Observing the planets. Conceptual computer artwork of an astronomical observatory (lower centre), and a montage of the nine planets of the solar system. This may represent the use of astronomical devices to study and observe the planets. The observations are done using different wavelengths of light that include visible light, infrared, radio, microwaves and X-rays. The planets are (clockwise spiral): Earth (above the observatory), Mars, Venus, Mercury, Neptune, Jupiter, Pluto, Uranus and Saturn.