How many constellations recognized by the IAU intersect the ecliptic, contrasting the traditional 12 signs?
Answer
13 constellations
While the ancient, traditional astrological framework utilized 12 signs based on dividing the $360^ ext{circ}$ ecliptic into 12 equal $30^ ext{circ}$ segments, modern astronomy recognizes that the actual boundaries of constellations, as defined by the International Astronomical Union (IAU), cause the Sun to pass through 13 distinct constellations that intersect the ecliptic plane. This difference arises because the actual physical boundaries of these stellar groupings are irregular and do not conform neatly to the ancient, equal angular divisions.
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