The Yebes Astronomical Centre (CAY) is located about 70 km. from Madrid, in Yebes (Guadalajara). It is placed at 980 m above sea level and provides good conditions for radio astronomy observations since the average Precipitable Water Vapour is 6 mm, reaching a minimum of 2 mm in winter. The wind speed is less than 5 m /s over 90% of the time and the number of days with snow precipitations does not exceed one week per year.
The OAN has 2 large radio telescopes in CAY. The first one, of 14 m. in diameter, was put into operation at the beginning of the eighties. In addition, a 40 m. radio telescope has been recently opened for centimetre and millimetre waves that will be devoted to Very Long Baseline Interferometry (VLBI) and single antenna observations.