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Chondrules in the chondrite classification Grassland. A millimeter scale is shown. Chondrules in the Carbonaceous Chondrite NWA 13887. A chondrule (from Ancient Greek χόνδρος chondros, grain) is a round grain found in a chondrite. Chondrules form as molten or partially molten droplets in space before being accreted to their parent asteroids.
The RCW Catalogue (from Rodgers, Campbell & Whiteoak) is an astronomical catalogue of Hα-emission regions in the southern Milky Way, described in (Rodgers et al. 1960).It contains 182 objects, including many of the earlier Gum catalogue (84 items) objects.
[1] [2] Moore compiled a list of 109 objects to match the commonly accepted number of Messier objects (he excluded M110 [3]), and the list was published in Sky & Telescope in December 1995. [ 3 ] Moore used his other surname – Caldwell – to name the list, since the initial of "Moore" is already used for the Messier catalogue.
The nebulae listed by Barnard have become known as Barnard objects. [2] A 1919 version of the catalogue listed 182 nebulae; [3] by the time of the posthumously published 1927 version, it listed 369. [4] Barnard's niece and assistant Mary Ross Calvert, also an astronomer and astrographer, took an important part in creating the catalogue. [5]
Dating using 206 Pb/ 204 Pb gives an estimated age of 4,566.6 ± 1.0 Ma, [6] matching ages for other chronometers. Another indication of their age is the fact that the abundance of non- volatile elements in chondrites is similar to that found in the atmosphere of the Sun and other stars in our galaxy .
[1] [2] They yield a weighted mean age of 4567.30 ± 0.16 Myr, which is often interpreted as representing the beginning of the formation of the planetary system (so-called ‘CAI time-zero). It is of note that all four Pb-Pb dated CAIs come from the same group of meteorite ( CV chondrites ).
[3] In 2006 a classification was published that assigned 7 groups to the primitive achondrites, but the classification remains controversial. The authors define primitive achondrites as meteorites "that exceeded their solidus temperature on the parent body" and thus would partially melt. Meteorites that have been fully melted are included if ...
The Catalogue of Nebulae and Clusters of Stars was first published in 1786 by William Herschel in the Philosophical Transactions of the Royal Society of London. [1] In 1789, he added another 1,000 entries, [2] and finally another 500 in 1802, [3] bringing the total to 2,500 entries. This catalogue originated the usage of letters and catalogue ...