At Astronomy Pic Of The Day there is a great shot of the Moon about to eclipse Jupiter and his moons.
Explanation: Skygazers around planet Earth enjoyed the close encounter of planets and Moon in July 15’s predawn skies. And while many saw bright Jupiter next to the slender, waning crescent, Europeans also had the opportunity to watch the ruling gas giant pass behind the lunar disk, occulted by the Moon as it slid through the night. Clouds threaten in this telescopic view from Montecassiano, Italy, but the frame still captures Jupiter after it emerged from the occultation along with all four of its large Galilean moons. The sunlit crescent is overexposed with the Moon’s night side faintly illuminated by Earthshine. Lined up left to right beyond the dark lunar limb are Callisto, Ganymede, Jupiter, Io, and Europa. In fact, Callisto, Ganymede, and Io are larger than Earth’s Moon, while Europa is only slightly smaller.
Did you know that in Patrick O’Brian‘s Aubrey/Maturin series (US HERE, UK HERE), Capt. Aubrey was working on a way to calculate longitude while at sea by observation of the moons of Jupiter? In The Mauritius Command we read:
[Capt. Aubrey’s] telescope was a disappointment. It was not that he could not see Jupiter: the planet gleamed in his eyepiece like a banded gold pea. But because of the ship’s motion he could not keep it there long enough or steadily enough to fix the local time of its moons’ eclipses and thus find his longitude. Neither the theory (which was by no means new) nor the telescope was at fault: it was the cleverly weighted cradle slung from the main topgallant mast stay that he had designed to compensate for the pitch and roll that did not answer, in spite of all his alterations; and night after night he swung there cursing and swearing, surrounded by midshipmen armed with clean swabs, whose duty it was to enhance the compensation by thrusting him gently at the word of command.
I think Jack would have enjoyed this sight!
Ah. Had to think for a minute about why we see Luna as a crescent and Jupiter as a disc.