40,270 articles
Opening of the Atlantic Ocean
The opening of the Atlantic Ocean began as Pangaea rifted apart about 201 million years ago, with Central Atlantic seafloor spreading starting around 190 Ma.
OpenStreetMap
OpenStreetMap (OSM) is a free, openly licensed collaborative world map database founded by Steve Coast in the UK in 2004, run by the OpenStreetMap Foundation, with over 10 million registered users and 10 billion nodes.
Operation Highjump
Operation Highjump (officially the U.S. Navy Antarctic Developments Program, 1946-47), Task Force 68 under Byrd and Cruzen: 4,700 men, 13 ships, aerial photomapping of Antarctica, Little America IV, early withdrawal from Ross Sea pack ice.
Operation Vijiji
Operation Vijiji, also rendered Operation Vijijini, was Tanzania's compulsory campaign of 1973 to 1976 resettling millions of rural people into planned ujamaa villages under President Julius Nyerere.
Ophel
The Ophel is the raised spur at the southern edge of Jerusalem's Temple Mount, between it and the City of David, with monumental Iron Age remains excavated since 1870.
Ophir
Ophir (Hebrew Ophir) is a biblical land or port, source of Solomon's gold, almug wood, apes, and peacocks, sailed to from Ezion-geber; its location, proposed in Arabia, East Africa, India, or Southeast Asia, remains unconfirmed.
Ophir Catenae
Ophir Catenae is an IAU-approved 577-km system of pit crater chains on Mars at 9.49S, 300.60E, south of Ophir Chasma near Valles Marineris, named in 2006 from a classical albedo feature and linked to groundwater-fed outflow channels.
Ophir Chasma
Ophir Chasma, a 317-km canyon in north central Valles Marineris, Mars, holding Ophir Mensa, sulfate-rich interior layered deposits, gray hematite, and large Amazonian landslides.
Ophir Labes
Ophir Labes is an IAU-approved landslide (labes) feature on Mars in Valles Marineris near Melas and Coprates Chasmata, about 92.53 km across, named in 1985 from a classical albedo feature.
Ophir Mensa
Ophir Mensa is a 103 km wide mesa of layered sulfate-rich sedimentary deposits in Ophir Chasma, Valles Marineris, Mars, IAU named 2013, containing kieserite, polyhydrated sulfates, jarosite, and hematite.
Ophir Planum
Ophir Planum, a 642-km-wide plateau (planum) on Mars near Valles Marineris, IAU-approved 1973 as a classical albedo feature name; Hesperian volcanic ridged plains with outflow channels.
Opimiano
Opimiano (Villa of Rufinus Vinicius Opimianus): Roman villa site at Grottaferrata near Rome's Via Latina and Ad Decimum catacombs, attributed via an inscription to the senator Opimianus, on two terraced substructures.
Opis
Opis (Akkadian Upî, Greek Ὦπις) was an ancient Babylonian city on the Tigris near modern Baghdad, best known as where Cyrus the Great broke the Babylonian army in 539 BCE.
Opole Voivodeship
Opole Voivodeship (województwo opolskie) is Poland's smallest province by population, created 1 January 1999 with capital Opole; 923.5 thousand residents, industrial-agricultural economy, highest per-capita GHG emissions in Poland.
Opone
Opone (Greek Ὀπώνη), also called Oponi, was an ancient market-town on the northern Somali coast, usually identified with the Hafun peninsula and described in the Periplus of the Erythraean Sea.
Oppegård
Oppegård was a municipality in Akershus, Norway (municipality number 0217), created in 1915 from Nesodden, with center Kolbotn; merged with Ski on 1 January 2020 to form Nordre Follo.
Oppenheimer (lunar crater)
Oppenheimer is a 201-km-wide floor-fractured impact crater on the lunar far side at 35.3°S, 166°W in the South Pole–Aitken basin, named for physicist J. Robert Oppenheimer (IAU 1970), with Vulcanian pyroclastic deposits on its floor.
Oppidum
Oppidum (plural oppida): Latin 'town' used by Caesar for Gallic centers, now the archaeological term for large Late Iron Age fortified settlements (at least 10 ha) across temperate Europe, from Bibracte to Manching, often low-density assembly and trade centers.
Oppidum des Caisses de Jean-Jean
Oppidum des Caisses de Jean-Jean, also Caisses de Saint-Jean: a 14-hectare fortified Iron Age and Roman-era settlement in the Alpilles at Mouriès, Bouches-du-Rhône, France, known for its thick multiple ramparts and horse-and-rider stelae.
Opryland USA
Opryland USA, a country music-themed amusement park in Nashville, Tennessee, operated 1972 to 1997 before closing for the Opry Mills mall; its rides were sold to Premier Parks.
Ops Corona
Ops Corona is a named corona on Venus at 68.5N, 89.0E, a quasi-circular volcano-tectonic feature with concentric fracture annulus; IAU name approved 1991 for a Greek fertility goddess.
Opština Vraneštica
Opština Vraneštica (Вранештица) was a small former municipality in western North Macedonia, seat at Vraneštica village; 109.13 km², 15 settlements, 1,322 inhabitants (2002), merged into Kičevo municipality in 2013.
Optatiana
Optatiana: Roman auxiliary fort and vicus at Sutor, Sălaj County, Romania, in Dacia Porolissensis, on the Tabula Peutingeriana; garrisoned by the numerus Maurorum Optatianensium, a Moorish cavalry unit of about 500 men.
OR Tambo District Municipality
OR Tambo District Municipality (DC15) is an Eastern Cape district municipality, seat Mthatha, named after Oliver Tambo, with five local municipalities, 1,364,943 mostly Xhosa-speaking people, and a water and sanitation mandate.
Oradea
Oradea (Nagyvárad, Großwardein) is a municipality in north-western Romania, seat of Bihor County, first recorded in 1113 as Civitas Varadiensis, known for Art Nouveau architecture and a medieval fortress.
Orai
Orai (उरई) is a city in Uttar Pradesh, India, headquarters of Jalaun district in Bundelkhand on the Kanpur-Jhansi NH27; 2011 population 190,595, third largest city of Jhansi division.
Oral, Kazakhstan
Oral (Uralsk, formerly Yaitsky gorodok), city on the Ural River at the Chagan confluence in northwestern Kazakhstan, center of West Kazakhstan Region; founded 1613 by Yaik Cossacks, renamed 1775 after Pugachev's revolt; population about 234,000.
Oran (وَهْرَان)
Oran (وهران) is Algeria's second-largest city, a western Mediterranean port captured by Spain in 1509, held until 1792, taken by France in 1831, and the birthplace of raï music.
Oran Province
Oran Province (ولاية وهران, Wilaya d'Oran) is Algeria's wilaya no. 31 in the northwest, capital Oran city; 2,114 km², 26 communes, second commercial port, Arzew oil port, raï music birthplace.
Orange County, California
Orange County, California: county formed August 1, 1889 from Los Angeles County; county seat Santa Ana; about 3.1-3.2 million residents, 34 cities, 42 miles of coastline, home of Disneyland.