Question: What year was the phenomenon used to explain the color of binary stars described?
Context: Mercedes Tharam Richards (Kingston, 14 May 1955 – Hershey, 3 February 2016), née Davis, was a Jamaican astronomy and astrophysics professor.  Her investigation focused on computational astrophysics, stellar astrophysics and exoplanets and brown dwarfs, and the physical dynamics of interacting binary stars systems.  However, her pioneering research in the tomography of interacting binary star systems and cataclysmic variable stars to predict magnetic activity and simulate gas flow is her most known work. RS Canum Venaticorum variables are a type of variable star.  They are close binary stars having active chromospheres which can cause large stellar spots.  These spots are believed to cause variations in their observed luminosity.  Systems can exhibit variations on timescales of years due to variation in the spot surface coverage fraction, as well as periodic variations which are, in general, close to the orbital period of the binary system.  Some systems exhibit variations in luminosity due to their being eclipsing binaries.  Typical brightness fluctuation is around 0.2 magnitudes.  They take their name from the star RS Canum Venaticorum (abbreviated RS CVn). The O'Connell effect is an asymmetry in the photometric light curve of certain close eclipsing binary stars.  It was named after the astronomer D. J. K. O'Connell, SJ of Riverview College in New South Wales who in 1951 studied this phenomenon and distinguished it from the so-called periastron effect described by earlier authors, as it does not necessarily appear near the periastron, when tidal effects and an increase in mutual radiation may cause an increase in luminosity. Plaskett's Star, also known as HR 2422 and V640 Monocerotis, is a spectroscopic binary at a distance of around 6600 light-years.  It is one of the most massive binary stars known, with a total mass of around one hundred times that of the Sun.  Indeed, it was long thought to be the most massive known binary system, but evidence collected between 1996–2005 demonstrated that Eta Carinae, which was previously thought to be a massive individual star, is a binary system. Cloud computing has become a social phenomenon used by most people every day.  As with every important social phenomenon there are issues that limit its widespread adoption. The catalogue of spectroscopic binary orbits (SB) is a compilation of orbital data for spectroscopic binary stars which have been produced since 1969 by Alan Henry Batten of the Dominion Astrophysics Observatory and various collaborators. X-ray bursters are one class of X-ray binary stars exhibiting periodic and rapid increases in luminosity (typically a factor of 10 or greater) that peak in the X-ray regime of the electromagnetic spectrum.  These astrophysical systems are composed of an accreting compact object, and a main sequence companion 'donor' star.  A compact object in an X-ray binary system consists of either a neutron star or a black hole; however, with the emission of an X-ray burst, the companion star can immediately be classified as a neutron star, since black holes do not have a surface and all of the accreting material disappears past the event horizon.  The star's mass is drawn on to the surface of the neutron star where the hydrogen fuses to helium which accumulates until it fuses in a burst, producing X-rays. Christian Andreas Doppler ( ; ] ; 29 November 1803 – 17 March 1853) was an Austrian mathematician and physicist.  He is celebrated for his principle — known as the Doppler effect — that the observed frequency of a wave depends on the relative speed of the source and the observer.  He used this concept to explain the color of binary stars. The Doppler effect (or the Doppler shift) is the change in frequency or wavelength of a wave for an observer who is moving relative to the wave source.  It is named after the Austrian physicist Christian Doppler, who described the phenomenon in 1842. Algol variables or Algol-type binaries are a class of eclipsing binary stars that are related to the prototype member of this class, β Persei (Beta Persei, Algol) from an evolutionary point of view.  An Algol binary is a semidetached binary system where the primary component is an early type, main sequence star that does not fill its Roche lobe, while the cooler, fainter, larger, less massive secondary component lies above the main sequence in a Hertzsprung–Russell diagram and fills the Roche lobe.  Early in its history, the secondary star would have been more massive, evolving first to overfill its Roche lobe.  After rapid mass exchange, the lobe-filling star became less massive than its companion.
Answer: 1842