Answering the “Whys”: First Day of Spring

What do toddlers and astrophysicists have in common?  They both ask “Why?” 900 times a day!

One of the things I always taught my students when I taught high school was that science was simply one guy/lady asking “Hm, I wonder why this happens?”  and another guy/lady saying “Gee, I don’t know. Let’s find out!”

As any parent knows who has ever thrown their hands up in exasperation and said “Because I SAID SO!” …preschoolers are the kings and queens of asking WHY.  This has inspired my new series of blog segments entitled Answering the “WHYs“.  In these posts I will attempt to explain some of the everyday science phenomena that kids are often curious about.  Note: If you are already a science expert, please feel free to add your knowledge in the comments!  More info is always welcome, but before you correct me too much, please know that I am gearing my posts to explaining things to young children. 20170326_131055.jpg


Rotation – spinning around an axis (i.e. the earth completes one rotation each day)

Revolution – orbiting around another object (i.e. the earth completes one revolution around the sun each year)

  • Why is today the first day of spring?  (or…It already felt like spring weeks ago, why is spring starting now?  or… It’s snowing today, why is it spring already?)

The earth is tilted on its axis as it completes its yearly orbit around the sun. (You can use a globe or a basketball to show this ’tilt.’) The tilt of the earth does not change, but remains constant at 23.5º.  March 20, 2017 is declared the first day of spring (a.k.a. the vernal equinox) in the Northern Hemisphere because the earth’s axis is no longer pointed away from the sun as it was during the winter months.  Instead, the earth’s axis is positioned so that both the Northern and Southern Hemispheres receive 12 hours of daylight and 12 hours of night.  The sun’s rays are hitting directly at the earth’s equator.  (You can show this by shining a flashlight right at the middle line on the basketball.)  This positioning will happen again on September 21st after the earth moves halfway around the sun. In the Northern Hemisphere we call that the autumnal equinox, or the first day of fall.

  • Why is there day and night?

The earth rotates once on its axis approximately every 24 hours.  I say approximately because it actually takes 23 hours, 56 minutes, 4.2 seconds to spin around exactly one time. In my town of Columbus Indiana, today’s sunrise was at 7:47am and sunset will be at 7:55pm.  As the earth spins from west to east, we move into the light of the sun in the morning at sunrise and spin out of the light rays at sunset.  The video below provides a really nice visual! (But beware…my 3-yr-old son could probably watch this for an hour straight!)

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