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General Instructions, p.3 Planetary Section smooth out pencil lines and give more even shading. (e) A flashlight or other source of illumination which makes the drawing paper about the same brightness as the planetary image in the telescope. A red light is neither necessary nor desirable. I would strongly recommend that no attempt be made to start drawing for at least 20 minutes after going to the telescope. During this time more and more detail will become apparent, and by the time the drawing is begun one will have a good idea of what is visible. The main details should be sketched in to form reference points. Great care must be taken at this stage since the drawing may later be measured for positional information. Then the finer detail is added, starting with the preceding part of the disk since this is the side that is rotating away from us. After smoothing out the pencil-work with the "stump", the drawing should be compared with the planet to make certain that it is an accurate copy. The actual time spent drawing should not be more than about ten minutes so that the positions of the features do not change appreciably during the period. Since a beginner will often waste much time at the telescope in learning to manipulate pencil and stump, it might be a good idea to practise copying drawings and photographs published in magazines. Almost anyone can learn to make useful planetary drawings in time, and one accurate drawing is worth much more than a large number of pretty but careless sketches. ESTIMATING INTENSITIES The value of a drawing can be enhanced by the addition of quantitative estimates of the relative intensities of the features observed. For most planets a 0 - 10 scale is used where 0 is taken as the darimess of the sky background, and 10 as the brightest markings possible. Some rough guides to intermediate values are listed here: Venus: Average surface brightness = 9 Mars: Exceptionally dark markings = 1 Jupiter: Brighter zones = 7-8 Normal tone of greenish areas = 3 Darker belts = 2-3 Normal tone of reddish areas = 6 Polar regions = 4 Tone of clouds at the limb = 8 Saturn: Outer part of ring B = 9 Polar caps at brightest = 10 Due to the special problems in observing Mercury, a 0 darkest - 5 brightest scale is often used with the average surface brightness taken as 3. With experience one can become quite consistent in assigning intensity numbers. Observations should be recorded on a rough sketch in the apace provided. (Those familiar with standard Jovian nomenclature may prefer just to list the belts and zones with their observed intensities.) OTHER DATA TO ACCOMPANY DRAWING Under the "Remarks" section of the form various notes can be made on the colour and conspicuousness of the observed details. These may be recorded on another rough sketch or described verbally. The relative conspicuousness of Jupiter's belts and zones (considered separately) can be conveniently estimated by throwing the telescopic image out of focus and noting the orded in which the belts (or zones) reappear as the eyepiece is refocused. The most conspicuous should be marked "1", the next most conspicuous "2", etc. Geoffrey Gaherty, Jr, National CoÄordinator, Planetary Section, Standing Committee on Observational Activities. April 4, 1962. ________________________ Instruction Sheet No 1