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(or cooler) the object is. This is a consequence of the inverse logarithmic magnitude scale, in which brighter objects have smaller (more negative) magnitudes than dimmer ones. For comparison, the whitish Sun has a B-V index of 0.656 ± 0.005, whereas the bluish Rigel has a B-V of -0.03 (its B magnitude is 0.09 and its V magnitude is 0.12, B-V = -0.03). Traditionally, the color index uses Vega as a zero point.

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