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One astronomical unit (about 150 million kilometres; 93 million miles) is defined as the mean distance between the centers of the Sun and the Earth. The instantaneous distance varies by about ± 2.5 million kilometres (1.6 million miles) as Earth moves from perihelion around 3 January to aphelion around 4 July. [ 36 ]
Evolution of the solar luminosity, radius and effective temperature compared to the present-day Sun. After Ribas (2009) [3] The uncrewed SOHO spacecraft was used to measure the radius of the Sun by timing transits of Mercury across the surface during 2003 and 2006. The result was a measured radius of 696,342 ± 65 kilometres (432,687 ± 40 miles).
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).
The Carrington heliographic coordinate system, established by Richard C. Carrington in 1863, rotates with the Sun at a fixed rate based on the observed rotation of low-latitude sunspots. It rotates with a sidereal period of exactly 25.38 days, which corresponds to a mean synodic period of 27.2753 days. [9]: 221 [1] [2] [5]
An orbit will be Sun-synchronous when the precession rate ρ = dΩ / dt equals the mean motion of the Earth about the Sun n E, which is 360° per sidereal year (1.990 968 71 × 10 −7 rad/s), so we must set n E = ΔΩ E / T E = ρ = ΔΩ / T , where T E is the Earth orbital period, while T is the period of the spacecraft ...
Thus, the angular diameter of Earth's orbit around the Sun as viewed from a distance of 1 pc is 2″, as 1 AU is the mean radius of Earth's orbit. The angular diameter of the Sun, from a distance of one light-year, is 0.03″, and that of Earth 0.0003″. The angular diameter 0.03″ of the Sun given above is approximately the same as that of a ...
The Sun has reached a period of peak activity in an 11-year cycle known as the Solar Maximum, marked by recent geomagnetic storms and near-global aurora light displays.
Distance light travels in one Julian year (365.25 days) – Oort cloud: 75,000: ± 25,000: Distance of the outer limit of Oort cloud from the Sun (estimated, corresponds to 1.2 light-years) – Parsec: 206,265 – One parsec. The parsec is defined in terms of the astronomical unit, is used to measure distances beyond the scope of the Solar ...