CN FORUMS ARCHIVE Telescope Reviews: Venus 05.04.07

Percival Lowell may be better known for his Mars Canal Hypothesis (proposed in 1895 in Lowell's book "Mars" ( http://www.wanderer.org/references/lowell/Mars/ ) after observations made at the observatory using an 18-inch (46-cm) refractor), but he also explored the rest of the solar system, including our closest planetary neighbor Venus. Lowell, in August of 1896, turned the newly-erected 24-inch (60-cm) f/16 Refractor towards Venus while awaiting the planet Mars to aproach the Earth closer at opposition in December of the same year. Using such an aperture on the third brightest object in the heavens (-4.5m) it is understandable why Lowell was required to "stop down the aperture" (using an adjustable diaphragm at the 24" lens) to a diameter between 1.6 to 3 inches. At these small apertures the disk of Venus exhibited albedo features describes as "spokes of a wheel radiating from a central hub." Lowell believed these "spider-web features" to be permanent surface features comprised of "rock or sand weathered by aeons of exposure to the Sun" seen through the "diaphanous straw-colored veil" of a dense but strangely transparent atmosphere. With all our current knowledge of the dense atmosphere of Venus and spacecraft images it is difficult to understand why this Bostonian astronomer would believe in such a delusion. We must understand that what was known of the Moon and planets at the end of the nineteenth century was derived from visual observations (although photography was in it's nascency at this time). Spectroscopic observations made in the 1920's by Frank E. Ross provided the existence of a dense Venusian atmosphere.

Noted planetary historian William Sheehan and observer Thomas Dobbins upon researching the subject believe that Lowell may have been actually describing shadows cast by his retinal vessels by converting the stopped-down Lowell refractor into an opthalmoscope (an optical device used in the examination of the ocular fundus). It is interesting to compare the retina of the eye to the Venusian drawings made by Lowell. The similarity is very striking! This optical phenomena made possible by the Lowell refractor producing exit pupils between 0.29 to 0.54 millimeters at small apertures (1.6-3 inches (4-7.6 cm)).

Interesting links;
http://en.wikipedia.org/wiki/Martian_canal
http://www.lowell.edu/index.php
http://www.uapress.arizona.edu/onlinebks/mars/chap07.htm
http://en.wikipedia.org/wiki/Venus

Carlos

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