These satellite views of Earth show the start of the four seasons. From left to right, with respect to the northern hemisphere, we see the summer solstice, fall equinox, winter soltice, and spring equinox. Credit: NASA
So, during each of our year-long journeys around that orbit, Earth’s tilt causes our perspective on the Sun to change.
For half of the year, it climbs higher in our sky each day, until it reaches its highest point. For the rest of the year it gets lower in the sky every day, until it reaches its lowest point. Then, the pattern starts all over again.
This ‘solargraph’ image captures the Sun’s path across the sky, day by day, between June 21 and December 21, 2023, from atop Weather Network Headquarters. Credit: Bret Culp
READ MORE: What is a solargraph? How to record the Sun’s seasonal journey across our sky, all in one image
Using this astronomical timing to define our seasons works just fine, in general.
However, specifically when it comes to keeping track of our weather and climate, they don’t work quite as well. The start and end dates of the astronomical seasons typically fail to capture the weather that most defines a particular season. Also, they definitely do not mesh well with how we keep records of weather conditions throughout the year.
Shifting alignment
When keeping weather and climate records, consistency is essential.
Daily, weekly, monthly, and even yearly records satisfy this requirement quite well. A day is always 24 hours, a week is always 7 days, and except for the occasional leap year, we can count on each month staying the same length, and each year having 365 days. This helps atmospheric scientists to easily make comparisons, find extremes, and track trends in their weather records.
