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Introduction Like many people who return to astronomy I was interested in the hobby when I was younger but as the teen years went on I was drawn into other activities although I did observe occasionally with my trusty 8x30 Tasco binoculars from my back garden or when I went away on holiday. My wife suggested we buy a telescope a couple of years ago and I am now the proud owner of 3 scopes. A 4.5” Newtonian (semi-retired) and ETX 70 and an Orion Optics 8” f6 Newtonian that is now my main scope. The challenge I face where I live 51.5 degrees north and 0.26 west is the light pollution from London. The night sky isn’t black it is orange! I am fortunate because to my south is Richmond Park an area of 10 square miles with no lights. This means that light pollution to the South is lower than any other direction. On a good night the ZLM is 4-4.5. I can sometimes see all the stars of Ursa Minor but this is rare. Experience When I first started observing I spent many hours seeking ‘faint fuzzies’ and this proved to be exceptionally frustrating. Fortunately I do not give up easily and decided to find a way to enjoy the astronomy from my back garden. The moment of revelation came when I planned to view some double stars. The first target was Eta Casseopia and it was a sheer joy. Firstly I could see the object in my finderscope and when I focused in on the object there it was matching the description in my starter astronomy handbook (Collins Guide to Stars and Planets – I book a thoroughly recommend). 2 stars, Yellow and red hanging in space together. I was hooked. I had purchased a Norton’s Star atlas and started to work my way through the doubles listed. At the UK Astrofest 2005 I purchased 2 books ‘A Visual Atlas of Double Stars’ by Mike Ropelewski published by the Webb Society ‘Observing and Measuring Visual Double Stars’ edited by Bob Argyle. Both these books came with an extensive list of doubles to view I have observed 90 doubles from ‘ A Visual Atlas’ and have drawn 66 sketches of doubles some of which are not in the book. On average I view about 20 double stars a month (Weather permitting!!) The ‘Observing and Measuring…’ book contains a full list of the Washington Double Star list, the Tycho catalogue and much additional useful information on a CD-Rom. I am now moving beyond ‘the beginner’ level in Astronomy. I am comfortable with the constellations. I am even competent with setting circles!! And I have built up a reasonable quantity and quality of information from my observations. Equipment With the recent purchase of an Orion Optics 8” F6 Newtonian I have a ‘scope that will perform to a level that I will need if I am going to improve on my current expertise. Orion Optics 8” f6 I must emphasise I am in no way an expert but I hope to show you that anyone who has basic astronomical knowledge, a good scope, a stopwatch and a scientific calculator can make accurate observations of open/wide double stars. My measuring kit. 12.5mm Ortho, 2x Barlow, Stopwatch. Motivation In my (very) limited experience there are 2 main areas that can be explored with double stars or any astronomical passion and it is summed up by the title of Bob Argyle’s book. We can observe them visually or with webcams and CCDs, We can note the colour contrasts e.g. Alberio, gamma Andromeda or the similarity e.g. Castor. My sketch book is full of comments about the colours you can see and estimating the magnitudes of the components. We can also measure them accurately to possibly assist in the refining of stars orbits and from that the mass of the 2 components. As the Mass of the Star is central to calculating absolute magnitude and comparing this with apparent magnitude you can begin to calculate more accurate stellar distances. Observations and Calculations In chapter 12 of the ‘Observing and Measuring Visual Double Stars’ Tom Teague has written about simple techniques of measurement. These are the ring micrometer method, the chronometric method and the illuminated reticle eyepiece. I have an un-motored EQ5 mount and do not own a reticle eyepiece but I do own a 12.5mm orthoscopic eyepiece and a 2x Barlow. The eyepiece has a well constructed field stop made of metal and combined with the Barlow makes an ideal ring micrometer. The process of calculating the PA and separation using this method is convoluted but after a few attempts I can get results within a few minutes of starting the calculations. All you need to record the transits are a decent eyepiece (and a Barlow), a stop watch and pen and paper The first vital piece of information you need to know is how wide your field of view is. The way to do this is to choose 2 stars that are similar in brightness, quite close in RA and just under the width of your FOV in DEC. You can then take a number of timings as the stars enter and leave the FOV. Finding a pair of stars that fit the above description is easier said than done. I found the 2 stars Chi Hercules and HIP77763 were ideal for this purpose. Once you have found these stars you need their declination to at least 1 decimal place. I obtained this information from Simbad. http://simbad.u-strasbg.fr/sim-fid.pl Chi Hercules was 42:27:05.5 HIP77763 was 42:35:12.9 This information combined with the transit time allows for an accurate calculation of the field of view. There are additional factors to take into consideration e.g. atmospheric refraction but they are too advanced to be considered here. Below is a table with the timings I took. Field of View Measurements Timing1 Timing2 Timing3 Timing4 Timing5 Timing6 Timing7 Timing8 Timing9 Star South ingress(entry) 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Chi Herc North ingress 14.43 11.64 11.02 8.49 16.80 9.49 8.18 12.55 8.70 HIP77763 North Egress (exit) 41.83 44.42 44.39 45.64 41.96 45.49 43.52 43.88 43.52 HIP77763 South Egress 54.99 53.14 53.39 52.27 55.27 52.70 52.77 54.17 52.86 Chi Herc The CD-Rom contains software to calculate the field radius and after inputting this data the software gave a field radius figure of 351” Using the formulas from the book and taking the mean of the transits I also calculated a figure for the field radius and arrived at 331” In the spirit of compromise I decided to use to use a figure of 340” as my field radius. First attempt The first Double I chose to measure was Theta Lyra. I was a certainly wide enough at nearly 100” and with magnitudes of approximately 4.5 & 10 they would be easy to follow in the 8” scope. Timing measurements for Theta Lyra Field Radius 340" North Field Timing1 Timing2 Timing3 Timing4 Timing5 Mean A1 0.00 0.00 0.00 0.00 0.00 0.00 B1 9.39 10.24 11.30 10.71 10.42 10.41 A2 47.45 51.34 45.05 46.92 48.98 47.95 B2 53.20 56.74 49.02 51.42 54.02 52.88 PA 72.43 63.05 63.30 64.11 64.42 65.46 Sep 93.62 103.87 101.19 100.09 101.24 100.00 The actual measurements of Theta Lyra are PA 70 and Separation of 98.8”. My measurements show that separation is quite close but the position angle is off by 5 degrees. As it was my first attempt I was reasonably pleased and I knew that with a bit of practice I would become more accurate. I determined to try another pair that were reasonably bright and should be able to be measured with some degree of accuracy. I chose Zeta Lyra as they were stars of even brightness (4.3 and 5.6) and well separated. Second Attempt Below are 5 of measurements I made of Zeta Lyra Zeta Lyra Field Radius 340" South Field Timing 1 Timing 2 Timing 3 Timing 4 Timing 5 Mean A1 0.00 0.00 0.00 0.00 0.00 0.00 B1 5.79 6.25 4.85 5.12 5.74 5.55 B2 37.29 36.27 44.87 42.51 40.43 40.27 A2 39.41 38.57 45.72 43.70 42.42 41.96 PA 149.4 148.2 147.9 147.9 151.8 149.04 Sep 42.5 44.2 44.4 43.7 46.8 44.31 Field Radius 330" PA 150.8 149.4 149.7 149.5 153.3 150.53 Sep 44.3 45.8 46.7 45.7 49.0 46.28 I have included figures for a field radius of 330” for comparison to show how a small change in the filed stop diameter can influence the data. The actual figures for Zeta Lyra given in Norton’s Star Atlas are PA 150, Separation 44.0” and to achieve figures that are within a degree of the PA and less than 1 arc second out is a result I am very pleased with. In the Chapter written by Tom Teague he states that the ring micrometer method will give consistent results on very wide pairs e.g. pairs wider than 100+” separation. My measurements of Zeta Lyra show that accurate measurements can be made of Stars much closer than 100+”. I do not know if the equality of brightness helps the measurements or my skill level has improved. Stars that are fainter will be harder to spot when they enter the field of view and so the human error factor must be more significant. Calculations I have not included the full calculations but here is a snap shot of some of the ‘working out’ I have undertaken. The only piece of advice I will give you is keep a clear set of information available, I keep written records and input the raw data into excel. This is useful when you mess up the calculations and have to start again as I have had to on several occasions. There is also no getting away from the manual calculation process. It does take a bit of time and you have to check and recheck the information as it is very easy for errors to creep in. Being a UK resident means that there are plenty of cloudy nights to complete this exercise. I have not included any information on measuring atmospheric refraction that can ‘move’ the stars from their true position. This is mainly because I haven’t got my mind round the equations yet!! Conclusion Double Star measurement is a challenging but very rewarding element of the astronomy hobby. I have only just started in this particular area but I hope that this will inspire some more people to try this aspect of astronomy. You can use any type of telescope on any mount with any eyepiece. The only tool you have to buy is a stopwatch (I found my mobile phone had a stopwatch feature on it after I purchased the sports stopwatch!!). Double star measurement is also one of the few areas of astronomy that you can attempt on a partly cloudy, light polluted night. You do not need pristine night or a sky that is mag 6.5. The calculations are intricate but with a scientific calculator they are not difficult. This aspect of the hobby appeals to me because you are accurately measuring an object Hundreds of light years away using nothing more than a telescope and a cheap stopwatch and with these tools you could provide valuable information to the professional astronomy community. I am pleased with my initial attempts at measuring double stars and I will be looking at further doubles to measure. Wide and faint doubles are a neglected area so there is plenty of room for people to contribute. I would like to hear how any attempts at measurements went. I can be emailed on iancoster@fast24.co.uk Who knows if I live long enough I might be able to measure Porrima this way!! Clear Skies Ian