Columbia Encyclopedia

(Encyclopedia) star cluster, a group of stars near each other in space and resembling each other in certain characteristics that suggest a common origin for the group. Stars in the same cluster move at the same rate...

(Encyclopedia) International Geophysical Year (IGY), 18-month period from July, 1957, through Dec., 1958, during a period of maximum sunspot activity, designated for cooperative study of the solar-terrestrial enviro...

(Encyclopedia) silicate, chemical compound containing silicon, oxygen, and one or more metals, e.g., aluminum, barium, beryllium, calcium, iron, magnesium, manganese, potassium, sodium, or zirconium. Silicates may b...

(Encyclopedia) barium bârˈēəm [key] [Gr.,=heavy], metallic chemical element; symbol Ba; at. no. 56; at. wt. 137.327; m.p. 725℃; b.p. 1,640℃; sp. gr. 3.5 at 20℃; valence +2. Barium is a soft, silver-white, ...

(Encyclopedia) technetium tĕknēˈshēəm [key] [Gr. technetos=artificial], artificially produced radioactive chemical element; symbol Tc; at. no. 43; mass no. of most stable isotope 98; m.p. 2,200℃; b.p. 4,877�...

(Encyclopedia) cobalt, metallic chemical element; symbol Co; at. no. 27; at. wt. 58.9332; m.p. 1,495℃; b.p. about 2,870℃; sp. gr. 8.9 at 20℃; valence +2 or +3. Cobalt is a silver-white, lustrous, hard, brittle...

(Encyclopedia) rainbow, arc showing the colors of the spectrum, violet inside and red outside, which appears when the sun shines through water droplets. It often appears while the sun is shining after a brief thunde...

(Encyclopedia) shark, member of a group of almost exclusively marine and predaceous fishes. There are about 250 species of sharks, ranging from the 2-ft (60-cm) pygmy shark to 50-ft (15-m) giants. They are found in ...

(Encyclopedia) Tehran or Teheran both: tāˌəränˈ, –rănˈ [key], city (1991 pop. 6,475,527), capital of Iran and Tehran prov., N Iran, near Mt. Damavand. It is Iran's largest city and its administrative, comme...

(Encyclopedia) brown dwarf, in astronomy, celestial body that is larger than a planet but does not have sufficient mass to convert hydrogen into helium via nuclear fusion as stars do. Also called “failed stars,”...