A sextant is used to measure the angle between the horizon and sun, moon, Venus, or North Star

Used (before GPS) for navigation, especially at sea. Latitude can be determined directly (at noon) Longitude requires accurate timekeeping.

AnalemaDue to the slightly elliptical orbit of the Earth around the sun, the sun is not directly south at local solar noon. The Earth is closest (perihelion) in late December/early January.

The prime meridian is an imaginary line from pole to pole passing through Greenwich England

Royal Greenwich Observatory

Although the date line is nominally at 180° longitude from Greenwich, it has various jogs to avoid day changes inside countries (USSR for instance.) The latest jog put Eastern Kirabati in the Eastern segment.

What precision is required?

The distance between two points lying on the same longitude that are separated by 1° of latitude is 111 km.

One degree is not precise enough for most purposes. One-tenth of a degree will probably get you to a city or its suburbs (11 km).

Google Earth displays latitude and longitude in degrees and minutes. Write that value down for the various cities in your lab sheet and then convert to fractional degrees.

The formula below may be used to convert coordinates from

(deg,min,sec) to decimal degrees

secm in

d eg d eg60

60

ond su tes

d ecim a l rees rees

ff

f f+

= +

Local time may be determined from UTC by the formula below. Round

the result to get zone standard time.

deg

15

r ees E a s t

lo ca l

Long itu d eT U TC= +