Ultraviolet astronomy
 
The ultraviolet electromagnetic spectrum is blocked by the Earth’s atmosphere and, in order to make observations at these wavelengths, it is necessary to use rockets and satellite platforms. This domain contains a wealth of spectral lines suited to astrophysical interpretation. For example, the Lyman series is well within the ultraviolet region with Lα at 1215 A˚ ; some of the spectral lines associated with ionized atoms are particularly useful for investigating stellar winds and calculating mass loss by this mechanism.
By far the most successful enterprise in ultraviolet astronomy has been the International Ultraviolet Explorer (IUE) spacecraft which was operational for some 20 years.
The ‘IUE Observatory’ comprised the flight system and the ground control. The flight system included the spacecraft and means of attitude control, the telescope and analysing equipment and the data transmission circuitry. The ground stations were centred at the Goddard Space Flight Centre (NASA), Greenbelt, Maryland, USA and at the Villafranca Satellite Tracking Station (VILSPA) near Madrid, Spain, operated by the European Space Agency (ESA). Data were obtained on a routine basis—8 hr per day at VILSPA and 16 hr a day at Goddard.
The 45 cm f/15 Cassegrain telescope was operated directly in real time from the ground by a control computer linked to the on-board computer. Ultraviolet spectrometry was undertaken from 1150 to 3200 ˚A with SEC Vidicon cameras to record the data. The observer was able to monitor the measurements in real time and adjust the observational routine to enhance the scientific value of the work in hand.