Infrared telescopes work best in space. Why? Objects that are even a little bit warm put out infrared energy. So it makes sense to put an infrared telescope into space where it won't just detect all the warm things on Earth. Even in space, we must make the telescope very cold using refrigerator-type technology so that it won't just detect itself! Then the telescope can look around and see the infrared light coming from the rest of the Universe. The Spitzer Space Telescope is just such an instrument.