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Earth's western hemisphere showing topography relative to Earth's center instead of to mean sea level, as in common topographic maps. Earth has a rounded shape, through hydrostatic equilibrium, with an average diameter of 12,742 kilometers (7,918 mi), making it the fifth largest planetary sized and largest terrestrial object of the Solar System.
The average diameter of the orbit of the Moon relative to the Earth. Geospace: 6,363,000–12,663,000 km (110–210 Earth radii) 6.36×10 6 –1.27×10 7: 6.80–7.10: The space dominated by Earth's magnetic field and its magnetotail, shaped by the solar wind. Earth's orbit: 299.2 million km 2 AU: 2.99×10 8: 8.48
Posidonius calculated the Earth's circumference by reference to the position of the star Canopus.As explained by Cleomedes, Posidonius observed Canopus on but never above the horizon at Rhodes, while at Alexandria he saw it ascend as far as 7 + 1 ⁄ 2 degrees above the horizon (the meridian arc between the latitude of the two locales is actually 5 degrees 14 minutes).
Choice of units. The choice of solar mass, M ☉, as the basic unit for planetary mass comes directly from the calculations used to determine planetary mass.In the most precise case, that of the Earth itself, the mass is known in terms of solar masses to twelve significant figures: the same mass, in terms of kilograms or other Earth-based units, is only known to five significant figures, which ...
Earth's rotation period relative to the International Celestial Reference Frame, called its stellar day by the International Earth Rotation and Reference Systems Service (IERS), is 86 164.098 903 691 seconds of mean solar time (UT1) (23 h 56 m 4.098 903 691 s, 0.997 269 663 237 16 mean solar days).
A great many ellipsoids have been used to model the Earth in the past, with different assumed values of a and b as well as different assumed positions of the center and different axis orientations relative to the solid Earth. Starting in the late twentieth century, improved measurements of satellite orbits and star positions have provided ...
An oblate spheroid, highly exaggerated relative to the actual Earth A scale diagram of the oblateness of the 2003 IERS reference ellipsoid, with north at the top. The outer edge of the dark blue line is an ellipse with the same eccentricity as that of Earth.
Ignoring the influence of other Solar System bodies, Earth's orbit, also known as 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).