No, the theory that Venus orbits between the Sun and the Earth is not based solely on observing Venus during the day. The understanding of Venus's orbit and its position in relation to the Earth and the Sun is derived from careful observations and scientific measurements made over centuries.
The ancient Greeks were among the first to recognize Venus as a distinct planet and observe its movements in the sky. They realized that Venus, along with other visible planets, including Mercury, Mars, Jupiter, and Saturn, exhibited a different pattern of motion compared to the fixed stars. These observations led to the development of the geocentric model, which suggested that all celestial bodies, including the Sun, revolved around the Earth.
However, through subsequent observations and advancements in astronomy, the heliocentric model was established. This model, proposed by Nicolaus Copernicus in the 16th century, placed the Sun at the center of the solar system, with the planets, including Earth and Venus, orbiting around it.
The understanding that Venus orbits between the Sun and the Earth comes from a combination of observations, such as the varying positions of Venus in the sky throughout the year, its phases, and its angular separation from the Sun as seen from Earth. These observations provide evidence that Venus follows an orbit between the Sun and the Earth.
In summary, the positioning of Venus in its orbit relative to the Sun and the Earth is not solely based on daytime observations but rather on a comprehensive understanding of planetary motions derived from centuries of careful observation, analysis, and scientific modeling.