Give two advantages that a telescope lens or mirror of large diameter has over one of small diameter
The light-gathering power of an optical telescope is directly related to the diameter (or aperture) of the objective lens or mirror. Note that the area of a circle is proportional to the square of the radius. A telescope with a lens which has a diameter three times that of another will have nine times the light-gathering power. Larger objectives gather more light, and more sensitive imaging equipment can produce better images from less light.
Source:
http://en.wikipedia.org/wiki/Optical_telescope
what are the similarities and differences among the isotopes of an element?
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