54 Leonis is my second double star observation from the night of the 1st May (see my previous post for a discussion of this). Here is my image:-
This was a 5s exposure at ISO 1600 on a Nikon D90 at the prime focus of a 140mm Maksutov Cassegrain (an Orion OMC-140). The picture can be better seen by 'clicking' on it. The image is being viewed at full scale (in other words it has not been binned up). 54 Leo A and B are marked and are magnitude 4.48 and 6.29 respectively. The image scale is 0.5859 arcseconds per pixel and this is a 1200x1200 pixel crop of the original.
I now have a better method for orientating the image. I have posted this observation at the BAA. If you view this and then click on the link which says 54-Leo under the heading 'Objects' you will come to a page that lists all the observations of this double star and some additional information about the object. Again, if you click on the link which says In-The-Sky.org (a button in green) you will come to a very useful website run by BAA member Dominic Ford. This particular page has a finder chart on it and if you click on the magnifier in the corner you get another scalable view of this chart. Reducing the field of view to about 1 degree gives a nice plot of double star and the field stars around it.
I exported the chart as a PNG image and then opened it in Photoshop. At the same time I opened my original image of the double star and located the two reasonably bright field stars you can see in the chart near 54 Leo. Photoshop can be used to determine the angle between a line and the horizontal. Drawing a line between the two field stars on the chart gave me one angle. Repeating this for a line drawn between the same stars on my image gave me another. The difference between these two angles is how much I would need to rotate my image so that the two field stars in my image are in the same orientation as in the chart.
Having done this I could make some measurements of the separation and position angle (PA) of 54 Leo. A couple of measurements of the separation gave me 10.77 and 11.18 pixels. This averages to 10.98 pixels and, at 0.5859 arcseconds per pixel, this is 6.4 arcseconds. PA is a measurement of the angle of the fainter star relative to the brighter one. Imagine a line drawn from one to the other. The angle is measured from due north anticlockwise (through east) to the line. Again a couple of measurements gave 111.8 and 116.6 degrees which averages to 114 degrees. The published separation and PA for this double star is 6.6 arcseconds and 113 degrees, so in very good agreement.
All text and images © Duncan Hale-Sutton 2024
No comments:
Post a Comment