What's New on the Site? Upcoming W2U Events. Join Today - Benefits, No Ads! Special Offers for Teachers. Member Benefits. Teacher Newsletter. Partnership Opportunities. You might also be interested in: Traveling Nitrogen Classroom Activity Kit Check out our online store - minerals, fossils, books, activities, jewelry, and household items! Eccentricity of an Orbit You may think that most objects in space that orbit something else move in circles, but that isn't the case. Although some objects follow circular orbits, most orbits are shaped more like "stretched Pluto Pluto is a frigid ball of ice and rock that orbits far from the Sun on the frozen fringes of our Solar System.
Considered a planet, though a rather odd one, from its discovery in until , it was Kepler realized that the line connecting the planet and the Sun sweeps out equal area in equal time. Look at the diagram to the left. What Kepler Mechanics Mechanics is the term used to refer to one of the main branches of the science of physics.
Mechanics deals with the motion of and the forces that act upon physical objects. We need precise terminology Eris - a dwarf planet Eris is a dwarf planet in our Solar System. Eris was one of the first three objects classified as a dwarf planet, along with Pluto and Ceres. Eris was first spotted in January In a parabolic or hyperbolic orbit, however, an object approaches a central gravitational body from a distance, swings close just once, and escapes out to infinity.
Many comets follow such trajectories: they may orbit peacefully in the Oort Cloud for billions of years, but if perturbed get knocked into a hyperbolic orbit, falling into the inner solar system and then jetting back off into the emptiness of interstellar space.
At launch, a rocket may be in a hyperbolic trajectory before correcting itself and settling into a stable elliptical orbit around the Earth, followed by a boost to a hyperbolic trajectory that sends it off to a distant target. You can follow Paul on Twitter and Facebook. Join our Space Forums to keep talking space on the latest missions, night sky and more! And if you have a news tip, correction or comment, let us know at: community space.
If you take a string and tie it to both of the foci, you can draw the ellipse by kind of doing the same thing you did with the circle, and get a squashed circle. Learn more about the myths of orbital motion. Now, it turns out that the orbits of the planets are pretty circular.
But they are actually ellipses, and this was first worked out in the early s by Johannes Kepler. That honor is held by Aristarchus of Samos, a Greek philosopher who lived in the second century B. Given the lack of proper instrumentation, the debate over whether the Earth or Sun was the center of the universe continued over many centuries. 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.
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