Earth's orbit

The Earth's orbit - the orbit of the Earth in the solar system - is the path that the earth describes in its annual orbit around the sun.

Viewed from the Polarstern from the earth runs counter-clockwise around the Sun.

Elliptical shape

The Earth's orbit is described in good approximation by an ellipse with the Sun at one focus, as it follows from the first kepler 's law. This ellipse is different with a numerical eccentricity E of 0.0167 very little on a circular path. While the average distance ( semi-major axis) is 149.598 million kilometers ( one astronomical unit) to the sun, there are 147.1 million km and sonnenfernsten point ( aphelion ) 152.1 million km in point nearest the Sun ( perihelion ). These two extreme values ​​differ by only 1.67% from the mean. The earth ( 3 to 7 July ) its perihelion passage to January 3 ( January 2 to 5 ) and its aphelion passage about July 5.

Due to the gravitational influences of other planets takes the eccentricity of Earth's orbit currently slightly. It can take a long-term values ​​between 0.06 and almost close to zero. The main period of the variations is about 100,000 years ( Milanković cycles).

Also because of the influences of the other planets, the axis of the ellipse rotates slowly, and in the same direction in which the earth passes through the path ( prograde ). As a result of this so-called perihelion moves the perihelion in about 110,000 years, again with respect to the background of fixed stars around the Earth's orbit.

In one second, the distance between Earth and Sun sweeps over an area of ​​over 2 billion square kilometers. This value is constant after the second Kepler 's law.

Russian astrophysicist, published in June 2004, a publication by the average distance from the Sun is not constant, but every year by about 10 cm increased ( see also: variability of AE).

The average rotational speed of the Earth around the Sun is 29.783 km / s or 107,218 km / h and the length of Earth's orbit is about 940 million km. The earth moves per day, about 2.57 million kilometers in its orbit, which is about 202 Earth's diameter.

Orbital plane

As always, when a ground point through a path under the influence of a central strength, and the orbit of the earth lying in a plane. This orbital plane is also called the ecliptic plane and also serves as a reference plane for astronomical coordinates.

If we continue the path plane infinitely in all directions, it follows their line of intersection with the apparent celestial sphere a great circle around the sky (on the imaginary inside the apparent sky - vault ), which can also be referred to as the ecliptic. From the center of the Sun viewed from the Earth travels along the ecliptic line once a year around the sky. From Earth seen it is the sun that passes through the fixed stars along the ecliptic in the course of their annual migration. ( The apparent daily migration of the sun across the sky is merely due to the rotation of the earth: the sun moves here, together with the fixed stars in the sky, namely approximately parallel to the equator, not along the ecliptic. ) More details on this see the section path of the sun and in the Article sun.

The axis of rotation of the earth is not perpendicular to the web plane, but is slightly inclined. Accordingly, the equatorial plane of the earth and its projection is not on the apparent celestial sphere, the celestial equator, in the orbital plane. The angle between the ecliptic plane and the equatorial plane, called the obliquity of the ecliptic is currently about ε = 23.44 °. The line of intersection between the two planes is characterized both on the ecliptic, and on the equator of a common reference line. In one of the two defined by the reference line directions, the sun is at the moment the beginning of spring, when the wandering on the ecliptic sun passes the celestial equator, so it runs through the intersection of the ecliptic and equator. The direction of the vernal equinox is used as the zero point for astronomical coordinate systems.

Neither Equator yet ecliptic plane are fixed in space. The gravitational influence of the moon, sun and planets on the equatorial bulge of the earth produces a precession of the equatorial plane. The gravitational influence of the sun and planets on the orbital motion of the Earth produces a ( much weaker ) precession of the ecliptic plane. Therefore, the obliquity of the ecliptic as the angle of intersection of the two planes and the position of the vernal equinox are variable in time. The obliquity of the ecliptic varies with a period of about 40,000 years and with an amplitude of about 1 ° around a mean of about 23 °. The vernal equinox precesses in nearly 26,000 years, once with respect to the background of fixed stars around the Earth's orbit, in the earth's orbit the opposite direction ( retrograde ).

The inclination of the Earth's axis causes the seasons. The mentioned changes in eccentricity, obliquity and position of the vernal equinox lead by period to stronger or weaker forms of the seasons and are therefore probably one of the reasons for the change from warm periods and ice ages (see: Milankovitch cycles). It is not the position of the vernal equinox with respect to the fixed star background is important, but its position relative to the perihelion ( for reasons see seasons). Since the perihelion moves prograde to the Earth's orbit, the declining spring equinox is already taking with him again before he has completed a full revolution with respect to the fixed stars ( sidereal period). Therefore, the relative positions of the vernal equinox and perihelion repeat with a period of only about 21,000 years.

Among the perturbations exerted by the moon on the earth, see: Earth-Moon gravity

Orbital period

The orbital period of the Earth is called a year ( Earth year ). Depending on which reference point is chosen, different numerical values ​​for the length of the year.

After a sidereal year, the earth once again assumes the same position with respect to an (infinite imaginary far away and without self-motion ) fixed star. The length of the sidereal year is about 365.256 days. Meteor streams for example always cut the Earth's orbit at the same place, if they are not disturbed. The associated shower of shooting stars is repeated, therefore, with the period of one sidereal year.

After a tropical year the earth again assumes the same position relative to the vernal equinox. Since the spring equinox against the earth is running, the tropical year is slightly shorter than the sidereal and has a duration of about 365.242 days. For a number closer but slightly different definitions of the tropical year and the associated different figures see tropical year.

After an anomalistic year, the earth once again assumes the same position with respect to its perihelion. Since the perihelion moves prograde along the track, the anomalistic year is slightly longer than the sidereal year and has a duration of about 365.260 days. This is the actual orbital period, as it results from the third Kepler 's law with the help of the law of gravitation:

Ecliptic

Viewed from Earth, the sun appears to travel through the course of a year, the constellations of the ecliptic, according to which the twelve signs of the zodiac are named. This movement of the sun around the earth is called the apparent geocentric orbit.

For topocentric apparent path of the sun, as perceived by a real observer on Earth sight in the sky, see: Sun

In the sky mechanical representation of the geocentric position vector of the Sun is the heliocentric position vector of the earth exactly opposite, so in calculations the same set of formulas can be used. This is explained in the article Tropical year length.

Co-orbital objects

The earth is accompanied in its orbit around the sun by some co-orbital objects. This small celestial body orbiting the sun on paths on which they have a similar or even the same orbital period as the Earth. Due to the low relative velocity and with the help of resonance effects, the attraction of the earth can hold these objects more or less permanently in their co-orbital orbits.

So the earth deflects the near-Earth asteroid Cruithne on a horseshoe orbit along the Earth's orbit. Of these co-orbital cruisers Earth's orbit, the asteroid was 2003 YN107 from 1996 to 2006, a quasi- satellite of the Earth and will possibly be captured in the next match in the year 2120 as a real second moon of the Earth over the years. The co-orbital asteroid 2002 AA29 changes almost cyclically between a horseshoe orbit and a quasi- satellite orbit and will be the next time around the year 2600 again for 45 years, a quasi- satellite of the Earth.

In October 2010 a further object koorbitales Earth was discovered in 2010 TK7 that could be detected in July 2011 the first Earth Trojan. The 300 m wide asteroid orbits on a stable orbit around the Lagrangian point L4 and thus 60 ° ahead of Earth in its orbit around the sun.