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Cepheid Variables,
A Cepheid variable () is a type of variable star that pulsates radially, varying in both diameter and temperature. It changes in brightness, with a well-defined stable period (typically 1–100 days) and amplitude. Cepheids are important cosmic benchmarks for scaling galactic and extragalactic distances; a strong direct relationship exists between a Cepheid variable's luminosity and its pulsation period. This characteristic of classical Cepheids was discovered in 1908 by Henrietta Swan Leavitt after studying thousands of variable stars in the Magellanic Clouds. The discovery establishes the ''true luminosity'' of a Cepheid by observing its pulsation period. This in turn gives the distance to the star by comparing its known luminosity to its observed brightness, calibrated by directly observing the parallax distance to the closest Cepheids such as RS Puppis and Polaris. Cepheids change brightness due to the κ–mechanism, which occurs when opacity in a star increases with t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spectral Type
In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the rainbow of colors interspersed with spectral lines. Each line indicates a particular chemical element or molecule, with the line strength indicating the abundance of that element. The strengths of the different spectral lines vary mainly due to the temperature of the photosphere, although in some cases there are true abundance differences. The ''spectral class'' of a star is a short code primarily summarizing the ionization state, giving an objective measure of the photosphere's temperature. Most stars are currently classified under the Morgan–Keenan (MK) system using the letters ''O'', ''B'', ''A'', ''F'', ''G'', ''K'', and ''M'', a sequence from the hottest (''O'' type) to the coolest (''M'' type). Each letter class is then subdivided ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Harlow Shapley
Harlow Shapley (November 2, 1885 – October 20, 1972) was an American astronomer, who served as head of the Harvard College Observatory from 1921–1952, and political activist during the latter New Deal and Fair Deal. Shapley used Cepheid variable stars to estimate the size of the Milky Way Galaxy and the Sun's position within it.Bart J. Bok. ''Harlow Shapely 1885–1972 A Biographical Memoir''. National Academy of Sciences In 1953 he proposed his "liquid water belt" theory, a concept now known as a habitable zone.Richard J. Hugget, ''Geoecology: An Evolutionary Approach''. p. 10 Background Shapley was born on a farm five miles outside Nashville, Missouri, to Willis and Sarah (née Stowell) Shapley. He went to school in Jasper, Missouri, but not beyond elementary school. He worked as a journalist after studying at home and covering crime stories as a newspaper reporter for the ''Daily Sun'' in Chanute, Kansas, and intermittently for the ''Times'' of Joplin, Missouri. In Chanu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Binary System
A binary system is a system of two astronomical bodies of the same kind that are comparable in size. Definitions vary, but typically require the center of mass to be located outside of either object. (See animated examples.) The most common kinds of binary system are binary stars and binary asteroids, but brown dwarfs, planets, neutron stars, black holes and galaxies can also form binaries. A ''multiple system'' is similar but consists of three or more objects, for example triple stars and triple asteroids (a more common term than 'trinary'). Classification In a binary system, the brighter or more massive object is referred to as primary, and the other the secondary. Binary stars are also classified based on orbit. Wide binaries are objects with orbits that keep them apart from one another. They evolve separately and have very little effect on each other. Close binaries are close to each other and are able to transfer mass from one another. They can also be classified ba ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Radial Velocity
The radial velocity or line-of-sight velocity of a target with respect to an observer is the rate of change of the vector displacement between the two points. It is formulated as the vector projection of the target-observer relative velocity onto the relative direction or line-of-sight (LOS) connecting the two points. The radial speed or range rate is the temporal rate of the distance or range between the two points. It is a signed scalar quantity, formulated as the scalar projection of the relative velocity vector onto the LOS direction. Equivalently, radial speed equals the norm of the radial velocity, modulo the sign. In astronomy, the point is usually taken to be the observer on Earth, so the radial velocity then denotes the speed with which the object moves away from the Earth (or approaches it, for a negative radial velocity). Formulation Given a differentiable vector \mathbf r \in \mathbb^3 defining the instantaneous relative position of a target with respe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Harvard College Observatory Circular
The Harvard College Observatory (HCO) is an institution managing a complex of buildings and multiple instruments used for astronomical research by the Harvard University Department of Astronomy. It is located in Cambridge, Massachusetts, United States, and was founded in 1839. With the Smithsonian Astrophysical Observatory, it forms part of the Center for Astrophysics Harvard & Smithsonian. HCO houses the Harvard Plate Stacks, a collection of approximately 600,000 astronomical plates taken between the mid-1880s and 1989 (with a gap from 1953–1968). This 100-year coverage is a unique resource for studying temporal variations in the universe. The Digital Access to a Sky Century @ Harvard project scanned and 429,274 direct image plates, leaving nearly 200,000 spectra and other photographic plates yet to be digitized. In 2024, a new database, StarGlass, was created to combine the scientific data from the plates with the Plate Stack's archival holdings. History In 1839, the Har ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Annals Of The Astronomical Observatory Of Harvard College
The Harvard College Observatory (HCO) is an institution managing a complex of buildings and multiple instruments used for astronomy, astronomical research by the Harvard University Department of Astronomy. It is located in Cambridge, Massachusetts, United States, and was founded in 1839. With the Smithsonian Astrophysical Observatory, it forms part of the Harvard–Smithsonian Center for Astrophysics, Center for Astrophysics Harvard & Smithsonian. HCO houses the Harvard Plate Stacks, a collection of approximately 600,000 Photographic plate#Astronomy, astronomical plates taken between the mid-1880s and 1989 (with a gap from 1953–1968). This 100-year coverage is a unique resource for studying temporal variations in the universe. The Digital Access to a Sky Century @ Harvard project scanned and 429,274 direct image plates, leaving nearly 200,000 spectra and other photographic plates yet to be digitized. In 2024, a new database, StarGlass, was created to combine the scientific data ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
ζ Geminorum
Zeta Geminorum (ζ Geminorum, abbreviated Zeta Gem, ζ Gem) is a bright star with cluster components, distant optical components and a likely spectroscopic partner in the zodiac constellation of Gemini — in its south, on the left 'leg' of the twin Pollux. It is a classical Cepheid variable star, of which over 800 have been found in our galaxy. As such its regular pulsation and luminosity (proven in its class to correspond) and its relative proximity means the star is a useful calibrator in computing the cosmic distance ladder. Based on parallax measurements, it is approximately 1,200 light-years from the Sun. Zeta Geminorum is the primary or 'A' component of a multiple star system designated WDS J07041+2034. It bears traditional name Mekbuda, usually anglicised to . Nomenclature ''ζ Geminorum'' ( Latinised to ''Zeta Geminorum'') is the star's Bayer designation. WDS J07041+2034 A is its designation in the Washington Double Star Catalog. The designations of the two ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Adam & Charles Black
A & C Black is a British book publishing company, owned since 2002 by Bloomsbury Publishing. The company is noted for publishing ''Who's Who'' since 1849 and the ''Encyclopædia Britannica'' between 1827 and 1903. It offers a wide variety of books in fiction and nonfiction, and has published popular travel guides, novels, and science books. History The firm was founded in 1807 by Charles and Adam Black in Edinburgh. In 1851, the company purchased the copyrights to Sir Walter Scott's ''Waverly'' novels for £27,000. The company moved to the Soho district of London in 1889. During the years 1827–1903 the firm published the seventh, eighth and ninth editions of the ''Encyclopædia Britannica''. This was purchased from Archibald Constable after his company's failure to publish the seventh edition of the encyclopedia. Adam Black retired in 1870 due to his disapproval of his sons' extravagant plans for its ninth edition. This edition, however, would sell half a million sets and wa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Philosophical Transactions Of The Royal Society Of London
''Philosophical Transactions of the Royal Society'' is a scientific journal published by the Royal Society. In its earliest days, it was a private venture of the Royal Society's secretary. It was established in 1665, making it the second journal in the world exclusively devoted to science, after the ''Journal des sçavans'', and therefore also the world's longest-running scientific journal. It became an official society publication in 1752. The use of the word ''philosophical'' in the title refers to natural philosophy, which was the equivalent of what would now be generally called ''science''. Current publication In 1887 the journal expanded and divided into two separate publications, one serving the physical sciences (''Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences'') and the other focusing on the life sciences (''Philosophical Transactions of the Royal Society B: Biological Sciences''). Both journals now publish themed i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
John Goodricke
John Goodricke FRS (17 September 1764 – 20 April 1786) was an English amateur astronomer. He is best known for his observations of the variable star Algol (Beta Persei) in 1782. Life and work John Goodricke, named after his great-grandfather Sir John Goodricke 1617–1670 (see Goodricke baronets of Ribston Hall), was born in Groningen in the Netherlands, but lived most of his life in England. He became deaf in early childhood due to a severe illness. His parents sent him to Thomas Braidwood's Academy, a school for deaf pupils in Edinburgh, and in 1778 to the Warrington Academy. After leaving Warrington, Goodricke returned to live with his parents in York. There, he became friends with his neighbour Edward Pigott, whose father Nathaniel Pigott had built a sophisticated private observatory. Edward was already interested in variable stars, and he gave Goodricke a list of those that he thought were worthy of observation. Goodricke is credited with discovering the peri ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
