology - they thought Pegasus was a flying horse and Cassiopeia a goddess doing her hair!

Mike explained how we defined the brightness of stars with their magnitude where the larger the number the fainter the star so the very brightest are negative numbers – Sirius is -1.46 and the Moon is -12.6 with the Sun at -26.7 and Vega 0.00. The faintest star you can see with your eye is about 5. Binoculars will allow perhaps mag 9 and a decent scope 16 dependent upon the seeing and the power used of course. We saw a chart showing the apparent magnitude of a selection of stars.

Mike told us how the position of stars is described using RA and Dec which work in a similar way to Latitude and Longitude. RA means Right Ascension and Declination is the angle from the equator from zero to plus or minus 90°.

He also told us about astronomical distances where the main unit of measurement is the light year (ly). Light travels 6,000,000,000,000miles in a year.

He gave us all a chart of the area of sky he was talking about and on the back were some details of various objects together with some challenges for beginners and of course the more experienced.

We learnt about star clusters such as the Pleiades Cluster which was noted by Galileo Galilei in 1610. Messier noted it as M45 indicating it was not a comet. The Hyades Cluster is close by in Taurus and is rather older. The Double Cluster is between Persius and Cassiopeia. The Stickman Cluster is in Cassiopeia which also provides a home for M103.

Mike told us about our closest galaxy neighbour - M31 the Andromeda Galaxy it is 2.54lya and is just about visible with the naked eye at mag 3.4. We saw a wonderful image but he said you would not see this in a scope. It is 220,000 light years across and contains 1000,000,000,000 stars. Mike pointed out that you can see a star cluster within M31.

M33 is a side on galaxy with well displayed spiral arms it is called the Pinwheel Galaxy and is 3 million lya. C23 is an edge on galaxy with a dust lane across its length visible in larger scopes. It is mag 9.9 and 33million light years away.

Stephan´s Quintet in Pegasus is a group of 5 galaxies four of which are interacting it is quite hard to find.

Mike explained that meteor showers are seen when the Earth passes through the path of a comet such as Hale Bopp and Halley´s Comet. The next shower we can see is the Leonids on 15th to 20th Nov. The Zenith Hourly Rate varies from one or two to 10,000 plus about every 33 years, 1966 and 1999 were good years. He explained that the point in the sky where the meteors appear to come from is known as the radiant.


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