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Curious Nature: Astronomical change
Fall brings cooler weather, pumpkins and cozy sweaters. Leaves change, animals begin to hibernate and the days become shorter and shorter. But how do trees know to change colors, pika know to store up food and some animals know to don snowy-colored fur? The physical changes we associate with fall are triggered by changes in daylight caused by Earth’s tilt on its axis and its position around the sun. Fall officially starts on the day of the autumnal equinox. The name “equinox” comes from the latin word “aequus” meaning equal and “nox” meaning night. And, you guessed it, the spring and fall equinoxes mark the two days each year where day and night are almost exactly the same length. This year, the fall equinox will occur on September 22. But why exactly are day and night equal lengths? In astronomy, the fall equinox is the day that the sun shines with equal intensity on the southern and northern hemispheres. A common misconception is that the changes in season occur because one hemisphere is closer to the sun than the other at a given time; however, seasonal variations are caused by changes in the angle that the sun’s light hits the...
