Today marks the autumnal equinox, and for the Northern Hemisphere, the official start of fall. I always thought the hours of day and night were equal on this date. Turns out, I was wrong – daylight lasts a few minutes longer, for a few more days. This is basically because the sun takes several minutes to completely pass over the horizon at sunrise and sunset, and also because the atmosphere bends the light. For a more thorough explanation, see this be-a-smarter-mommy article at earthsky.org.
The day of true half-light, half-dark is not far off: Saturday, September 26 at my latitude, according to this handy chart. I realized this morning at the bus stop there is also the issue of terrain – we live on a hill and cannot see the true sunrise. That didn't stop me from wowing (and annoying) my kids today with my new-found knowledge, as well as starting us on these totally awesome autumnal equinox activities:
1. The ol’ basketball.trick. If you have a globe, use it and a flashlight to demonstrate how the Earth’s usual tilt toward the sun goes away on this day. No globe? Use a basketball. Or, show them this video.
2. Determine your latitude with a neat tool from NASA that generates a satellite map of a location, allowing you to drag the pointer to the exact street and lot. Have your kids check it against what they find with a GPS device or app, and with this nifty calculator find your date for exactly 12 hours of daylight.
3. Find due east and west from your front door. Mark each spot with a painted rock. Then you can easily track the sun’s southward movement as winter approaches, and its return north in the spring.
4. Document sunrise and sunset with a digital photograph that marks the time. Do this for several days around the equinox. When are day and night the same?