It is a rotating mass of gas, dust, stars and other objects, held together by mutual gravitational attraction. As the Earth is located within the dusty outer arms, there are large portions of the Milky Way that are obscured from view. In the center of the Milky Way is the core, a bar-shaped bulge with what is believed to be a supermassive black hole at its center.
This is surrounded by four primary arms that spiral from the core. This is a region of active star formation that contains many younger, population I stars. The disk is surrounded by a spheroid halo of older, population II stars, as well as relatively dense concentrations of stars known as globular clusters. Between the stars lies the interstellar medium , a region of sparse matter. In the densest regions, molecular clouds of molecular hydrogen and other elements create star-forming regions.
These begin as a compact pre-stellar core or dark nebulae , which concentrate and collapse in volumes determined by the Jeans length to form compact protostars. As the more massive stars appear, they transform the cloud into an H II region ionized atomic hydrogen of glowing gas and plasma. The stellar wind and supernova explosions from these stars eventually cause the cloud to disperse, often leaving behind one or more young open clusters of stars. These clusters gradually disperse, and the stars join the population of the Milky Way. Kinematic studies of matter in the Milky Way and other galaxies have demonstrated that there is more mass than can be accounted for by visible matter.
A dark matter halo appears to dominate the mass, although the nature of this dark matter remains undetermined.
The study of stars and stellar evolution is fundamental to our understanding of the Universe. The astrophysics of stars has been determined through observation and theoretical understanding; and from computer simulations of the interior. When destabilized, cloud fragments can collapse under the influence of gravity, to form a protostar.
A sufficiently dense, and hot, core region will trigger nuclear fusion , thus creating a main-sequence star. Almost all elements heavier than hydrogen and helium were created inside the cores of stars. The characteristics of the resulting star depend primarily upon its starting mass. The more massive the star, the greater its luminosity, and the more rapidly it fuses its hydrogen fuel into helium in its core. Over time, this hydrogen fuel is completely converted into helium, and the star begins to evolve.
The fusion of helium requires a higher core temperature. A star with a high enough core temperature will push its outer layers outward while increasing its core density. The resulting red giant formed by the expanding outer layers enjoys a brief life span, before the helium fuel in the core is in turn consumed. Very massive stars can also undergo a series of evolutionary phases, as they fuse increasingly heavier elements. The final fate of the star depends on its mass, with stars of mass greater than about eight times the Sun becoming core collapse supernovae ;  while smaller stars blow off their outer layers and leave behind the inert core in the form of a white dwarf.
The ejection of the outer layers forms a planetary nebula. At a distance of about eight light-minutes, the most frequently studied star is the Sun , a typical main-sequence dwarf star of stellar class G2 V, and about 4. The Sun is not considered a variable star , but it does undergo periodic changes in activity known as the sunspot cycle. This is an year oscillation in sunspot number. Sunspots are regions of lower-than- average temperatures that are associated with intense magnetic activity. The Sun has also undergone periodic changes in luminosity that can have a significant impact on the Earth.
The visible outer surface of the Sun is called the photosphere. Above this layer is a thin region known as the chromosphere. This is surrounded by a transition region of rapidly increasing temperatures, and finally by the super-heated corona. At the center of the Sun is the core region, a volume of sufficient temperature and pressure for nuclear fusion to occur. Above the core is the radiation zone , where the plasma conveys the energy flux by means of radiation. Above that is the convection zone where the gas material transports energy primarily through physical displacement of the gas known as convection.
It is believed that the movement of mass within the convection zone creates the magnetic activity that generates sunspots. A solar wind of plasma particles constantly streams outward from the Sun until, at the outermost limit of the Solar System, it reaches the heliopause.
As the solar wind passes the Earth, it interacts with the Earth's magnetic field magnetosphere and deflects the solar wind, but traps some creating the Van Allen radiation belts that envelop the Earth. The aurora are created when solar wind particles are guided by the magnetic flux lines into the Earth's polar regions where the lines the descend into the atmosphere. Planetary science is the study of the assemblage of planets , moons , dwarf planets , comets , asteroids , and other bodies orbiting the Sun, as well as extrasolar planets.
The Solar System has been relatively well-studied, initially through telescopes and then later by spacecraft. This has provided a good overall understanding of the formation and evolution of the Sun's planetary system, although many new discoveries are still being made. The Solar System is subdivided into the inner planets, the asteroid belt , and the outer planets. The inner terrestrial planets consist of Mercury , Venus , Earth, and Mars.
The outer gas giant planets are Jupiter , Saturn , Uranus , and Neptune. The planets were formed 4. Through a process that included gravitational attraction, collision, and accretion, the disk formed clumps of matter that, with time, became protoplanets.
The radiation pressure of the solar wind then expelled most of the unaccreted matter, and only those planets with sufficient mass retained their gaseous atmosphere. The planets continued to sweep up, or eject, the remaining matter during a period of intense bombardment, evidenced by the many impact craters on the Moon.
During this period, some of the protoplanets may have collided and one such collision may have formed the Moon. Once a planet reaches sufficient mass, the materials of different densities segregate within, during planetary differentiation. This process can form a stony or metallic core, surrounded by a mantle and an outer crust.
The core may include solid and liquid regions, and some planetary cores generate their own magnetic field , which can protect their atmospheres from solar wind stripping. A planet or moon's interior heat is produced from the collisions that created the body, by the decay of radioactive materials e.
Some planets and moons accumulate enough heat to drive geologic processes such as volcanism and tectonics. Those that accumulate or retain an atmosphere can also undergo surface erosion from wind or water. Smaller bodies, without tidal heating, cool more quickly; and their geological activity ceases with the exception of impact cratering.
Astronomy and astrophysics have developed significant interdisciplinary links with other major scientific fields. Archaeoastronomy is the study of ancient or traditional astronomies in their cultural context, utilizing archaeological and anthropological evidence. Astrobiology is the study of the advent and evolution of biological systems in the Universe, with particular emphasis on the possibility of non-terrestrial life.
Astrostatistics is the application of statistics to astrophysics to the analysis of vast amount of observational astrophysical data.
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The study of chemicals found in space, including their formation, interaction and destruction, is called astrochemistry. These substances are usually found in molecular clouds , although they may also appear in low temperature stars, brown dwarfs and planets. Cosmochemistry is the study of the chemicals found within the Solar System, including the origins of the elements and variations in the isotope ratios. Both of these fields represent an overlap of the disciplines of astronomy and chemistry.
As " forensic astronomy ", finally, methods from astronomy have been used to solve problems of law and history.
Astronomy is one of the sciences to which amateurs can contribute the most. Collectively, amateur astronomers observe a variety of celestial objects and phenomena sometimes with equipment that they build themselves. Common targets of amateur astronomers include the Sun, the Moon, planets, stars, comets, meteor showers , and a variety of deep-sky objects such as star clusters, galaxies, and nebulae.
Astronomy clubs are located throughout the world and many have programs to help their members set up and complete observational programs including those to observe all the objects in the Messier objects or Herschel catalogues of points of interest in the night sky. One branch of amateur astronomy, amateur astrophotography , involves the taking of photos of the night sky. Many amateurs like to specialize in the observation of particular objects, types of objects, or types of events which interest them. Most amateurs work at visible wavelengths, but a small minority experiment with wavelengths outside the visible spectrum.
This includes the use of infrared filters on conventional telescopes, and also the use of radio telescopes. The pioneer of amateur radio astronomy was Karl Jansky , who started observing the sky at radio wavelengths in the s. A number of amateur astronomers use either homemade telescopes or use radio telescopes which were originally built for astronomy research but which are now available to amateurs e. Amateur astronomers continue to make scientific contributions to the field of astronomy and it is one of the few scientific disciplines where amateurs can still make significant contributions.
Amateurs can make occultation measurements that are used to refine the orbits of minor planets. They can also discover comets, and perform regular observations of variable stars. Improvements in digital technology have allowed amateurs to make impressive advances in the field of astrophotography. Although the scientific discipline of astronomy has made tremendous strides in understanding the nature of the Universe and its contents, there remain some important unanswered questions. Answers to these may require the construction of new ground- and space-based instruments, and possibly new developments in theoretical and experimental physics.
From Wikipedia, the free encyclopedia. Scientific study of celestial objects and phenomena. This article is about the scientific study of celestial objects. For other uses, see Astronomy disambiguation. Not to be confused with astrology , the pseudoscience. Main article: History of astronomy. Further information: Archaeoastronomy and List of astronomers.
Main article: Observational astronomy. Main article: Radio astronomy. Main article: Infrared astronomy. Main article: Optical astronomy. Main article: Ultraviolet astronomy. Main article: X-ray astronomy. Main article: Gamma ray astronomy. Main articles: Astrometry and Celestial mechanics. Main article: Theoretical astronomy.
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Universe events since the Big Bang Nature timeline. This box: view talk edit. Matter-dominated era. Single-celled life. Multicellular life. Dark Ages. Earliest stars. Earliest galaxy. Omega Centauri. Andromeda Galaxy. Milky Way spirals.
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Earliest life. Earliest oxygen. Atmospheric oxygen. Sexual reproduction. Earliest plants. Cambrian explosion. Earliest mammals. Earliest apes. See also: Human timeline , and Life timeline. Main article: Physical cosmology. Main article: Extragalactic astronomy. Main article: Galactic astronomy. Main article: Star. See also: Solar astronomy. Main article: Sun. See also: Solar telescope. Main articles: Planetary science and Planetary geology.
Main article: Amateur astronomy. Main article: List of unsolved problems in astronomy. Main articles: Outline of astronomy and Glossary of astronomy. Classical Astronomy and the Solar System — Introduction. Classical Astronomy and the Solar System. Translated by Brewer, W. Berlin, New York: Springer. Archived from the original on 9 June Retrieved 17 November The Astronomy Cafe. Archived from the original on 8 July Retrieved 20 June Archived from the original on 1 November Results for "astronomy". Archived from the original on 17 June Results for "astrophysics".
The Physical Universe. Chichester, England: Wiley. Philosophical Transactions of the Royal Society. Archived from the original on 30 October Retrieved 28 October In Cancik, Hubert; Schneider, Helmuth eds. Brill's New Pauly. Archive for History of Exact Sciences. Sign in Register. Enter e-mail address Show Enter password Remember me.
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His star charts are handy guides to help you find your way. He even includes a section on astrophotography if you're interested in taking pictures, including options with unspecialized equipment. Since the text of the book is written at a junior high level, your teenage kids likely will enjoy the book as well. Whether you're an amateur astronomer, casual stargazer or anything in between, " Things to See in the Night Sky" is your one-stop shop for information on where, when and how to spot some of the brightest and most easily recognizable sights in the sky. Written by Dean Regas, an astronomer and public outreach educator at the Cincinnati Observatory in Ohio, the book breaks down everything you need to know to stargaze like a pro.
Beginners can use this book as an introduction to stargazing, while more experienced readers will find the book to be a useful field guide that can serve as a reference for locating and identifying stars, constellations, meteor showers, eclipses and even satellites. The book focuses on "naked-eye" objects, so you don't need telescopes, binoculars or any other equipment to utilize this handy skywatching guide.
Read an interview with the author here. In "The Zoomable Universe," astrophysicst Caleb Scharf takes readers from the size of the observable universe step-by-step down to the shortest theoretical measurable length. Along the way, Scharf and the book's illustrator, Ron Miller, explore the formation of the universe, our galaxy and Earth, the makeup of life and quantum physics, and the complexity that develops when you look beyond the surface at any scale.
The large, colorful book has a lot of ground to cover, but it delves into enough detail to spark readers' curiosity, and additional graphics by 5W Infographics pack more information into less space. As it speeds through orders of magnitude, from the largest to the smallest, it stops in lots of fascinating corners of the universe along the way. Fifty years ago, only a handful of scientists were hunting for signals from other civilizations as part of the Search for Extraterrestrial Intelligence SETI. But Tarter continued to fight, helping to found a private agency that would survive government changes, hunting for private donors to look beyond this world and helping move the search for intelligent life from the fringes into mainstream science.
Author Lucas Ellerbroek highlights the passion of exoplanet researchers as they learn about the countless planets circling other stars. Throughout history, solar eclipses have transformed from terrifying omens to the subject of scientific study. In "Sun Moon Earth: The History of Solar Eclipses from Omens of Doom to Einstein and Exoplanets," astronomer-artist Tyler Nordgren traces the natural history of eclipses and how they have inspired eclipse chasers to travel the world and witness the natural phenomenon.
Nordgren's narrative also details how observations of total solar eclipses have contributed to scientific discoveries about the sun, moon and Earth's place in the universe throughout history. Read an interview with the book's author here. The search for planets beyond Earth's solar system has revealed countless surprises, including the existence of strange and unexpected worlds that astronomers would have never imagined existed only a few decades ago. A new book titled "Exoplanets: Diamond Worlds, Super Earths, Pulsar Planets and the New Search for Life Beyond Our Solar System" Smithsonian Books, explores the history of exoplanet research, illustrates the many different types of planets that have been discovered to date and discusses how astronomers plan to further study these newfound alien worlds.
The solar system is a wild place, and even Earth's immediate neighborhood is much more chaotic than maps would suggest — researchers discover more than near-Earth asteroids every month. A new book by Carrie Nugent, an asteroid researcher from Caltech, goes through how we find asteroids and near-Earth objects and what we would do if one was heading toward us. Over the past century, humankind's influence over our environment has increased dramatically.
In "Earth in Human Hands," Grinspoon explores the ways that, for good or bad, humans have seized control of the planet. The choice is whether we do so mindlessly, or whether we act in a responsible, considerate manner. Such a dilemma may be common to all life, and the most successful, long-lasting civilizations in the galaxy may live on planets they have engineered to be stable over extensive periods of time, making them more difficult to identify than rapidly-expanding societies.
You can read an interview with Grinspoon and watch video clips of him discussing the book with Space. It has been the top-selling stargazing guide for over 20 years. Now in its revised fourth edition, the book contains everything you need to know about what's up in the sky through the year The bookre chapter is dedicated to stargazing technology, like binoculars and telescopes.
An entiked with information that even the most experienced stargazers will find comes in handy.