The shadow knows!
Oh, spring has sprung! And so has my first installment to my Observational Astronomy section!
Ah, the first day of spring! Or true spring, as I call it. Oh, yes, in some locations, it's still cold and nasty, but as I once wrote in a Pittsburgh Post-Gazette article, the arrival of spring just “dealt Old Man Winter a well-deserved death blow!” That instant came this year when the vernal equinox, that heralds spring, occurred at 5:01 a.m. EDT today (March 20, 2025).
At least Old Man Winter is pretty much a shadow of his former self. Here are examples from past years.
Why is today so important if the weather's not so great? It's spring, right? Because the seasons are astronomical events, not weather events. To me, there is no such thing as meteorological spring, except to allow weather people to have a fixed date to attach data. Without the astronomical tilt of our planet, there would be no seasons. True spring is what I call this season.
Spring is here, as EarthSky.org succinctly puts it: the vernal equinox “marks the Sun’s crossing above Earth’s equator, moving from south to north. Earth’s tilt on its axis is what causes this northward shift of the sun’s path across our sky.”
When Earth's movement on its axis causes the northern hemisphere to tilt away from the Sun, we get winter – and the Sun rides southernmost in our sky. That causes – guess what? – midday shadows to be at their longest. In March, on the first day of spring, shadows are at a medium length. Then in June, shadows are at their shortest.
What's amazing is that we diminutive humans actually can observe Earth's tilt on its rotational axis! Join Pete's Geek and Nerd Team and take photos of the shadow of a certain fixed object near you, but at different times of the year and as close to solar noon as possible (add at least an hour for DST; you'll be close enough). You'll easily see the difference!
At about 1:38 p.m. today, I caught a few springtime shadow photos.
In this first photo taken closest to solar noon, the Sun is to my left, so I'm facing due west.
Finally, I noticed that the shadow on our garage ran parallel to the garage itself in this north-facing photo. That happens because our house was built exactly north-south. Our flag's shadow also is visible near the bottom.
Another way to observe Earth's tilt is to watch, at this time of year, the location of sunset or sunrise, and how each seems to move northward each day! And the Sun rises due east and sets due west.
Finally, if you're inclined to balance an egg on end or stand a broom upright, go ahead. But there is nothing magical about today that allows that to be possible. On any other day of the year, it's possible, too. Really.
Thank you for coming along and having fun. I very much appreciate it, and I hope I can encourage you to keep looking up! See you soon, stargazers!
Can't wait to look at the sky with you!
ReplyDeleteI found that the trick to egg balancing was to add a little salt, but that's cheating... Great post!
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