Sunday, June 19, 2016

The Sub Solar Point Tomorrow At 6:34pm EDT

Happy Midsummer's Eve 


This means midsummer's day will arrive tomorrow. To be precise at 6:36PM EDT the Summer Solstice will occur. 

At that point in time the 'Subsolar-Point' will reach its most northern latitude. The subsolar point it the location on the earth where the sun is directly overhead.  This point travels around the earth once every 24 hours and travels is located between the tropic of cancer and the tropic of capricorn latitude lines depending on where the earth is in its orbit about the sun.

These latitude lines are determined by the the tilt of the axis of the earth with respect to the plane of its orbit about the sun. 


The name of this latitude line in the northern hemisphere is "The Tropic of Cancer". At the location of the 'Subsolar-Point' tomorrow at 6:36PM EDT it will be precisely LOCAL SOLAR NOON

All this happens because the tilt of the earth's axis of rotation does not change as the earth orbits the sun.  This means that the earth is tilted toward the sun parts of the year and tilted away from the sun other parts of the year.  When the north pole is maximally tilted toward the sun then the subsolar point reaches it most northern latitude.

This year the location of this most northern subsolar point in time and place will be near where the tropic of cancer crosses the Hawaiian Island Chain. 

To figure out exactly where this is all you need to do is add the number of degrees minutes and seconds of the time of the solstice to some know longitude. 

The Solstice this year will be at 22:34 UTC 20 June 2016 - so at 10:34 in the evening at the prime meridian the subsolar point will reach the tropic of cancer. That means 10 hours 34 minutes to the west of Greenwich England on the tropic of cancer the most northern subsolar point will occur (and mid summer will have arrived!) 

To sort out what the actual latitude and longitude is we note that the latitude is pretty easy; 23.5 degrees: The exact same number as the inclination of the axis of rotation of the earth to its orbital plane about the sun. 

The longitude is also easy since all you need to do is convert 10 hours and 34 minutes to degrees of longitude. The entire planet has 360 degrees of longitude. The planet also rotates on its axis every 24 hours. So divide 360 by 24 and you get 15. This means that the subsolar point moves 15 degrees of longitude every single hour. 

So what is the longitude of 10 hours and 34 minutes? Well 10 times 15 gives 150 so that is longitude 150 degrees west. And the 34 minutes of clock time: That comes out to be 34 minutes of longitude as since there are 60 minutes of longitude in every degree of longitude. 

So at 23 degrees 30 minutes north latitude and 150 degrees and 34 minutes west longitude at local solar noon the apparent location of the sun will be directly overhead and that is the most northern point local solar noon it will reach all year! 

You can plug into Google Earth/Maps these two numbers and see where that is.  Here is a URL you can click: (23°30'00.0"N 150°34'00.0"W).  So, you should do this tomorrow at the time of the solstice.

Here is a Google Earth .KMZ file you can use and some screen shots.