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Porto (Portuguese pronunciation: [ˈpoɾtu]), also known as Oporto in English, is the second largest city in Portugal, after Lisbon, and one of the major urban areas in Southern Europe. Its administrative limits (an area of 41.66 km²/16 sq.mi) include a population of 237,584 (2011) inhabitants distributed within 15 civil parishes. The urbanized area of Porto, which extends beyond the administrative limits of the city, has a population of 1.3 million (2011) in an area of 389 km² (150 sq mi), making it the second-largest urban area in Portugal. The Porto Metropolitan Area includes approximately 1.7 million people, and is recognized as a Gamma-level global city by the Globalization and World Cities (GaWC) Study Group, being one of the four cities in the peninsula with global city status (the others being Madrid, Barcelona and Lisbon).

Located along the Douro river estuary in northern Portugal, Porto is one of the oldest European centres, and registered as a World Heritage Site by UNESCO in 1996. Its settlement dates back many centuries, when it was an outpost of the Roman Empire. Its Latin name, Portus Cale, has been referred to as the origin for the name "Portugal," based on transliteration and oral evolution from Latin. In Portuguese the name of the city is spelled with a definite article as "o Porto" (English:  the port). Consequently, its English name evolved from a misinterpretation of the oral pronunciation and referred to as "Oporto" in modern literature and by many speakers.

Night or nighttime is the period of time between the sunset and the sunrise when the Sun is below the horizon. This occurs after dusk. The opposite of night is day (or "daytime" to distinguish it from "day" as used for a 24-hour period). The start and end points of time of a night vary based on factors such as season, latitude, longitude and timezone.

At any given time, one side of the planet Earth is bathed in light from the Sun (the daytime) and the other side of the Earth is in the shadow caused by the Earth blocking the light of the sun. This shadow is what we call the darkness of night. Natural illumination is still provided by a combination of moonlight, planetary light, starlight, diffuse zodiacal light, gegenschein, and airglow. In some circumstances, bioluminescence, aurorae and lightning can provide some illumination. The glow provided by artificial illumination is sometimes referred to as light pollution because it can interfere with observational astronomy and ecosystems.

The District of Porto (Portuguese pronunciation: [ˈpoɾtu], Portuguese: Distrito do Porto), sometimes Oporto in English, is located on the north-west coast of Portugal. The district capital is the city of Porto, the second largest city in the country. It is bordered by the Aveiro and Viseu districts to the south, Braga district to the north and Vila Real district to the east. Its area is 2395 km² and its population is 1,781,826.

Portugal ⁱ/ˈpɔrtʃʉɡəl/ (Portuguese: Portugal, IPA: [puɾtuˈɣaɫ]), officially the Portuguese Republic (Portuguese: República Portuguesa) is a country situated in southwestern Europe on the Iberian Peninsula. Portugal is the westernmost country of Europe, and is bordered by the Atlantic Ocean to the West and South and by Spain to the North and East. The Atlantic archipelagos of the Azores and Madeira are part of Portugal. The country is named after its second largest city, Porto, whose Latin name was Portus Cale.