Explanation

Mars, as it moves through the sky, occasionally passes close to bright stars in constellations. In this case: Pollux is one of the two bright stars in the constellation Gemini, the other being Castor. Mars will be seen skimming south of Pollux, not Castor. Sirius and Betelgeuse belong to other constellations — Canis Major and Orion, respectively — and are not in Gemini. So, Mars will be visible skimming south of Pollux in Gemini.