Why does New York have seasons, and why is the Sun higher and the day longer in summer?
Explain how the tilt of Earth's axis and its revolution change the angle and duration of insolation through the year, producing the seasons, the solstices and the equinoxes.
A Regents answer on insolation and the seasons: why the 23.5 degree axial tilt and Earth's revolution change the angle and duration of insolation, the solstices and equinoxes, the Sun's path across the sky at New York latitudes, and why summer is warm even though Earth is near aphelion.
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What this topic is asking
The Regents wants you to explain the seasons correctly: they are caused by the tilt of Earth's axis and revolution, not by distance from the Sun. You must connect the tilt to the changing angle of insolation and duration of insolation, and identify the solstices and equinoxes.
What insolation is
Why the seasons happen
Earth's axis is tilted 23.5 degrees from vertical and stays pointing the same way in space (parallelism) as Earth revolves. So during the year, each hemisphere tilts toward, then away from, the Sun:
- When the Northern Hemisphere tilts toward the Sun, it gets a higher Sun angle and longer days, so it is summer there.
- Six months later it tilts away, getting a lower Sun angle and shorter days, so it is winter.
Crucially, the seasons are not caused by changing distance to the Sun. Earth is actually closest to the Sun in early January (perihelion), in the middle of Northern Hemisphere winter, which proves distance is not the cause.
The key dates
| Date | Sun's vertical rays at | Northern Hemisphere |
|---|---|---|
| About June 21 (summer solstice) | Tropic of Cancer (23.5 degrees N) | Highest Sun, longest day, summer begins |
| About December 21 (winter solstice) | Tropic of Capricorn (23.5 degrees S) | Lowest Sun, shortest day, winter begins |
| About March 21 (vernal equinox) | Equator (0 degrees) | Sun rises due east, sets due west, ~12 h day |
| About September 23 (autumnal equinox) | Equator (0 degrees) | Sun rises due east, sets due west, ~12 h day |
The Sun's path across the New York sky
For a mid-latitude New York observer:
- June 21: the Sun follows its highest and longest arc, rising north of east and setting north of west.
- March and September equinoxes: a medium arc, rising due east and setting due west.
- December 21: the lowest and shortest arc, rising south of east and setting south of west.
At every date the Sun reaches its highest point (solar noon) in the southern sky, because New York is north of the Tropics.
Angle of insolation and intensity
Try this
Q1. State the tilt of Earth's axis and the event on about June 21. [2 points]
- Cue. 23.5 degrees; the summer solstice (Sun's vertical rays at the Tropic of Cancer).
Q2. Explain why the equinoxes have about 12 hours of daylight everywhere. [2 points]
- Cue. The Sun's vertical rays are over the Equator and neither hemisphere is tilted toward the Sun, so the day and night are equal.
Exam-style practice questions
Practice questions written in the style of NYSED exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Regents (style)1 marksPart A. The main reason New York State experiences seasons is the (1) changing distance between Earth and the Sun (2) tilt of Earth's axis as Earth revolves around the Sun (3) rotation of Earth on its axis (4) eccentricity of Earth's orbit. Justify your choice.Show worked answer →
A 1-point multiple-choice question. The answer is (2).
The seasons are caused by the 23.5 degree tilt of Earth's axis combined with revolution: as Earth orbits, the Northern Hemisphere tilts toward the Sun in June (summer, high Sun, long days) and away in December (winter, low Sun, short days). Distance (1) and eccentricity (4) actually put Earth closest to the Sun in early January (Northern Hemisphere winter), so they cannot cause the seasons. Rotation (3) causes day and night. The trap is the common belief that summer is when Earth is closest to the Sun.
Regents (style)3 marksPart C. (a) Identify the date on which the Sun's vertical rays strike the Tropic of Cancer (23.5 degrees N). (b) Describe how the duration of insolation in New York on that date compares with the duration on December 21. (c) Explain why the angle of insolation affects the intensity of energy received at the surface.Show worked answer →
A 3-point extended-response question.
(a) 1 point: about June 21 (the summer solstice).
(b) 1 point: the duration of insolation (length of daylight) in New York is longest on about June 21 and shortest on December 21, so the day is much longer in June than in December.
(c) 1 point: a higher angle of insolation concentrates the Sun's energy on a smaller area (more direct rays), so the intensity (energy per unit area) is greater; a low angle spreads the same energy over a larger area, reducing intensity.
Markers reward the June 21 date, the longer-day comparison, and the direct-rays/energy-per-area reasoning for intensity.
Related dot points
- Explain Earth's rotation and revolution, the evidence for each, and how they produce the apparent daily motion of celestial objects at 15 degrees per hour, including the use of Polaris to find latitude.
A Regents answer on Earth's rotation and revolution: the evidence for each, the apparent daily motion of the Sun, Moon and stars at 15 degrees per hour, Foucault's pendulum and the Coriolis effect, and how the altitude of Polaris gives an observer's latitude in the Northern Hemisphere.
- Calculate the eccentricity of an elliptical orbit using the Reference Tables equation (distance between foci divided by length of the major axis) and relate eccentricity to orbital shape and orbital velocity.
A Regents answer on orbital eccentricity: ellipses and foci, the Reference Tables formula (distance between foci over the length of the major axis), worked calculations rounded to the nearest thousandth, and how eccentricity and the Sun's off-center position affect orbital velocity and apparent solar diameter.
- Describe the phases of the Moon, solar and lunar eclipses, and the tides as consequences of the motions and gravitational interactions of the Earth, Moon and Sun.
A Regents answer on the Earth-Moon-Sun system: the cause of the Moon's phases, why solar and lunar eclipses are rare, the roughly two-week phase cycle, and how the Moon's and Sun's gravity produce spring and neap tides.
- Describe the layered structure and composition of the atmosphere and explain how energy is transferred by radiation, conduction and convection, including how surfaces absorb and reflect insolation.
A Regents answer on the atmosphere and energy transfer: the layered structure (troposphere to thermosphere) and temperature profile on the Reference Tables, the composition (nitrogen, oxygen, trace gases), the three modes of heat transfer (radiation, conduction, convection), and how surface color and texture affect the absorption and reflection of insolation, with worked exam questions.
- Explain the factors that control climate (latitude, elevation, proximity to water, ocean currents, mountain barriers and prevailing winds) and distinguish climate from weather.
A Regents answer on climate controls: the difference between weather and climate, how latitude, elevation, proximity to large bodies of water, ocean currents, mountain barriers (orographic effect and rain shadows) and prevailing winds set a region's temperature and precipitation, and why coastal and inland climates differ, with worked exam questions.
Sources & how we know this
- Reference Tables for Physical Setting/Earth Science (2011 edition) — New York State Education Department (2011)
- Regents Examination in Physical Setting/Earth Science — New York State Education Department (2026)