Why does Earth have seasons, and how do the tilt and revolution control the angle of sunlight?
Explain that Earth's seasons are caused by the tilt of its axis (about 23.5 degrees) as it revolves around the Sun, which changes the directness of sunlight and the length of daylight (Virginia 2018 Earth Science SOL ES.11).
A SOL-level answer on the seasons for the Virginia Earth Science EOC: why the tilt of Earth's axis, not its distance from the Sun, causes the seasons, how the directness of sunlight (insolation) and daylight length change, the solstices and equinoxes, and why the hemispheres have opposite seasons, with worked exam questions.
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What this topic is asking
Virginia Earth Science SOL standard ES.11 asks you to explain the seasons: that they are caused by the tilt of Earth's axis as Earth revolves around the Sun, not by distance. The EOC tests this with the classic misconception item (distance versus tilt), with diagrams of Earth at the solstices and equinoxes, and with reasoning about the directness of sunlight and day length. It connects to the energy-transfer ideas in the atmosphere module (more direct sunlight delivers more energy).
What causes the seasons
This distance-versus-tilt point is one of the most commonly tested misconceptions on the EOC.
Directness of sunlight and day length
When a hemisphere is tilted toward the Sun, two things make it warmer:
- More direct sunlight. The Sun is higher in the sky, so its rays strike the surface closer to straight on, concentrating the energy over a smaller area (more insolation per square meter).
- Longer days. The hemisphere tilted toward the Sun has more hours of daylight, so it receives energy for longer each day.
When tilted away, the sunlight is slanted (spread over a larger area, weaker) and the days are shorter, so it is cooler. The combination of angle and day length, not distance, drives the temperature difference between summer and winter.
Solstices and equinoxes
Opposite seasons in the two hemispheres
Because the tilt points one hemisphere toward the Sun while the other points away, the Northern and Southern Hemispheres always have opposite seasons. When it is summer in Virginia (Northern Hemisphere), it is winter in Australia (Southern Hemisphere). At the equinoxes, both hemispheres receive about equal sunlight and have similar mild conditions.
Try this
Q1. State the cause of Earth's seasons. [1]
- Cue. The tilt of Earth's axis (about 23.5 degrees) as Earth revolves around the Sun (not distance from the Sun).
Q2. Explain why a hemisphere tilted toward the Sun is warmer. [2]
- Cue. Sunlight strikes it more directly (higher Sun angle, energy concentrated) and the days are longer, so it receives more energy and is warmer.
Exam-style practice questions
Practice questions written in the style of VDOE exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
VA Earth Science SOL 2023 (style)1 marksWhat is the main cause of Earth's seasons? (A) Earth's changing distance from the Sun. (B) the tilt of Earth's axis as it revolves around the Sun. (C) the phases of the Moon. (D) changes in the Sun's energy output.Show worked answer →
A 1-point multiple-choice item on the cause of seasons.
The correct answer is B. Seasons are caused by the tilt of Earth's axis (about 23.5 degrees) combined with its revolution around the Sun: the tilt changes how directly sunlight strikes each hemisphere and how long the days are. Earth's distance from the Sun (A) varies only slightly and is not the cause (Earth is actually closest to the Sun during Northern Hemisphere winter). The Moon (C) and small changes in solar output (D) do not cause the seasons.
The test rewards the key idea: the axial tilt, not distance, causes the seasons.
VA Earth Science SOL 2024 (style)2 marksIt is summer in the Northern Hemisphere. (a) Explain why the Northern Hemisphere is warm at this time in terms of the angle of sunlight and day length. (b) State what season the Southern Hemisphere is experiencing and why.Show worked answer →
A 2-point item on the seasons.
(a) 1 point: in Northern Hemisphere summer, the North Pole is tilted toward the Sun, so sunlight strikes the Northern Hemisphere more directly (higher Sun angle, energy concentrated) and the days are longer, giving more heating and warmer temperatures.
(b) 1 point: the Southern Hemisphere is experiencing winter, because it is tilted away from the Sun, so it receives more slanted (less direct) sunlight and shorter days; the hemispheres always have opposite seasons.
Markers reward linking the tilt-toward-Sun to direct sunlight and long days in (a) and the opposite (tilted away, winter) for the Southern Hemisphere in (b).
Related dot points
- Explain how Earth's rotation causes day and night, how the Moon's orbit causes its phases, and how the alignment of the Sun, Earth and Moon causes solar and lunar eclipses (Virginia 2018 Earth Science SOL ES.11).
A SOL-level answer on the Earth-Moon-Sun system for the Virginia Earth Science EOC: how rotation causes day and night, the cause and sequence of Moon phases, why eclipses happen only at certain alignments, the difference between a solar and a lunar eclipse, and why eclipses are not monthly, with worked exam questions.
- Describe the structure of the solar system (the Sun, terrestrial and gas-giant planets, and small bodies), explain that orbits are elliptical (Kepler), and explain how gravity and inertia keep planets in orbit (Virginia 2018 Earth Science SOL ES.2 and ES.11).
A SOL-level answer on the solar system for the Virginia Earth Science EOC: the Sun and the inner terrestrial versus outer gas-giant planets, asteroids, comets and other small bodies, the nebular hypothesis, Kepler's elliptical orbits, and how gravity and inertia combine to keep planets orbiting, with worked exam questions.
- Describe the composition and layers of the atmosphere and explain how energy is transferred by radiation, conduction and convection, including the greenhouse effect (Virginia 2018 Earth Science SOL ES.8).
A SOL-level answer on the atmosphere for the Virginia Earth Science EOC: the composition (mostly nitrogen and oxygen), the layers (troposphere, stratosphere with the ozone layer, mesosphere, thermosphere), and the three ways energy moves (radiation, conduction, convection) plus the greenhouse effect, with worked exam questions.
- Distinguish weather from climate, explain the factors that control climate (latitude, elevation, water, ocean currents, prevailing winds), and describe the evidence for climate change and the enhanced greenhouse effect (Virginia 2018 Earth Science SOL ES.9).
A SOL-level answer on climate for the Virginia Earth Science EOC: the difference between weather and climate, the factors that control climate (latitude, elevation, proximity to water, ocean currents, prevailing winds), the evidence for climate change, the enhanced greenhouse effect, and its impacts on Virginia, with worked exam questions.
- Explain that stars produce energy by nuclear fusion, describe the Hertzsprung-Russell diagram and the relationship between a star's color, temperature and luminosity, and outline the life cycle of a star (Virginia 2018 Earth Science SOL ES.12).
A SOL-level answer on stars for the Virginia Earth Science EOC: how stars produce energy by nuclear fusion, what the Hertzsprung-Russell diagram shows about color, temperature and luminosity, the main sequence, and how a star's life cycle depends on its mass, with worked exam questions.
Sources & how we know this
- 2018 Science Standards of Learning (Earth Science) — Virginia Department of Education (2018)
- SOL Practice Items (All Subjects) — Virginia Department of Education (2024)