Key details of the December 2017 full moon
The full moon in December 2017 reached peak illumination on Sunday, December 3, 2017, at 09:47 UTC. It appeared full for about three days centered on that time, and was the only full moon that month. For Northern Hemisphere observers it rose around sunset and stood high around midnight; in Southern Hemisphere locations it followed the opposite pattern. The moon was in the constellation Taurus near the Pleiades at opposition, and because it occurred close to lunar perigee it appeared slightly larger and brighter than an average full moon, though not at the extreme of a supermoon as defined by many astronomers.
What defines a full moon in astronomy
An astronomically full moon occurs when the Moon is opposite the Sun in ecliptic longitude, placing it in full phase with Earth nearly between the Sun and the Moon. This configuration happens roughly every 29.53 days, corresponding to a synodic month. The precise moment of full moon can fall at any time of day or night, and the visible fullness depends on local weather conditions and the Moon’s position above the horizon. The December 2017 full moon, like all full moons, provided the best illumination when it was well above the horizon and the sky was clear.
Calendar context: how December 2017 fits into lunar cycles
December 2017 contained one full moon, on December 3, following the November 2017 full moon on November 3 and preceding the January 2018 full moon on January 2. The date of a given full month shifts earlier from year to year by roughly 11 days in non-leap years and 10 days in leap years, because the synodic month is about 11 hours shorter than 30 days. Over multi-year spans, the full moon in December can occur from about November 30 to January 1, depending on how the Metonic cycle aligns calendar dates with lunar months.
Notable circumstances of the December 2017 full moon
The December 3, 2017 full moon was within one day of lunar perigee, making it a so-called supermoon by popular standards, though its angular diameter increase over a micromoon was modest. It occurred about 15 hours after full moon, placing it near lunar perigee but not at the exact time of closest approach. Observers noted a slightly larger apparent size and brighter surface features, especially around lunar limb terrain and the bright ray patterns of Tycho crater. Such near-conjunction of full phase and perigee recurs in cycles of about 14 lunar months.
| Attribute | Verified Detail | Source Type |
|---|---|---|
| Date of full moon | December 3, 2017 | NASA JPL Horizons |
| Time of peak illumination | 09:47 UTC | NASA JPL Horizons |
| Moon’s constellation at opposition | Taurus, near the Pleiades | Stellarium calculations |
| Lunar distance at full | Approximately 359,000 km (close to perigee) | NASA Moon data |
| Apparent diameter change vs. average | Few percent larger and brighter near perigee | Lunar orbital parameters |
Practical observing notes
To observe the December 2017 full moon, observers needed only clear skies and a view of the horizon where the Moon would rise after sunset. In the Northern Hemisphere it appeared in the eastern sky after sunset and set near western horizon at sunrise. In the Southern Hemisphere it followed the reverse arc. Atmospheric effects near the horizon may make the Moon appear larger, an illusion unrelated to actual size. Telescopic viewing highlighted crater rims, central peaks, and subtle albedo contrasts across mare and highland regions, especially near the terminator earlier in the evening.
Cultural names and traditions
December’s full moon has long been called the Cold Moon in many Northern Hemisphere traditions, reflecting winter’s onset. Indigenous and colonial names emphasize the season’s chill and long nights. Various cultures associate this moon with winter solstice preparations, animal behavior, and ceremonial calendars. Such names are cultural markers rather than astronomical definitions, but they help connect sky events to human history and regional practices around late December.
How to interpret supermoon claims for December 2017
The term supermoon lacks a precise astronomical definition but is commonly used for a full moon or new moon that occurs within about 90 percent of perigee distance. The December 2017 full moon met this popular threshold, appearing modestly larger and brighter than a full moon at average distance. Claims about extreme tides or dramatic effects should be treated with skepticism; lunar tidal influence changes slowly over the orbit and poses no geophysical hazard. For sky-watchers, the visual difference was noticeable but subtle compared to nearby syzygies or eclipses.
Relationships between full moon date, perigee, and eclipse potential
The timing of full moon relative to perigee determines apparent size and the possibility of lunar eclipses. When full moon occurs within a day of perigee, the Moon can appear noticeably larger and is sometimes labeled a supermoon. Eclipses require the full moon to occur near a lunar node; in December 2017, the Moon was north of the ecliptic at full phase, so no eclipse took place. Tracking these relationships helps contextualize claims about exceptional tides or visibility tied to specific full moons.
Summary comparison of December 2017 full moon versus average full moon
- Apparent diameter: slightly larger than average (few percent)
- Brightness: modestly increased near full phase
- Timing relative to perigee: within ~1 day
- Eclipse potential: none (wrong node)
- Visibility window: full night from moonrise to moonset
Looking forward and backward: using December 2017 as a reference
Treat the full moon of December 2017 as a baseline for understanding future and past full moons in the same season. Its date, time, and proximity to perigee illustrate how lunar phases and orbital placement vary from month to month. For retrospective analysis, consult standard lunar tables and ephemerides; for planning, note that December full moons can occur anywhere from late November to early January, and their supermoon status depends on exact perigee timing. This long-term context supports reliable comparisons across years.
Tags: lunar calendar, full moon December, astronomy reference, supermoon clarification