Key answer and definition
The first day of spring in 2018 was Saturday, March 20. This date marks the March equinox in the astronomical calendar for the Northern Hemisphere. In this evergreen explainer, we define astronomical seasons, distinguish them from meteorological seasons, and provide precise timing, context, and reference details that remain useful year after year.
Astronomical vs meteorological seasons
Astronomical seasons are tied to Earth’s tilt and orbit, with solstices and equinoxes as season boundaries. Meteorological seasons use fixed date ranges by month for climate and statistical convenience. Because leap years and orbital mechanics shift the equinox moment slightly each year, the calendar date of astronomical spring varies between March 19 and March 21.
Equinox basics
An equinox occurs when the Sun crosses the celestial equator, making day and night nearly equal in length. Around March 20 (northward equinox) and September 22 or 23 (southward equinox), this geometry produces roughly 12 hours of daylight globally. The term equinox derives from Latin aequus (equal) and nox (night), but daytime is often a few minutes longer due to atmospheric refraction and the Sun’s angular size.
Exact timing and UTC details
In 2018, the March equinox occurred on March 20 at 16:15 Coordinated Universal Time (UTC). Convert to local time by applying your time zone: for example, UTC−5 yields 11:15 a.m. EST on March 20. Because time zones differ, the local calendar day can be March 19, 20, or 21 depending on where you are. Below is a simplified table showing how the same astronomical event maps to different regional clocks and calendar dates.
| Attribute | Verified Detail | Source Type |
|---|---|---|
| Season | Spring (Northern Hemisphere) | Astronomical definition |
| Event | March equinox (northward) | Astronomical calculation |
| UTC datetime | March 20, 2018 at 16:15 UTC | Official astronomical data |
| Local date range | March 19–March 21 depending on time zone | Time zone conversion |
| Daylight and night | Approximately 12 hours each | Equinox geometry |
Practical calendar context
Spring 2018 began on March 20 and ended on June 20, the June solstice. For planning and record-keeping, many organizations use meteorological spring (March 1 to May 31), which offers fixed periods for comparison. Below is a concise comparison of the two conventions.
| Definition | Start date | End date |
|---|---|---|
| Astronomical spring | March 20 (equinox) | June 20 (solstice) |
| Meteorological spring | March 1 | May 31 |
Notable details and common questions
- Leap years nudge the equinox earlier slightly in universal time, which can shift the local calendar date by a day.
- Because atmospheric refraction and the Sun’s disk size lengthen the day, the equinox is not exactly 12 hours of daylight; it is slightly more.
- The opposite event in 2018 was the September equinox on September 22 at 22:54 UTC, marking astronomical autumn in the Northern Hemisphere.
- Cultural and seasonal celebrations often align with astronomical dates, but fiscal and climate reporting may follow meteorological months.
Why the date varies between March 19 and March 21
The calendar date shifts because a solar year is about 365.2422 days and our civil calendar uses whole days and leap-year rules. Over long time spans, the equinox can range from March 19 to March 21; in the 21st century, it rarely falls outside that band. For any given year, precise instant can be looked up from astronomical almanacs or official observatories.
Quick reference checklist
- Season label: spring (Northern Hemisphere)
- Event: northward equinox
- UTC moment: March 20, 2018 at 16:15 UTC
- Local date by zone: March 19 (early zones), March 20 (most zones), March 21 (late zones)
- Daylight: near equal, slightly longer than 12 hours due to refraction
Related concepts
Understanding equinoxes helps clarify many seasonal references. Related terms include solstice, equatorial celestial coordinates, length of day, and daylight saving time. For regional planning, confirm whether a context uses astronomical or meteorological definitions.
Bottom line
In summary, the first day of spring in 2018 was March 20 in the astronomical sense, occurring at 16:15 UTC. Depending on your time zone, the local calendar day could have been March 19, 20, or 21. This evergreen explanation covers the definition, timing, conventions, and nuances so you can confidently interpret the date of spring for any year.