A microwave is a high-frequency radio wave. They are broadly defined as having a wavelength between 1 millimeter and 1 meter, or narrowly between 3 mm and 300 mm. Microwaves have many uses including radar, radio astronomy, and to heat food in a microwave oven. Unlike longer radio waves, they do not bend around land obstacles but go in line of sight. Still, they are much used for communication because they can have a high bandwidth. Almost all spacecraft communicate by microwave radio.