This tutorial covers the methods I have been using to create some of my recent double star sketches. For the digital portion, I will discuss methods used in Adobe Photoshop CS2. These techniques should translate pretty well to earlier versions of Photoshop as well as The Gimp. The double star I use as an example is Struve 3053--a surprising and beautiful yellow and blue pair in Cassiopeia.
Step 1 - The Observation
Aside from soaking up and enjoying the view of the double, the key things I want to record as accurately as possible are the position angle of the stars, their separation, their relative magnitudes, any discernible color, and the context of any surrounding stars.
The first thing I make note of is color. For me, the impression of color is strongest during that first look through the eyepiece. (Even under conditions where I'm never strongly dark adapted.) So I'll immediately note what colors stand out. I start with looking for the basics: Red to Orange to Yellow to White to Blue and shades in between. Sometimes, as you may have noticed, the contrasting colors a double throws at you don't follow the rules. So from there I'll just throw a description right back at it that reminds me of something I'm familiar with, like 'key lime pie green'. I haven't brought colored pencils or pantone swatch books into the equation for this. I just try to be as descriptive as possible with any colors that don't fit the mold.
When it comes to estimating position angle, I have to lay some groundwork. I don't own a filar micrometer, so my estimates aren't of any scientific use, but I try to get as close as I can. To do this, I try to mark cardinal directions around the sketch as carefully as I can ahead of time. Since I have an equatorial telescope with a polar alignment scope, I'll perform a polar alignment before observing. Then all I need to do is nudge the declination axis back and forth a couple times to note North-South. If you are using an alt-azimuth scope or otherwise won't be doing polar alignment on an EQ scope, paying careful attention to East-West drift of stars through the field will also allow accurate placement of cardinal directions. With those directions noted around the sketch circle, I move on to estimating position angle of the stars based on an imaginary clock face.
Estimating the separation of the double isn't a precise science for me either. For widely separated stars, I just try to determine what fraction of the field of view separates them: one-tenth...one-twentieth & so on.
Step 2 - Sketching the View
Once I've spent some time observing the double, I start to sketch the double star and any stars I see in the view using a 2H pencil. The reason I like to use a harder lead at this point is that it allows me to lightly plot the stars so that the faint stars are nice and delicate right from the start. It also makes any need for erasing a lot easier at this stage if I decide I need to correct something. After the stars are plotted where they belong, I use that same 2H pencil with a little more pressure and swirling to bulk up the boldness of the brighter stars. If a particularly bright star demands it, I'll use an HB weight pencil. This is of course my personal preference. You may prefer to use a #2 or HB pencil exclusively, or even pen and ink. Use what you are comfortable with. (See Figure 1)