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Sirius is a visual binary, so we can see both stars and their proper motion. If only the primary star of a binary star can be seen, it will appear to wobble in its proper motion across the celestial sphere because of the gravitational influence of the unseen companion. A binary system inferred from such wobbling motion of the primary is called an astrometric binary; we shall discuss astrometric binaries shortly. In the image shown above the sizes of the stars are exaggerated to make them easy to see. In reality they would be just points on this scale, and Sirius A would be much larger than Sirius B.