almanac

# almanac — Date, Time, and Calendar Reference Quick reference for calendar arithmetic, business days, holidays, and astronomical events. ## Business Days **Business day**: Monday-Friday, excluding holidays. **US Federal Holidays** (2026): - New Year's Day: January 1 - Martin Luther King Jr. Day: Third Monday in January - Presidents' Day: Third Monday in February - Memorial Day: Last Monday in May - Juneteenth: June 19 - Independence Day: July 4 - Labor Day: First Monday in September - Columbus Day: Second Monday in October - Veterans Day: November 11 - Thanksgiving Day: Fourth Thursday in November - Christmas Day: December 25 **Observed holidays**: If a federal holiday falls on Saturday, it's observed on Friday. If on Sunday, observed on Monday. ## Time Zones | Zone | UTC Offset | Major Cities | |------|-----------|--------------| | UTC | +0 | Greenwich | | EST/EDT | -5/-4 | New York, Eastern US | | CST/CDT | -6/-5 | Chicago, Central US | | MST/MDT | -7/-6 | Denver, Mountain US | | PST/PDT | -8/-7 | Los Angeles, Pacific US | | JST | +9 | Tokyo | | CET/CEST | +1/+2 | Berlin, Central Europe | | BST | +1 | London (summer) | | GMT | +0 | London (winter) | ## Astronomical Events (2026) | Event | Date | |-------|------| | Spring Equinox | March 20 | | Summer Solstice | June 21 | | Autumn Equinox | September 22 | | Winter Solstice | December 21 | **Moon phases** (approximate): - New moon: Every 29.5 days - First quarter: ~7 days after new - Full moon: ~14-15 days after new - Last quarter: ~22 days after new ## Date Calculations **Workday calculations**: - Add/subtract business days (skip weekends and holidays) - Check if a date is a business day - Find next/previous business day **Date arithmetic**: - Days between dates - Add/subtract days, weeks, months, years - Week of year (ISO 8601: week starts Monday, week 1 contains first Thursday) ## Seasonal Information | Season (Northern Hemisphere) | Months | |------------------------------|--------| | Spring | March, April, May | | Summer | June, July, August | | Autumn | September, October, November | | Winter | December, January, February | ## Scripts | Script | Use | |--------|-----| | `script/is-business-day.nu "2026-04-15"` | Check if date is a business day | | `script/add-business-days.nu "2026-04-15" 5` | Add 5 business days to date | | `script/days-between.nu "2026-04-01" "2026-04-15"` | Calculate days between dates | | `script/week-of-year.nu "2026-04-15"` | Get ISO week number for date | | `script/moon-phase.nu "2026-04-15"` | Get moon phase for date | Scripts return structured JSON or human-readable output based on flags. ## Common Patterns **Check if today is a business day**: ```bash nu script/is-business-day.nu (date now | format date "%Y-%m-%d") ``` **Calculate project deadline** (10 business days from today): ```bash nu script/add-business-days.nu (date now | format date "%Y-%m-%d") 10 ``` **Check if a deadline falls on a weekend**: ```bash nu script/is-business-day.nu "2026-04-12" # Saturday ``` ## Time Zone Conversion When converting time zones: 1. Always specify source and target zones 2. Account for DST transitions 3. Use UTC as the canonical intermediate format Example: Convert 2026-04-15 14:00 EST to JST - EST → UTC: +5 hours → 2026-04-15 19:00 UTC - UTC → JST: +9 hours → 2026-04-16 04:00 JST ## Leap Years A year is a leap year if: - Divisible by 4, but not by 100, OR - Divisible by 400 2024: leap year 2025: not 2026: not 2028: leap year