Wednesday 8 July 2020

Venus approaches aphelion.

The planet Venus will reach apihelion (the furthest point on its orbit to the Sun) at 2.43 pm GMT on Friday 10 July 2020, when it will be 0.73 AU (109 206 000 km) from the Sun. This is only 0.01 AU (1 496 000) more distant than the planet's periphelion (closest point on its orbit from the Sun), as Venus has the least eccentric circular orbit of any planet in our Solar System, this is about 1% the distance between the Earth and the Sun.

 The relative positions of Mars, Earth, Venus and Mercury on 10 July 2020. From the point of view of an Earth based observer the Venusian perihelion will make no difference to the planets visibility. JPL Small Body Database Browser.

Because Venus is closer to the Sun than the Earth, its year is somewhat shorter, only 224.7 Earth days compared to 365.25 for the Earth, and Venus's last aphelion fell on 28 November 2019. Despite a Venusian Year having passed since this date, the planet has not yet completed a full day, as a Venusian day is actually longer than its year, at 243 Earth days, with Venus rotating clockwise on its axis while orbiting the Sun anti-clockwise. Exactly why this occurs is uncertain, as all other planets both orbit and rotate in an anti-clockwise direction; it is uncertain whether the planet has reached this situation by slow evolution of its orbit over billions of years from an unstable condition within the original protoplanetary disk from which all the planets formed, or whether its modern orbit results from an encounter with some other body at some point in the past. Either way Venus is unique in that (were it possible to see the sky from the planet's surface) the Sun would appear to pass across the sky from west to east, and that the time it took to complete a circuit from the perspective of a viewer on the surface would be significantly from the length of the planet's 'day'. This is because the shorter Venusian year affects the movement of the Sun across the sky more than the longer day, so that it is possible to talk about a 'Solar Day' on Venus (the length of time it takes a feature on the planet's surface to pass from directly under the Sun round to back directly under the Sun), only 116.75 days.

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