Seasons Calculator

Earth-Orbit Season Ring

Season Quick Facts

The four astronomical turning points and what they begin in each hemisphere.

Equinox & Solstice Dates by Year

Dates are UTC and drift ±1 day with the leap-year cycle. For meteorological seasons instead, see Day of Year.

How the Boundaries Are Defined

Astronomical Season Reference

Lengths per the US Naval Observatory; unequal because Earth's orbit is elliptical (Kepler's second law).

No saved snapshots yet. Tap "Save to History" to remember up to six season readings.

How to Read the Orbit Ring

1. Find the tilted-Earth marker on the orbit ring — its dashed axis shows the 23.4° tilt and its position marks where today falls on Earth's journey around the Sun.
2. Read the coloured arc the marker sits on: green for spring, amber for summer, orange for autumn, sky-blue for winter (Northern-Hemisphere order from the March equinox).
3. Set your hemisphere with the toggle — Southern flips every label, so the June solstice that begins Northern summer begins Southern winter.
4. Watch the live countdown tick down the days, hours, minutes, and seconds to the next equinox or solstice.
5. Save the snapshot to log the season and countdown, or check the year-by-year table for any future equinox and solstice date.

The Astronomy of the Seasons

In 2026, a landscape gardener planning a planting calendar needs to know not the meteorological season but the astronomical one — the exact moment the Sun crosses the celestial equator or reaches its highest declination. The recurring question — which season are we actually in, and how many days until the next equinox or solstice — is what this tilted-Earth orbit ring answers. The seasons are not caused by Earth's distance from the Sun; they are caused by the planet's 23.4° axial tilt, which leans the Northern and Southern Hemispheres alternately toward and away from sunlight as Earth orbits.

Astronomical seasons are defined by four moments on Earth's orbit. The March equinox (around 20 March) and September equinox (around 22 September) are the two instants when the Sun is directly above the equator and day and night are nearly equal worldwide — 'equinox' is Latin for 'equal night'. The June solstice (around 21 June) and December solstice (around 21 December) are the instants when the Sun reaches its northernmost or southernmost point in the sky; 'solstice' comes from sol (Sun) and sistere (to stand still), because the Sun's daily path appears to pause before reversing.

The International Astronomical Union (IAU) and national almanac offices fix these boundaries by the Sun's apparent ecliptic longitude: 0° at the March equinox, 90° at the June solstice, 180° at the September equinox, and 270° at the December solstice. This is why the astronomical seasons start on slightly different dates each year and can drift by a day or two — the tropical year is about 365.2422 days, not a whole number, so the leap-year system nudges the instants around. Meteorologists, by contrast, use fixed three-month blocks (e.g. Northern summer = June, July, August) for cleaner record-keeping.

The hemispheres are mirror images. When the Northern Hemisphere tilts toward the Sun at the June solstice, it gets its longest day and the start of Northern summer — while the Southern Hemisphere leans away into its shortest day and the start of Southern winter. That is the whole reason the hemisphere toggle on this tool flips every label: the June solstice begins summer in New York and winter in Sydney on the very same instant. A correct seasons calculator must therefore always ask which hemisphere you are in.

The axial tilt itself is remarkably stable but not perfectly fixed. Earth's obliquity oscillates between about 22.1° and 24.5° over a 41,000-year cycle, one of the Milankovitch cycles that pace the ice ages, and the current value of roughly 23.44° is slowly decreasing. Over the same vast timescales the equinoxes drift around the calendar through the precession of the equinoxes — a 25,772-year wobble of Earth's axis first explained by Hipparchus around 130 BC and given its physical cause by Isaac Newton's gravitation in 1687.

The practical reason this page exists is that 'when does summer start' has two completely different answers — and most calendars only show one. A teacher building a term plan, a farmer timing a sowing, an astronomer logging an observation, or anyone simply curious whether the days are about to get longer or shorter all need the astronomical boundary, plus a live countdown to the next turning point. The orbit ring plots the four season arcs, marks today's position, and counts down to the next equinox or solstice in days, hours, and minutes.

Humans have tracked these four turning points for millennia. Neolithic monuments such as Stonehenge in England and Newgrange in Ireland are aligned to the solstice sunrises, and cultures from the Maya to the Persians built calendars around the equinoxes — Nowruz, the Persian New Year, still begins at the March equinox. The orbit ring in this tool is the same ancient idea rendered in software: a single picture of where Earth sits on its journey around the Sun, and how long until the light turns.