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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 ...
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).
An illustration of the constellation Perseus (after Perseus from Greek mythology) from the star atlas published by the Polish astronomer Johannes Hevelius in 1690. A star catalogue is an astronomical catalogue that lists stars.
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.
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.
An O-type main-sequence star (O V) is a main-sequence (core hydrogen-burning) star of spectral type O and luminosity class V. These stars have between 15 and 90 times the mass of the Sun and surface temperatures between 30,000 and 50,000 K.
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.
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.