Physci text 07

Latitude and longitude

GPS Seek

Latitude and longitude are first introduced using either a search for a person at a known latitude and longitude or a geocaching hunt also using latitude and longitude. This activity is based on a discovery learning model - no introduction is given to latitude and longitude. 

Summer 2023 "Binky" was hidden at:

• Degrees and decimal minutes: N 06° 54.545' E 158° 09.610' 

• Degrees, minutes, and seconds: N 06° 54' 32.7" E 158° 09' 36.6"

• Degrees and decimal degrees: N 06.909083° E 158.160166°

The format for mobile devices and GPS units will vary.

Arcminutes to meters laboratory exploration

In this laboratory students seek a relationship between arcminutes and meters. By walking along a line of latitude or longitude while measuring the distance in meters and taking latitude or longitude readings, data will be generated that leads to a conversion factor between arcminutes and meters. The conversion factor can then be used to determine how close in meters a GPS enabled device can locate an object. 

• Along a line of latitude, the longitude values increase or decrease.

• Along a line of longitude, the latitude values increase or decrease.

Latitude and longitude are measured in degrees and arcminutes. There are 60 arcminutes in one degree. There are 360 degrees in one circle. Note that arcminutes of latitude and longitude are effectively measures of distance not duration, of space not time.

On Earth the equator is 0 degrees latitude. The north pole is north 90 degrees, +90°. The south pole is south 90 degrees, -90°. The equator is half-way between the north and south pole. Pohnpei is located about six degrees north of the equator, almost seven degrees. On the Palikir campus, a global positioning satellite receiver (GPS) will display a latitude value close to N 6° 54.580'. The 54.580' digits are the minutes of arc, the apostrophe is the symbol for minutes. Arcminutes measure an angle. On the Earth's surface, however, an arcminute can be expressed as a distance. Arcminutes are sometimes just called minutes, which can be very confusing!

On Earth the prime meridian is 0 degrees longitude. Pohnpei is located 158 degrees to the east of the prime meridian. The furthest east is 180 degrees. At 180 degrees east one is also 180 degrees west of the prime meridian. East longitude is positive, west longitude is negative. The GPS will display a longitude value near 158° 09.600' on the Palikir campus of the college.

The student use a global positioning satellite (GPS) receiver or cell phone app to walk along either a line of latitude or a line of longitude. Lines of latitude run east - west. Lines of longitude run north - south. The students either walk along a line latitude heading due east, or walk along a line of longitude heading due north. Walking east along the line of latitude will cause the longitude value to increase. Walking north on a line longitude will cause the latitude to increase. In the Federated States of Micronesia these directions, east or north, will keep the slope positive for the relationship between minutes of arc and meters. The other value should be held constant to remain on that line of latitude or longitude.

The latitude or longitude is determined using a GPS enabled device. A measuring wheel is optimal for measuring the distance in meters. On the Palikir campus distances of up to 180 meters are used with readings typically taken every 30 meters.

For this exercise the GPS device or app should be set to read in degrees and decimal minutes. On Android the app GPS Essentials is a recommended app. 

In the settings for an app look for Position Format or a similar setting.

Set that to Degrees, Minutes, Fractions.

Earthquakes and seismology

The island of Raur in Woleai atoll after the big waves of The Good Friday Typhoon in March 29, 1907 that washed away more than 200 people of Raur and Paliyaw with an earthquake also took place in Ulithi at the same time.