Spring Equinox: Why Day and Night Come Out Nearly Equal in March

On one day in March, the length of day and night seems to even out. The word equinox says as much, since it comes from Latin words for equal and night. The real story is a little more careful. Day and night come out very close to equal, and a few extra minutes of light show up almost everywhere. This guide explains why.

It also shows where the March equinox sits in the 2026 calendar, what it does to the noon Sun and how to find it in the Orbit Dial. The date comes from the U.S. Naval Observatory table. The science comes from NASA, NOAA and the Naval Observatory.

What the March equinox is

NASA's Night Sky Network says the equinox marks the exact moment when the center of the Sun crosses the plane of our planet's equator. That is a moment, not a whole day. It happens twice a year, in March and September.

The cause is the tilt of Earth's axis. The National Weather Service explains that there are only two times of the year when the axis is tilted neither toward nor away from the Sun. NASA's Helio and You page puts it as a balance: spring and autumn arrive when the hemispheres are roughly equal in their tilt toward the Sun.

Two things follow. At the equator, the Sun is directly overhead at noon on both equinoxes, says the National Weather Service. And NASA notes that these are the only times of the year when Earth's North and South Poles are lit by sunlight at the same time.

The drawing above shows the March equinox for a place at 40 degrees north latitude.

The 2026 date and time

The Naval Observatory's table for 2026 lists the March equinox on March 20 at 14:46 Universal Time (UT). Set to Eastern Time, the same table gives 10:46 DT, which is 10:46 a.m. Eastern Daylight Time. When this guide was published on November 10, 2026, that moment had already passed.

NASA's Night Sky Network gives the same moment as 14:46 UTC. It pairs that time with 7:46 AM EDT, which does not match the Eastern Time column of the Naval Observatory table. Trust the table: 10:46 a.m. Eastern.

The date is not fixed from year to year. The National Centers for Environmental Information (NCEI, part of NOAA) lists March 21 as the approximate date of the spring equinox. It says the exact dates vary because an extra day is needed every fourth year.

Day and night: nearly equal, not exactly

NOAA's NESDIS page on the changing seasons says the equinoxes mark when the Sun is exactly above the equator, and that this makes day and night equal length. That is a good first picture. The Naval Observatory is more exact: day and night are not exactly of equal length at the time of the March and September equinoxes.

Two reasons explain the gap. Sunrise is defined as the instant when the leading edge of the Sun's disk becomes visible, so the Sun's size adds light. And the atmosphere bends sunlight, which NASA says adds several minutes of light to every day. The Naval Observatory puts numbers on the result. On the equinox, the day is about 7 minutes longer than the night at latitudes up to about 25 degrees, and 10 minutes or more at latitude 50 degrees.

The National Weather Service gives a table of day lengths for the equinox and the several days before and after it.

The two sources round their numbers differently, but they agree on the pattern. The extra minutes grow as you move toward the poles.

How high the Sun stands at noon

At an equinox the Sun sits on the celestial equator, according to the University of Nebraska-Lincoln's astronomy pages. That line meets your meridian at an altitude of 90 degrees minus your latitude. NASA's Radio JOVE training module gives the same rule: the altitude of the noon Sun on the equinoxes equals 90 degrees minus your latitude. Its example is a person at 40 degrees north, where the noon Sun stands 50 degrees high.

This is the simplest case of the noon-height rules. On the solstices you add or subtract about 23.5 degrees. On an equinox you add nothing, because the Sun is on the celestial equator. Our guide to the Sun's height at noon works through more places.

Common mistakes

• Thinking day and night are exactly equal. The Naval Observatory says they are not. Near the equator the day runs several minutes longer than the night, and the gap grows toward higher latitudes.
• Treating the equinox as a whole day. NASA calls it an exact moment, when the center of the Sun crosses the plane of the equator. The clock time depends on your time zone.
• Calling it the first day of spring everywhere. NASA says Southern Hemisphere observers meet their autumnal, or fall, equinox in March.
• Mixing astronomical and meteorological spring. NCEI says Northern Hemisphere meteorological spring is March, April and May, based on the temperature cycle. Astronomical spring starts at the equinox, around March 20 or 21.
• Expecting equal day and night on the equinox date. NASA says the date for that split depends on your latitude and may fall a few days before or after the equinox.

Try it in the instrument

Open the Orbit Dial and set the sky to the March equinox, the first day of spring in the Northern Hemisphere. The dial takes a date in 2026 and a latitude, and it shows the height of the noon Sun and the length of the day. The target date is March 20, the date in the Naval Observatory's table. The game accepts a window of dates, not one exact minute, and the window gets narrower from Bronze to Gold.

Use the rule from this guide to check yourself. Slide the latitude on the target date. The noon Sun height should follow 90 degrees minus your latitude, and it should reach 90 degrees at the equator. The day length should stay close to 12 hours at every latitude. A simplified model like the dial leaves out the few extra minutes that the Sun's size and the atmosphere add in real life.

This date is also special because the tilt, 23.4 degrees in the Naval Observatory's seasons page, adds nothing to the noon height. The Sun sits on the celestial equator, so only your latitude matters.

Questions people ask

What does "equinox" mean?

NASA's Night Sky Network says the word comes from Latin and translates to equal night. The name points to the nearly equal hours of day and night around the date.

When are day and night truly equal?

Not on the equinox itself. The Naval Observatory says that at 40 degrees north, equal day and night fall about March 17 and September 26. At 5 degrees north they fall about February 25 and October 15. The dates depend on latitude.

Is it autumn in the Southern Hemisphere at the March equinox?

Yes. NASA says Southern Hemisphere observers notice shorter days and longer, cooler nights, signaled by their autumnal equinox. In the Northern Hemisphere the same moment is the vernal, or spring, equinox.

Do both poles get sunlight at the March equinox?

Yes. NASA says the equinoxes are the only times of the year when Earth's North and South Poles are lit by sunlight at the same time.

Sources

• Earth's Seasons - Equinoxes, Solstices, Perihelion, and Aphelion, U.S. Naval Observatory, Astronomical Applications Department. https://aa.usno.navy.mil/calculated/seasons?year=2026&tz=0&tz_sign=1&tz_label=true&dst=false&submit=Get+Data. Opened November 10, 2026.
• Length of Day and Night at the Equinoxes, U.S. Naval Observatory, Astronomical Applications Department. https://aa.usno.navy.mil/faq/equinoxes. Opened November 10, 2026.
• Embracing the Equinox, NASA Science, Night Sky Network. https://science.nasa.gov/solar-system/skywatching/night-sky-network/embracing-the-equinox/. Opened November 10, 2026.
• The Seasons, the Equinox, and the Solstices, National Weather Service, Cleveland, OH (NOAA). https://www.weather.gov/cle/seasons. Opened November 10, 2026.
• Citizen Science Training Modules, Training Module 0.0: Introduction to the Sun, NASA Radio JOVE Project (radiojove.gsfc.nasa.gov). https://radiojove.gsfc.nasa.gov/citizen_science/training/TM0.0_The_Sun_Introduction.pdf. Opened November 9, 2026.
• Paths of the Sun - Motions of the Sun - NAAP, University of Nebraska-Lincoln, Astronomy Education (NAAP). https://astro.unl.edu/naap/motion3/sunpaths.html. Opened November 10, 2026.
• Helio and You: Seasons on Earth, Mars, and Beyond, NASA Science. https://science.nasa.gov/helio-and-you-seasons-on-earth-mars-and-beyond/. Opened November 10, 2026.
• Meteorological Versus Astronomical Seasons, NOAA National Centers for Environmental Information. https://www.ncei.noaa.gov/news/meteorological-versus-astronomical-seasons. Opened November 10, 2026.
• Changing of the Seasons, NOAA NESDIS. https://www.nesdis.noaa.gov/our-environment/solar-phenomena/changing-of-the-seasons. Opened November 10, 2026.
• The Seasons and the Earth's Orbit, U.S. Naval Observatory, Astronomical Applications Department. https://aa.usno.navy.mil/faq/seasons_orbit. Opened November 10, 2026.

We opened each source ourselves on the date shown. The drawings are our own and were checked against the numbers in these sources.

Read next

• Autumn EquinoxThe September equinox is one moment, and it lands on different calendar days in different time zones.
• The Sun’s Height at NoonThe Sun's height at noon follows one rule: 90 degrees minus your latitude at the equinox, then up or down by the tilt at the solstices.