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Index (O)

OA - OC

OD - OF

OG - OJ

OK - ON

OO - OR

OS - OV

OW - OZ

Moment of truth
The Voyager I spacecraft is the most distant man-made object in the universe. It was launched in 1977 and as in 2002, it was more than 8 billions miles from the Earth.


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obtuse angle Math.
An angle greater then 90 and less than 180.

occultation Astron.
An event whereby a celestial body passess in front of another thus block the view of the latter. For instance, occultation of the planet Jupiter can occur as the Moon passes in front and blocking the view of the Jupiter from Earth.

ochre Min.
A yellow or red earth clay containing iron(III) oxide, Fe2O3. The word is derived from Greek ochros, meaning yellow. It has been used as pigments since prehistoric times and has been found in archeological burial sites.

octet rule Chem.
The chemistry rule that governs the tendency of an atom to form the electronic configuration of the nearest inert gas, that is, with 8 (or 2 in the case of helium) electrons at the outer-most electronic shell, during a chemical reaction. This is achieved by either removal or gained of electrons (to form ionic bonds) or share electrons (to form covalent bond). The rule also indicates complete electron shell round the atom makes it chemically inert.

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