Checking our Position (Latitude) with a Sextant
Posted by: Rory Wilson
Wednesday, July 18, 2007
2:00 PM Indian Ocean
Our first step:
Hhmmmm. We are measuring how high the sun is in the sky at noon. This is the highest it gets and because this angle is in a very accurate table, all we need to do is measure our angle! We then make a couple of adjustments, and then we know our north - south position, or latitude.
To measure this angle, we use a sextant. This tool is very accurate. It is the way that ships navigated from around 1700 until we launched satellites and began using the GPS (Global Postiioning System) for navigation.
Check it out:
Scott, one of our scientists, brought this replica bronze sextant along on the trip. With some practice, we were practicing sights on deck in preparation for our sun sight.
We need to know when noon is. It is 12:00, right? Well, not exactly. To make life easier, there are time zones so that in each zone, the middle of the day is about 12:00. But if we are at one edge or another, the actual mid-day is either earlier or later. Out here, we are actually at the later edge of a time zone, so our local noon is closer to 1:00PM. We go out on deck after 1200 and start looking at where the angle of sun is the lowest. Hhmmmm. The sun is north of us, so we have to measure from the north horizon up to the sun. It turns out that with a simple subtraction problem, we have our latitude.
We also went up to the bridge and were able to try out the ship's sextant. They keep this on the bridge and the crew can navigate with this in an emergency.
Scott and Jackie both are now becoming ocean navigators in addition to being petrologists!
We are having another session on the bridge tonite.
Will let you know how it goes.
JULY
7/30 - Final day at sea: on the way into Singapore
7/26 - A Day in the Life of a Teacher at Sea
7/18 - Checking our Position (Latitude) with a Sextant
7/16 - Monsoon Blues in the Indian Ocean
7/15 - WAVES, Rough Weather, but an exciting day... WHALES
7/11 - Not the Best Day for Science at Sea
7/9 - Discoveries on the 90 East Ridge
7/5 - Closer to Home, Life Here Onboard
7/2 - Ocean Careers: Texas to Russia
JUNE
6/30 - Easy Cruising Day: Now in the Southeast Trade Winds
6/27 - We Crossed the Equator Today, Heading South.
6/21 - Night Time Fun in the Indian Ocean
6/20 - Transit Gale in the Indian Ocean
6/17 - Arrived in Phuket, Thailand (finally)
