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Steven Branting Teaching with Sextants Program Title: Lost at Sea: The Search for Longitude Subject(s): Earth Science Grade Level: 7-12

Students use their sextants to take a Sun shot at local noon.

That was the question that kept coming up during Steven Branting's creative thinking and pre- engineering course two years ago. His students wanted to know how maritime sextants and astrolabes worked.

Which is what led Branting, who teaches at Jenifer Junior High School and Lewiston High School in Idaho, to develop a comprehensive unit around the use of the modern-day marine sextant. With grants from a local company and his school board, Branting created a unit that begins with the history of navigation, and includes material on how to:

• solve problems of grids on curved surfaces

• calibrate sextants to ensure mirror accuracy

• determine and take a local noon shot

• use an ephemeris to find "equation of time" and "declination" for any given date

• calculate latitude and longitude from a local noon sighting

• use an artificial horizon

NOVA's "Lost at Sea: The Search for Longitude," which premiered Fall 1998, was a natural tie-in. Branting uses clips from the program to help students understand the role timekeeping plays in navigation and the need for accurate timepieces.

The materials for Branting's unit include a student handout, classroom transparency set, student and teacher sextants, Internet access (to connect to the U.S. Naval Observatory clock) and a copy of the NOVA video.

Branting, a facilitator of gifted education, has developed several additional uses of the sextant as a teaching tool in mathematics and geology. A sextant can be used:

• As a pelorus, an instrument meant to determine a ship's bearing in relation to a distant object. Turning the sextant to a horizontal position, this capability can be adapted to calculate the distance to an object using the trigonometric tangent function.

• to calculate the distance to tree leaves that have created images of the Sun on the ground.

• to measure the angle of repose for talus slopes (the slopes of rock at the base of a cliff) in basalt formations.

Branting's unit can be found on NOVA Online. —Karen Hartley