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See the waxing Moon meet the outermost planet on 10 October

6 Oct 2019, 06:50 UTC
See the waxing Moon meet the outermost planet on 10 October
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The 12-day-old Moon lies in the same low-power binocular field as Neptune late into the evening of Thursday, 10 October 2019. At 11pm BST, observers in the UK can find the pair highest in the southern sky against the constellation of Aquarius. The glare of the gibbous lunar disc will present a challenge, but look one-third of the way from magnitude +4.2 naked-eye star phi (φ) Aquarii to 83 Aquarii to find the magnitude +7.8 ‘star’ that is the outermost planet. This simulated view shows field stars as faint as Neptune. AN graphic by Ade Ashford.In an earlier observing story, I wrote about Neptune’s close encounter with a magnitude +4.2 naked-eye star called phi (φ) Aquarii in the first week of September. The outmost planet’s great distance – currently some 29 times farther away from the Sun than Earth – means that its retrograde (east-to-west) motion against the stars of Aquarius is slow. Hence even by the end of October, Neptune lies no more than 1.3° (or two-and-a-half lunar diameters) from φ Aquarii.
Using φ Aquarii as a stellar stepping stone to Neptune is not too challenging, but if you’re looking for a really convenient celestial marker to the outermost ...

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