Shooting the Sun

By Katherine Duke '05
Photos by Samuel Masinter '04

Think of the proverbial “billions and billions” of stars in the universe, and the hundreds or thousands we can see from Earth. Now consider that, for centuries before the advent of computers or GPS navigation, experienced sailors used 57 of those stars, plus the sun and moon, to determine their own locations in the vastness of the sea. That’s what 12 students began learning to do in Henry Parker Hirschel’s course, “Celestial Navigation.”


Ben Lin '12 (left) and Elizabeth Carbone '12 use sextants at Avery Point, Conn.

In the 1970s and ’80s, Hirschel worked his way up to the position of deck officer at the Woods Hole Oceanographic Institution; now he’s an instructor captain for the Steamship Authority in Woods Hole, Mass. He’s taught “Celestial Navigation” over Interterm for three years in a row. Some students sign up because they’ve grown up sailing with their families, and others because they’re interested in celestial mechanics on a more theoretical level. (Still others—I’m just guessing here—signed up because they secretly long to be pirates). This year, they spent hours of class time, some of it up on Merrill Beach, learning how to “shoot the sun”—that is, how to measure the sun’s angle in the sky using sextants (“If anyone drops this sextant,” Captain Henry warned them, holding up the most expensive and finely crafted one, “they get sent to Williams College for the rest of the year.”) Then they practiced using their measurements, the relevant tables in the voluminous Nautical Almanac and the necessary arithmetic to figure out their latitude.

Ryan Milov '10 shoots the sun on Avery Point.
On Thursday, Jan. 21, the students put their skills to use off-campus. I tagged along as the class loaded into a van, with Captain Henry and a student navigator at the helm, and drove to Avery Point on the Groton, Conn., campus of the University of Connecticut. Their first challenge was to look out over New London Harbor and do a “noon sight”—a calculation of latitude based on measurement of the sun’s angle at Local Apparent Noon (the few minutes during which the sun is at its highest point in the sky over a particular location). I had enough trouble just finding the sun in the sextant, but I did enjoy hearing Captain Henry tell of some legendary nautical phenomena, including St. Elmo’s fire and the green flash.


Students in the Celestial Navigation course draw lines on a Mercator plotting sheet.

The next task, a “p.m. sun sight,” was even trickier: The students tookmultiple sextant readings as the sun made its way across the sky, used these readings to draw precise lines on a Mercator plotting sheet, and finally determined our location based on where the lines intersected. I could only vaguely grasp how they were doing this. And to think of how many generations of sailors and mathematicians, how many flashes of genius and rounds of trial-and-error, it must have taken for the human race to invent the sextant and to develop the Nautical Almanac—it was like pondering the size of the ocean or the sky itself.

Captain Henry was pleased with the accuracy of the students’ reckoning of our longitude and latitude—they weren’t far off from what he rather intimidatingly called “Truth.” “I think you’re all to academy standards, as far as I can see,” he said. The next day, as the culmination of the course, the class would go out on an actual boat, to Block Island, R.I. But, the captain reminded them, they were all just at the “neophyte” stage. To get enough real practice at celestial navigation takes nothing short of days and days at sea.

View more photos of the Avery Point trip on the college's Flickr page.