I haven’t been able to get out for any observing recently. But I have been up to something. In case you hadn’t noticed–and I know you have–I’m working on a double star project right now. In the process, I felt the need to come up with a consistent method for conveying stellar magnitudes. Something that goes a step further than the method I discussed in the double star tutorial I put together a couple months ago. Since I’m already coloring the stars digitally I figured I would take care of magnitude differences digitally as well. Some astronomical sketchers may not care for this approach, since it does reduce and can even eliminate the hand-drawn appearance of the sketch. I can definitely appreciate that sentiment. I struggled with it quite a bit as I debated how to handle the magnitudes.
In the end, I decided that there would be a lot of benefit to consistently comparing magnitudes across multiple sketches. Manipulating the sketches in Photoshop (or any other paint program) provides a very simple and reliable way of doing this. I worked out a list of paint brush sizes that I now use to plot the stars over the scanned sketch. I also apply a systematically larger glow around the brighter stars. I also set up a custom paintbrush to draw in diffraction rings for the magnified inset views of the closest doubles.
After using this process on my latest round of double star sketches, I went back and updated my older sketches. I still have the original sketches posted with each entry, but the double star sketch gallery has been updated with all the new images.
I still need to figure out the best way to write a tutorial about this part of the process, since it’s pretty pedantic. But until then, here is a reference image of the brush sizes I use based on magnitude. (Note that I generate these sketches at a larger size and reduce them before posting here, so these brush dimensions appear larger in the original file.)
2 Replies to “Double Star Sketch Update”
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This is a real good reference in estimating the various mags of stars.This info is going to really come in handy!!.I am really bad at estimating and hate to throw out numbers willy nilly for the sake of sounding right.
Good job!
Hi Andrew, thanks for the comment. I’m not really confident myself at looking through the eyepiece and rattling off a number to estimate the visual magnitude of a star or other object. I do try to gauge relative magnitudes of stars as much as possible by noting or sketching which are brighter or fainter than others in the field. But that doesn’t really get me to an absolute number for any of them.
I’ve been saving that part for later when I go to the Vizier site or Simbad. Then I can check out a few double star databases, including the Washington Double Star database to see if there is general agreement on the magnitudes. At that point, I can tell how large or small to make the stars on the digital version of my sketch.
As an imager, I imagine there may be a way for you to shoot images of stars at consistent exposure times, and then check to see how large the star has bloomed in the exposure, and how bright the profile of pixels is to come up with an educated stab at the magnitude. I believe there was an article about that in Sky and Telescope recently…I’ll have to give that a look.
Anyway, I’m sure I’m not better than you are at estimating those numbers visually. But I’m trying to do research afterward and convey them consistently in the digital sketches.
Take care,
Jeremy