That is one of Kepler's Laws, stated by Johannes Kepler.
Johannes Kepler was the first to state that planets move in elliptical orbits.
No. Earth moves in an ellipse around the Sun; when it is closest to the Sun (at its periapsis, in January), it moves faster, and when it is furthest from the Sun (at its apapsis), it moves slower.
Obviously. Since they move in an ellipse around the Earth (or other central body), they change direction all the time. The only way NOT to change direction would be to move in a straight line; satellites don't do that.
All planets actually follow an elliptical orbit.
To be in a perfect orbit around the Sun, maintaining always the same distance, at a specific distance a planet would need a very specific speed. Since it is unlikely that it just happens to have the correct speed, it will move around the Sun in an ellipse instead.
Kepler
The person who first stated this was Johannes Kepler.
Johannes Kepler was the first to state that planets move in elliptical orbits.
Planetary orbits are usually in the shape of an ellipse.
Johannes Kepler proposed that planets move around the sun in an elliptical orbit through his three laws of planetary motion. This idea was further supported by Isaac Newton's law of universal gravitation, which provided a mathematical explanation for Kepler's laws.
Planets remain almost perfectly spherical as they move around the sun. The paths they follow are ellipses, with the sun at one focus of each ellipse.
Johannes Kepler formulated this idea in his work "Astronomia Nova" in 1609. He described the movement of planets in elliptical orbits with the Sun located at one of the foci.
The same as planets - they move around the Sun in ellipses, the Sun being in one of the focal points of the ellipse. Read about Kepler's Laws for more details.
The same as planets - they move around the Sun in ellipses, the Sun being in one of the focal points of the ellipse. Read about Kepler's Laws for more details.
An ellipse.
No. Earth moves in an ellipse around the Sun; when it is closest to the Sun (at its periapsis, in January), it moves faster, and when it is furthest from the Sun (at its apapsis), it moves slower.
Obviously. Since they move in an ellipse around the Earth (or other central body), they change direction all the time. The only way NOT to change direction would be to move in a straight line; satellites don't do that.