Urk (Dutch pronunciation: [ʏrk]) is a municipality and a town in the Flevoland province in the central Netherlands.
Urk is first mentioned in historical records dating to the 10th century, when it was still an island in the Almere, a lake that would become part of the Zuiderzee in the 13th century after a series of incursions by the North Sea. In 1939, a dike from the mainland to Urk ended the town's island status, just as the Afsluitdijk project was changing the salt water Zuiderzee surrounding Urk to the less saline IJsselmeer. Later in the 20th century, seabed areas surrounding Urk were reclaimed from the sea and became the Noordoostpolder.
The mainstay of the town's economy has always been fishing, and the products of the sea coming in through Urk's harbour continue to be exported widely, although today Urk's fishing boats must travel greater distances to gather them than was required in most historical periods. Religious life has also traditionally been very important to Urk's inhabitants, with active, conservative congregations of the Dutch Reformed denominations playing key roles in the life of the community.
This is a list of craters on Mars. There are hundreds of thousands of impact crater on Mars, but only some of them have names. This list here contains only named Martian craters starting with the letter O – Z (see also lists for A – G and H – N).
Large Martian craters (greater than 60 km in diameter) are named after famous scientists and science fiction authors; smaller ones (less than 60 km in diameter) get their names from towns on Earth. Craters cannot be named for living people, and small crater names are not intended to be commemorative - that is, a small crater isn't actually named after a specific town on Earth, but rather its name comes at random from a pool of terrestrial place names, with some exceptions made for craters near landing sites. Latitude and longitude are given as planetographic coordinates with west longitude.