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| Description: (a) A planet and its star both orbit around their common center of mass, always staying on opposite sides of that point. The planet’s motion around the center of mass often provides astronomers with the information that a planet is present. (b) As a planet moves toward or away from us, its star moves in the opposite direction. Using spectroscopy, we can measure the Doppler shift of the star’s spectrum, which reveals the effects of the unseen planet or planets. (c) If a star and its planet are moving across the sky, the motion of the planet causes the star to orbit its center of mass. This motion appears as a wobbling of the star across the celestial sphere. (d) If a planet happens to move in a plane that takes it across its star (that is, the planet transits the star), as seen from Earth, then the planet will hide some of the starlight, causing the star to dim. This change in brightness will occur periodically and can reveal the presence of a planet. Picture Stats: Views: 872 Filesize: 135.15kB Height: 416 Width: 1350 Source: https://biology-forums.com/index.php?action=gallery;sa=view;id=15953 |