Solstices, equinoxes, and seasons

Science Review by Bruce Betts, PhD June 19, 2026 This year, June 21 marks the summer solstice in the northern hemisphere, the beginning of summer. The science-journalism coverage adds useful context, while the strongest evidential footing still comes from the underlying data, papers or institutional documentation.

This matters because Earth science becomes stronger when local observations can be placed inside a broader physical pattern that spans time and geography. The planet operates as a coupled system in which atmospheric, oceanic, cryospheric and solid-Earth processes interact across timescales from days to millions of years. A measurement that captures one variable at one location and one moment has limited interpretive value until it is embedded in the longer series and wider spatial coverage that allow natural variability to be separated from forced change. At this moment in Earth's journey around the Sun, our planet is positioned so that the north pole is tilted as close toward the Sun as it gets all year. That tilt of Earth’s axis is what makes seasons so different from one another, especially closer to the poles.

In the city of Montreal, the average daily high temperature in June is 24°C (75°F), while the average daily high temperature in December drops to -1°C (30°F). These extremes aren't caused by Earth’s distance from the Sun changing.

At different times of year, different parts of the planet receive different amounts of sunlight as Earth rotates. Using Montreal as an example again, on the summer solstice, the city gets more than 15 hours of daylight.

Because the equator lies midway between the poles, Earth's tilt causes much smaller seasonal changes in day length and sunlight there than at higher latitudes. Between June and December, daylight only fluctuates by about 15 to 45 minutes, depending on the exact location.

The broader interest lies in linking the observation to climatic, geophysical or environmental dynamics that extend well beyond the immediate event or location. Earth science is unusual in that its most important questions operate on timescales that no single research career can observe directly, making the archival record, whether in ice, sediment, rock or satellite data, as important as any new measurement. Results that can be embedded in that record, and that either confirm or challenge the patterns it reveals, carry disproportionate scientific weight.

Instead, Earth is positioned so that the Sun shines directly over the equator, and Earth's rotational axis is perpendicular to the Earth-Sun line. Earth isn’t the only place in our Solar System with seasons.

Because this item comes through The Planetary Society as science journalism, it should be treated as contextual reporting rather than primary evidence. Good science reporting can identify why a result matters, connect it to the wider literature and make technical work readable, but the decisive evidence remains in the original paper, dataset, mission release or technical record. That distinction is especially important when a story is later repeated by aggregators, because repetition increases visibility, not evidential strength.

The next step is to place the result inside longer time series and to compare it with independent instruments and independent sites. Earth system observations gain most of their interpretive power from network density and temporal depth, not from any single measurement however precise. Model simulations that assimilate the new data will help clarify whether the observation fits comfortably within known natural variability or represents a shift that existing models do not reproduce.

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