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  2. Sidereal time - Wikipedia

    en.wikipedia.org/wiki/Sidereal_time

    Mercury's sidereal day is about two-thirds of its orbital period, so by the prograde formula its solar day lasts for two revolutions around the Sun – three times as long as its sidereal day. Venus rotates retrograde with a sidereal day lasting about 243.0 Earth days, or about 1.08 times its orbital period of 224.7 Earth days; hence by the ...

  3. Venus - Wikipedia

    en.wikipedia.org/wiki/Venus

    Because of the retrograde rotation, the length of a solar day on Venus is significantly shorter than the sidereal day, at 116.75 Earth days (making the Venusian solar day shorter than Mercury's 176 Earth days — the 116-day figure is close to the average number of days it takes Mercury to slip underneath the Earth in its orbit [the number of ...

  4. Astronomical unit - Wikipedia

    en.wikipedia.org/wiki/Astronomical_unit

    Comparison of the ephemeris positions with time measurements expressed in Barycentric Dynamical Time (TDB) leads to a value for the speed of light in astronomical units per day (of 86,400 s). By 2009, the IAU had updated its standard measures to reflect improvements, and calculated the speed of light at 173.144 632 6847 (69) au/d (TDB).

  5. Orbit of Venus - Wikipedia

    en.wikipedia.org/wiki/Orbit_of_Venus

    Venus was 0.7205 au from the Sun on the day of transit, decidedly less than average. [ 9 ] Moving far backwards in time, more than 200,000 years ago Venus sometimes passed by at a distance from Earth of barely less than 38 million km, and will next do that after more than 400,000 years.

  6. Kepler's laws of planetary motion - Wikipedia

    en.wikipedia.org/wiki/Kepler's_laws_of_planetary...

    Mathematically, an ellipse can be represented by the formula: r = p 1 + ε cos ⁡ θ , {\displaystyle r={\frac {p}{1+\varepsilon \,\cos \theta }},} where p {\displaystyle p} is the semi-latus rectum , ε is the eccentricity of the ellipse, r is the distance from the Sun to the planet, and θ is the angle to the planet's current position from ...

  7. Rotation period (astronomy) - Wikipedia

    en.wikipedia.org/wiki/Rotation_period_(astronomy)

    The other type of commonly used "rotation period" is the object's synodic rotation period (or solar day), which may differ, by a fraction of a rotation or more than one rotation, to accommodate the portion of the object's orbital period around a star or another body during one day.

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  9. Synodic day - Wikipedia

    en.wikipedia.org/wiki/Synodic_day

    A synodic day (or synodic rotation period or solar day) is the period for a celestial object to rotate once in relation to the star it is orbiting, and is the basis of solar time. The synodic day is distinguished from the sidereal day , which is one complete rotation in relation to distant stars [ 1 ] and is the basis of sidereal time.