One of the main questions that people have about Uranus is why is it so cold, especially when you learn that it's actually colder than Neptune, which is a lot further from the Sun. The difference between the heat in these two planets isn't proven, but the most likely way to explain this is that Uranus generates less heat from it's core than Neptune does - this may be because Uranus rotates on its side, allowing it's internal heat to 'spill out'.