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During the 1970s to 1980s, the increasing number of artificial satellites in Earth orbit further facilitated high-precision measurements, and the relative uncertainty was decreased by another three orders of magnitude, to about 2 × 10 −9 (1 in 500 million) as of 1992. Measurement involves observations of the distances from the satellite to ...
Ignoring the influence of other Solar System bodies, Earth's orbit, also called Earth's revolution, is an ellipse with the Earth–Sun barycenter as one focus with a current eccentricity of 0.0167. Since this value is close to zero, the center of the orbit is relatively close to the center of the Sun (relative to the size of the orbit).
Gravity decreases with altitude as one rises above the Earth's surface because greater altitude means greater distance from the Earth's centre. All other things being equal, an increase in altitude from sea level to 9,000 metres (30,000 ft) causes a weight decrease of about 0.29%.
For example, to reduce the gravity of the Earth by a factor of one million, one needs to be at a distance of 6 million kilometres from the Earth, but to reduce the gravity of the Sun to this amount, one has to be at a distance of 3.7 billion kilometres.
This is because the distance between Earth and the Sun is not fixed (it varies between 0.983 289 8912 and 1.016 710 3335 au) and, when Earth is closer to the Sun , the Sun's gravitational field is stronger and Earth is moving faster along its orbital path. As the metre is defined in terms of the second and the speed of light is constant for all ...
The percentage columns show the distance from the orbit compared to the semimajor axis. E.g. for the Moon, L 1 is 326 400 km from Earth's center, which is 84.9% of the Earth–Moon distance or 15.1% "in front of" (Earthwards from) the Moon; L 2 is located 448 900 km from Earth's center, which is 116.8% of the Earth–Moon distance or 16.8% ...
For an object of mass the energy required to escape the Earth's gravitational field is GMm / r, a function of the object's mass (where r is radius of the Earth, nominally 6,371 kilometres (3,959 mi), G is the gravitational constant, and M is the mass of the Earth, M = 5.9736 × 10 24 kg).
The term "unit distance" is also used for the length (A). From this definition, the mean distance of Earth from the Sun works out to 1.000 000 03 au, but with perturbations by the other planets, which do not average to zero over time, the average distance is 1.000 000 20 au. [6]