ryanmaclean 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:
nu script/is-business-day.nu (date now | format date "%Y-%m-%d")
Calculate project deadline (10 business days from today):
nu script/add-business-days.nu (date now | format date "%Y-%m-%d") 10
Check if a deadline falls on a weekend:
nu script/is-business-day.nu "2026-04-12" # Saturday
Time Zone Conversion
When converting time zones:
- Always specify source and target zones
- Account for DST transitions
- 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