Saturn was first observed by people before recorded history. It is the sixth planet from the sun, and the second largest in the solar system, a gas giant ranked behind only Jupiter. Saturn is composed primarily of hydrogen, with smaller amounts of helium and other trace elements. Its interior is made of a small core of rock and ice, surrounded by a thick layer of metallic hydrogen and a gaseous outer later. Saturn is best known for its prominent system of rings, which are mostly comprised of ice particles, rocky debris, and dust. Astronomers believe the rings may have been formed from larger moons that were shattered by impacts from comets and meteoroids. The planet also has at least 62 moons; most of them are quite small, but the largest is Titan, which is bigger than the planet mercury and is the only moon in the entire solar system to have a significant atmosphere.
Infrared radiation is an invisible form of light that we usually detect as heat, like the sun shining on our face, or the warmth of a campfire. It has all the same properties as visible light: for example, it can be focused and reflected. The only difference is that it has a longer wavelength, which means we can't see it with the naked eye. Light is made of tiny particles called photons, and the wavelength tells us how fast those particles are vibrating. The shorter the wavelength, the faster the particles are moving. Shorter light waves look blue, and longer ones look red. The wavelength of infrared light is so long that we can't see it at all. Any warm object gives off infrared radiation. By checking in the infrared spectrum, engineers can find heat leaks in buildings, doctors can find hidden tumors in the body, and biologists can locate diseased plants in a forest. Astronomers use infrared imaging to detect warm dust around new stars that are not yet "hot" enough to emit visible light.
