Goals: Following the successful Venera 7, which found the atmospheric pressure at Venus' surface to be half of what that capsule had been designed to withstand, Venera 8 was designed to land a capsule safely on Venus with less of its mass devoted to resisting pressure and more to thermal protection, instruments and a stronger parachute.
Accomplishments: The Venera 8 lander transmitted data for more than 50 minutes after touching down on the planet's surface. During descent, it recorded a sharp change in illumination between 30 and 35 kilometers altitude. Temperature at the landing site was 470 give or take 8°C; pressure was 90 give or take 1.5 atmospheres (about 90 times Earth's atmospheric pressure at sea level). With the Sun at a low angle, the light level at the surface was found to be similar to that on Earth just before dawn, prompting the designers of Venera 9 and 10 to include floodlights. However, Venera 8's successors found noon-time conditions to be much brighter, similar to a dull, cloudy day on Earth.
Siddiqi, Asif A. Beyond Earth: A Chronicle of Deep Space Exploration, 1958-2016. NASA History Program Office, 2018.