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ROYAL ASTRONOMICAL SOCIETY OF CANADA Planetary Section SPECIAL INSTRUCTIONS FOR OBSERVING JUPITER Instruction. Sheet No 1 contains information regarding drawings of Jupiter and estimates of the intensity and conspicuousness of the planet's belts and zones. The present sheet describes two important quantitative programs: the timing of satellite phenomena and central meridian transits. SATELLITE PHENOMENA Observations have shown that the phenomena of Jupiter's satellites predicted in the Observer's 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 tenth of a minute of occultations, eclipses, and transits can therefore be of value. Observations shouldbe, recorded on Form No 2. The satellite, type of phenomenon, and predicted time should be recorded in the appropriate places from the Handbook or Ephemeris. The observed times of first and second contact should be `recorded in the centre section of the form. In order to distinguish clearly times of interior and exterior contacts, a high magnification is recommended. Note should be made on the back of the form if anything unusual is observed. CENTRAL MERIDIAN TRANSITS The timing of transits should form the majcr part of every observer's Jupiter program. The nature of this work is described in the Journal for April 1962, p.p.79-80 (copies available from the writer). The following additional information will be found useful by the prospective transit observer. Form No 3 or its equivalent should be used. to record observations. Universal Time is preferred since it usually avoids a change of date during a night's observations. Trans its should be, assigned consecutive serial numbers through a given apparition. The description should begin with a two-letter code indicating whether the marking Is dark (D) or bright (W) and whether it is the preceding end (p), centre (c), or following end (f) which is on the C.M.; this should be followed by a more detailed description using the nomenclature given overleaf. The location is given in terms of the belts and zones. At first the beginner may find it helpful to supplement his descriptions with a simple sketch. Observers are urged to calculate the spot longitudes themselves using the central meridian tables in the Handbook and the ancillary tables given below. To be of fullest value, observations should be submitted fortnightly. To keep errors to a minimum, one eyepiece should be used conslstently, and an attempt made to keep the line of the observer's eyes parallel to the belts. The observer should record only features of which he is absolutely certain; erroneous observations only make the longitude charts more difficult to interpret. Change of Longitude in Given Intervals of Time System I: System II: h o m o m o h o m o m o 1 36.6 10 6.1 1 0.6 1 36.3 10 6.0 1 0.6 2 73.2 20 12.2 2 1.2 2 72.5 20 12.1 2 1.2 3 109.7 30 18.3 3 1.8 3 108.8 30 18.1 3 1.8 4 146.3 40 24.4 4 2.4 4 145.1 40 24.2 4 2.4 5 182.9 50 30.5 5 3.0 5 181.3 50 30.2 5 3.0 6 219.5 60 36.6 6 3.7 6 217.6 60 36.3 6 3.6 7 256.1 7 4.3 7 253.8 7 4.2 8 292.7 8 4.9 8 290.1 8 4.8 9 329.2 9 5.5 9 326.4 9 5.4 10 5.8 10 6.1 10 2.6 10 6.0