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The Urban Astronomer

Blue Neptune

27 May 2009, 16:04 UTC
Blue Neptune
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A first for me: Early this morning before sunrise was the first of three conjunctions between Neptune and Jupiter. This rare "triple conjunction" started this morning with a close passage of Jupiter near Neptune in Capricorn. The separation was less than half a degree (less than a moon-width) and the difference visually between giant Jupiter and its four moons and blue Neptune was dramatic. Neptune looks essentially like a dim blue star through binoculars -- and is invisible to the unaided eye.I had never taken the time to look for Neptune in the past. Because it is so dim and nearly impossible to resolve to anything but a pinpoint of light, I had never been motivated to seek it in a field of dim stars. But with Jupiter as my guide, it was an easy find and a magical moment to see those two solar system objects in one field of view. The alignment of two very distant planets - one 450 million miles away, the other almost 3 billion miles away - in a compact cluster less than half a degree apart was nothing short of remarkable. Now that the two planets have lined up once, they will soon ...

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