Yebes Observatory RT40m
| Location(s) | Yebes, Province of Guadalajara, Castilla–La Mancha, Spain | 
|---|---|
| Coordinates | 40°31′31″N 3°05′19″W / 40.525208°N 3.088725°W | 
| Altitude | 931 m (3,054 ft) | 
| Diameter | 40 m (131 ft 3 in) | 
| Collecting area | 1,250 m2 (13,500 sq ft) | 
| Website | astronomia | 
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The Yebes Observatory RT40m, or ARIESXXI, is a radio telescope which is part of the observatory at Yebes, Spain. It is a 40-metre Cassegrain–Nasmyth telescope.