Context: Astronomical seeing refers to the blurring and twinkling of astronomical objects such as stars caused by turbulent mixing in the Earth's atmosphere that causes variations of the optical refractive index. The "astronomical seeing" conditions on a given night at a given location describe how much the Earth's atmosphere perturbs the images of stars as seen through a telescope., The Canary Islands, also known as the Canaries, are an archipelago and autonomous community of Spain located on the Atlantic Ocean, west of Morocco. The Canaries are among the outermost regions (OMR) of the European Union proper. It is also one of the eight regions with special consideration of historical nationality recognized as such by the Spanish Government., A telescope is an optical instrument that aids in the observation of remote objects by collecting electromagnetic radiation (such as visible light). The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s, by using glass lenses. They found use in both terrestrial applications and astronomy. , El Dorado Hills (EDH) is an unincorporated census-designated place (CDP) located in El Dorado County, California, east of the state capital of Sacramento. The population was 42,108 at the 2010 census, up from 18,016 at the 2000 census. This population growth is attributed through the combination of actual population increase within the 2000 CDP boundaries and expansion of the boundaries. The area of EDH was expanded from in 2000 to in 2010., In optics, the refractive index or index of refraction "n" of a material is a dimensionless number that describes how light propagates through that medium. It is defined as 
where "c" is the speed of light in vacuum and "v" is the phase velocity of light in the medium. For example, the refractive index of water is 1.333, meaning that light travels 1.333 times faster in a vacuum than it does in water., The Instituto de Astrofísica de Canarias (IAC) is an astrophysical research institute located in the Canary Islands. It was founded in 1975 at the University of La Laguna., La Palma, also San Miguel de La Palma, is the most north-westerly island of the Canary Islands, Spain. La Palma has an area of 706 km making it the fifth largest of the seven main Canary Islands. The total population is about 86,000, of which 18,000 (2003 data) live in the capital, Santa Cruz de la Palma and about 20,000 (2004 data) in Los Llanos de Aridane. La Palma has "sister city" status with El Dorado Hills, California. With an area of 708.32 square kilometres La Palma is fifth largest of the seven main islands, whilst the Roque de los Muchachos, at 2,426 metres, is second only to the peaks of the Teide massif on Tenerife., Mount Teide (, "Teide Peak") is a volcano on Tenerife in the Canary Islands, Spain. Its 3,718-metre (12,198 ft) summit is the highest point in Spain and the highest point above sea level in the islands of the Atlantic., Santa Cruz de la Palma (Spanish for "Holy Cross of La Palma") is a city and a municipality in the eastern part of the island of La Palma in the province of Santa Cruz de Tenerife of the Canary Islands. It is situated on the east coast. Santa Cruz de la Palma is the second largest city (after Los Llanos de Aridane) and is the capital of the island. It is located along an old lava flow coming out from the Caldereta (small caldera), a volcano located just south of the city., The European Northern Observatory is the name by which the Instituto de Astrofísica de Canarias and its observatories (the Teide Observatory on Tenerife and the Roque de los Muchachos Observatory on La Palma) are collectively known. It was named in response to the successful collaboration of the member countries in the European Southern Observatory organisation., Macaronesia is a collection of four archipelagos in the North Atlantic Ocean off the coast of the continents of Europe and Africa. Apart from the Azores, which are considered mainly as part of Europe, the other islands of Macaronesia are closer to Africa. Macaronesian islands belong to three countries: Portugal, Spain, and Cape Verde., Roque de los Muchachos Observatory (Spanish: "Observatorio del Roque de los Muchachos", ORM) is an astronomical observatory located in the municipality of Garafía on the island of La Palma in the Canary Islands. The observatory site is operated by the Instituto de Astrofísica de Canarias, based on nearby Tenerife. ORM is part of the European Northern Observatory., Spain, officially the Kingdom of Spain, is a sovereign state largely located on the Iberian Peninsula in southwestern Europe, with two large archipelagos, the Balearic Islands in the Mediterranean Sea and the Canary Islands off the North African Atlantic coast, two cities Ceuta and Melilla in the North African mainland and several small islands in the Alboran Sea near the Moroccan coast. Its mainland is bordered to the south and east by the Mediterranean Sea except for a small land boundary with Gibraltar; to the north and northeast by France, Andorra, and the Bay of Biscay; and to the west and northwest by Portugal and the Atlantic Ocean. It is the only European country to have a border with an African country (Morocco) and its African territory accounts for nearly 5% of its population, mostly in the Canary Islands but also in Ceuta and Melilla., Teide Observatory ( Spanish : Observatorio del Teide ) is an astronomical observatory on Mount Teide , Tenerife , operated by the Instituto de Astrofísica de Canarias . Opened in 1964 , it became one of the first major international observatories , attracting telescopes from different countries around the world because of the good astronomical seeing conditions . Later the emphasis for optical telescopes shifted more towards Roque de los Muchachos Observatory on La Palma . It is considered one of the world 's major observatories ., Roque de los Muchachos (English: "Rock of the Boys") is a rocky mound at the highest point on the island of La Palma in the Canary Islands, Spain. The rocks are found at an elevation of 2,423 m above sea level, not far from the Observatorio del Roque de los Muchachos, where some of the world's largest telescopes are situated; the altitude and the dryness of the climate here give rise to excellent observing conditions. The rocks are contained with the Parque Nacional de la Caldera de Taburiente., Garafía is a municipality in the island of La Palma, Santa Cruz de Tenerife (Canary Islands). Located in the northwest of the island, in the middle od two whims of nature: the ravines of Franceses (by the North) bordering Barlovento and Izcagua by the South (born at the foot of the Roque de los Muchachos), bordering Punta Gorda . The administrative capital, home to the City Council, is called Santo Domingo and has a length of 25.50 km coastline. with cliffs of incredible beauty but very steep and difficult to access, which can only be reached on foot, demanding a great effort to those not used to walking on rough terrain. Yes, their landscapes not leave anyone indifferent by the canopy of deep green vegetation that tupe those cliffs and see the ravines in contrast to the blue of the sky and its wild seas, as an example cited the gorgeous Beach Bujarén in Santo Domingo, with its roques; is the North of La Palma: a magical, unique, and unparalleled place., Tenerife is the largest and most populated island of the seven Canary Islands. It is also the most populated island of Spain, with a land area of and 898,680 inhabitants, 43 percent of the total population of the Canary Islands. Tenerife is the largest and most populous island of Macaronesia., Subject: teide observatory, Relation: part_of, Options: (A) 1975 (B) atlantic ocean (C) atmosphere (D) balearic islands (E) canary islands (F) city (G) city council (H) community (I) country (J) earth (K) english (L) european northern observatory (M) european union (N) foot (O) france (P) government (Q) green (R) islands (S) mediterranean sea (T) medium (U) municipality (V) nature (W) optics (X) part (Y) radiation (Z) research institute ([) rock (\) roque de los muchachos observatory (]) sky (^) state (_) the city (`) the middle (a) university (b) v (c) volcano
Output: european northern observatory