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Seasons and Day Length from Solstices and Equinoxes

Good to see you again. Last lesson separated major weather hazards by their defining clues: warm ocean water for hurricanes, a funnel-shaped column for tornadoes, snow and strong wind for blizzards, and a long precipitation shortage for drought.

This is the final rapid review for your test. You will learn to identify solstices, equinoxes, seasons, and longest or shortest days by first noticing the hemisphere. For questions about Illinois or the United States, use the Northern Hemisphere column.

The big idea: Earth’s tilt causes seasons

Earth is tilted about on its axis. As Earth travels around the Sun, that tilt means one hemisphere receives more direct sunlight and longer daylight while the other receives less direct sunlight and shorter daylight.

Changing of the Seasons | NESDIS | National Environmental Satellite, Data, and Information Service

Read NOAA’s “Changing of the Seasons” for the central cause-and-effect idea: Earth’s tilt determines which hemisphere has summer or winter, and solstices and equinoxes mark important points in the yearly cycle.

In the opening explanation, read the tilt explanation. Focus on the comparison: a hemisphere tilted toward the Sun has summer, while the hemisphere tilted away has winter. Then read the next paragraph beginning solstices and equinoxes. Memorize that a summer solstice is the longest day, a winter solstice is the shortest day, and an equinox has equal day and night.

Two rules solve most questions:

  1. Tilted toward the Sun means summer and more daylight.
  2. Tilted away from the Sun means winter and less daylight.

The hemispheres experience opposite seasons. When it is summer in Illinois, it is winter in Australia.

Earth is shown at the March and September equinoxes and the June and December solstices. Its \(23.5^\circ\) tilted axis keeps the same direction in space, so the Northern and Southern Hemispheres receive different amounts of daylight during the year.

Solstice: the longest or shortest day

A solstice occurs twice each year: once in June and once in December. A solstice is about the most extreme day length of the year.

For the Northern Hemisphere:

  • The summer solstice occurs around June 20 or 21. It begins summer and is the LONGEST DAY OF THE YEAR.
  • The winter solstice occurs around December 21 or 22. It begins winter and is the SHORTEST DAY OF THE YEAR.

At the June solstice, the Northern Hemisphere is tilted toward the Sun. It has longer daylight hours. At the December solstice, it is tilted away from the Sun, so daylight is shortest.

The Southern Hemisphere has the exact opposite pattern:

DateNorthern HemisphereSouthern Hemisphere
Around June 20–21SUMMER SOLSTICE; longest dayWINTER SOLSTICE; shortest day
Around December 21–22WINTER SOLSTICE; shortest daySUMMER SOLSTICE; longest day

A useful memory cue is:

June: Northern summer. December: Northern winter.
Everything is reversed south of the Equator.

Equinox: equal day and night

An equinox occurs twice each year, around March and September. On an equinox, the Sun is directly over the Equator, and day and night are about equal in length.

The word equinox can help you remember it: equi means equal, and nox means night.

DateNorthern HemisphereSouthern HemisphereDay length
Around March 20–21VERNAL EQUINOX; spring beginsAUTUMNAL EQUINOX; autumn beginsAbout equal day and night
Around September 22–23AUTUMNAL EQUINOX; autumn beginsVERNAL EQUINOX; spring beginsAbout equal day and night

For your test, the key answer is:

The equinox marks the start of SPRING or AUTUMN.

Do not choose summer or winter for an equinox. Those seasons begin at the solstices.

How to answer any season question

Use this quick method.

Step 1: Find the date or event

  • March means an equinox.
  • June means a solstice.
  • September means an equinox.
  • December means a solstice.

Step 2: Find the hemisphere

  • Northern Hemisphere includes the United States.
  • Southern Hemisphere includes Australia.

Step 3: Match it to the season and day length

For example:

  • “It is June 21 in Illinois.”
    Illinois is in the Northern Hemisphere. The answer is SUMMER SOLSTICE and LONGEST DAY.

  • “It is June 21 in Australia.”
    Australia is in the Southern Hemisphere. The answer is WINTER SOLSTICE and SHORTEST DAY.

  • “It is September 22 in the United States.”
    The answer is AUTUMNAL EQUINOX, the beginning of AUTUMN, with nearly equal day and night.

One important correction to the original study list: “In what hemisphere is the winter solstice the shortest day of the year?” does not have only one hemisphere as an answer. A hemisphere’s own winter solstice is always its shortest day:

  • Northern Hemisphere: December winter solstice is shortest.
  • Southern Hemisphere: June winter solstice is shortest.

If the question gives December and asks which hemisphere has the shortest day, choose NORTHERN HEMISPHERE. If it gives June, choose SOUTHERN HEMISPHERE.

Rapid multiple-choice review

Answer in your head, then check the answer directly below.

1. What causes Earth’s seasons?
A. Earth is much closer to the Sun in summer
B. Earth’s axial tilt
C. The Moon blocks sunlight
D. Earth stops rotating

B. EARTH’S AXIAL TILT

2. In the Northern Hemisphere, which event is the longest day of the year?
A. March equinox
B. September equinox
C. Summer solstice
D. Winter solstice

C. SUMMER SOLSTICE

3. In the United States, the winter solstice occurs around which date?
A. March 20–21
B. June 20–21
C. September 22–23
D. December 21–22

D. DECEMBER 21–22

4. On an equinox, day and night are approximately what?
A. Equal in length
B. The longest of the year
C. The shortest of the year
D. Six hours long everywhere

A. EQUAL IN LENGTH

5. The March equinox begins which season in the Northern Hemisphere?
A. Summer
B. Autumn
C. Spring
D. Winter

C. SPRING

6. During the June solstice, Australia is in which season?
A. Summer
B. Winter
C. Spring
D. Autumn

B. WINTER

7. During the December solstice, the Southern Hemisphere has its what?
A. Longest day of the year
B. Shortest day of the year
C. Vernal equinox
D. Autumnal equinox

A. LONGEST DAY OF THE YEAR

8. Which event begins autumn in the Northern Hemisphere?
A. March equinox
B. June solstice
C. September equinox
D. December solstice

C. SEPTEMBER EQUINOX

Last-minute flashcards

  • Earth’s tilt — 23.5 DEGREES
  • Cause of seasons — EARTH’S TILT AS IT ORBITS THE SUN
  • Summer solstice — LONGEST DAY
  • Winter solstice — SHORTEST DAY
  • Equinox — EQUAL DAY AND NIGHT
  • March equinox in Northern Hemisphere — SPRING BEGINS
  • September equinox in Northern Hemisphere — AUTUMN BEGINS
  • June solstice in Northern Hemisphere — SUMMER; LONGEST DAY
  • December solstice in Northern Hemisphere — WINTER; SHORTEST DAY
  • June solstice in Southern Hemisphere — WINTER; SHORTEST DAY
  • December solstice in Southern Hemisphere — SUMMER; LONGEST DAY
  • United States’ hemisphere for season questions — NORTHERN HEMISPHERE
  • Australia’s hemisphere for season questions — SOUTHERN HEMISPHERE

Key takeaways

Start every season question by identifying the hemisphere. The two hemispheres have opposite seasons.

  • A SUMMER SOLSTICE is a hemisphere’s LONGEST DAY.
  • A WINTER SOLSTICE is a hemisphere’s SHORTEST DAY.
  • An EQUINOX has approximately EQUAL DAY AND NIGHT.
  • In the Northern Hemisphere, June means summer and December means winter.
  • In the Southern Hemisphere, June means winter and December means summer.

For the fastest final review, memorize the four Northern Hemisphere dates: March = spring equinox; June = summer solstice; September = autumn equinox; December = winter solstice.

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