Originally posted by James Hutchins
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Originally posted by James Hutchins
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Originally posted by James Hutchins
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Originally posted by James Hutchins
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When you are "measuring", it means that you are using some guidelines.
If you are "guessing" then you better base your guesses on guidelines that make sense.
For example, if you have two stars (a and b) and you know the distance to A, but not to B.
You note that B has the same spectrum as A (same composition) and has the same temperature.
You are then allowed to "suppose" that B should be similar to A in many respects, including the amount of light that it gives off. This is allowed because "in general", stars that have the same mass will work the same, look the same, have the same composition, etc.
If B appears only 1/4 as bright as A (and you know the distance to A) then you are allowed to "guess" that B must be twice as far as A (because light intensity decreases as the square of the distance: twice as far = 1/4 the brightness; three times as far = 1/9 the brightness).
Thus your "guess" is based on rules that have been tested.
However, you are not allowed to simply look at B and say: I'll just claim it is the same distance as A and that, therefore, it must be smaller. THAT would be a guess that is NOT supported by any logic.
There are many rules that are used when measuring the distance to stars. Each one is true "in general" but there can be occasional exceptions.
Originally posted by James Hutchins
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We use CE and BCE (common era / before common era).
The universe is ~13.72 billion years. The Earth is ~4.5 billion years old. The Chinese calendar does not use A.D. and B.C. A little knowledge of History would not go amiss. Christianity was the universal religion of the Roman Empire. They controlled everything in what you would call the Western World, including the calendar. It's also important to note that the earth has existed for thousands of years before the calendar was invented. Modern time measurement needed a species to get advanced enough to figure it out first.




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