Astronauts can determine that they are orbiting around a spherical planet through various observations and measurements. Here are some ways they can establish this:
Earth's Curvature: As astronauts orbit higher above the Earth's surface, they can observe the curvature of the planet. The horizon appears curved, and they can see the distinct shape of a round Earth. This visual evidence is a strong indication that they are orbiting a spherical body.
Global Coverage: During their orbit, astronauts can communicate with ground-based stations around the world. The ability to establish real-time communication with stations located on different continents further supports the understanding that Earth is a spherical planet.
Orbital Trajectory: The trajectory an astronaut follows while in orbit is determined by the planet's gravitational pull and the spacecraft's velocity. These trajectories are carefully calculated to achieve stable orbits around a spherical Earth. The mathematics and physics involved in orbital mechanics rely on the assumption of a spherical planet.
Images from Space: Astronauts often capture photographs and videos from space that clearly show the spherical shape of the Earth. These images are widely shared with the public and serve as visual evidence of Earth's curvature.
Spacecraft Navigation: The spacecraft used by astronauts have sophisticated navigational systems that take into account the spherical shape of Earth. These systems utilize algorithms and equations based on a spherical Earth model to accurately determine their position, velocity, and trajectory during orbital missions.
It's important to note that the knowledge of Earth's spherical shape is not exclusive to astronauts. Scientists have been studying the shape of our planet for centuries using various methods, including satellite observations, geodesy, and measurements from different locations on Earth's surface. The consensus among scientists, supported by extensive evidence, is that Earth is indeed a roughly spherical body.