Biology Forums - Study Force

In order for a pair of stars to be classified as a visual binary, which one of the following conditions must be true?
A)   The stars must be orbiting around each other, and both stars must be visible through telescopes from the Earth.
B)   The stars must be orbiting around each other, and absorption or emission lines from both stars must be visible in the spectrum.
C)   The stars must be orbiting around each other, and one must periodically cross in front of the other (i.e., it must eclipse the other) as seen from the Earth.
D)   The stars must lie in almost the same direction from the Earth but must not be orbiting around each other.

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