John Henry Reynolds was a British astronomer who served as the president of the Royal Astronomical Society who frequently corresponded with American astronomer Edwin Hubble, developed a formula for measuring the surface brightness of what?
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John Reynolds (astronomer) John Henry Reynolds (1874–1949) was a British astronomer who served as the president of the Royal Astronomical Society between 1935 and 1937 and is known for his work on the classification of stellar bodies. An amateur, he was the son of Alfred John Reynolds, the Lord Mayor of Birmingham, who owned a company which cut nails. In 1899, at age 25, he was elected a Fellow of the Royal Astronomical Society and in 1907, he financed the construction of a 30-inch reflecting telescope in Helwan, Egypt, the first large telescope to study objects in the such southerly skies. He also hand-constructed a 28-inch telescope in Harborne. Images from the Reynolds telescope was later used by Gérard de Vaucouleurs in his system of classifying galaxies; Reynolds also published his own classification for spiral galaxies in 1920. Edwin Hubble frequently corresponded with Reynolds, and some of his findings into the classification of stellar bodies seems at least inspired by his work. The Hubble–Reynolds law, a formula for measuring the surface brightness of elliptical galaxies, is named after them.
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Edwin Hubble Edwin Powell Hubble (November 20, 1889 – September 28, 1953) was an American astronomer. He played a crucial role in establishing the fields of extragalactic astronomy and observational cosmology and is regarded as one of the most important astronomers of all time.
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Meg Urry Claudia Megan "Meg" Urry is an American astrophysicist, who was from 2015–2016 the President of the American Astronomical Society, formerly on the Hubble space telescope faculty and was chair of the Department of Physics at Yale University 2007–2013. She is notable not only for her contributions to astronomy and astrophysics, including work on black holes and multiwavelength surveys, but also for her work addressing sexism and gender equity in astronomy, and science and academia more generally.
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Harvard College Observatory 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, USA, and was founded in 1839. With the Smithsonian Astrophysical Observatory, it forms part of the Harvard–Smithsonian Center for Astrophysics.
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Earthlight (astronomy) Earthlight is the partial illumination of the dark portion of the moon's surface by light reflected from the Earth and from the Earth's airglow. It is also known as Earthshine (see also Planetshine), the Moon's ashen glow, or "the old Moon in the new Moon's arms".
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Solar constant The solar constant, a measure of flux density, is the mean solar electromagnetic radiation (the solar irradiance) per unit area that would be incident on a plane perpendicular to the rays, at a distance of one astronomical unit (AU) from the Sun (roughly the mean distance from the Sun to the Earth). The solar constant includes all types of solar radiation, not just the visible light. It is measured by satellite as being 1.361 kilowatts per square meter (kW/m²) at solar minimum and approximately 0.1% greater (roughly 1.362 kW/m²) at solar maximum. The solar "constant" is not a physical constant in the modern CODATA scientific sense; that is, it is not like the Planck constant or the speed of light, which are absolutely constant in physics. The solar constant is merely an average of the actually varying value. It has been shown to vary in the past 400 years over a range of less than 0.2 percent.
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Strömgren photometric system Strömgren photometric system (uvby) (sometimes also referred as Strömgren - Crawford photometric system) is four-colour medium-band photometric system (plus H-beta filters) for stellar classification. It was pioneered by the Danish astronomer Bengt Strömgren in 1956 and extended by his colleague the American astronomer David L. Crawford in 1958.
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Surface brightness fluctuation Surface brightness fluctuation (SBF) is a secondary distance indicator used to estimate distances to galaxies. It is useful to 100 Mpc (parsec). The method measures the variance in a galaxy's light distribution arising from fluctuations in the numbers of and luminosities of individual stars per resolution element. The technique uses the fact that galaxies are made up of a finite number of stars. The number of stars in any small patch of a galaxy will vary from point to point, creating a noise-like fluctuation in its surface brightness. While the various stars present in a galaxy will cover an enormous range of luminosity, the SBF can be characterized as having an average brightness. A galaxy twice as far away appears twice as smooth as a result of the averaging. Older elliptical galaxies have fairly consistent stellar populations, thus it closely approximates a standard candle. In practice, corrections are required to account for variations in age or metallicity from galaxy to galaxy. Calibration of the method is made empirically from Cepheids or theoretically from stellar population models.
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Brightness Brightness is an attribute of visual perception in which a source appears to be radiating or reflecting light. In other words, brightness is the perception elicited by the luminance of a visual target. It is not necessarily proportional to luminance. This is a subjective attribute/property of an object being observed and one of the color appearance parameters of color appearance models. Brightness refers to an absolute term and should not be confused with Lightness.
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Peak of eternal light A peak of eternal light (PEL) is a point on an astronomical body within the Solar System that is always in sunlight. Such a peak must have high altitude and be on a body with very small axial tilt. The existence of such peaks was first postulated by Beer and Mädler in 1837. The pair said of the lunar polar mountains, "...many of these peaks have (with the exception of eclipses caused by the Earth) eternal sunshine." These polar peaks were later mentioned by Camille Flammarion in 1879, who speculated that there may exist "pics de lumière éternelle" at the poles of the Moon. PELs would be advantageous for space exploration and colonization due to the ability of an electrical device located there to receive solar power regardless of the time of day or day of the year, and the relatively stable temperature range.
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Radiant exposure In radiometry, radiant exposure is the radiant energy "received" by a "surface" per unit area, or equivalently the irradiance of a "surface" integrated over time of irradiation, and spectral exposure or is the radiant exposure per unit frequency or wavelength, depending on whether the spectrum is taken as a function of frequency or of wavelength. The SI unit of radiant exposure is the joule per square metre (), while that of spectral exposure in frequency is the joule per square metre per hertz () and that of spectral exposure in wavelength is the joule per square metre per metre ()—commonly the joule per square metre per nanometre ().
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Harry Hemley Plaskett Harry Hemley Plaskett FRS (July 5, 1893 – January 26, 1980) was a Canadian astronomer who made significant contributions to the fields of solar physics, astronomical spectroscopy and spectrophotometry. From 1932 to 1960, he served as the Savilian Professor of Astronomy at the University of Oxford, and in 1963 was awarded the Gold Medal of the Royal Astronomical Society.
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Milky Way The Milky Way is the galaxy that contains our Solar System. The descriptive "milky" is derived from the appearance from Earth of the galaxy – a band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye. The term "Milky Way" is a translation of the Latin "via lactea ", from the Greek γαλαξίας κύκλος ("galaxías kýklos ", "milky circle"). From Earth, the Milky Way appears as a band because its disk-shaped structure is viewed from within. Galileo Galilei first resolved the band of light into individual stars with his telescope in 1610. Until the early 1920s, most astronomers thought that the Milky Way contained all the stars in the Universe. Following the 1920 Great Debate between the astronomers Harlow Shapley and Heber Curtis, observations by Edwin Hubble showed that the Milky Way is just one of many galaxies.
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Super black Super black is a surface treatment developed at the National Physical Laboratory in the United Kingdom. It absorbs approximately 99.6% of visible light at normal incidence, while conventional black paint absorbs about 97.5%. At other angles of incidence, super black is even more effective: at an angle of 45°, it absorbs 99.9% of light.
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Magnitude (astronomy) In astronomy, magnitude is a logarithmic measure of the brightness of an object, measured in a specific wavelength or passband, usually in the visible or near-infrared spectrum. An imprecise but systematic determination of the magnitude of objects was introduced in ancient times by Hipparchus.
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Hydrosphere The hydrosphere (from Greek ὕδωρ "hydōr", "water" and σφαῖρα "sphaira", "sphere") is the combined mass of water found on, under, and above the surface of a planet, minor planet or natural satellite.
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Supergranulation Supergranulation is a particular pattern of convection cells on the Sun's surface called supergranules. It was discovered in the 1950s by A.B.Hart using Doppler velocity measurements showing horizontal flows on the photosphere (flow speed about 300 to 500 m/s, a tenth of that in the smaller granules). Later work (1960s) by Leighton, Noyes and Simon established a typical size of about 30000 km for supergranules with a lifetime of about 24 hours.
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Visible-light astronomy Visible-light astronomy encompasses a wide variety of observations via telescopes that are sensitive in the range of visible light (optical telescopes). It includes "imaging", where a picture of some sort is made of the object; "photometry", where the amount of light coming from an object is measured, "spectroscopy", where the distribution of that light with respect to its wavelength is measured, and "polarimetry" where the polarisation state of that light is measured. An example of spectroscopy is the study of spectral lines to understand of what kind of matter light is going through. Visible astronomy also includes looking up at night (). Visible-light astronomy is part of optical astronomy, and differs from astronomies based on invisible types of light in the electromagnetic radiation spectrum, such as radio waves, infrared waves, ultraviolet waves, X-ray waves and gamma-ray waves.
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W. Albert Hiltner William Albert Hiltner (1914–1991) was an American astronomer, noted for his work leading up to the discovery of interstellar polarization. He was an early practitioner of precision stellar photometry, and a pioneering observer of the optical counterparts of celestial x-ray sources. Director of the Yerkes Observatory for many years, while there he designed and built a rotatable telescope for polarization studies and developed photometric instrumentation. He was the acting director of the Cerro Tololo Interamerican Observatory, then president of the Associated Universities for Research in Astronomy from 1968 until 1971, and was appointed Director of the University of Michigan Detroit Observatory in 1970,a post he held until 1982. He established MDM Observatory and led the construction of the Hiltner Telescope which is named for him.
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Interferometric visibility The interferometric visibility (also known as interference visibility and fringe visibility, or just visibility when in context) quantifies the contrast of interference in any system which has wave-like properties, such as optics, quantum mechanics, water waves, or electrical signals. Generally, two or more waves are combined and as the phase difference between them varies, the power or intensity (probability or population in quantum mechanics) of the resulting wave oscillates, forming an interference pattern. The pattern may be visible all at once because the phase difference varies as a function of space, as in a 2-slit experiment. Alternately, the phase difference may be manually controlled by the operator, for example by adjusting a vernier knob in an interferometer. The ratio of the size or amplitude of these oscillations to the sum of the powers of the individual waves is defined as the visibility.
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A. Grace Cook Alice Grace Cook (1877 - 27 May 1958), known as Grace Cook or A. Grace Cook was a British astronomer. She joined the British Astronomical Association in 1911, and was elected a Fellow of the Royal Astronomical Society in 1916, part of the first group of women elected as fellows. She was renowned for her work observing meteors, and also observed naked-eye phenomena including the zodiacal light and aurorae. During World War One Cook, with Fiammetta Wilson, headed the British Astronomical Association's Meteor Section. Cook observed comets and Milky Way novae and was among the discoverers of V603 Aquilae, a nova that occurred in 1918. This work earned her the Edward C. Pickering Fellowship from the Maria Mitchell Association in 1920–1921. From 1921 to 1923 Cook was sole director of the British Astronomical Association's Meteor Section. With Joseph Alfred Hardcastle, Cook worked to identify and describe 785 New General Catalogue objects on a series of photographic plates taken by John Franklin-Adams.
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John Machin John Machin (bapt. c. 1686 – June 9, 1751), a professor of astronomy at Gresham College, London, is best known for developing a quickly converging series for Pi in 1706 and using it to compute Pi to 100 decimal places.