Mariner 10 took the first close-up photo of Venus on February 5, 1974. It's still the best and most mesmerizing.
Made using an ultraviolet filter in its imaging system, the photo has been color-enhanced to bring out Venus's cloudy atmosphere as the human eye would see it. Venus is perpetually blanketed by a thick veil of clouds high in carbon dioxide and its surface temperature approaches 900 degrees Fahrenheit.
No wonder Earthlings thought it was full of wonderful seas and forests when they looked at it through the telescope. It looks like Earth's twin. [NASA]