The planet Neptune will reach Solar Conjunction (i.e. be directly on
the other side of the
Sun from the Earth) at 1.56 pm GMT on Sunday 4 March 2018. This
means that it will both be at its furthest from the Earth this year,
about 30.94 AU (30.94 times the average distance between the Earth and
the
Sun, or about 4 629 000 000 km), and while not completely obscured by the Sun, due to differences in the
tilts of the orbits of Earth and Neptune, it will be close enough to the
Sun to be invisible for several weeks.
The relative positions of Neptune and Earth at Solar Conjunction (not to scale). Bob's Spaces.
Neptune orbits the Sun at an average distance of 30.11 AU, completing one
orbit around the Sun every 165 years. This means that the planet is
almost stationary compared to the faster moving Earth, so that it
reaches Solar Conjunction only four days later each year than the year
before, and reaches opposition (when it is directly opposite the Sun
seen from the Earth), roughly six months later.
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