Venus Unveiled?

Press, Volume CI, Issue 29994, 1 December 1962, Page 19

Venus Unveiled?

With luck, some of the mysteries of Venus will be solved in toe next few weeks by Mariner H. which is now only four million miles away from Venus. Reception of Mariner’s radio signals is still good and everyone hopes that they will stay that way while Mariner passes within 21,000 miles of Venus in 14 days’ time. The instruments abroad Mariner H will then probe toe Venusian clouds which for years have foiled astronomers in their attempts to discover the true nature of the atmosphere and surface of toe planet. When viewing conditions from toe earth have been at their best, telescopes have revealed dark patches suggestive of breaks in toe dense cloud cover. At other times, when Venus is close to the earth and appears as a thin crescent, a faint illumination can sometimes be glimpsed extending from the cusps right around the rim of the planet. This is due to scattering of toe sun’s rays by

clouds high in the Venusian atmosphere. The ring of light is often broken, indicating a broken cloud layer. And that is about toe limit of what can be seen from toe earth. Some idea of the difficulty of observing Venus in detail may be gauged from the composite illustration showing Venus at various distances from the earth. When Venus is on toe far side of toe sun, some 150 million miles away, we see it under full illumination and it appears round. As it swings around its orbit and catches up the earth it becomes gibbous, then crescent, and toe crescent gets thinner as Venus passes between the earth and the sun. When Venus draws closer to the earth it naturally appears larger; but toe increase in apparent diameter is neatly offset by the diminishing size of toe illuminated crescent. This accounts for toe fact that Venus remains surprisingly constant in brilliance although its distance from the earth varies from 150 to less than 30 million miles.