620401PlanetaryInstr1_p3

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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.
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Instruction Sheet No 1