In , Polish astronomer Nicolaus Copernicus published a mathematical treatise that promoted the idea of the Sun being the center of the solar system. But his treatment was complicated, and it was Kepler who used data to come up with the realization that the orbit of planets were ellipses.
In fact, Kepler came up with three laws. They are: 1 the orbit of a planet is an ellipse, with the Sun at one of the two foci; 2 the line connecting the planet and Sun sweeps out equal areas during equal intervals of time and; 3 the square of the orbital period of a planet is proportional to the cube of the semi-major axis of its orbit. The semi-major axis is the distance from the center of the ellipse to the edge along the longest distance.
In a mathematical sense, the third law is the most interesting, as it allows astronomers to relate how long it takes for a planet to go once around the Sun to its distance from the Sun. For instance, the closest the Earth gets to the Sun is 91 million miles or about million kilometers.
When the Earth is at aphelion, it is nearly 95 million miles or about million kilometers from the Sun. It also means that the foci are actually not that far apart, only about 4 million miles. To give some perspective, the radius of the Sun is about , miles and the distance between the Sun and Mercury is 29 million miles perihelion. Because the distance between the planet and Sun is smaller at perihelion than at aphelion, it must mean that the planet moves faster at perihelion.
For the Earth, the difference is 30 kilometers per second at perihelion and 29 kilometers per second at aphelion, or a little over half a mile per second difference. Learn more about the misconceptions of science.
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Beginner Can we find the place where the Big Bang happened? Most Popular. But, if you look at an ellipse from the right angle, it will appear circular. So, consider it a matter of viewpoint! Michael Hall, Canberra, Australia The shape of planetary orbits follows from the observed fact that the force of gravity between two objects depends on the square of the distance between them.
If you double the distance between two objects, the attractive force between them drops to a quarter of it's original value. If you triple the distance it drops to a ninth. Isaac Newton demonstrated mathematically that this law implied that the path followed by an object in a gravity field would be a parabola, a hyperbola or an ellipse. The first two are open ended. If something entered the solar system on a parabolic or hyperbolic path, we would see it just once before it disappeared into the distance.
Prior to Newton, Kepler showed by measurement that the observable planets had elliptical orbits. Ellipses are closed so the planets we see in elliptical orbits stick around. A circle is a special case of an ellipse and it is theoretically possible for an orbit to be circular. In the real world, a such an orbit is unlikely. Mike Burton, Twickenham, UK A circle is a special case of an ellipse with the major and minor axes equal.
To get a perfectly circular orbit of a certain radius requires the planet to have a certain velocity, which is extremely unlikely. It makes the most sense if you think of the velocity being greatest at the closest point and lowest at the furthest point. The low velocity moves it closer while the high velocity moves it back out further.
The total energy of the object in orbit kinetic energy plus potential energy remains constant. You probably know how things fall when they are thrown: A ball follows a curved path known as a parabola, the path of a ball is not circular, and it is certainly not a circle centred on the middle of the Earth.
So you don't expect things moving under gravity always to move in circles. Planets move under the action of gravity, just as if they were giant balls thrown around the sun, and they follow curved paths that are not circles. The exact shape can be calculated though the maths is complex and the shape is one of a family of curves: either an ellipse or a hyperbola.
The stable orbits of the planets are all ellipses, and usually nearly circular. Comets can have orbits that are long thin ellipses, or are hyperbolic, in which case the comet doesn't orbit, but passes the sun and has enough energy to escape from the sun forever.
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