The speed at which Earth orbits the Sun can be determined through scientific observations and calculations. The point of reference for measuring Earth's orbital speed is not the Sun's surface, but rather the center of mass of the Sun-Earth system. This is because both the Sun and the Earth orbit around their common center of mass, which is very close to the Sun's center due to the Sun's much larger mass.
Here's a simplified explanation of how scientists determine Earth's orbital speed:
Kepler's Laws: Scientists use Johannes Kepler's laws of planetary motion as a foundation. Kepler's first law states that planets move in elliptical orbits with the Sun at one of the foci of the ellipse.
Astronomical Observations: Astronomers observe the positions of celestial objects, including the Sun and other planets, over time. By tracking the apparent motion of these objects, they can gather data on their positions and calculate their velocities relative to Earth.
Radar and Spacecraft Measurements: Radar measurements and data from space probes can provide more precise information about the distance between Earth and other objects in the solar system. By measuring the time it takes for a radar signal to bounce off a planet and return to Earth, scientists can calculate the object's distance and its change in position over time.
Mathematical Modeling: Using the observed data, scientists apply mathematical models and calculations to determine Earth's orbital speed. These models incorporate Newton's laws of motion, which describe the gravitational interactions between the Sun and Earth, and allow for the estimation of Earth's velocity.
It's important to note that Earth's orbital speed is not constant throughout the year. It varies slightly due to factors such as Earth's elliptical orbit, the gravitational influence of other celestial bodies, and the Sun's gravitational pull. However, the average orbital speed of Earth is approximately 29.78 kilometers per second (about 18.5 miles per second) or about 107,000 kilometers per hour (about 67,000 miles per hour).
By using precise observational techniques and sophisticated mathematical models, scientists can accurately determine Earth's average orbital speed around the Sun, providing a valuable understanding of our planet's motion in the solar system.