Using the North Star to determine latitude in the Northern Hemisphere

Navigation is the science of identifying positions on Earth.  Ancient mariners and explorers, as well as travelers today, determine the latitude of any location north of the equator by measuring the altitude of Polaris (north star) above the horion.  For example, the latitude of New York City is approximately 41° north of the equator, so the angle of altitude of Polaris above the horizon is 41°.

Our next topic of discussion and learning is determining the bases of our system of time on Earth.  Basically, we base our system of time on observations of the sun.  Noon (mid-day) is defined as th time the sun reaches the highest point in the sky.  The day is divided into 24 hours because that is the time it takes for the Earth to do one full rotation.  You can calculate your approximate longitude if you know the present time at the prime meridian of Greenwich and your local time.  To find longitude, you must first determine the difference in time between local and Greenwich time.  This time difference multiplied by 15° per hour equals your longitude (the rate at which the Earth rotates on its axis is 15° per hour).

The video below shows how to locate Polaris in the night sky.


Homework:  due Tuesday, December 7, 2010

Textbook: read pages 77-79, on measuring time.  Do questions 2 and 3.
Review book: read pages 20-23. Do questions 12-28 on pages 23-25.

All students should have purchased the review book by now.  If not, you must make the purchase ASAP, at the science department office in room 305.

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