The atmosphere of Earth acts like any window in serving two very important functions: to let light in and to permit us to look out and to guard Earth from dangerous or uncomfortable things. A normal glazed window lets us keep our house warm by keeping out cold air. In such a way, the Earth’s atmospheric window helps to keep our planet to a comfortable temperature by holding back radiated heat and protecting us from dangerous levels of ultraviolet light. Just like a window which prevents rain, dirt, and unwelcome insects and animals from coming in, scientists have discovered that space is full of a great many very dangerous things against which our atmosphere guards us.