Eastern Europe

Eastern Europe is the eastern part of the European continent. There is no consensus as to the precise area it refers to, partly because the term has a wide range of geopolitical, geographical, cultural, and socioeconomic connotations. There are "almost as many definitions of Eastern Europe as there are scholars of the region". A related United Nations paper adds that "every assessment of spatial identities is essentially a social and cultural construct". One definition describes Eastern Europe as a cultural (and econo-cultural) entity: the region lying in Europe with main characteristics consisting in Byzantine, Orthodox, and some Turco-Islamic influences. Another definition was created during the Cold War and used more or less synonymously with the term Eastern Bloc. A similar definition names the formerly communist European states outside the Soviet Union as Eastern Europe. Historians and social scientists increasingly view such definitions as outdated or relegating, but they are still heard in everyday speech and used for statistical purposes.

Europe

Europe (ⁱ/ˈjʊərəp/ or /ˈjɜːrəp/) is a continent that comprises the westernmost part of Eurasia. Europe is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, and the Mediterranean Sea to the south. To the east and southeast, Europe is generally considered as separated from Asia by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways of the Turkish Straits. Yet the borders of Europe—a concept dating back to classical antiquity—are arbitrary, as the primarily physiographic term "continent" also incorporates cultural and political elements.

Europe is the world's second-smallest continent by surface area, covering about 10,180,000 square kilometres (3,930,000 sq mi) or 2% of the Earth's surface and about 6.8% of its land area. Of Europe's approximately 50 countries, Russia is by far the largest by both area and population, taking up 40% of the continent (although the country has territory in both Europe and Asia), while Vatican City is the smallest. Europe is the third-most populous continent after Asia and Africa, with a population of 739–743 million or about 11% of the world's population. Europe has a climate heavily affected by warm Atlantic currents, tempering winters and enabling warm summers on most of the continent, even on latitudes that have severe climates in North America and Asia. Further from the Atlantic, seasonal differences increase, but the mildness of the climate remains.

United States

Coordinates: 40°N 100°W / 40°N 100°W / 40; -100

The United States of America (USA), commonly referred to as the United States (U.S.) or America, is a federal republic composed of 50 states, a federal district, five major territories and various possessions. The 48 contiguous states and Washington, D.C., are in central North America between Canada and Mexico. The state of Alaska is in the northwestern part of North America and the state of Hawaii is an archipelago in the mid-Pacific. The territories are scattered about the Pacific Ocean and the Caribbean Sea. At 3.8 million square miles (9.842 million km²) and with over 320 million people, the country is the world's third or fourth-largest by total area and the third most populous. It is one of the world's most ethnically diverse and multicultural nations, the product of large-scale immigration from many countries. The geography and climate of the United States are also extremely diverse, and the country is home to a wide variety of wildlife.

Aurora

An aurora, sometimes referred to as a polar light, is a natural light display in the sky, predominantly seen in the high latitude (Arctic and Antarctic) regions. Auroras are produced when the magnetosphere is sufficiently disturbed by the solar wind that the trajectories of charged particles in both solar wind and magnetospheric plasma, mainly in the form of electrons and protons, precipitate them into the upper atmosphere (thermosphere/exosphere), where their energy is lost. The resulting ionization and excitation of atmospheric constituents emits light of varying colour and complexity. The form of the aurora, occurring within bands around both polar regions, is also dependent on the amount of acceleration imparted to the precipitating particles. Precipitating protons generally produce optical emissions as incident hydrogen atoms after gaining electrons from the atmosphere. Proton auroras are usually observed at lower latitudes. Different aspects of an aurora are elaborated in various sections below.