Question

1. how can the spectra of a star help a scientist determine whether a star is moving toward or away from earth? if the dark lines increase in number within the emissions spectra, the star is moving away from earth. and if the dark lines in the emissions spectra decrease in number, the star is moving toward earth. if the dark lines in the emissions spectra are shifting toward the blue end, the star is approaching earth. in contrast, if the dark lines are shifting toward the red - end, the star is moving away from earth. if the dark lines in the emissions spectra are not visible, the star is moving away from earth. if the dark lines in the emissions spectra are visible, the star is moving toward earth. if the dark lines in the emissions spectra are shifting toward the blue end, the star is moving away from earth. in contrast, if the dark lines are shifting toward the red - end, the star is moving toward earth.

Explanation:

The Doppler - effect in astronomy is used. When a star moves towards Earth, the dark lines in its emission spectra shift towards the blue end (blue - shift). When it moves away, they shift towards the red end (red - shift). The presence or absence of visible dark lines doesn't indicate motion direction; it's the shift that matters.

Answer:

If the dark lines in the emissions spectra are shifting toward the blue end, the star is approaching Earth. If the dark lines are shifting toward the red end, the star is moving away from Earth.