Ptolemy V Epiphanes, son of the siblings Ptolemy IV Philopator and Arsinoe III of Egypt, was the fifth ruler of the Ptolemaic dynasty from July/August 204 to September 180 BC. Ptolemy inherited the throne at the age of five; the new regent, Agathocles was reviled and was toppled by a revolution in 202 BC, but the series of regents who followed proved incompetent and the kingdom was paralysed. The Seleucid king Antiochus III and the Antigonid king Philip V took advantage of the kingdom's weakness to begin the Fifth Syrian War, in which the Ptolemies lost all their territories in Asia Minor and the Levant, as well as most of their influence in the Aegean Sea. Ptolemy V faced a widespread Egyptian revolt led by self-proclaimed Pharaohs, which resulted in the loss of most of Upper Egypt and parts of Lower Egypt as well. Ptolemy V came of age in 196 BC and was crowned as Pharaoh in Memphis, an occasion commemorated by the creation of the Rosetta Stone. After this, he made peace with Antiochus III and married his daughter Cleopatra I in 194/3 BC.

This disgusted the Romans who had entered into hostilities with Antiochus on Ptolemy's behalf - after their victory, they distributed the old Ptolemaic territories in Asia Minor to Pergamum and Rhodes rather than returning them to Egypt. However, Ptolemaic forces reconquered the south of the country, bringing all of Upper Egypt back under Ptolemaic control in 186 BC. In his last years, Ptolemy began manoeuvring for renewed warfare with the Seleucid empire, but these plans were cut short by his sudden death in September 180 BC poisoned by courtiers worried about the cost of the war. Ptolemy's reign saw increased prominence of courtiers and the Egyptian priestly elite in Ptolemaic political life - a pattern that would continue for most of the rest of the kingdom's existence, it marked the collapse of Ptolemaic power in the wider Mediterranean region. Arthur Eckstein has argued that this collapse sparked the'power transition crisis' which led to the Roman conquest of the eastern Mediterranean.

Ptolemy V was the only child of Ptolemy IV and his sister-wife Arsinoe III. The couple had come to power young and ancient historiography remembered Ptolemy IV as being given over to luxury and ceremony, while leaving the government of Egypt to two courtiers and Agathocles. In his early reign, Ptolemy IV defeated the rival Seleucid empire in the Fourth Syrian War preventing the Seleucid king Antiochus III from seizing Coele Syria for himself, his reign, however was troubled by native Egyptian revolts. Between 206 and 205 BC, Ptolemy lost control of Upper Egypt altogether, to the self-styled Pharaoh Hugronaphor. Ptolemy V was born in 210 BC on 9 October and made co-regent with his father shortly thereafter on 30 November. In July or August of 204 BC, when Ptolemy V was five years old, his father and mother died in mysterious circumstances, it appears that there was a fire in the palace that killed Ptolemy IV, but it is unclear whether Arsinoe III perished in this fire or was murdered afterwards to prevent her from becoming regent.

An uncertain amount of time elapsed after the death of Ptolemy IV and Arsinoe III, during which Sosibius and Agathocles kept their deaths secret. Some time before September 204 BC, the royal bodyguard and army officers were gathered at the royal palace and Sosibius announced the death of the ruling couple and presented the young Ptolemy V to be acclaimed as king, wrapping the diadem around his head. Sosibius read out Ptolemy IV's will, which made Sosibius and Agathocles regents and placed Ptolemy V in the personal care of his mistress Agathoclea and her mother Oenanthe. Polybius thought that this will was a forgery produced by Sosibius and Agathocles themselves and modern scholars tend to agree with him. Sosibius is not heard of again after this event and it is assumed that he died. Hölbl suggests. Agathocles took a number of actions to solidify the new regime. Two months' pay were granted to the soldiers in Alexandria. Prominent aristocrats were dispatched overseas - to secure recognition of the succession from foreign powers and to prevent the aristocrats from challenging Agathocles supremacy at home.

Philammon, said to have carried out the murder of Arsinoe III, was sent to Cyrene as governor, in order to assert Ptolemaic rule there. Pelops, governor of Cyprus, was sent to Antiochus III to ask him to continue to respect the peace treaty made with Ptolemy IV at the end of the Fourth Syrian War. Ptolemy, Sosibius' son, was sent to Philip V of Macedon to attempt to arrange an alliance against Antiochus III and a marriage between Ptolemy V and one of his daughters. Ptolemy of Megalopolis was sent to Rome seeking support against Aniochus III; these missions were failures. Over the following year, Antiochus seized Ptolemaic territory in Caria, including the city of Amyzon and by late 203 BC he and Philip V had made a secret agreement to divide the Ptolemaic territories between themselves. War with Antiochus III was expected - Agathocles had sent an embassy under Scopas the Aetolian to hire mercenaries in Greece in preparation for a conflict, although Polybius claims that his true purpose was to replace the Ptolemaic troops with mercenaries loyal to him.

Agathocles and Agathoclea had been unpopular before Ptolemy IV's death. This unpopularity was exacerbated by the widespread belief that they had bee

Navigation is a field of study that focuses on the process of monitoring and controlling the movement of a craft or vehicle from one place to another. The field of navigation includes four general categories: land navigation, marine navigation, aeronautic navigation, space navigation, it is the term of art used for the specialized knowledge used by navigators to perform navigation tasks. All navigational techniques involve locating the navigator's position compared to known locations or patterns. Navigation, in a broader sense, can refer to any skill or study that involves the determination of position and direction. In this sense, navigation includes pedestrian navigation. In the European medieval period, navigation was considered part of the set of seven mechanical arts, none of which were used for long voyages across open ocean. Polynesian navigation is the earliest form of open-ocean navigation, it was based on memory and observation recorded on scientific instruments like the Marshall Islands Stick Charts of Ocean Swells.

Early Pacific Polynesians used the motion of stars, the position of certain wildlife species, or the size of waves to find the path from one island to another. Maritime navigation using scientific instruments such as the mariner's astrolabe first occurred in the Mediterranean during the Middle Ages. Although land astrolabes were invented in the Hellenistic period and existed in classical antiquity and the Islamic Golden Age, the oldest record of a sea astrolabe is that of Majorcan astronomer Ramon Llull dating from 1295; the perfecting of this navigation instrument is attributed to Portuguese navigators during early Portuguese discoveries in the Age of Discovery. The earliest known description of how to make and use a sea astrolabe comes from Spanish cosmographer Martín Cortés de Albacar's Arte de Navegar published in 1551, based on the principle of the archipendulum used in constructing the Egyptian pyramids. Open-seas navigation using the astrolabe and the compass started during the Age of Discovery in the 15th century.

The Portuguese began systematically exploring the Atlantic coast of Africa from 1418, under the sponsorship of Prince Henry. In 1488 Bartolomeu Dias reached the Indian Ocean by this route. In 1492 the Spanish monarchs funded Christopher Columbus's expedition to sail west to reach the Indies by crossing the Atlantic, which resulted in the Discovery of the Americas. In 1498, a Portuguese expedition commanded by Vasco da Gama reached India by sailing around Africa, opening up direct trade with Asia. Soon, the Portuguese sailed further eastward, to the Spice Islands in 1512, landing in China one year later; the first circumnavigation of the earth was completed in 1522 with the Magellan-Elcano expedition, a Spanish voyage of discovery led by Portuguese explorer Ferdinand Magellan and completed by Spanish navigator Juan Sebastián Elcano after the former's death in the Philippines in 1521. The fleet of seven ships sailed from Sanlúcar de Barrameda in Southern Spain in 1519, crossed the Atlantic Ocean and after several stopovers rounded the southern tip of South America.

Some ships were lost, but the remaining fleet continued across the Pacific making a number of discoveries including Guam and the Philippines. By only two galleons were left from the original seven; the Victoria led by Elcano sailed across the Indian Ocean and north along the coast of Africa, to arrive in Spain in 1522, three years after its departure. The Trinidad sailed east from the Philippines, trying to find a maritime path back to the Americas, but was unsuccessful; the eastward route across the Pacific known as the tornaviaje was only discovered forty years when Spanish cosmographer Andrés de Urdaneta sailed from the Philippines, north to parallel 39°, hit the eastward Kuroshio Current which took its galleon across the Pacific. He arrived in Acapulco on October 8, 1565; the term stems from the 1530s, from Latin navigationem, from navigatus, pp. of navigare "to sail, sail over, go by sea, steer a ship," from navis "ship" and the root of agere "to drive". The latitude of a place on Earth is its angular distance north or south of the equator.

Latitude is expressed in degrees ranging from 0° at the Equator to 90° at the North and South poles. The latitude of the North Pole is 90° N, the latitude of the South Pole is 90° S. Mariners calculated latitude in the Northern Hemisphere by sighting the North Star Polaris with a sextant and using sight reduction tables to correct for height of eye and atmospheric refraction; the height of Polaris in degrees above the horizon is the latitude of the observer, within a degree or so. Similar to latitude, the longitude of a place on Earth is the angular distance east or west of the prime meridian or Greenwich meridian. Longitude is expressed in degrees ranging from 0° at the Greenwich meridian to 180° east and west. Sydney, for example, has a longitude of about 151° east. New York City has a longitude of 74° west. For most of history, mariners struggled to determine longitude. Longitude can be calculated. Lacking that, one can use a sextant to take a lunar distance that, with a nautical almanac, can be used to calculate the time at zero longitude.

Reliable marine chronometers were unavailable until the late 18th century and not affordable until the 19th century. For about a hundred years, from about 1767 until about 1850, mariners lacking a chronometer used the method of lunar distances to determine Greenwich time to find their longitude. A mariner with a chronometer could check its reading using a lunar determination of Greenwich tim

Doridoidea known as dorid nudibranchs, are a taxonomic superfamily of medium to large, shell-less sea slugs, marine gastropod mollusks in the clade Doridacea, included in the clade Nudibranchia. The word "Doridoidea" comes from the generic name Doris, in turn copied from the name of the sea nymph, Doris, in Greek mythology. According to the Taxonomy of the Gastropoda, families within the superfamily Doridoidea include: Actinocyclidae O'Donoghue, 1929 Chromodorididae Bergh, 1891 Discodorididae Bergh, 1891 Dorididae Rafinesque, 1815 The family Cadlinidae Bergh, 1891 was considered a synonym of the Chromodorididae. Research by R. F. Johnson in 2011 has shown, she has therefore brought back the name Cadlinidae from synonymy with Chromodorididae. The chromodorid nudibranchs without Cadlina are now monophyletic and turn out to be a possible sister to the Actinocyclidae Actinocyclidae O'Donoghue, 1929 Cadlinidae Bergh, 1891 Chromodorididae Bergh, 1891 Discodorididae Bergh, 1891 Dorididae Rafinesque, 1815 The next families are considered synonyms.

But these names can still be found on the internet. Cryptobranch dorid nudibranchs, are nudibranch sea slugs within the clade Doridacea; these slugs are called "cryptobranch," meaning "hidden gill", because they are able to retract their gills into a gill pocket, in contrast to nudibranchs in the traditional group phanerobranchs, which taxon is paraphyletic. A. Valdés distinguishes two major clades within the Cryptobranchia: the dorids; the Labiostomata include the monophyletic families: Actinocyclidae, Chromodorididae and Discodorididae. The cryptobranchs include the following genera that are regarded as valid