Ideally, you should have one for each exposure duration, but using a long one and varying the amount of substraction should also work.
2.
Then R is a " homomorphic " relation from addition to substraction, but not from addition to multiplication . talk ) 10 : 02, 9 June 2010 ( UTC)
3.
:: : My mistake, the escape velocity at the position of Voyager 1 is 4 km / s but the substraction must be done with orbital energy not speed .-- talk ) 07 : 54, 4 August 2010 ( UTC)
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