Geography (Ptolemy)

The Geography (Greek: Γεωγραφικὴ Ὑφήγησις, Geōgraphikḕ Hyphḗgēsis, lit. "Geographical Guidance"), also known by its Latin names as the Geographia and the Cosmographia, is a gazeteer, an atlas, and a treatise on cartography, compiling the geographical knowledge of the 2nd-century Roman Empire. Originally written by Ptolemy in Greek at Alexandria around AD 150, the work was a revision of a now-lost atlas by Marinus of Tyre using additional Roman and Persian gazetteers and new principles. Its translation into Arabic in the 9th century and Latin in 1406 was highly influential on the geographical knowledge and cartographic traditions of the medieval Caliphate and Renaissance Europe.

Manuscripts

Versions of Ptolemy's work in antiquity were probably proper atlases with attached maps, although some scholars aver that the references to maps in the text were later additions.

No Greek manuscript of the Geography survives from earlier than the 13th century. A letter written by the Byzantine monk Maximus Planudes records that he searched for one for Chora Monastery in the summer of 1295; one of the earliest surviving texts may have been one of those he then assembled. In Europe, maps were sometimes made redrawn using the coördinates provided by the text, as Planudes was forced to do. Later scribes and publishers could then copy these new maps, as Athanasius did for the emperor Andronicus II Palaeologus. The three earliest surviving texts with maps are those from Constantinople (Istanbul) based on Planudes's work.

Geography (disambiguation)

Geography is the study of the earth and its features, inhabitants, and phenomena.

Geography may also refer to:

Eratosthenes

Eratosthenes of Cyrene (/ɛrəˈtɒsθəniːz/; Greek: Ἐρατοσθένης, IPA: [eratostʰénɛːs]; c. 276 BC – c. 195/194 BC) was a Greek mathematician, geographer, poet, astronomer, and music theorist. He was a man of learning, becoming the chief librarian at the Library of Alexandria. He invented the discipline of geography, including the terminology used today.

He is best known for being the first person to calculate the circumference of the Earth, which he did by applying a measuring system using stadia, which was a standard unit of measure during that time period. His calculation was remarkably accurate. He was also the first to calculate the tilt of the Earth's axis (again with remarkable accuracy). Additionally, he may have accurately calculated the distance from the Earth to the Sun and invented the leap day. He created the first map of the world incorporating parallels and meridians, based on the available geographical knowledge of the era.

Eratosthenes was the founder of scientific chronology; he endeavored to revise the dates of the chief literary and political events from the conquest of Troy. In number theory, he introduced the sieve of Eratosthenes, an efficient method of identifying prime numbers.

Degree

Degree may refer to:

As a unit of measurement

Field extension

In abstract algebra, field extensions are the main object of study in field theory. The general idea is to start with a base field and construct in some manner a larger field that contains the base field and satisfies additional properties. For instance, the set Q(√2) = {a + b√2 | a, b ∈ Q} is the smallest extension of Q that includes every real solution to the equation x² = 2.

Definitions

Let L be a field. A subfield of L is a subset K of L that is closed under the field operations of L and under taking inverses in L. In other words, K is a field with respect to the field operations inherited from L. The larger field L is then said to be an extension field of K. To simplify notation and terminology, one says that L / K (read as "L over K") is a field extension to signify that L is an extension field of K.

If L is an extension of F which is in turn an extension of K, then F is said to be an intermediate field (or intermediate extension or subextension) of the field extension L / K.

Degree symbol

The degree symbol (°) is a typographical symbol that is used, among other things, to represent degrees of arc (e.g. in geographic coordinate systems), hours (in the medical field), degrees of temperature, alcohol proof, or diminished quality in musical harmony. The symbol consists of a small raised circle, historically a zero glyph.

In Unicode it is encoded at U+00B0 ° DEGREE SIGN (HTML ° · °).

History

The first known recorded modern use of the degree symbol in mathematics is from 1569 where the usage seems to show that the symbol is a small raised zero, to match the prime symbol notation of sexagesimal subdivisions of degree such as minute ′, second ″, and tertia ‴ which originates as small raised Roman numerals.

Typography

In the case of degrees of arc, the degree symbol follows the number without any intervening space.

Online and offline

The terms "online" and "offline" have specific meanings in regard to computer technology and telecommunications in which "online" indicates a state of connectivity, while "offline" indicates a disconnected state. Common vernacular extended from their computing and telecommunication meanings and refers specifically to an Internet connection. Lastly, in the area of human interaction and conversation, discussions taking place during a business meeting are "online", while issues that do not concern all participants of the meeting should be "taken offline" — continued outside of the meeting.

Definitions

In computer technology and telecommunication, online and offline are defined by Federal Standard 1037C. They are states or conditions of a "device or equipment" or of a "functional unit". To be considered online, one of the following may apply to a system: it is under the direct control of another device; it is under the direct control of the system with which it is associated; or it is available for immediate use on demand by the system without human intervention.