Neptune is currently the most distant planet from the sun, with an orbital radius of 4.5 milliard kilometers (2.8 milliard miles, or 30 Astronomical Units). Even though its diameter is about four times that of the Earth (49,420 vs. 12,742 km), ground-based telescopes reveal a tiny blue disk that subtends less than 1/1200 of a degree (2.3 arc-seconds).
Neptune has therefore been a particularly challenging object to study from the ground because its disk is badly blurred by the Earth's atmosphere.
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Neptune in full splendour.
September 8, 2006 21:50 - 21:58 UT.
Altitude: 21.75 degrees; True distance: 29.1628199 AU [4363 million km];
Magnitude: 7.8; Phase: 1.000.
Imaging: LX200, 10 inch, f/10 with 2,5x Televue PowerMate operating at f/25 [focal length 6250 mm].
Camera: Vesta Pro SC3a colour RAW, 46 exposures of 4 seconds.



This SkyMap screen print shows how low Neptune was in my skies: just over the roof of my home ...

This is my first image of Neptune which of course calls for a colour version.
September 7, 2006 22:10 UT.
Altitude: 22,3 degrees, True distance: 29.1547947 AU [4362 million km].
Imaging: LX200, 10 inch, f/10 with 2,5x Televue PowerMate operating at f/25 [focal length 6250 mm].
Camera: Vesta Pro SC3a b/w RAW, 7 exposures of 5 seconds.