With this method, you don't need predetermined magnitudes for the comparison stars, initially. You simply choose two stars, with "A" being brighter than "B", ensuring that the variable star's brightness is somewhere between these two comparison stars. Let's say that the variable is three-quarters of the way between the brightness of A and B. In other words, the variable is closer to the fainter star than the brighter star. You would record your estimate as "A(3)V(1)B."
Now let us reduce these estimates. We'll say that the A star is 9™80 and that the B star is 10™ 30 in this case. The difference between these two comparison stars is 0m5. Now we divide 0.5 by the sum of 3 and 1 and the result is Ol'nS. From the brighter star, we calculate:
Or, using the fainter star, we calculate:
Of course, we would round to 10™ 2 since the accuracy of our comparison stars will limit the accuracy of our estimate.
These three methods will allow you to experiment with making variable-star estimates. Perhaps you may wish to use each method on the same variable-star observation, to see how they compare. Then, you may want to compare your estimates with other variable-star observers using VSNET, AAVSO or BAA VSS. In a short time, you'll become confident with one method and that will be the one that you use.
Let us now take a look at how estimating brightness is done when using instruments.
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