SPACE JOCKEY

If you’re looking to record your planetary observations, you don’t need any fancy imaging equipment or a specialized camera. With some patience, a pencil and a piece of paper you can accurately sketch what you see through a pair of binoculars or the eyepiece of your telescope. To take things one step further, you can then easily transpose your pencil sketches to the digital domain by using an image editing package like Photoshop or the freely available GIMP.

Before you begin, make sure you have some basic tools: a HB pencil, a sharpener, an eraser, something to lean on (a clip board is good) and a red light torch. What kind of paper you choose to use is entirely personal choice, but for ‘roughs’ as I like to call them I just use notebook paper while for sketches that I am going to re-work I prefer to use acid free cartridge paper. As one final preparation I like to draw a circle to represent the field of view using the inner tube from a roll of brown packaging tape. You can use what ever you want for this e.g. a coffee jar, a stencil etc but make sure that the diameter is not too big and not too small — somewhere in the region of 100mm.

The first thing to remember about sketching any celestial object is that patience is everything! Factors such as your dark adaption, the seeing and sky transparency will affect the visual information that you can pull from your observation. Take as long as you can to familiarize yourself with every single detail before you apply pencil to paper. To help you pin point the location of objects within your field of view, imagine that it is over laid by a clock face with 12 o’clock at 0°, 3 o’clock at 90°, 6 o’clock at 180° and 9 o’clock at 270°.

While making your sketch be sure to denote the brightness of any moons or surrounding stars by using varying degrees of pressure and size to intimate their magnitude with the pencil. Also indicate any planetary features that you observe e.g. equatorial bands, colour etc. Any outer glow that you see can be delineated using isophotes (lines that are drawn through areas of constant brightness).

Once you feel happy with your basic pencil sketch, then you are ready to move on to producing a digital version of it. As I have mentioned above you will need to use an image editor like Adobe Photoshop, however the methods I will discuss below should be fairly easy to translate to another package like The Gimp.

For the purpose of this exercise I used Adobe Photoshop CS2 to reproduce a rough pencil sketch of Venus that I made at the end of last year using my now defunct 60mm f/13 Tasco refractor with a  Huygens 5mm eyepiece.

Step 1: Create a new canvas

In Photoshop create a new document File>New and enter the dimensions and resolution. I like to use a pixel size of 2000 by 2000 pixels with a resolution of between 300 and 500 ppi. I prefer to create high resolution images that I can scale down to 72 ppi for use on the web but you can use whatever settings you feel meet your needs. As you will most likely want to display your work on the web I would suggest leaving the colour mode at 8 bit RGB.

Step 2: Set the field of view

Create a new layer then select the elliptical marquee tool. Hold down the shift key and drag out a circle about 1500 by 1500 pixels and centre it on the canvas. Before deselecting the selection use your paint bucket tool  to fill it with black i.e. #000000.

Step 3: Create the planetary disc

We once again turn to the elliptical marquee tool for this job, but first you need to create a new layer. I prefer to start off big and scale the disc down once I have painted in any details, so make the selection about 2/3 the size of the field of view. Remember and hold down the shift key so that you can drag out a circular selection. Now fill the selection with an appropriate colour  — based on the notes I had taken, I used white i.e. #ffffff to colour Venus’ planetary disc.

Step 4: Adding Venus’ phase

This is very easy to do and requires nothing more than making a selection around the planetary disc and transforming it. To do this right click on the planetary disc layer icon and select layer transparency. Now go to your select menu and click on transform selection. In the transform bar that appears above click on the maintain aspect ratio button and increase the size of the selection by inputting 400% into the width and height fields.

Making sure that you have selected the elliptical marquee tool, nudge the selection over to your left so that it covers just under half of the planetary disc (use your guides to help you achieve this). Now use Ctrl Shift I to invert the selection so that you can erase the part of the disc on your right using your eraser tool. Once you have finished erasing the part of the disc that you do not want use Ctrl D to deselect the selection.

After completing the steps above you will now focus on scaling the planetary disc down. With the disc layer highlighted, hit Ctrl T which will initiate transform mode. Click on the maintain aspect ratio button and downsize the disc by inputting 7% into the width and height fields. At this point you will also tilt the disc by inputting -20° into the set rotation field.

Bear in mind that when you do all of this to your own pencil sketches to match the scale of your original sketch as closely as possible. As a final touch apply a gaussian blur which you can find under: Filter > Blur > Gaussian. The view through your telescope does not provide the same crisp outlines that Adobe Photoshop offers. The settings you use here will depend greatly on the seeing and transparency conditions of your sky, but try to be conservative in your judgment.

Step 5: Adding glow

You should now have an image that resembles the one shown just above, but before finishing things off you will add some additional glow around the waning disc of Venus. To achieve this use a large soft brush (around 250 - 300px should do) and set it’s mode to screen, then lower the brush’s opacity to about 10%. Now create a new layer just above the disc layer and set the foreground colour to pure white: #ffffff. Begin to dab your brush (about two times ought to do it) over the planetary disc until you feel you have an acceptable amount of glow that matches your sketch.

Step 6: Finalizing the sketch

To finally complete the image you will probably want to add some additional information, such as cardinal points, equipment used, weather conditions, RA and DE data etc. How you choose to do this is personal preference, but be sure to save a copy of your digital sketch as a PSD file so you have a master file to return to and edit if needed.

Taking the time to produce a refined planetary cyber-sketch from a rough, but detailed pencil drawing is both visulally beneficial and rewarding. This tutorial just skims the surface of what you can achieve using digital tools, but don’t be afraid to experiment and build on the very simple techniques that I have discussed here. Give it a try — you’ve got everything to gain and nothing to lose!