The anticipation of autumn brings a sense of change, prompting questions about when this season truly begins. While calendars offer specific dates, the “feeling” of fall often arrives earlier or later, depending on natural signals and geographic factors. This subjective experience of cooler air, shifting light, and vibrant colors marks the transition from summer’s warmth to winter’s chill.
Official Start Dates
Autumn is formally recognized through two distinct systems: astronomical and meteorological. Astronomical autumn commences with the autumnal equinox, typically falling between September 21 and 23 in the Northern Hemisphere. This event occurs when the Sun crosses the celestial equator, resulting in nearly equal periods of daylight and darkness worldwide. The date varies annually due to Earth’s elliptical orbit and leap years.
In contrast, meteorological autumn adheres to a fixed calendar schedule for consistency in weather record-keeping and forecasting. Meteorologists define autumn in the Northern Hemisphere as the months of September, October, and November. This division simplifies seasonal statistics by grouping months with similar temperatures.
Nature’s Cues and Sensory Shifts
The “feeling” of fall emerges through sensory changes in the environment. Temperatures begin to drop, leading to noticeably cooler evenings and crisp mornings. Daylight hours progressively shorten, and sunsets occur earlier, changing the quality of natural light.
A visual cue is the transformation of deciduous tree leaves from green to brilliant yellows, oranges, and reds. This change happens as trees reduce chlorophyll production due to shorter days and cooler temperatures, revealing other pigments like carotenoids and anthocyanins. The air acquires distinct autumn scents, earthy, woody, or spicy, reminiscent of damp leaves, woodsmoke, and seasonal produce. Morning dew also becomes more prevalent, glistening on surfaces as temperatures cool overnight.
Wildlife also exhibits behavioral shifts as autumn approaches. Many bird species embark on their southward migration to warmer climates. Animals like squirrels and chipmunks become busier, gathering and storing food in preparation for the colder months. Some species, such as bears and rodents, increase their food intake for hibernation, while others may change their coat colors or exhibit altered activity patterns.
How Location Influences Autumn’s Arrival
Geographical location dictates when the feeling of autumn begins. Latitude plays a substantial role, with regions at higher latitudes experiencing cooler temperatures and earlier leaf color changes. Northern regions typically see the signs of fall emerge sooner than southern regions.
Altitude also impacts the timing of autumn’s onset. Higher elevations generally experience cooler temperatures earlier in the season. Consequently, fall foliage often begins to transform at higher mountain elevations and then progresses downwards into valleys over several weeks, hastening the seasonal changes.