Joseph Kerski
speaker
638 appearances
3 recordings
1 series
first heard Jun 2026
last heard 1 Aug
Joseph Kerski’s voice in public audio — every appearance, attributed to the second.
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recordings per month · last 12 monthsRecordings per month over the last 12 months — 3 in all, peaking in Aug 2026 with 1.
Appearances
Unlike the backstaff, the sextant permitted stars in the sun to be observed, and since it was measured in relative angles, the
It did not need to be held relatively or completely steady.
Steady.
These devices also used a vernier scale, allowing the user to measure more precisely when reading a uniformly divided straight or circular measurement scale.
The vernier scale indicates where the measurement lies in between two of the marks on the main scale.
Sextants were widely used until rather recently, actually.
Charles Lindbergh used a bubble sextant on his record breaking flights across the ocean.
Radio navigation was developed during and after World War II, followed by GPS beginning in the nineteen eighties.
through to today's global navigation satellite systems around the world, GNSS.
Now let's also chat for a moment about the magnetic compass.
That was a major revolution in geography as well.
A compass needle proved to be more accurate than sighting angles on a wood or brass instrument and points to the north magnetic pole in the northern hemisphere or the south magnetic pole in the southern hemisphere.
The compass thus provided the heading or the direction in which a ship was traveling, and could be used to determine where the ship should be traveling.
Mariners maps in the age of exploration often showed the headings between key ports, and these heading charts and maps were therefore jealously guarded by their owners and their nations.
So that is our tool, actually a set of tools this episode, cross staffs, astrolabes, and other devices determining positions on the planet.
This episode our event
is the twenty eleven Japan earthquake and tsunami.
Now on a personal note here folks, it's still one of the clearest memories I have of any of the hundreds of work trips I've taken over my entire career.
My colleagues and I, along with over ten thousand others, had just arrived in San Francisco for the annual meeting of the National Science Teachers Association.
It was the evening of eleventh march twenty eleven.
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