For a Pair of Stars to Be Classified as a Visual

question 226

Multiple Choice

For a pair of stars to be classified as a visual binary, which one of these conditions must be true?

• A) The stars must be orbiting around each other, and both stars must be visible through telescopes from 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 Earth.
• D) The stars must lie in almost the same direction from Earth but must not be orbiting around each other.

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