Autumn isn't just marked by the calendar. Each September, Earth's subtle tilt brings the autumn equinox—one of two times a year when day and night are nearly equal in length. It marks the beginning of autumn in the Northern Hemisphere. From solar alignments to changing leaves, nature offers its own quiet signals that the season has shifted. While for most of us it may seem like just another day, ancient cultures paid close attention to this change. Sites like Chichén Itzá in Mexico and England's Stonehenge were designed to align with the rising or setting sun during equinox days.

One of the best places to catch the change in season? Fishlake National Forest in Utah, United States. As September rolls in, the aspen trees seen in today's image begin their annual transformation, turning vivid shades of yellow that ripple across the hills. The forest covers more than 5,900 square kilometres of lakes, trails and mountains that shine with fall colour. There's something grounding about watching the season change in sync with something much older than the Gregorian calendar we follow.