Final answer:
On a given day, the Sun remains in the same zodiac constellation from sunrise to sunset. When the Sun rises in the constellation Gemini, it will also set while still being within the boundaries of Gemini on that same day.
Step-by-step explanation:
When the Sun rises in the constellation Gemini, it means that Gemini is the current zodiac sign where the Sun resides. However, since the Sun and stars move across the sky due to the Earth's rotation, the position of the constellations changes accordingly. So, when the Sun sets later that same day, it will still be in Gemini; the Sun doesn't move quickly enough relative to the stars to pass through an entire constellation in one day. The perception that the Sun has moved across the sky from east to west is due to Earth's rotation. Given the cycle of the rising and setting of stars and the Sun, which the ancients used to define the signs of the zodiac, it's clear the sunsets in the west, but the Sun itself, in terms of zodiac position, remains in the same constellation within a single day.