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In lugnet.space, Daniel Jassim writes:
> > In lugnet.space, Don Heyse writes:
> > Pretty picture, but the first thing that comes to mind is the planet
> > looks wrong.
>
> Thank you for your suggestions. I was trying to keep this recipe as basic as
> possible--sort of an intro for those who haven't tried this. Thus, that
> particular picture was not an exercise in astronomical accuracy but more for
> simply using the Photoshop tools, effects and methods I've been trying out.
> I plan on going into more detail in future posts and sample planetary
> renderings but please feel free to share a more accurate rendering that you
> created and the steps you took. I am eager to learn.
Actually my "more accurate rendering" was done with pencil and paper.
I suppose I could scan it.
As for astronomical accuracy, I just thought somewhere in the back of
my mind that the lit spot on the planet was somehow different from the
way the moon looks in the sky. I stared at it for a while and eventually
the math section in my brain took over and I started scribbling on
paper to see what was wrong with it. I quickly realized the dark/light
border was equivalent to a longitude line on a sketch of a globe. If
you draw a circle and put a bunch of longitude lines on it, you see they
all meet at the endpoints of a diameter line. Then if you draw a line
perpendicular to the diameter line (call it the equator) and complete
the longitude curves into different size circles (and actually I'm not
positive they aren't elipses), you'll notice the centers of all these
circles fall on the equator line. They don't however all fall on the
edge of the planet circle.
So I guess what this means is your original technique of using two
circles is basicly right. You just have to make sure you drag the
2nd circle toward the center of the first circle, and stop when the
intersection points of the two circles are at the endpoints of some
diameter line. You don't actually have to start right at the edge
of the planet circle. Try starting a little before the edge, or a
bit after the edge and you'll see you get a different but correct
looking longitude line as long as you follow the rule about dragging
the circle to the right spot.
I guess the other lesson here is that I'm a bit of a nut. Oh well.
Don
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