AthensAthens (ˈæθɪnz ; Athína aˈθina; Athênai (pl.) athɛ̂ːnai̯) is a major coastal urban area in the Mediterranean and it is both the capital and the largest city of Greece. With its urban area's population numbering over three million, it is also the eighth largest urban area in the European Union. Athens dominates and is the capital of the Attica region and is one of the world's oldest cities, with its recorded history spanning over 3,400 years, and its earliest human presence beginning somewhere between the 11th and 7th millennia BC.
History of AthensAthens is one of the oldest named cities in the world, having been continuously inhabited for perhaps 5,000 years. Situated in southern Europe, Athens became the leading city of Ancient Greece in the first millennium BC, and its cultural achievements during the 5th century BC laid the foundations of Western civilization. During the early Middle Ages, the city experienced a decline, then recovered under the later Byzantine Empire and was relatively prosperous during the period of the Crusades (12th and 13th centuries), benefiting from Italian trade.
Acropolis of AthensThe Acropolis of Athens (; Akrópoli Athinón) is an ancient citadel located on a rocky outcrop above the city of Athens, Greece, and contains the remains of 2.5 ancient buildings of great architectural and historical significance, the most famous being the Parthenon. The word Acropolis is from the Greek words ἄκρον (akron Antisamos, "highest point, extremity") and πόλις (polis, "city"). The term acropolis is generic and there are many other acropoleis in Greece.
OzoneOzone (ˈoʊzoʊn) (or trioxygen) is an inorganic molecule with the chemical formula O3. It is a pale blue gas with a distinctively pungent smell. It is an allotrope of oxygen that is much less stable than the diatomic allotrope O2, breaking down in the lower atmosphere to O2 (dioxygen). Ozone is formed from dioxygen by the action of ultraviolet (UV) light and electrical discharges within the Earth's atmosphere. It is present in very low concentrations throughout the latter, with its highest concentration high in the ozone layer of the stratosphere, which absorbs most of the Sun's ultraviolet (UV) radiation.
National and Kapodistrian University of AthensThe National and Kapodistrian University of Athens (NKUA; Εθνικό και Καποδιστριακό Πανεπιστήμιο Αθηνών, Ethnikó ke Kapodistriakó Panepistímio Athinón), usually referred to simply as the University of Athens (UoA), is a public university in Zografou, a suburban town in the Athens agglomeration, Greece. It has been in continuous operation since its establishment in 1837 and is the oldest higher education institution of the modern Greek state and the first contemporary university in both the Balkan Peninsula and the Eastern Mediterranean.
Ozone depletionOzone depletion consists of two related events observed since the late 1970s: a steady lowering of about four percent in the total amount of ozone in Earth's atmosphere, and a much larger springtime decrease in stratospheric ozone (the ozone layer) around Earth's polar regions. The latter phenomenon is referred to as the ozone hole. There are also springtime polar tropospheric ozone depletion events in addition to these stratospheric events.
Ground-level ozoneGround-level ozone (O3), also known as surface-level ozone and tropospheric ozone, is a trace gas in the troposphere (the lowest level of the Earth's atmosphere), with an average concentration of 20–30 parts per billion by volume (ppbv), with close to 100 ppbv in polluted areas. Ozone is also an important constituent of the stratosphere, where the ozone layer (2 to 8 parts per million ozone) exists which is located between 10 and 50 kilometers above the Earth's surface.
LidarLidar (ˈlaɪdɑːr, also LIDAR, LiDAR or LADAR, an acronym of "light detection and ranging" or "laser imaging, detection, and ranging") is a method for determining ranges by targeting an object or a surface with a laser and measuring the time for the reflected light to return to the receiver. LIDAR may operate in a fixed direction (e.g., vertical) or it may scan multiple directions, in which case it is known as LIDAR scanning or 3D laser scanning, a special combination of 3-D scanning and laser scanning.
Length measurementLength measurement, distance measurement, or range measurement (ranging) refers to the many ways in which length, distance, or range can be measured. The most commonly used approaches are the rulers, followed by transit-time methods and the interferometer methods based upon the speed of light. For objects such as crystals and diffraction gratings, diffraction is used with X-rays and electron beams. Measurement techniques for three-dimensional structures very small in every dimension use specialized instruments such as ion microscopy coupled with intensive computer modeling.
Polar vortexA circumpolar vortex, or simply polar vortex, is a large region of cold, rotating air that encircles both of Earth's polar regions. Polar vortices also exist on other rotating, low-obliquity planetary bodies. The term polar vortex can be used to describe two distinct phenomena; the stratospheric polar vortex, and the tropospheric polar vortex. The stratospheric and tropospheric polar vortices both rotate in the direction of the Earth's spin, but they are distinct phenomena that have different sizes, structures, seasonal cycles, and impacts on weather.
