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mass extinction

(Encyclopedia)mass extinction, the extinction of a large percentage of the earth's species, opening ecological niches for other species to fill. There have been at least ten such events. The five greatest were thos...

Tsiolkovsky, Konstantin Eduardovich

(Encyclopedia)Tsiolkovsky, Konstantin Eduardovich kənstəntyēnˈ ĕdwärˈdəvĭchˈ tsēōlkŏvˈskē [key], 1857–1935, Russian inventor and rocket expert. He lost his hearing in childhood, and, as he could no...

opposition

(Encyclopedia)opposition, in astronomy, alignment of two celestial bodies on opposite sides of the sky as viewed from earth. Opposition of the moon or planets is often determined in reference to the sun. Only the s...

sod house

(Encyclopedia)sod house, house with walls made of strips of sod laid horizontally in courses like bricks. Sod houses were common in the frontier days on the western plains of the United States, where wood and stone...

pisé de terre

(Encyclopedia)pisé de terre: see rammed earth. ...

Kwanzaa

(Encyclopedia)Kwanzaa or Kwanza both: kwänˈzə [key], secular seven-day festival in celebration of the African heritage of African Americans, beginning on Dec. 26. Developed by Maulana Karenga and first observed ...

Jones, Bill T.

(Encyclopedia)Jones, Bill T. (William Tass Jones), 1952–, American dancer and choreographer, b. Bunnell, Fla. A gay African American who has experienced dual prejudices, he has often brilliantly transformed his a...

altitude

(Encyclopedia)altitude, vertical distance of an object above some datum plane, such as mean sea level or a reference point on the earth's surface. It is usually measured by the reduction in atmospheric pressure wit...

thulium

(Encyclopedia)thulium tho͞oˈlēəm [key] [from Thule, an ancient name for Scandinavia], metallic chemical element; symbol Tm; at. no. 69; at. wt. 168.93421; m.p. about 1,545℃; b.p. 1,947℃; sp. gr. 9.3; valenc...

North Pole

(Encyclopedia)North Pole, northern end of the earth's axis, by convention at lat. 90°N. Because the earth's rotational axis wobbles slightly over time, the location where the northern end of the axis intersects th...