Astrobiology Glossary

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Term Definition
Observable Universe The portion of the entire universe that can be seen from Earth.
Oort Cloud A vast spherical region in the outer reaches of our solar system where a trillion long-period comets (those with orbital periods greater than 200 years) reside. Comets from the Oort Cloud come from all directions, often from as far away as 50,000 astronomical units.
Opacity The degree to which light is prevented from passing through an object or a substance. Opacity is the opposite of transparency. As an object's opacity increases, the amount of light passing through it decreases. Glass, for example, is transparent and most clouds are opaque.
Open Cluster Also known as a galactic cluster, an open cluster consists of numerous young stars that formed at the same time within a large cloud of interstellar dust and gas. Open clusters are located in the spiral arms or the disks of galaxies. The Pleiades is an example of an open cluster.
Open Universe A geometrical model of the universe in which the overall structure of the universe extends infinitely in all directions. The rules of geometry in an open universe are like those that would apply on a saddle-shaped surface.
Optical Telescope A telescope that gathers and magnifies visible light. The two basic types of optical telescopes are refracting (using lenses) and reflecting (using mirrors). The Hubble Space Telescope is an example of a reflecting telescope.
Organelle Membrane enclosed structures in eukaryotic cells such as the mitochondria and chloroplasts.
Ozone Layer A region in the upper atmosphere that has high concentrations of ozone (triatomic oxygen, 03). The ozone layer protects the Earth by absorbing the Sun's high-energy ultraviolet radiation.

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Quote of the Day

When we say 'science' we can either mean any manipulation of the inventive and organizing power of the human intellect: or we can mean such an extremely different thing as the religion of science, the vulgarized derivative from this pure activity manipulated by a sort of priestcraft into a great religious and political weapon.
- Wyndham Lewis (1882 - 1957)

Quiz Me

What was the first nearly complete dinosaur discovered in America?
A.Tyrannosaurus
B.Apatosaurus
C.Triceratops
D.Hadrosaurus
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Fact of the Day

One way birds learn is by trial and error. Scientists have discovered that many of their learned motor patterns are linked to appetite. For instance, young doves must learn to drink water. The pecking of domestic chicks improves about 30 hours after hatching. They snatch up a grain with increased efficiency. Simple trial-and-error learning is also believed to be very important in birds' nest-building.

Word of the Day

picaresque
Pronunciation: /pik-uh-RESK/
adj : of or relating to roguish heroes and their adventures
"The party was filled with beatniks, hippies, and sundry picaresque characters."