Happy Fall - if you're living in the Northern Hemisphere.  Otherwise - Happy Spring for my Southern Hemisphere friends. 

What do we wish to our fellow humans orbiting the Earth in the International Space Station? 

Anyway, today marks the September Equinox, the start of Fall in New England, at least.  The word "Equinox" means "equal night."  That is, theoretically, we'll have a day with 12 hours of sunshine and 12 hours of night.  Equal. 

In practice, things aren't so equal.  Because the Earth has an atmosphere (I'm not complaining), the Sun will (by refraction) actually continue to appear above the horizon even when it has dipped just below.  And the Sun's light gives us dawn and dusk even at those below the horizon times.  Not exactly equal. 

Why is the Equinox happening today at 10:21 A.M., then? 

The Earth spins on its axis, but that spin axis is tilted by about 23½º.  During the (Northern Hemisphere's) Summer Solstice, the North Pole is angled most towards the Sun, which is overhead at a latitude of 23½ºN.  About three months after the Summer Solstice the Sun crosses the "Celestial Equator," which is the Earth's Equator projected into space.  At this moment we turn to Fall. 

Because of leap years, the Equinox is not always on September 22. 

All this orbital dynamics is often more easily explained using a planetarium.  If you're interested in learning more about Blue Star Planetarium, check out the website here, or email your questions any time.

Marc

I'm a Summer kind of guy.  I love Summer.  I spent over a year in south Florida in one stretch and it was great.  It was the longest Summer I had, until years later when I worked at a college planetarium in the United Arab Emirates.  That was Summer to the max.  We stayed there three and a half years, apart from travel back to the U.S. during Summer recesses.  It was always Summer, and it was good. 

I don't know why, but this year I've pretty much had it with the Summer.  Maybe it was the mix of hot days and almost no rain for weeks, though that was certainly the case in Dubai.  I guess I'm just getting older - bring on the Fall!

I introduce the blog this week in this way to contrast this Summer to what happened 200 years ago - 1816, the "year without a Summer."  Read more about it here.  

To summarize - during the Summer of 1816 there were severe frosts every month.  Crops were drastically reduced, leading to famine across the U.S., Europe, and China.  New England was particularly hit hard.

What caused the "year without a Summer?"  It has been attributed to the ash in the atmosphere from the 1815 volcanic eruption of Mount Tambora (now in Indonesia).  This was the largest volcanic eruption in at least 1300 years, and lowered the global average temperature by about 1ºC.  That small temperature change can and will make a big difference. 

So I will try to not complain about the Summer this year, but I'm still looking forward to Autumn... :)

Marc R.
www.bluestarplanetarium.com