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With the period-luminosity relation providing a way to accurately measure distances on an inter-galactic scale, a new era in modern astronomy unfolded with an understanding of the structure and scale of the universe. [27] The discovery of the expanding universe by Georges Lemaitre and Hubble were made possible by Leavitt's groundbreaking research.
From this measurement and the apparent magnitudes of both stars, the luminosities can be found, and by using the mass–luminosity relationship, the masses of each star. These masses are used to re-calculate the separation distance, and the process is repeated a number of times, with accuracies as high as 5% being achieved.
Classical Cepheid variables are 4–20 times more massive than the Sun, [11] and around 1,000 to 50,000 (over 200,000 for the unusual V810 Centauri) times more luminous. [12] Spectroscopically they are bright giants or low luminosity supergiants of spectral class F6 – K2. The temperature and spectral type vary as they pulsate.
Henrietta Swan Leavitt (/ ˈ l ɛ v ɪ t /; July 4, 1868 – December 12, 1921 [2]) was an American astronomer. [1] Her discovery of how to effectively measure vast distances to remote galaxies led to a shift in the scale and understanding of the scale and the nature of the universe. [3]
The New York Times Book Review (NYTBR) is a weekly paper-magazine supplement to the Sunday edition of The New York Times in which current non-fiction and fiction books are reviewed. It is one of the most influential and widely read book review publications in the industry. [ 2 ]
In astronomy, a phase curve describes the brightness of a reflecting body as a function of its phase angle (the arc subtended by the observer and the Sun as measured at the body). The brightness usually refers the object's absolute magnitude, which, in turn, is its apparent magnitude at a distance of one astronomical unit from the Earth and Sun.
By comparing this known luminosity to an object's observed brightness, the distance to the object can be computed using the inverse-square law. These objects of known brightness are termed standard candles, coined by Henrietta Swan Leavitt. [13] The brightness of an object can be expressed in terms of its absolute magnitude. This quantity is ...
In contrast, the term brightness in astronomy is generally used to refer to an object's apparent brightness: that is, how bright an object appears to an observer. Apparent brightness depends on both the luminosity of the object and the distance between the object and observer, and also on any absorption of light along the path from object to ...