This is Ephemeris for Wednesday, December 17th. Today the Sun will be up for 8 hours and 48 minutes, setting at 5:03, and it will rise tomorrow at 8:15. The Moon, 2 days before new, will rise at 7:26 tomorrow morning.
Let’s take our weekly look at the whereabouts of the naked-eye planets. Saturn is the brightest star-like object in the southern sky as soon as it gets dark. In a telescope Saturn sports a very thin ring, six tenths of a degree from being edge on and slowly opening. In a couple of months the rings will be much more visible in telescopes. Jupiter will rise at 7:02 PM in the east-northeast, below Castor and Pollux, the bright stars of Gemini. Jupiter’s 4 brightest moons can be seen even in binoculars, and shift position night to night. In the morning sky, Mercury just might be spotted very low in the east-southeast by 7:30. The next opportunity to spot Mercury will be in the evening in mid-February.
The astronomical event times given in this blog are for the Traverse City/Interlochen area of Michigan (Lat 44.7° N, Long 85.7° W; EST, UT – 5 hours) unless stated otherwise. Times will be different for other locations.
Addendum
Jupiter and Saturn along with the zodiacal constellations, and the path of the Sun (ecliptic) in orange, in this panorama at 9 PM tonight, December 17, 2025. Created using Stellarium.
Mercury (though not as bright as this) and the thin crescent waning Moon at 7:30 AM tomorrow morning, December 18, 2025. The Moon is enlarged to be double its normal size, but will be actually invisible that close to the horizon. Created using Stellarium.
Telescopic Saturn, and Jupiter (north up) as they would be seen in a small telescope with the same magnification at 9 PM tonight, December 17, 2025, Saturn will be 17.5″ in diameter, but its rings, being nearly edge on, may show up brighter than seen here, and extend to 40.8″. They are tilted 0.6° from being edge on. Jupiter will be 45.8″ in diameter. Mercury appears too small to be shown here, but its apparent diameter will be 5.5″. The (”) symbol means seconds of arc, or 1/3600th of a degree. Created using Cartes du Ciel (Sky Charts), LibreOffice Draw and GIMP.
The naked-eye planets and the Moon at sunset and sunrise on a single night, starting with sunset on the right on December 17th, 2025. The night ends on the left with sunrise on the 18th. Click or tap on the image to enlarge it. Created using my LookingUp app and GIMP.
This is a low precision ephemeris of the Sun Moon and naked eye planet positions for today and tomorrow, December 17th and 18th, 2025. Some of the columns are self-explanatory, others are not. The transit column is the time that the body crosses the meridian and is due south. Elong, for elongation, is the angle between the Sun and that body. RA is right ascension, which is the object’s east-west position on the celestial sphere in hours and minutes. Dec is declination which is the north-south position of the object on the celestial sphere in degrees and minutes. R is the distance of that object from the Sun in astronomical units. An astronomical unit is about 93 million miles or 150 million kilometers. And Delta is the distance of that object from the Earth, also in astronomical units. I omit the ‘m’ in am and pm for compactness. The data was generated using my LookingUp for DOS app and displayed as a table by my Ephemeris Helper app.
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