{"schema":"https://ver.cy/schemas/card/1.0.0","id":"vr.tr.december-21","code":"thing-q2603","url":"https://ver.cy/models/thing/q2603/","name":"December 21","alternateNames":[],"kind":"thing","status":"published","version":"0.2.0-wave.4","language":"en","classifiers":{"family":"Thing Registry","category":"Cross-cutting context","entryKind":"thing","plane":"XCT","domain":["XCT.TME"],"industry":[],"navPath":"","tags":[],"facets":{}},"whatItIs":"December 21, day 355 (day 356 in leap years) of the year in the Gregorian calendar, with 10 days remaining in both common and leap years. December 21 is the usual date of the December solstice, the shortest day in the Northern Hemisphere, observed in festivals from Yalda in Iran to Dongzhi in East Asia, and the anniversary of the Lockerbie bombing of Pan Am Flight 103 in 1988, of the Pilgrims landing at Plymouth in 1620 by one reckoning, and of the first crossword puzzle published in 1913.","purpose":"Let an agent handle December 21 as a calendar date with weekday computation, observances attributed to their traditions and sourced events.","scope":{"in":[],"out":[],"boundaries":[]},"distinguishingFeatures":["The twenty-first day of December","Weekday varies by year","Observances vary by place","Julian and Gregorian dates differ by 13 days in this era"],"structure":{"bundles":[{"id":"date","name":"Date","description":"Calendar facts.","layers":[{"id":"weekday","name":"Weekday","description":"Computation.","findings":[{"id":"weekday-finding","name":"Weekday","description":"Weekday.","questions":[{"text":"On which weekday does December 21 fall in this year?","kind":"measurement"},{"text":"Is it a leap year?","kind":"boundary"}]}]},{"id":"calendar","name":"Calendar","description":"Julian or Gregorian.","findings":[{"id":"calendar-finding","name":"Calendar","description":"Calendar system.","questions":[{"text":"Is the Julian or Gregorian calendar meant?","kind":"boundary"},{"text":"What is the equivalent date in the other calendar?","kind":"measurement"}]}]}]},{"id":"observances","name":"Observances","description":"Holidays.","layers":[{"id":"holiday","name":"Holiday","description":"Public holiday.","findings":[{"id":"holiday-finding","name":"Holiday","description":"Holiday status.","questions":[{"text":"Is December 21 a public holiday or observance here?","kind":"provenance"},{"text":"Which tradition or law sets it?","kind":"provenance"}]}]},{"id":"attribution","name":"Attribution","description":"Traditions.","findings":[{"id":"attribution-finding","name":"Attribution","description":"Attributed observances.","questions":[{"text":"Which countries or communities observe something on this date, according to them?","kind":"provenance"},{"text":"Is the observance attributed rather than assumed?","kind":"boundary"}]}]}]},{"id":"history","name":"History","description":"Past events.","layers":[{"id":"events","name":"Events","description":"On this day.","findings":[{"id":"events-finding","name":"Events","description":"Historical events.","questions":[{"text":"Which notable events happened on December 21, according to reliable sources?","kind":"provenance"},{"text":"Are dates given in the same calendar?","kind":"boundary"}]}]},{"id":"anniversaries","name":"Anniversaries","description":"Recurring.","findings":[{"id":"anniversaries-finding","name":"Anniversaries","description":"Anniversaries.","questions":[{"text":"Which anniversaries fall on this date this year?","kind":"provenance"},{"text":"Which are round numbers?","kind":"measurement"}]}]}]},{"id":"planning","name":"Planning","description":"Scheduling.","layers":[{"id":"countdown","name":"Countdown","description":"Days until.","findings":[{"id":"countdown-finding","name":"Countdown","description":"Countdown.","questions":[{"text":"How many days until the next December 21?","kind":"measurement"},{"text":"From which date?","kind":"definition"}]}]},{"id":"work","name":"Work","description":"Working day.","findings":[{"id":"work-finding","name":"Work","description":"Working day.","questions":[{"text":"Is it a working day for this organisation?","kind":"provenance"},{"text":"Do deadlines move?","kind":"boundary"}]}]}]}]},"agentConduct":{"may":["Give the day number of December 21 and its observances, such as solstice festivals like Yalda and Dongzhi.","Note that the solstice falls on December 21 or 22 depending on the year and time zone."],"mustNot":["Present the solstice as always on December 21.","Present northern winter festivals as universal when it is summer in the south.","List on-this-day events without a source.","Mix Julian and Gregorian dates for events before the calendar change."],"requiresHuman":["Scheduling public messages tied to a religious or cultural solstice festival."]},"ethics":{"considerations":["Solstice festivals carry religious and cultural meaning for many peoples.","Northern seasonal framing overlooks the Southern Hemisphere."],"affectedParties":["Communities that hold solstice festivals","People in the Southern Hemisphere","Readers"]},"owners":{"steward":"Nobody: the public calendar held in common; each observance belongs to the body that set it.","roles":[],"masterSystems":[]},"relations":[{"target":"Q11187254","type":"parent","note":"registry parent class"},{"target":"December","type":"related","note":"month"},{"target":"December 20","type":"related","note":"date"},{"target":"calendar date","type":"related","note":"category"},{"target":"ISO 8601","type":"related","note":"notation"}],"interaction":{"identity":{"applicability":"required","items":["Vercy registry: vr.tr.december-21","Wikidata: Q2603 (https://www.wikidata.org/wiki/Q2603)","ISO 8601: --12-21 recurring date"]},"properties":{"applicability":"not-applicable","items":["day of year: 355 or 356 day - common year, leap year where different","days remaining: 10 days"]},"recognition":{"applicability":"optional","items":["Written 21 December or December 21","ISO format --12-21","Observances vary by country and tradition","A date on calendars."]},"capabilities":{"applicability":"required","items":["compute its weekday in a given year","check local and international observances","find sourced historical events","schedule events"]},"hazards":{"applicability":"required","items":["Assuming observances are universal","Unsourced on-this-day events","Mixing Julian and Gregorian dates"]},"interfaces":{"applicability":"required","items":["ISO 8601","National public holiday laws"]},"context":{"applicability":"required","items":["A calendar date for scheduling, holidays and anniversaries.","the recurring calendar date","specific dated days in given years"]}},"sources":[{"title":"Wikidata item Q2603: December 21","url":"https://www.wikidata.org/wiki/Q2603","note":"identity and sense of the item"},{"title":"Wikipedia: December 21","url":"https://en.wikipedia.org/wiki/December_21","note":"general description of the item"}],"openQuestions":["Should dated days be separate entries?","How should observances be linked?","How should events be sourced?"],"resources":{"spec":"/models/things/publications/thing-q2603/spec.json"},"provenance":{"origin":"thing registry research (pass 2)","builtFrom":["models/things/publications/thing-q2603/spec.json"],"providers":["Claude"],"researchStatus":"unreviewed","generatedAt":"2026-09-13T14:10:43Z","builder":"tools/build_cards.py@1.0.0"},"completeness":{"sections":{"classifiers":"filled","whatItIs":"filled","purpose":"filled","distinguishingFeatures":"filled","structure":"filled","agentConduct":"filled","ethics":"filled","owners":"filled","relations":"filled","interaction.identity":"filled","interaction.properties":"not-applicable","interaction.recognition":"filled","interaction.capabilities":"filled","interaction.hazards":"filled","interaction.interfaces":"filled","interaction.context":"filled","sources":"filled"},"notes":{"_gate":"Published through the thing publication gate 1.0 on 2026-10-06T19:51:58+00:00: completeness 1.00; sense: Wikidata description; 2 live sources; review by codex: pass","interaction.properties":"Plane XCT: no invented physical properties."},"score":1.0}}