620207Planetary2_p2

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Bulletin No 2 (continued)	                                        Planetary Section


Drawings, With practice almost anyone can learn to draw well enough to record the
appearance of astronomical objects. The idea is to copy the telescopic image accurately,
not to strive for "pretty" effects. The value of a drawing can be greatly increased
by the addition of semi-quantitative data such as estimates of conspicuousness, intensity,
and. colour as described below.

Conspicuousness Estimates. This involves estimating the relative ease with which the
belts or zones can be seen. The telescope's eyepiece is racked out of focus to present
a featureless disk. As it is refocused the order in which the belts (or zones) reappear
gives a good raasuro of their conspicuousness.

Intensity Estimates. The relative intensities of the belts and zones can be estimated
using a 0-10 scale. The information revealed by these observations is quite different
from that obtained from conspicuousness listings; here the actual shade of the feature
is estimated rather than its overall impression.

Colour Estimates. These are necessarily subjective but nonetheless of use if great
care is taken to eliminate spurious effects. A reflector is almost obligatory for this
sort of work.

Central Meridian Transits. The observer times to the nearest minute the tranaits of
bright and dark markings across the central meridian of Jupiter's disk (estimated by
eye). Although the accuracy of a given timing may be low, a sufficient number of timings
of the same feature on various occasions during a month or more yields a rotation period
of accuracy at least equal to the best spectroscopic work. Almost all our knowledge
of Jupiter's atmospheric currents over the last 70 years is based on amateur observations
of this type. Except for the most prominent markings a 6-inch or larger is required.

Photography. Good photographs provide a useful check on visual observations and also
can be measured to derive the latitudes of the belts. Due to the limitations of the
photographic process, a 6Äinch is probably the minimum for successful results.

Satellite Phenomena. Observations have shown that the phenomena of Jupiter's satellites
predicted in the Handbook are frequently in error by several minutes. The exact nature
of these variations from theory has yet to be determined; timings to the nearest 0.1
minute of occultations, eclipses, and transits can therefore be of value.

Lest the sheer quantity of programs frighton those who have done little along these
lines, I certainly do not expect everyone to participate in all fields! My own method
of getting started was to make drawings (a lot of them pretty horrid) at every opport-
unity until I could honestly feel that I was making a fair representation of what my
telescope could show. The serious planetary observer must have the ability to consider
his work objectively; unless he continually seeks to maintain the highest standards,
his observations will be of value to no one.

In spite of the emphasis I have placed on Jupiter, I do of course welcome any observations
of the other planets. As the Section's program gains momentum it will be expanded to
inolude these, and this in turn will lead to the appointment of Assistant Co-ordinators.

It is my hope that this Bulletin will stimulate further interest in planetary work.
Your comments and suggestions will shape the ultimate form which our program will take.

                                               Geoffrey Gaherty, Jr, National CoÄordinator,
                                               Planetary Section, Standing Committee
                                                    on Observational Activities.
                                               636 Sydenham Avenue, Montreal 6, Que.