The trajectory of an object under the influence of gravity through space is called orbit, regardless of whether the object is a spaceship, planet, star, or galaxy. Once an orbit has been determined, the future positions of the object can be calculated.
2 points in any orbit of our solar system has been given special names. The place where the planet is closest to the sun (Helios in Greek) and moving fastest is called the perihelion of its orbit, and the place where it is farthest and slowest is For the moon or a satellite orbiting the earth (gee in Greek) are the corresponding terms perigee and apogee.
Orbits Of Planets
Today Newton’s work allows us to compute and predict the orbits of the planets with amazing precision. Now eight planets, starting with Mercury, the closest to the Sun, and extending outward to Neptune. The average orbital data of the planets are summarized in Table. (Ceres is the largest of the asteroids, which is now considered a dwarf planet.
|Planet||Semi Major Axis (AU)||Period (y)||Eccentricity|
According to Kepler’s laws, Mercury must have the shortest orbital period (88 earth days); Hence it has the highest orbital speed averaging 30 miles per second. At the opposite extreme, Neptune has a period of 165 years and an average orbital speed of only 5 kilometers per second.
All planets have relatively low eccentric orbits. the eccentric orbit is that of Mercury (0.21); the rest have eccentricities less than 0. It is fortunate that Mars, among other rest, mars has a greater eccentricity than many of the other planets. Otherwise, Brahe’s pre-telescopic observations would not have been enough for Kepler to conclude that its orbit was in the shape of an ellipse rather than a circle.
Planetary orbits are also bounded near a common plane that is near the plane of the Earth’s orbit (called the ecliptic). The strange orbit of the dwarf planet Pluto is inclined about 17 ° with respect to the ecliptic, and that of the planet dwarf Eris (which is even further from the Sun than Pluto) is at 44°, but all major planets are within 10 ° from the common plane of the solar system.
Orbits Of Asteroids And Comets
In addition to the eight planets, there are many smaller objects in the solar system, some of which are moons (natural satellites) orbiting all planets except Mercury and Venus. There are also two classes of smaller objects in heliocentric orbits: asteroids & comets. It is believed that both asteroids and comets are tiny remnants of material left over from the process of forming the solar system.
In general, asteroids have smaller semi-axial orbits than comets .They are between 2.2 and 3.3 AU, in the region known as the asteroid belt (see Comets and Asteroids: Debris of the Solar System). The asteroid belt (represented by its largest member, Ceres) is located in the middle of a gap between the orbits of Mars and Jupiter. This is because these two planets are so far apart that stable orbits of small bodies can exist in the region between them.
Comets generally have larger and more eccentric orbits than asteroids. Usually the eccentricity of their orbits is 0.8 or more. Therefore, according to Kepler’s second law, they spend most of their time away from the sun and move very slowly. As they approach perihelion, comets accelerate and move faster through the inner parts of their orbits.