“Across mountains, lakes, and frozen fields, the sun reminds Canada to breathe again.” – MJ Martin
Introduction
Understanding why Earth experiences seasons requires stepping back and looking at the geometry of the Earth–Sun system. Contrary to a common misconception, the changing seasons are not caused by variations in Earth’s distance from the Sun. Instead, they arise from the tilt of Earth’s rotational axis relative to its orbital plane and the way this tilted globe moves through space over the course of a year. Earth–Sun geometry governs how sunlight is distributed across the planet, determining day length, solar angle, and ultimately climate patterns that define spring, summer, autumn, and winter.
The Tilted Earth: The Fundamental Cause of Seasons
Earth rotates on an axis that is tilted approximately 23.5 degrees relative to the plane of its orbit around the Sun. This axial tilt is fixed in direction as Earth travels around its orbit, meaning that at different points in the year, one hemisphere is angled toward the Sun while the other is angled away. When a hemisphere is tilted toward the Sun, it receives more direct sunlight and longer daylight hours, producing warmer temperatures. When it is tilted away, sunlight strikes at a lower angle and days are shorter, leading to cooler conditions. This tilt, not distance, is the primary driver of seasonal change.
Solstices: Extremes of Light and Darkness
The solstices mark the points in the year when Earth’s tilt is most strongly oriented toward or away from the Sun. Around 21 June, the June Solstice occurs. At this time, the Northern Hemisphere is tilted toward the Sun, receiving the most direct sunlight of the year and experiencing its longest day. This marks the beginning of astronomical summer in the north and winter in the Southern Hemisphere, where days are shortest and sunlight is weakest.
Conversely, around 21 December, the December Solstice occurs. The Southern Hemisphere is then tilted toward the Sun, bringing summer conditions south of the equator, while the Northern Hemisphere is tilted away and enters winter. The solstices represent the extremes of seasonal contrast, defining the longest and shortest days of the year.
Equinoxes: Balance Between Day and Night
Midway between the solstices are the equinoxes, which occur around 21 March and 23 September. On these dates, Earth’s axis is neither tilted toward nor away from the Sun. The Sun appears directly above the equator, and daylight and darkness are approximately equal everywhere on Earth. The March Equinox marks the beginning of spring in the Northern Hemisphere and autumn in the Southern Hemisphere, while the September Equinox marks the opposite seasonal transition. These moments of balance highlight how Earth’s tilt redistributes sunlight evenly across both hemispheres.
Earth’s Orbit: Elliptical but Misunderstood
Earth’s path around the Sun is not a perfect circle but a slightly elliptical orbit. This fact often leads to confusion about the cause of seasons. Earth reaches perihelion, its closest point to the Sun, around 3 January, and aphelion, its farthest point, around 3 July. If distance were responsible for seasons, the Northern Hemisphere would experience summer in January and winter in July. Instead, January is winter in the north and summer in the south, clearly demonstrating that distance plays a negligible role compared to axial tilt.
Why Distance Does Not Cause Seasons
The difference in Earth–Sun distance between perihelion and aphelion is only about three percent, resulting in a relatively small change in the amount of solar energy Earth receives. This variation is far outweighed by the effect of sunlight angle and day length caused by Earth’s tilt. When sunlight strikes Earth at a steeper angle, it is concentrated over a smaller surface area and delivers more energy. When it arrives at a shallow angle, it spreads out and is less effective at heating the surface. Seasonal temperature changes are therefore a geometric consequence of tilt, not proximity.
Summary: Geometry Shapes Our Seasons
Earth’s seasons are a direct result of geometry in motion. The 23.5-degree axial tilt determines how sunlight is distributed across the planet as Earth orbits the Sun, producing solstices, equinoxes, and the familiar rhythm of seasonal change. While Earth’s orbit is slightly elliptical, distance variations play only a minor role. By understanding Earth–Sun geometry, we gain a clearer appreciation of how predictable celestial mechanics shape life, climate, and the passage of time on our planet.
About the Author:
Michael Martin is the Vice President of Technology with Metercor Inc., a Smart Meter, IoT, and Smart City systems integrator based in Canada. He has more than 40 years of experience in systems design for applications that use broadband networks, optical fibre, wireless, and digital communications technologies. He is a business and technology consultant. He was a senior executive consultant for 15 years with IBM, where he worked in the GBS Global Center of Competency for Energy and Utilities and the GTS Global Center of Excellence for Energy and Utilities. He is a founding partner and President of MICAN Communications and before that was President of Comlink Systems Limited and Ensat Broadcast Services, Inc., both divisions of Cygnal Technologies Corporation (CYN: TSX).
Martin served on the Board of Directors for TeraGo Inc (TGO: TSX) and on the Board of Directors for Avante Logixx Inc. (XX: TSX.V). He has served as a Member, SCC ISO-IEC JTC 1/SC-41 – Internet of Things and related technologies, ISO – International Organization for Standardization, and as a member of the NIST SP 500-325 Fog Computing Conceptual Model, National Institute of Standards and Technology. He served on the Board of Governors of the University of Ontario Institute of Technology (UOIT) [now Ontario Tech University] and on the Board of Advisers of five different Colleges in Ontario – Centennial College, Humber College, George Brown College, Durham College, Ryerson Polytechnic University [now Toronto Metropolitan University]. For 16 years he served on the Board of the Society of Motion Picture and Television Engineers (SMPTE), Toronto Section.
He holds three master’s degrees, in business (MBA), communication (MA), and education (MEd). As well, he has three undergraduate diplomas and seven certifications in business, computer programming, internetworking, project management, media, photography, and communication technology. He has completed over 60 next generation MOOC (Massive Open Online Courses) continuous education in a wide variety of topics, including: Economics, Python Programming, Internet of Things, Cloud, Artificial Intelligence and Cognitive systems, Blockchain, Agile, Big Data, Design Thinking, Security, Indigenous Canada awareness, and more.