The planet Neptune will reach Solar Conjunction (i.e. was directly on the other side of the Sun from the Earth) at 2.46 am GMT on Thursday 2 March 2017. 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 4 332 000 000 km), and completely obscured by the Sun.
Since the orbits of the planets are not in complete alignment, Neptune will not be completely behind the Sun at conjunction but passes within 50 arc minutes of it (the sky, imagined as a sphere around the Earth, is split into 360 degrees, and each of these is split into 60 arc minutes), though this still means it cannot be observed due to the glare of the Sun.
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