September Equinox / First Day of Astronomical Autumn
U.S. Naval Observatory season data define the equinox as the astronomical season boundary and provide target-year instants. The local civil date can differ by time zone and hemisphere context must be preserved.
Date and recurrence
September equinox; 23 September 2026 at 00:05 UTC (civil date can differ by time zone)
The date is source-dependent or variable. A target-year source is required before assigning it to a calendar.
Scope and status
The verified scope stored for this record is Astronomical / Northern Hemisphere autumn begins at the September equinox; Southern Hemisphere season is spring. The site preserves that boundary and does not infer broader government, global or public-holiday status from the observance name alone.
Also known as
First Day of Autumn
Topic and context
What this page does not assume
- Keep the source-defined country, community, organizer or institutional scope; do not silently broaden it.
- Do not treat the title alone as proof of government recognition or public-holiday status.
- Do not add a creator, founding story or origin claim unless the supporting evidence establishes it.
- Refresh the target year before publishing a new date when the record is not safely portable.
Sources
- U.S. Naval Observatory — Earth’s SeasonsOfficial Astronomical Authority
- U.S. Naval Observatory — 2026 seasons calculationOfficial Astronomical Authority
Frequently asked questions
When is September Equinox / First Day of Astronomical Autumn?
September equinox; 23 September 2026 at 00:05 UTC (civil date can differ by time zone) The stored recurrence guidance is: Resolve the September equinox instant for the target year from an astronomical ephemeris, then convert to the reader’s local time zone; northern-hemisphere autumn / southern-hemisphere spring.
Does September Equinox / First Day of Astronomical Autumn fall on the same date every year?
It is not safely predictable from a fixed rule; the target year needs a current source.
Is September Equinox / First Day of Astronomical Autumn an official public holiday?
The authority record verifies it within this scope: Astronomical / Northern Hemisphere autumn begins at the September equinox; Southern Hemisphere season is spring. That recognition does not by itself make it a statutory public holiday; the site only makes public-holiday claims when the supporting authority record explicitly does so.
Who established or recognizes September Equinox / First Day of Astronomical Autumn?
The stored designation basis is: U.S. Naval Observatory season data define the equinox as the astronomical season boundary and provide target-year instants. The local civil date can differ by time zone and hemisphere context must be preserved.. Supporting provenance includes U.S. Naval Observatory — Earth’s Seasons. The site does not infer a separate creator or founder unless reviewed evidence establishes one.
Is September Equinox / First Day of Astronomical Autumn international or country-specific?
No single country is assigned to this record in the authority dataset. The source-defined scope is: Astronomical / Northern Hemisphere autumn begins at the September equinox; Southern Hemisphere season is spring. Use that scope rather than assuming worldwide or country-specific status.
How is this page verified?
The factual layer is source-backed and keeps its date rule, scope, provenance and editorial guardrails attached to the authority record. This record was checked on 2026-09-09.