Neptune at Opposition


Neptune reaches opposition on September 2nd meaning it’s at its closest approach to Earth over the next while. It’s up almost all night in the southern sky within the constellation Aquarius, below and right of Pegasus.

You’ll need a good horizon to see it however as it’s very low on the horizon this far north, never getting higher than 27 degrees.

During opposition Neptune will be at a distance of 28.94 AU with a disk size of 2.4 arcsec. In a good telescope of 6 inches or more you should be able to see a tiny blue disk and perhaps its companion Triton.

Neptune was first observed in a telescope in 1846.  It’s existence was implied from solar system models rather than from direct observation.  Like Saturn and Jupiter, it’s a gas giant with an atmosphere largely composed of hydrogen and helium, but this far out it also contains some “ices” such as water, ammonia, and methane.  

Neptune also has some of the weirdest and wildest weather in the solar system, with recorded wind speeds as high as 2,100 kilometres per hour!  This is what drives some of the mesmerising cloud streaking witnessed during Voyager 2’s flyby.  It’s also an extremely cold place – its cloud tops have recorded temperatures as low as -220 C.  Not surprising given how far it is from the sun.

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