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  2. Henry Draper Catalogue - Wikipedia

    en.wikipedia.org/wiki/Henry_Draper_Catalogue

    The Henry Draper Catalogue (HD) is an astronomical star catalogue published between 1918 and 1924, giving spectroscopic classifications for 225,300 stars; it was later expanded by the Henry Draper Extension (HDE), published between 1925 and 1936, which gave classifications for 46,850 more stars, and by the Henry Draper Extension Charts (HDEC), published from 1937 to 1949 in the form of charts ...

  3. Stellar classification - Wikipedia

    en.wikipedia.org/wiki/Stellar_classification

    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).

  4. Hertzsprung–Russell diagram - Wikipedia

    en.wikipedia.org/wiki/Hertzsprung–Russell_diagram

    The spectral type is not a numerical quantity, but the sequence of spectral types is a monotonic series that reflects the stellar surface temperature. Modern observational versions of the chart replace spectral type by a color index (in diagrams made in the middle of the 20th Century, most often the B-V color) of the stars.

  5. Sextans - Wikipedia

    en.wikipedia.org/wiki/Sextans

    It is an ageing A-type star of spectral class A0 III [7] located 280 ± 20 light-years away [8] from the Solar System. At the age of 385 million years, [9] it is exhausting hydrogen at its core and leaving the main sequence. γ Sextantis is the second brightest star in the constellation with an apparent magnitude of 5.05.

  6. Asteroid spectral types - Wikipedia

    en.wikipedia.org/wiki/Asteroid_spectral_types

    The Ld-type is a new class and has more extreme spectral features than the L-type asteroid. The new class of O-type asteroids has since only been assigned to the asteroid 3628 Božněmcová . A significant number of small asteroids were found to fall in the Q , R , and V types, which were represented by only a single body in the Tholen scheme.

  7. Multispectral pattern recognition - Wikipedia

    en.wikipedia.org/wiki/Multispectral_pattern...

    This process consists in a series of numerical operations to search for the spectral properties of pixels. From this process, a map with m spectral classes is obtained. Using the map, the analyst tries to assign or transform the spectral classes into thematic information of interest (i.e. forest, agriculture, urban).

  8. Spectral sequence - Wikipedia

    en.wikipedia.org/wiki/Spectral_sequence

    In homological algebra and algebraic topology, a spectral sequence is a means of computing homology groups by taking successive approximations. Spectral sequences are a generalization of exact sequences, and since their introduction by Jean Leray (1946a, 1946b), they have become important computational tools, particularly in algebraic topology, algebraic geometry and homological algebra.

  9. Spectrum - Wikipedia

    en.wikipedia.org/wiki/Spectrum

    [2] [3] Soon the term referred to a plot of light intensity or power as a function of frequency or wavelength, also known as a spectral density plot. Later it expanded to apply to other waves, such as sound waves and sea waves that could also be measured as a function of frequency (e.g., noise spectrum, sea wave spectrum).

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