Saturday, June 02, 2007

The Longest Day

Every school kid knows this one. The longest day of the year (most hours of sunlight) is June 21 - the Summer Solstice. The sun takes its highest (most northerly) path in our sky giving us the most hours of daylight. I taught this very thing for 20+ years.

Not true! Well not here anyway...we are south of the Tropic of Cancer! ‘So what’, you say...read on.

The sun rises in the east and sets in the west every day but it does not follow the exact same trail day by day. During the course of a year the trail that the sun follows will creep north from December to June and then creep back south from June to December and that’s what makes our seasons. What is the farthest north the sun ever goes in its yearly trek? Let’s ask this another way as my astronomy professor used to put it...”Where would you stand on June 21 to be in the shade of your own sombrero at noon? The answer would be somewhere on the Tropic of Cancer (22.5 degrees north latitude). That’s the farthest north the sun goes and that then makes for the longest arc through the sky for the day and voila’ the summer solstice. But wait a minute...we’re now south of the tropic of cancer. That means the sun will be directly over our heads before June 21 and THAT will be our longest day. Hey...that should be around now...and it is!

The picture is of me roughly standing in the shade of my own hat taken around noon on June 2. Notice how tiny my shadow is (and just because of my sveltness!) . This means that we’ll have another ‘longest day’ when the sun passes overhead again on its way south sometime after June 21.

Wow...fun new ‘rules’ now that we live in the tropics! Oh, and by the way, why is that latitude called the Tropic of Cancer? When the sun is over that line on June 21 it is actually sitting within the constellation of Cancer. Tropic of Capricorn is the same thing in the southern hemisphere for the winter solstice on Dec. 21.*


*That’s actually a big lie but it used to be true. Way back when the Greeks made up the stories that go with the zodiac the sun WAS in Cancer on June 21. Because the earth’s orbit is an ellipse and the ellipse itself slowly changes its orientation around the sun the entire zodiac is off by about one constellation. In other words your ‘sign’ is supposed to be for which ‘house’ the sun was in when you were born. They set that up with the calendar centuries ago. So now when they assign ‘signs’ just by the date it really has nothing to do with astronomical things at all!

5 comments:

Anonymous said...

nice legs! Mary Lu

floridaglades said...

So you mean astrology is like professional wrestling?
What if you were born under the sign of St. Joe's Hospital?

LeahC said...

hey dad-

you're so svelt....you chest looks a little sunburned....careful with that one.

Anonymous said...

kewl, so you'll have another 'longest day' 19 days after the 21st on the sun's way back down! It's like two summers for the price of one!

Bubba Smiff in Annapolis

Anonymous said...

OK,
so next time I'll read the whole blog before I make a comment that you already made yerself!

Happy Cruising,

Bubba