Astronomy and the ultraviolet spectrum. This part of the electromagnetic spectrum includes Extreme Ultraviolet (left) and Ultraviolet (UV, at right); Extreme UV borders on X-rays, while UV borders on optical wavelengths. UV light is strongly absorbed by the atmosphere, including the ozone layer (yellow band). Instruments for detecting UV must be carried above atmospheric interference on rockets, the space shuttle (upper right) or satellites. Extreme UV is partly absorbed by interstellar gas (grey wedge at upper left). Sources of UV include the Sun (upper center), galaxies (swirls at upper right) and hot stars (points at upper right).