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Dictionary of Science - A

Updated: Aug 16


[Optics] - A defect in the image formed by a lens or curved mirror. It consists of 'chromatic aberration' and ' spherical aberration'.

Chromatic aberration is caused by the difference in refraction of various colors by the glass, thus causing color fringes.

Spherical aberration is caused by the curvature of the lens or mirror which makes the rays from the object come to focus in different positions.

[Astronomy] - The apparent displacement in the position of a star as a result of the earth's motion around the sun. Light appears to come from a point that is displaced slightly in the direction of the earth's motion.

image defects, chromatic aberration, spherical aberration, astronomy


The fourth and final chamber of the stomach of ruminants. It empties into the small intestine.

The abomasum is referred to as the ‘true stomach’ as it is in this chamber that protein digestion occurs, in acidic conditions

ABO system

An important human blood group system. The system is based on the presence or absence of antigens A and B on the surface of red blood cells and of antibodies against these in blood serum.

Abscisic acid

A naturally occurring plant growth substance that appears to be involved primarily in seed maturation, stress responses, and regulating closure of leaf pores (stomata). In seeds, it promotes the synthesis of storage protein and prevents premature germination.


The separation of a leaf, fruit, or other part from the body of a plant. This process is suppressed until there is enough amount of plant growth substances transported to the "abscission zone". This zone is formed at the base of the part, within which a layer of cells breaks down.

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