Orbital Parameters of the Earth
Figure 2 depicts the three parameters that describe the Earth s orbit around the sun: (1) eccentricity, (2) axial tilt (or obliquity), and (3) time of perihelion (or precession).One of the consequences of elliptical orbits is that planets orbit not about the center of the ellipse, but about a point off-center known as the focus. This offset is far more noticeable than a slightly elliptical shape. So early astronomers proposed circular orbits known as deferents that were shifted off center.
Definition of apogee. 1 : the point in the orbit of an object (such as a satellite) orbiting the earth that is at the greatest distance from the center of the earth also : the point farthest from a planet or a satellite (such as the moon) reached by an object orbiting it — compare perigee.
An ellipse is a shape that looks like an oval or a flattened circle. In geometry, an ellipse is a plane curve which results from the intersection of a cone by a plane in a way that produces a closed curve. Circles are special cases of ellipses, obtained when the cutting plane is perpendicular to the cone's axis.
The orbital speed can be found using v = SQRT(G*M/R). The R value (radius of orbit) is the earth's radius plus the height above the earth - in this case, 6.59 x 106 m. Substituting and solving yields a speed of 7780 m/s.
The eccentricity, e, and either the semi-major axis, a, or the distance of periapsis, q, are used to specify the shape and size of an orbit. The angle of the ascending node, Ω, the inclination, i, and the argument of periapsis, ω, or the longitude of periapsis, ϖ, specify the orientation of the orbit in its plane.
The orbital period is the time a given astronomical object takes to complete one orbit around another object, and applies in astronomy usually to planets or asteroids orbiting the Sun, moons orbiting planets, exoplanets orbiting other stars, or binary stars.
To compute other numbers describing the shape of the orbit, here's what you do:
- Periapsis distance = a(1-e)
- Apoapsis distance = a(1+e)
- Orbital period = 2π√(a3/GM)
- Orbital period (solar orbit, in years, with a in AU) = a1.5 (and recall that 1 AU = 149.60×106 km)
How Do Objects Stay in Orbit? An object in motion will stay in motion unless something pushes or pulls on it. Without gravity, an Earth-orbiting satellite would go off into space along a straight line. With gravity, it is pulled back toward Earth.
A Sun-synchronous orbit (SSO, also called a heliosynchronous orbit) is a nearly polar orbit around a planet, in which the satellite passes over any given point of the planet's surface at the same local mean solar time.
The traditional orbital elements are the six Keplerian elements, after Johannes Kepler and his laws of planetary motion. When viewed from an inertial frame, two orbiting bodies trace out distinct trajectories.
The ascending node is usually quoted as the angular position at which a celestial body passes from the southern side of a reference plane to the northern side, hence 'ascending'. For objects orbiting the Sun, the most convenient reference plane is the orbital plane of the Earth.
In the case of objects outside the Solar System, the ascending node is the node where the orbiting secondary passes away from the observer, and the descending node is the node where it moves towards the observer. The line of nodes is the intersection of the object's orbital plane with the plane of reference.
The lunar nodes are the two points where the Moon's orbital path crosses the ecliptic, the Sun's apparent yearly path on the celestial sphere.
A polar orbit is one in which a satellite passes above or nearly above both poles of the body being orbited (usually a planet such as the Earth, but possibly another body such as the Moon or Sun) on each revolution. It therefore has an inclination of (or very close to) 90 degrees to the body's equator.
There are essentially three types of Earth orbits: high Earth orbit, medium Earth orbit, and low Earth orbit. Many weather and some communications satellites tend to have a high Earth orbit, farthest away from the surface.
Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a reference plane and the orbital plane or axis of direction of the orbiting object. If the orbit swung between 20° north latitude and 20° south latitude, then its orbital inclination would be 20°.
Earth orbits the Sun at an average distance of 149.60 million km (92.96 million mi), and one complete orbit takes 365.256 days (1 sidereal year), during which time Earth has traveled 940 million km (584 million mi).
The solar system is made up of the sun and everything that orbits around it, including planets, moons, asteroids, comets and meteoroids.
It's thought to have arisen from an amorphous cloud of gas and dust in space. The original cloud was spinning, and this spin caused it to flatten out into a disk shape. The sun and planets are believed to have formed out of this disk, which is why, today, the planets still orbit in a single plane around our sun.
Kepler's first law - sometimes referred to as the law of ellipses - explains that planets are orbiting the sun in a path described as an ellipse. The resulting shape will be an ellipse. An ellipse is a special curve in which the sum of the distances from every point on the curve to two other points is a constant.
The Earth completes one orbit every 365.242199 mean solar days, a fact which goes a long way towards explaining why need an extra calendar day every four years (aka. during a leap year). The planet's distance from the Sun also varies as it orbits.
