Astrophysics is the branch of astronomy that employs the principles of physics and chemistry "to ascertain the nature of the astronomical objects, rather than their positions or motions in space". Among the objects studied are the Sun, other stars, extrasolar planets, the interstellar medium and the cosmic microwave background. Emissions from these objects are examined across all parts of the electromagnetic spectrum, the properties examined include luminosity, density and chemical composition; because astrophysics is a broad subject, astrophysicists apply concepts and methods from many disciplines of physics, including mechanics, statistical mechanics, quantum mechanics, relativity and particle physics, atomic and molecular physics. In practice, modern astronomical research involves a substantial amount of work in the realms of theoretical and observational physics; some areas of study for astrophysicists include their attempts to determine the properties of dark matter, dark energy, black holes.
Topics studied by theoretical astrophysicists include Solar System formation and evolution. Astronomy is an ancient science, long separated from the study of terrestrial physics. In the Aristotelian worldview, bodies in the sky appeared to be unchanging spheres whose only motion was uniform motion in a circle, while the earthly world was the realm which underwent growth and decay and in which natural motion was in a straight line and ended when the moving object reached its goal, it was held that the celestial region was made of a fundamentally different kind of matter from that found in the terrestrial sphere. During the 17th century, natural philosophers such as Galileo and Newton began to maintain that the celestial and terrestrial regions were made of similar kinds of material and were subject to the same natural laws, their challenge was. For much of the nineteenth century, astronomical research was focused on the routine work of measuring the positions and computing the motions of astronomical objects.
A new astronomy, soon to be called astrophysics, began to emerge when William Hyde Wollaston and Joseph von Fraunhofer independently discovered that, when decomposing the light from the Sun, a multitude of dark lines were observed in the spectrum. By 1860 the physicist, Gustav Kirchhoff, the chemist, Robert Bunsen, had demonstrated that the dark lines in the solar spectrum corresponded to bright lines in the spectra of known gases, specific lines corresponding to unique chemical elements. Kirchhoff deduced that the dark lines in the solar spectrum are caused by absorption by chemical elements in the Solar atmosphere. In this way it was proved that the chemical elements found in the Sun and stars were found on Earth. Among those who extended the study of solar and stellar spectra was Norman Lockyer, who in 1868 detected bright, as well as dark, lines in solar spectra. Working with the chemist, Edward Frankland, to investigate the spectra of elements at various temperatures and pressures, he could not associate a yellow line in the solar spectrum with any known elements.
He thus claimed the line represented a new element, called helium, after the Greek Helios, the Sun personified. In 1885, Edward C. Pickering undertook an ambitious program of stellar spectral classification at Harvard College Observatory, in which a team of woman computers, notably Williamina Fleming, Antonia Maury, Annie Jump Cannon, classified the spectra recorded on photographic plates. By 1890, a catalog of over 10,000 stars had been prepared that grouped them into thirteen spectral types. Following Pickering's vision, by 1924 Cannon expanded the catalog to nine volumes and over a quarter of a million stars, developing the Harvard Classification Scheme, accepted for worldwide use in 1922. In 1895, George Ellery Hale and James E. Keeler, along with a group of ten associate editors from Europe and the United States, established The Astrophysical Journal: An International Review of Spectroscopy and Astronomical Physics, it was intended that the journal would fill the gap between journals in astronomy and physics, providing a venue for publication of articles on astronomical applications of the spectroscope.
Around 1920, following the discovery of the Hertsprung-Russell diagram still used as the basis for classifying stars and their evolution, Arthur Eddington anticipated the discovery and mechanism of nuclear fusion processes in stars, in his paper The Internal Constitution of the Stars. At that time, the source of stellar energy was a complete mystery; this was a remarkable development since at that time fusion and thermonuclear energy, that stars are composed of hydrogen, had not yet been discovered. In 1
The observable universe is a spherical region of the Universe comprising all matter that can be observed from Earth or its space-based telescopes and exploratory probes at the present time, because electromagnetic radiation from these objects has had time to reach the Solar System and Earth since the beginning of the cosmological expansion. There are at least 2 trillion galaxies in the observable universe. Assuming the Universe is isotropic, the distance to the edge of the observable universe is the same in every direction; that is, the observable universe has a spherical volume centered on the observer. Every location in the Universe has its own observable universe, which may or may not overlap with the one centered on Earth; the word observable in this sense does not refer to the capability of modern technology to detect light or other information from an object, or whether there is anything to be detected. It refers to the physical limit created by the speed of light itself; because no signals can travel faster than light, any object farther away from us than light could travel in the age of the Universe cannot be detected, as the signals could not have reached us yet.
Sometimes astrophysicists distinguish between the visible universe, which includes only signals emitted since recombination —and the observable universe, which includes signals since the beginning of the cosmological expansion. According to calculations, the current comoving distance—proper distance, which takes into account that the universe has expanded since the light was emitted—to particles from which the cosmic microwave background radiation was emitted, which represent the radius of the visible universe, is about 14.0 billion parsecs, while the comoving distance to the edge of the observable universe is about 14.3 billion parsecs, about 2% larger. The radius of the observable universe is therefore estimated to be about 46.5 billion light-years and its diameter about 28.5 gigaparsecs. The total mass of ordinary matter in the universe can be calculated using the critical density and the diameter of the observable universe to be about 1.5 × 1053 kg. In November 2018, astronomers reported that the extragalactic background light amounted to 4 × 1084 photons.
Since the expansion of the universe is known to accelerate and will become exponential in the future, the light emitted from all distant objects, past some time dependent on their current redshift, will never reach the Earth. In the future all observable objects will freeze in time while emitting progressively redder and fainter light. For instance, objects with the current redshift z from 5 to 10 will remain observable for no more than 4–6 billion years. In addition, light emitted by objects situated beyond a certain comoving distance will never reach Earth; some parts of the universe are too far away for the light emitted since the Big Bang to have had enough time to reach Earth or its scientific space-based instruments, so lie outside the observable universe. In the future, light from distant galaxies will have had more time to travel, so additional regions will become observable. However, due to Hubble's law, regions sufficiently distant from the Earth are expanding away from it faster than the speed of light and furthermore the expansion rate appears to be accelerating due to dark energy.
Assuming dark energy remains constant, so that the expansion rate of the universe continues to accelerate, there is a "future visibility limit" beyond which objects will never enter our observable universe at any time in the infinite future, because light emitted by objects outside that limit would never reach the Earth. This future visibility limit is calculated at a comoving distance of 19 billion parsecs, assuming the universe will keep expanding forever, which implies the number of galaxies that we can theoretically observe in the infinite future is only larger than the number observable by a factor of 2.36. Though in principle more galaxies will become observable in the future, in practice an increasing number of galaxies will become redshifted due to ongoing expansion, so much so that they will seem to disappear from view and become invisible. An additional subtlety is that a galaxy at a given comoving distance is defined to lie within the "observable universe" if we can receive signals emitted by the galaxy at any age in its past history, but because of the universe's expansion, there may be some age at which a signal sent from the same galaxy can never reach the Earth at any point in the infinite future (so, for example, we might never see what the galaxy looked like 10 billion years after the Bi
Martín Cortés de Albacar
Martín Cortés de Albacar was a Spanish cosmographer. In 1551 he published the standard navigational textbook Arte de navigar Cortés was born in Bujaraloz, province of Zaragoza, Aragon. From 1530, in Cádiz, he taught the art of navigation to pilots. Cortés' book, Breve compendio... Arte de navegar was promoted by Steven Borough who had it translated into English by Richard Eden and published in 1561 entitled The Art of Navigation; as such it became the first English manual of navigation and the primary text for European navigation throughout the early 17thC, enjoyed by such as Martin Frobisher and Francis Drake. Arte de navegar was a practical book in which Cortés discussed, in a concise manner, navigation and problems such as magnetic declination for which he hypothesised a Celestial magnetic pole, he included many models for making instruments. And the text contained the earliest known description of the Nocturnal and how to make and use a sea astrolabeCortés' calculations were critical in allowing explorers to ascertain their location when out of sight of land.
In 1574, the mathematician William Bourne, produced a popular version of the book, entitled A Regiment for the Sea. Bourne was critical of some aspects of Arte de Navegar and produced a manual of more practical use to the seaman, he died aged 72
Abu Yahya Zakariya' ibn Muhammad al-Qazwini or Zakarya Qazvini was a Persian physician, astronomer and proto-science fiction writer of Arab descent. He belonged to a family of jurists, he drew his origin from an Arab family and was a descendant of the Medinian Sahabi Anas bin Malik. Born in Qazvin, Zakariya Qazvini served as a legal expert and judge in several localities in Iran and at the city of Baghdad, he travelled around in Mesopotamia and the Levant, entered the circle patronized by the governor of Baghdad, Ata-Malik Juvayni. It was to the latter that Qazvini dedicated his famous cosmography titled "The Wonders of Creation"; this treatise illustrated, was immensely popular and is preserved today in many copies. It was translated into his native Persian language, also into Turkish. Qazvini was well known for his geographical dictionary "Monument of Places and History of God's Bondsmen". Both of these treatises reflect extensive learning in a wide range of disciplines. Qazvini wrote a futuristic proto-science fiction Arabic tale entitled Awaj bin Anfaq, about a man who travelled to Earth from a distant planet.
Qazvini mentioned how alchemists dubbed "swindlers" claimed to have carried out the transmutation of metals into gold. List of Persian scientists and scholars T. Lewicki,'Kazwini' in The Encyclopaedia of Islam, 2nd edition, ed. by H. A. R. Gibbs, B. Lewis, Ch. Pellat, C. Bosworth et al. 11 vols. vol. 4, pp 865–7 L. Richter-Bernburg,'al-Qazwini, Zakariyya' ibn Muhammad', in Encyclopedia of Arabic Literature, ed. by Julie Scott Meisami and Paul Starkey, vol. 2, pp 637–8. Persis Berlekamp, Wonder and Cosmos in Medieval Islam. Islamic Medical Manuscripts at the National Library of Medicine. U. S. National Library of Medicine, Bethesda, MD, his cosmography was edited by F. Wüstenfeld, ‘Aja'ib al-makhluqat – a partial German translation was published by A. Giese, Al-Qazwini, Die Wunder des Himmels und der Erde. Zakarija ben Muhammed ben Mahmud el-Cazwini's: Kosmographie.. Volume: 1 His geographical dictionary was edited by Wüstenfeld as Athar al-bilad. Ahmad, S. Maqbul. "Al-Qazwīnī, Zakariyā Ibn Muḥammad Ibn Maḥmūd, Abū Yaḥyā".
Complete Dictionary of Scientific Biography. Encyclopedia.com. Turning the Pages Several pages from Al-Qazwini's Kitab Aja’ib al-makhluqat wa Gharaib al-Mawjudat, known as “The Cosmography” or “The Wonders of Creation.” Kitāb al-ʻajāʾib wa al-gharāʼib. Full online version from the Getty Library
Genesis creation narrative
The Genesis creation narrative is the creation myth of both Judaism and Christianity. The narrative is made up of two stories equivalent to the first two chapters of the Book of Genesis. In the first, Elohim creates the heavens and the Earth in six days rests on, blesses and sanctifies the seventh. In the second story, now referred to by the personal name Yahweh, creates Adam, the first man, from dust and places him in the Garden of Eden, where he is given dominion over the animals. Eve, the first woman, is created as his companion. Borrowing themes from Mesopotamian mythology, but adapting them to the Israelite people's belief in one God, the first major comprehensive draft of the Pentateuch was composed in the late 7th or the 6th century BCE and was expanded by other authors into a work like the one we have today; the two sources can be identified in the creation narrative: Jahwistic. The combined narrative is a critique of the Mesopotamian theology of creation: Genesis affirms monotheism and denies polytheism.
Robert Alter described the combined narrative as "compelling in its archetypal character, its adaptation of myth to monotheistic ends". Different interpretations of the genre of the Genesis creation narrative, meaning the intention of the author and the culture within which they wrote, exist; as scholar of Jewish studies, Jon D. Levenson, puts it: How much history lies behind the story of Genesis? Because the action of the primeval story is not represented as taking place on the plane of ordinary human history and has so many affinities with ancient mythology, it is far-fetched to speak of its narratives as historical at all." Although tradition attributes Genesis to Moses, biblical scholars hold that it, together with the following four books, is "a composite work, the product of many hands and periods." A common hypothesis among biblical scholars today is that the first major comprehensive draft of the Pentateuch was composed in the late 7th or the 6th century BCE, that this was expanded by the addition of various narratives and laws into a work like the one existing today.
As for the historical background which led to the creation of the narrative itself, a theory which has gained considerable interest, although still controversial, is "Persian imperial authorisation". This proposes that the Persians, after their conquest of Babylon in 538 BCE, agreed to grant Jerusalem a large measure of local autonomy within the empire, but required the local authorities to produce a single law code accepted by the entire community, it further proposes that there were two powerful groups in the community – the priestly families who controlled the Temple, the landowning families who made up the "elders" – and that these two groups were in conflict over many issues, that each had its own "history of origins", but the Persian promise of increased local autonomy for all provided a powerful incentive to cooperate in producing a single text. The creation narrative is made up of two stories equivalent to the two first chapters of the Book of Genesis; the first account employs a repetitious structure of divine fiat and fulfillment the statement "And there was evening and there was morning, the day," for each of the six days of creation.
In each of the first three days there is an act of division: day one divides the darkness from light, day two the "waters above" from the "waters below", day three the sea from the land. In each of the next three days these divisions are populated: day four populates the darkness and light with Sun and stars. Consistency was evidently not seen as essential to storytelling in ancient Near Eastern literature; the overlapping stories of Genesis 1 and 2 are contradictory but complementary, with the first concerned with the creation of the entire cosmos while the second focuses on man as moral agent and cultivator of his environment. The regimented seven-day narrative of Genesis 1 features an omnipotent God who creates a god-like humanity, while the one-day creation of Genesis 2 uses a simple linear narrative, a God who can fail as well as succeed, a humanity, not god-like but is punished for acts which would lead to their becoming god-like; the order and method of creation differs. "Together, this combination of parallel character and contrasting profile point to the different origin of materials in Genesis 1 and Genesis 2, however elegantly they have now been combined."The primary accounts in each chapter are joined by a literary bridge at Genesis 2:4|, "These are the generations of the heavens and of the earth when they were created."
This echoes the first line of Genesis 1, "In the beginning God created the heaven and the earth", is reversed in the next phrase, "...in the day that the LORD God made the earth and the heavens". This verse is one of ten "generations" phrases used throughout Genesis, which provide a literary structure to the book, they function as headings to what comes after, but the position of this, the first of the series, has been the subject of much debate. Comparative mythology provides historical and cross-cultura
Kinematics is a branch of classical mechanics that describes the motion of points and systems of bodies without considering the forces that caused the motion. Kinematics, as a field of study, is referred to as the "geometry of motion" and is seen as a branch of mathematics. A kinematics problem begins by describing the geometry of the system and declaring the initial conditions of any known values of position, velocity and/or acceleration of points within the system. Using arguments from geometry, the position and acceleration of any unknown parts of the system can be determined; the study of how forces act on bodies falls within kinetics, not kinematics. For further details, see analytical dynamics. Kinematics is used in astrophysics to describe the motion of celestial bodies and collections of such bodies. In mechanical engineering and biomechanics kinematics is used to describe the motion of systems composed of joined parts such as an engine, a robotic arm or the human skeleton. Geometric transformations called rigid transformations, are used to describe the movement of components in a mechanical system, simplifying the derivation of the equations of motion.
They are central to dynamic analysis. Kinematic analysis is the process of measuring the kinematic quantities used to describe motion. In engineering, for instance, kinematic analysis may be used to find the range of movement for a given mechanism and working in reverse, using kinematic synthesis to design a mechanism for a desired range of motion. In addition, kinematics applies algebraic geometry to the study of the mechanical advantage of a mechanical system or mechanism; the term kinematic is the English version of A. M. Ampère's cinématique, which he constructed from the Greek κίνημα kinema, itself derived from κινεῖν kinein. Kinematic and cinématique are related to the French word cinéma, but neither are directly derived from it. However, they do share a root word in common, as cinéma came from the shortened form of cinématographe, "motion picture projector and camera," once again from the Greek word for movement but the Greek word for writing. Particle kinematics is the study of the trajectory of a particle.
The position of a particle is defined as the coordinate vector from the origin of a coordinate frame to the particle. For example, consider a tower 50 m south from your home, where the coordinate frame is located at your home, such that East is the x-direction and North is the y-direction the coordinate vector to the base of the tower is r =. If the tower is 50 m high the coordinate vector to the top of the tower is r =. In the most general case, a three-dimensional coordinate system is used to define the position of a particle. However, if the particle is constrained to move in a surface, a two-dimensional coordinate system is sufficient. All observations in physics are incomplete without those observations being described with respect to a reference frame; the position vector of a particle is a vector drawn from the origin of the reference frame to the particle. It expresses both the distance of the point from its direction from the origin. In three dimensions, the position of point P can be expressed as P = = x P ı ^ + y P ȷ ^ + z P k ^, where x P, y P, z P are the Cartesian coordinates and ı ^, ȷ ^ and k ^ are the unit vectors along the x, y, z coordinate axes, respectively.
The magnitude of the position vector | P | gives the distance between the origin. | P | = x P 2 + y P 2 + z P 2. The direction cosines of the position vector provide a quantitative measure of direction, it is important to note. The position vector of a given particle is different relative to different frames of reference; the trajectory of a particle is a vector function of time, P, which defines the curve traced by the moving particle, given by P = x P ı ^ + y P ȷ ^ + z P k ^, where
The Persians are an Iranian ethnic group that make up over half the population of Iran. They share a common cultural system and are native speakers of the Persian language, as well as related languages; the ancient Persians were a nomadic branch of the ancient Iranian population that entered the territory of modern-day Iran by the early 10th century BC. Together with their compatriot allies, they established and ruled some of the world's most powerful empires, well-recognized for their massive cultural and social influence covering much of the territory and population of the ancient world. Throughout history, the Persians have contributed to various forms of art and science, own one of the world's most prominent literatures. In contemporary terminology, people of Persian heritage native to present-day Afghanistan and Uzbekistan are referred to as Tajiks, whereas those in the eastern Caucasus, albeit assimilated, are referred to as Tats; however the terms Tajik and Persian were synonymous and were used interchangeably, many of the most influential Persian figures hailed from outside Iran's present-day borders to the northeast in Central Asia and Afghanistan and to a lesser extent to the northwest in the Caucasus proper.
In historical contexts in English, "Persians" may be defined more loosely to cover all subjects of the ancient Persian polities, regardless of ethnic background. The English term Persian derives from Latin Persia, itself deriving from Greek Persís, a Hellenized form of Old Persian Pārsa. In the Bible, it is given as Parás —sometimes Paras uMadai —within the books of Esther, Daniel and Nehemya. A Greek folk etymology connected the name to a legendary character in Greek mythology. Herodotus recounts this story, devising a foreign son, from whom the Persians took the name; the Persians themselves knew the story, as Xerxes I tried to use it to suborn the Argives during his invasion of Greece, but failed to do so. Although Persis was one of the provinces of ancient Iran, varieties of this term were adopted through Greek sources and used as an official name for all of Iran for many years. Thus, in the Western world, the term Persian came to refer to all inhabitants of the country; some medieval and early modern Islamic sources used cognates of the term Persian to refer to various Iranian peoples, including the speakers of the Khwarezmian language, the Mazanderani language, the Old Azeri language.
10th-century Iraqi historian Al-Masudi refers to Pahlavi and Azari as dialects of the Persian language. In 1333, medieval Moroccan traveler and scholar Ibn Battuta referred to the people of Kabul as a specific sub-tribe of Persians. Lady Mary Sheil, in her observation of Iran during the Qajar era, describes Persians and Leks to identify themselves as "descendants of the ancient Persians". On March 21, 1935, the former king of Iran, Reza Shah of the Pahlavi dynasty, issued a decree asking the international community to use the term Iran, the native name of the country, in formal correspondence. However, the term Persian is still used to designate the predominant population of the Iranian peoples living in the Iranian cultural continent; the earliest known written record attributed to the Persians is from the Black Obelisk of Shalmaneser III, an Assyrian inscription from the mid-9th century BC, found at Nimrud. The inscription mentions Parsua as a tribal chiefdom in modern-day western Iran; the ancient Persians were a nomadic branch of the Iranian population that, in the early 10th century BC, settled to the northwest of modern-day Iran.
They were dominated by the Assyrians for much of the first three centuries after arriving in the region. However, they played a major role in the downfall of the Neo-Assyrian Empire; the Medes, another branch of this population, founded the unified empire of Media as the region's dominant cultural and political power in c. 625 BC. Meanwhile, the Persian dynasty of the Achaemenids formed a vassal state to the central Median power. In c. 552 BC, the Achaemenids began a revolution which led to the conquest of the empire by Cyrus II in c. 550 BC. They spread their influence to the rest of what is called the Iranian Plateau, assimilated with the non-Iranian indigenous groups of the region, including the Elamites and the Mannaeans. At its greatest extent, the Achaemenid Empire stretched from parts of Eastern Europe in the west, to the Indus Valley in the east, making it the largest empire the world had yet seen; the Achaemenids developed the infrastructure to support their growing influence, including the creation of Pasargadae and the opulent city of Persepolis.
The empire extended as far as the limits of the Greek city states in modern-day mainland Greece, where the Persians and Athenians influenced each other in what is a reciprocal cultural exchange. Its legacy and impact on the kingdom of Macedon was notably huge for centuries after the withdrawal of the Persians from Europe following the Greco-Persian Wars; the empire collapsed in 330 BC following the conquests of Alexander the Great, but reemerged shortly after as the Parthian Empire. During the Achaemenid era, Persian colonists settled in Asia Minor. In Lydia, near Sardis, there was the Hyrcanian plain, according to Strabo, got its name from the Persian settlers that were moved from Hyrcania. Near Sardis, there was the plain of Cyrus, which further signified the presence of numerous Persian settlements in