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This means that the Sun is (a mean of) 6 + 3 ⁄ 4 times wider than the Earth, or that the Sun is 13 + 1 ⁄ 2 Earth-radii wide. The Moon and Sun must then be 20 + 1 ⁄ 4 and 387 Earth-radii away from us in order to subtend an angular size of 2º.
Comoving distance and proper distance. Comoving distance is the distance between two points measured along a path defined at the present cosmological time. For objects moving with the Hubble flow, it is deemed to remain constant in time. The comoving distance from an observer to a distant object (e.g. galaxy) can be computed by the following ...
(The numerical value of the Hubble length in light years is, by definition, equal to that of the Hubble time in years.) The Hubble distance would be the distance between the Earth and the galaxies which are currently receding from us at the speed of light, as can be seen by substituting D = cH −1 into the equation for Hubble's law, v = H 0 D.
Solar radius is a unit of distance used to express the size of stars in astronomy relative to the Sun. The solar radius is usually defined as the radius to the layer in the Sun 's photosphere where the optical depth equals 2/3: [1] 695,700 kilometres (432,300 miles) is approximately 10 times the average radius of Jupiter, 109 times the radius ...
The cosmic distance ladder (also known as the extragalactic distance scale) is the succession of methods by which astronomers determine the distances to celestial objects. A direct distance measurement of an astronomical object is possible only for those objects that are "close enough" (within about a thousand parsecs) to Earth. The techniques ...
The distance d from the Sun to S now follows from simple trigonometry: tan( 1 / 2 θ) = E-Sun / d, so that d = E-Sun / tan( 1 / 2 θ), where E-Sun is 1 AU. The more distant an object is, the smaller its parallax. Stellar parallax measures are given in the tiny units of arcseconds, or even in thousandths of arcseconds ...
The planet, with a mass about 1.9 times that of Earth, is orbiting the white dwarf about 4,200 light-years away from our solar system near the bulge at the center of the Milky Way galaxy ...
The position of the Sun in the sky is a function of both the time and the geographic location of observation on Earth 's surface. As Earth orbits the Sun over the course of a year, the Sun appears to move with respect to the fixed stars on the celestial sphere, along a circular path called the ecliptic. Earth's rotation about its axis causes ...