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10 December, 05:02

What was the physical principle used by edwin hubble to demonstrate that the "spiral nebulae" are very distant and large?

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  1. 10 December, 05:56
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    The physical principle used by Edwin Hubble to demonstrate that the "spiral nebulae" are very distant and large was the inverse-square law of light. The Cepheid variable stars in the spiral nebulae obey a period-luminosity relation; by measuring the period of a Cepheid star, its average luminosity can be determined, and then, by comparing this with its average apparent brightness, its distance can be calculated.
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