Venüs, or Venus, is the second planet from the Sun in our solar system. It is similar in size and composition to Earth, often referred to as Earth's "sister planet." Venüs has a thick atmosphere composed mainly of carbon dioxide, with clouds of sulfuric acid, making it the hottest planet, with surface temperatures reaching around 465 degrees Celsius (869 degrees Fahrenheit). The surface of Venüs is rocky and covered with volcanoes and vast plains. It rotates very slowly on its axis, taking about 243 Earth days to complete one rotation, while it orbits the Sun in about 225 Earth days. This unique rotation leads to unusual day-night cycles on the planet.