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A Big Bang on the Moon, and Orion's Never-Ending Chase

by Geoff Chester, USNO Public Affairs | 16 January 2024

by Geoff Chester, USNO Public Affairs | 16 January 2024

The Moon, 2022 May 11, 01:50 UT, imaged from Alexandria, Virginia
with a 10.2-cm (4-inch) f/6.5 Explore Scientific AR 102 refractor, 2X Tele Vue "Big Barlow" lens,
and a ZWO ASI183MC CMOS imager.
The Mare Imbrium basin is the large circular area dominating the upper left quadrant.

The Moon waxes in the evening sky this week, climbing northward along the ecliptic to join the splendid winter constellations.  First Quarter occurs on the 17th at 10:53 pm Eastern Standard Time.  Luna will be close to bright Jupiter on the evening of the 18th.  You will find her lurking just east of the Pleiades star cluster two nights later.  She closes the week drawing a bead on Castor and Pollux, the Twin Stars of Gemini.  

The waxing phases around the time of first quarter are my favorite times to do a little Moon gazing.  This is when the terminator line slowly moves from the battered lunar “highlands” to slowly reveal the smoother lava plains of the Mare Imbrium and Oceanus Procellarum features.  These areas are considerably “younger” than the highlands, but they still preserve a surface frozen in time some 3.9 billion years ago.  The Imbrium basin in particular reveals circular walls as each night passes, and it should be apparent that this is a crater of vast dimensions.  It was formed by the impact of a 250-kilometer (155 mile) sized object that left a 1150-kilometer (715 mile) scar that broke into the proto-Moon’s mantle and filled with molten rock.  The relative paucity of craters on these giant features tells us that, fortunately, many of the larger bodies that populated the early solar system aren’t around anymore.

As the Moon waxes, her brightening glare begins to wash out the sky’s fainter stars.  However, at this time of the year we have a view of many of the sky’s brightest stars, and what is, perhaps the most familiar constellation in the heavens.  Fie striding figure of Orion is now resplendent in the night, crossing the meridian at 10:00 pm local time.  Positioned astride the celestial equator, Orion is visible from just about every inhabited place on the planet, and because of this he figures in the sky lore of almost every culture that has left records of their views of the night sky.    The ancient Babylonians knew him as “The True Shepherd of Anu”, the chief of their sky gods.  Ancient Egyptians identified him as “Sah” in some of their earliest written accounts dating to c. 2400 BCE, who evolved onto Osiris, the god of the dead and resurrection.  Pharaohs decorated their tombs with elaborate texts and images to guide their transformation into Osiris in their afterlife.  Many other societies, from ancient China to North American native peoples, worshipped the three stars that form Orion’s “Belt”.

Today we see Orion as he was presented in ancient Greek mythology, where he was depicted as a mighty Hunter, the son of the Gorgon Euryale and the sea god Poseidon.  In one of many legends, Orion was sent to the island of Chios to dispatch the wild beasts that were terrorizing the inhabitants.  Flushed with his success, he boasted that he would kill every wild animal on Earth.  This, of course, drew the ire of Gaia, goddess of the Earth, who vowed to kill the impertinent Orion.  She sent a lowly scorpion to do the deed, and the plot almost succeeded.  Orion was saved by Ophiuchus, who gave him an antidote for the scorpion’s venom.  Zeus placed them all in the sky, but in such a way that Scorpius and Orion are never visible at the same time.  And, to ensure that Scorpius and Orion stay apart, Ophiuchus stands directly above the scorpion in the summer sky.

Saturn remains visible low in the southeastern sky as evening twilight fades.  However, his proximity to the horizon when darkness fully falls leaves little time for a good look at the ringed planet through the telescope.  Saturn sets at around 8:00 pm, so you’ll need to act quickly to see him at all.

Jupiter crosses the meridian at the end of evening twilight.  The giant planet dominates the evening hours as he arcs westward with the passing hours.  If you have a small telescope, you can see an unusual sight if you point it at Old Jove on the evening of the 22nd.  At 7:00 pm EST you will see the planet with just two of its four bright Galilean moons, Ganymede and Callisto.  At 7:15 pm the moon Europa will gradually peek out from behind Jupiter’s limb.  At 7:34 pm Io will emerge out of eclipse by Jupiter’s shadow, and for a few minutes all four moons will be visible.  This won’t last long, though; at 7:40 pm Europa will enter Jupiter’s shadow, emerging at 9:55 pm to restore the sight of four moons.

You can still find dazzling Venus in morning twilight, low in the southeastern sky.  If you have a pair of binoculars and a flat horizon in that direction, look about halfway between Venus and the horizon for the reddish glow of Mercury early in the week.  The fleet planet passed greatest elongation from the Sun last week, so he is now slipping deeper into the twilight glow.  


Commander, Naval Meteorology and Oceanography Command | 1100 Balch Blvd. | Stennis Space Center, Mississippi 39529

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