The original paper pages for these sketches are available online as a PDF file.
OBSERVATIONS OF VENUS
by the Montreal Centre of the R.A.S.C.
by: Klaus R. Brasch, 1961 March 18th.
Serious observations of Venus by members of the Montreal Centre were begun during the apparition 1959-60.
Because accurate visual observations of surface markings, Ashen Light, and other phenomena of the planet are difficult to make, no definite observations programme was undertaken at that time. An effort was made however, to try to obtain simultaneous observations by different observers, with various instruments, for the purpose of confirmation. In this case we were quite successful on several occasions, and if nothing else was accomplished, it gave us experience and encouragement to continue observing this rather unrewarding planet.
For 1960-61, a much more ambitious and elaborate programme was undertaken. Observations were again to be made simultaneously, in the afternoon and early evening, in addition however intensity estimates of the markings were made. The same scale as that used by the A.L.P.O., with 0 as sky black, to 10 the brightest, was adopted. On this scale the darkest markings seldom were judged below 8, illustrating the faintness of these features.
A further and very interesting type of observation was made with a violet Wratten 47-B filter. The planet was first observed without a filter and, if anything was seen, a drawing was made. Then the planet was observed with the filter and a second drawing made. In general the markings were more conspicuous with the filter, and often appeared to have different shapes than when seen without it.
On several occasions parallel band-like structures were seen, beginning at the terminator and thinning out toward the limb. The cusp areas at the north and south ends of the terminator were often seen much more definitely with the filter.
On the whole, a blue or violet filter was found to have considerable use in revealing sharper and more conspicuous detail than could otherwise be seen.
Another rather intriguing experiment was undertaken more or less for curiosity's sake.
As is generally known, no definite rotation period for Venus has as yet been established. Although indications are that the period is more than a week and less than a month, times ranging from a few hours to one Venusian year have been quoted.
Certain observers at Pic du Midi Observatory in France, hold the belief that Venus like Mercury has a rotation period of the same length as one year of the planet and consequently always presents us with the same face. It is the belief of these people that Venus is covered with high, dense clouds, in which occasional breaks sometimes reveal markings of lower levels. By superimposing numerous observations they have thus produced a map of what they believe to be more or less permanent markings. A reproduction of this map can be found in the La Rousse Encyclopedia of Astronomy.
Based on the above assumption. and for a lack of a more concrete programme, we have attempted a similar experiment despite the fact that none of us has much faith in the idea.
Several of the best drawings by the most experienced observers and only those made with instruments of 6" or over under fair and upward seeing conditions, were transferred onto tracing paper, superimposed, and an outline made of the darkest and most prominent markings.
In this manner a map of each observer's observations was made and, finally, with allowances made for different drawing styles, a final map was produced from about 30 observations.
From these slides it can be seen that, although a limited degree of agreement is indicated, it cannot be said to be very convincing.
However it should be bought in mind that our map is based on rather few observations made with smaller instruments, inferior seeing and less experienced observers than the one made at Pic due Midi. Furthermore our map was based entirely on direct observations, while the french map is based mainly on filter observations.
A further experiment that may be undertaken, is one in which the same superimposing method may be used coinciding with a certain rotation period, in which case appropriate calculations and corrections would have to be made. This however would be very difficult to do and very time consuming.
Thus as with all experiments and observations of Venus, nothing is definitely proven or disproven, no conclusions can be reached, and in fact one knows no more about the planet than before, except that people will go on observing and speculating about this truly fascinating planet.
March 18th, 1961.