This essay has nothing to do with medicine or health, but I couldn’t let 10:21 AM September 22, 2016 without sharing some excitement.  (Note:  all times cited are in Eastern Daylight Savings time, our time right now)

What happens at 10:21 AM?  It is a moment when several planetary facts that define where we are in the universe come together and allow us to see something extraordinary.  These facts all come together twice every year, at a moment called the equinox.

The equinox happens when summer ends and fall begins, and again when winter ends and spring begins.

At both these moments, across the entire world, if you look back 12 hours from that moment, and forward 12 hours from that moment, you have a 24 hour period, a day, in which day and night are equal.  That’s right, from 10:21 PM on September 21 through 10:21 PM September 22, there will be equal parts day and night, almost exactly 12 hours of each.   And the amazing thing is that will be true, on every spot of planet Earth, all at the same time!  Think about that a moment.  During that 24 hour period, Cleveland will have 12 hours of day and 12 hours of night, but so will Mexico City, and Tokyo, and Buenos Aires, and Alaska, and the North Pole, and the South Pole.

These 24 hour periods of equal day and night that happen twice every year, are known as the equinox (meaning equal night).  Only during the 24 hours of the equinox does everyone on the planet have the same time for sunrise and sunset, no one is more in light, and no one is more in dark.

How can this be?   It doesn’t make sense since for all other days in the year we are either lighter or darker than somewhere else.

The easiest way I have come to understand how this can be true is to think about how our days get longer and shorter over the course of a  year, and how opposite our pattern is from anywhere in the temperate Southern hemisphere, say in Cape Town, South Africa.

Let’s start with home, with Cleveland.  Starting this week, nights will start getting longer than days.  The sun will continue to set earlier and earlier, and rise later and later.  Gradually, but certainly, by December, many of us will once again be driving home in the dark.  The night will be longest by December 21, and then the trend reverses.  As we all know, not long after Christmas and Hanukkah, the longest nights begin to fade as day lengthens.  We will do through another equinox in March and the triumph of day will peak in June, when we once again will be able to sit on our patios til 9PM in full daylight.

At exactly the same time, Cape Town, and other cities south of the Equator, are going to start enjoying longer days this week.  By their December, while we struggle to shine some light is in a long night with our menorahs and Christmas lights (the timing of these festivals has everything to do with this being our darkest time), our friends in Cape Town will be enjoying barbecues and get togethers at 9PM on their patios.

Now, here is the very cool part.  As we go from this week to next June, our nights will get longer and longer peaking in December, then shorter and shorter with days at their longest in June.   As Cape Town goes from this week to next June, their days will get longer and longer peaking in December, then shorter and shorter with nights at their longest in June.  If you think about it, you can’t go from long nights to long days without passing through a moment when they are equal.  And, you can’t go from long days to long nights without passing through a moment when they are equal.  And that moment when they are equal is the exact same moment in every place on the planet!

This moment when all change crosses together is most dramatic in the Arctic and Antarctic.  There too days lengthen then shorten year after year, but far more extremely.  In Northern Alaska summers include many days of no night at all, and winters are famous for night with no day.  But again, you can’t go from days that are all night to days that are all day without passing through a day where night and day are exactly equal.  The same is of course true for Antarctica.   As with Cleveland and Cape Town, so it is with the Arctic and Antarctic, their parallel swings from long nights to long days, always in opposite directions, hit that moment when night and day are equal, and all at the same time.

And finally, what is so amazing about all this is that it only happens as a result of the fact our planet spins on an axis that is tilted (about 23.5 degrees), and our planet spins around the sun in an orbit, and our planet and sun spin around the galaxy.  We spin on our axis every day at 1,000 miles an hour.  We fly around the sun once a year at 66,000 miles an hour, and our solar system twirls around the galaxy at a whopping 490,000 miles per hour.  We are of course unaware we are making any of these moves, let alone that we are flying at speeds that are hard to even imagine.

But this symphony of movement becomes visible at least to our eyes twice a year at the autumn and spring equinox, when every spot on our planet gets 12 hours of day and 12 hours of night, the sun rises and sets at the same time from North to South Pole, at the Equator, in Cleveland, and everywhere else.

Enjoy the equinox!

To your health,

Dr. Lavin