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est. 1956

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Science at the Croydon Astronomical Society

The Transit of Venus on 6th June 2012

The European Southern Observatory has a page of information on both transits - they are intending to try to determine the size of the Earth’s Orbit from these measurements. This was used as the historic method of measuring the size of the Solar System but has now been superseeded by radar measurements. It should still be interesting to see how accurate the measurements are.

The Transit of Mercury on 7th May 2003

To aid those planning your observations here in PDF format is a list of the altitude and azimuth of both the Sun and Mercury for the Transit for our Observatory at Kenley. Note that the Sun is very low around 6 degrees at First Contact.Also its azimuth is 70 degrees so you need a site with a clear north east horizon to get a good view or better still take a video. In both cases you must not look at the Sun directly or with any optical instruments unless you have taken proper precautions.


The Eye - your key to observing the Universe

The eye is a vital tool to detect photons that come through a telescope – coupled with the brain it is a very sophisticated detector that interacts with the image in subtle ways. To understand how to get the best from your personal detector you need to understand how the eye brain system functions. One place to look is The Joy of Visual Perception: A Web Book. This ‘book’ also contains an extensive list of links to other sites dealing with human vision.

There is a copy of a presentation on ‘Eyes on the Universe’ by John Murrell CAS available here (910k PDF file). This has been given to a number of astronomical societies including the CAS, Wadhurst AS and The Society of Popular Astronomy.

You may also like to read Eye and Brain, The psychology of Seeing by Richard L Gregory, Oxford University Press {ISBN 0 19 852412} and Chapters 1,2 and 3 of Visual Astronomy of the Deep Sky by Roger N Clark, Cambridge University Press {ISBN 0 521 36155 9}.

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Telescopes for Amateur Astronomers

A wide variety of telescopes are available for amateur astronomers, in April 2002 we held a special meeting dedicated to showing our members some of the many types available. The introduction to the meeting by John Murrell is available here in pdf format. The calculations described in this presentation are programmed in an Excel 97 spreadsheet that enables you to calculate the performance of a telescope given two of the basic parameters – diameter, focal length or focal ratio.

This is available below - try it and see if it is useful. This also calculates the parameters if you have a CCD camera attached to the telescope.

21st April 2003 The calculation spreadsheet has been updated it now allows you to select the camera you are using from the supplied list and copies the details into the calculation sheet rather than you having to do the copying manually. If you have a camera that is not on the list you can enter the details in the User Section. You should also be able to calculate the FoV and other CCD details for standard camera lenses if you use these on your CCD - just enter the focal length and the f/number in the telescope sheet.

My telescope calculation spreadsheet TeleCCD has now been updated to version 7 and is available here. The changes are fairly minor - I have updated the CCD camera list to include the Canon 10D as this is popular with astro-photographers. Also I have added an entry for 35mm film to the CCD page so you can determine your parameters if you use film.

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Observing Logs

Serious Observers need to record their results so that they can be analysed later or  for the less serious Observers we need accurate notes to jog our memory ! -


Ideal for answering those inevitable questions when you shown your slides at the Astronomy Club:



An outline of the requirements for Observing Logs were outlined in a lecture given to the society by John Murrell. The slides for this lecture together with the lectures notes are available in PDF format here.

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To ensure that the results are useful we need to ensure that the correct time is recorded. Our page Science at the CAS: Observation Time will allow you to set your clocks and lead you to definitions of the different flavours of time.

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If you have a CCD camera and are interested in contributing vital observations of variable stars the American Association of Variable Star Observers have a useful manual here that will tell you how to make measurements that will be useful to professional astronomers. If you submit any observations please let us know.

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One of our concerns is the ever increasing level of light pollution which is making visual observation very difficult. Additional information on light pollution may be found on our light pollution page. To allow the effects of light pollution to be recorded and assessed we are trying to develop a standardized means of photographing the night sky so that we can compare the levels of light pollution at different sites and try to monitor any changes.

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Roy Easto has written our own software package to allow the manipulation of images from our Starlight Express SXF Camera and Framestore - the user manual for the software and how to download and install. Your own copy can be found on our ccduser page.

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