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History[ edit ] Early 20th-century comparison of elemental, solar, and stellar spectra Although astronomy is as ancient as recorded history itself, it was 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.
Consequently, it was held that the celestial region was made of a fundamentally different kind of matter from that found in the terrestrial sphere; either Fire as maintained by Platoor Aether as maintained by Aristotle.
Among those who extended the study of solar and stellar spectra was Norman Lockyerwho in detected bright, as well as dark, lines in solar spectra.
Working with the chemist, Edward Franklandto 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, which was called heliumafter the Greek Heliosthe Sun personified.
Pickering undertook an ambitious program of stellar spectral classification at Harvard College Observatoryin which a team of woman computersnotably Williamina FlemingAntonia Mauryand Annie Jump Cannonclassified the spectra recorded on photographic plates.
Bya catalog of over 10, stars had been prepared that grouped them into thirteen spectral types. Following Pickering's vision, by Cannon expanded the catalog to nine volumes and over a quarter of a million stars, developing the Harvard Classification Scheme which was accepted for worldwide use in Keeleralong with a group of ten associate editors from Europe and the United States,  established The Astrophysical Journal: This was a particularly remarkable development since at that time fusion and thermonuclear energy, and even that stars are largely composed of hydrogen see metallicityhad not yet been discovered.
Despite Eddington's suggestion, this discovery was so unexpected that her dissertation readers convinced her to modify the conclusion before publication. However, later research confirmed her discovery.
Observational astrophysics[ edit ] Supernova remnant LMC N 63A imaged in x-ray blueoptical green and radio red wavelengths. The X-ray glow is from material heated to about ten million degrees Celsius by a shock wave generated by the supernova explosion.
Observational astronomy is a division of the astronomical science that is concerned with recording data, in contrast with theoretical astrophysicswhich is mainly concerned with finding out the measurable implications of physical models.
It is the practice of observing celestial objects by using telescopes and other astronomical apparatus.
The majority of astrophysical observations are made using the electromagnetic spectrum. Radio astronomy studies radiation with a wavelength greater than a few millimeters.
Example areas of study are radio wavesusually emitted by cold objects such as interstellar gas and dust clouds; the cosmic microwave background radiation which is the redshifted light from the Big Bang ; pulsarswhich were first detected at microwave frequencies. The study of these waves requires very large radio telescopes.
Infrared astronomy studies radiation with a wavelength that is too long to be visible to the naked eye but is shorter than radio waves.
Infrared observations are usually made with telescopes similar to the familiar optical telescopes. Objects colder than stars such as planets are normally studied at infrared frequencies. Optical astronomy is the oldest kind of astronomy.
Telescopes paired with a charge-coupled device or spectroscopes are the most common instruments used.
The Earth's atmosphere interferes somewhat with optical observations, so adaptive optics and space telescopes are used to obtain the highest possible image quality.
In this wavelength range, stars are highly visible, and many chemical spectra can be observed to study the chemical composition of stars, galaxies and nebulae. UltravioletX-ray and gamma ray astronomy study very energetic processes such as binary pulsarsblack holesmagnetarsand many others.
These kinds of radiation do not penetrate the Earth's atmosphere well. There are two methods in use to observe this part of the electromagnetic spectrum— space-based telescopes and ground-based imaging air Cherenkov telescopes IACT.
Other than electromagnetic radiation, few things may be observed from the Earth that originate from great distances. A few gravitational wave observatories have been constructed, but gravitational waves are extremely difficult to detect.
Neutrino observatories have also been built, primarily to study our Sun. Cosmic rays consisting of very high energy particles can be observed hitting the Earth's atmosphere. Observations can also vary in their time scale. Most optical observations take minutes to hours, so phenomena that change faster than this cannot readily be observed.
However, historical data on some objects is available, spanning centuries or millennia. On the other hand, radio observations may look at events on a millisecond timescale millisecond pulsars or combine years of data pulsar deceleration studies.
The information obtained from these different timescales is very different. The study of our very own Sun has a special place in observational astrophysics. Due to the tremendous distance of all other stars, the Sun can be observed in a kind of detail unparalleled by any other star.
Our understanding of our own Sun serves as a guide to our understanding of other stars. The topic of how stars change, or stellar evolution, is often modeled by placing the varieties of star types in their respective positions on the Hertzsprung—Russell diagramwhich can be viewed as representing the state of a stellar object, from birth to destruction.Amy K.
Anderson, “Image/Text and Text/Image: Reimagining Multimodal Relationships through Dissociation” Abstract: “W.J.T. Mitchell has famously noted that we are in the midst of a “pictorial turn,” and images are playing an increasingly important role in digital and multimodal communication.
Tips on Writing a Theoretical Rationale Frame your study in the theory: In the front half, let the hypothesis emerge out of your theoretical rationale (theory is predictive).
In the second half, interpret your results in theoretical terms (theory is explanatory).
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