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Why don't circular orbits have perihelion or aphelion? What's the reason behind this?
In astrophysics, the shape of an orbit is crucial in interpreting the motion of a celestial body. A circular orbit is one in which a celestial body moves around its center of mass at a fixed distance. The characteristic of a circular orbit is that the speed, angular velocity, potential energy and kinetic energy remain unchanged, and there is no perihelion or aphelion. So, what is the reason behind this?
A circular orbit is just what the name suggests, a perfect circle, which means that the celestial body is always at the same distance from the center at any time.
Basic characteristics of circular orbits
The motion in a circular orbit is uniform, which means that the linear velocity of the celestial body remains constant. According to basic physics principles, the motion of celestial bodies must meet certain conditions in order to remain in circular orbits. The centripetal force for circular motion is gravity, and these conditions will not lead to the occurrence of perihelion or aphelion.
Kinetic analysis
In a circular orbit, the centripetal acceleration is driven by gravity. According to Newton's laws of motion, this acceleration must be constant. For a circular orbit, this means that the speed of an object in the circular orbit is not affected by its position, so the distance of the object from the center of the star remains unchanged. All energy changes occur in the same way, without any change in distance.
A circular orbit ensures that all conditions required for a celestial body to remain constant during its motion, making it impossible to form a perihelion or aphelion.
Movement Affected by Gravity
The effects of gravity behave in a very unique way in a circular orbit. The formation of a circular orbit means that the celestial body does not need to adjust the speed and direction of its movement, so the pull of gravity can just overcome the centrifugal force and maintain its moving state. In contrast, in an elliptical orbit, an object will have perihelion and aphelion due to changes in velocity and gravity at different locations.
Comparison of circular and elliptical orbits
Compared to circular orbits, elliptical orbits do not have constant distances, which ultimately leads to the occurrence of perihelion and aphelion. In an elliptical orbit, an object speeds up as it moves closer to the central mass and slows down as it moves away. Therefore, this change makes the distance from the center of mass significantly different at different times. This is completely different from the stability of a circular orbit.
ConclusionIn the movement of celestial bodies, circular orbits provide an idealized situation that helps us understand the laws of movement.
In summary, the motion characteristics of circular orbits prevent celestial bodies from forming perihelion and aphelion, because celestial bodies move at a fixed distance and stable speed. This not only affects the rhythm of celestial movement, but also makes circular orbits an important model for studying astronomical dynamics. So, in practice, how do we use this knowledge to improve the design of space missions?
