Venus is the hottest planet in the solar system, with an average surface temperature of 872 degrees Fahrenheit. The average temperature for the whole planet is 864 F. The reason for its high temperatures is not its proximity to the sun, but its heavy atmosphere composed mainly of carbon dioxide.
Temperatures on Venus are highly uniform, not only because of its dense atmosphere, but because of its minimum axis tilt of 3.36 degrees, as opposed to Earth's 23.4 degree tilt, which produces significant seasonal change in mean temperatures. Scientists believe that Venus' atmosphere was once like Earth's, but a runaway greenhouse effect made it the way it is today. This is why it receives a great deal of attention by those who study climate change.