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THE ROYAL ASTRONOMICAL SOCIETY OF CANADA Bulletin No. 7 - Part 2 PLANETARY SECTION MARS COLOUR REFERENCE SYSTEM The purpose of this project is to compile a colour map of Mars utilizing a system which, it is hoped, win eliminate the difficulties which arise from the inability of observers to objectively convey to others the subtle colours seen On Mars. Colour sketches can be made, of course, but media which are capable of giving a true representation are difficult to use at the telescope and are also time consuming. The system selected is designed to make it unnecessary for the observer to decide upon a name for a colour seen; he simply records a code number which refers to a particular hue and tint in the reference system. In this maimer a more objective summary of all obser- vations submitted can be made. The Colour Reference System consists of two series - I - a red-yellow group consisting of 6 strips, each containing 7 colour "chips", providing 42 shades; II - a grey group consisting of 5 strips, each containing 7 "chips", providing 35 shades. The observer thus has a total of 77 shades fran which to select a possible match for the colours seen on Mars. The shades selected for this experiment have been taken from the Du Pont "Colorizer" paint system and have been chosen fran among the 1322 available tints on the basis of colour observations made at previous apparitions of Mars. The shades encompass a wider range than has been observed in the past but are included in order to avoid confining observers to a "prejudiced" selection. Beneath each "chip" on a strip is a code number by which that particular shade is to be identified. In the upper right corner of each strip is found a number which can be used to readily arrange the strips in order of hue, as follows: Red-Yellow Series Strip No.25 Grey Series - Strip No.125 26 149 33 155 41 157 42 158 57 The observer may experiment in order to find the most convenient manner in which to handle the colour strips but it is suggested that they may be fastened together, in two groups, by means of a fastener inserted through the holes at the top, or they may be glued or stapled to a sheet of cardboard. One method requires that the strips be viewed in turn while the other peitts them to be seen all at once. Essential pieces of equipnent are a small clip-board to hold the sketching paper; a good light source, preferably a 60 or 100 watt frosted white bulb placed at the telescope; and sufficient extension cord to reach a source of house current. The presence of a strong light near the telescope is not detrimental, as in other types of observing, owing to the brightness of the Martian image, and is necessaxy for proper viewing of the colour chips.