# Chapter 10: Latitude and Longitude

**At Grade**Created by: CK-12

Any location on Earth is described by two numbers — its **latitude** and its **longitude**. If a pilot or a ship's captain wants to specify position on a map, these are the “coordinates” they would use.

Actually, these are two **angles**, measured in degrees, “minutes of arc” and “seconds of arc.” These are denoted by symbols e.g. 35\begin{align*}^{\circ}\end{align*} 43' 9" means an angle of 35 degrees, 43 minutes and 9 seconds (do not confuse this with the notation (',") for feet and inches!). A degree contains 60 minutes of arc and a minute contains 60 seconds of arc — and you may omit the words “of arc” where the context makes it absolutely clear that these are **not** units of time.

Calculations often represent angles by small letters of the Greek alphabet, and that way latitude will be represented by \begin{align*} \lambda \end{align*} (lambda, Greek L), and longitude by \begin{align*} \phi \end{align*} (phi, Greek F). Here is how they are defined.

PLEASE NOTE: Charts used in ocean navigation often use the OPPOSITE notation — \begin{align*} \lambda \end{align*} for LONGITUDE and \begin{align*} \phi \end{align*} for LATITUDE. The convention followed here resembles the one used by mathematicians in 3 dimensions for spherical polar coordinates (http://www.phy6.org/stargaze/Scelcoor.htm#q65.

An illustration of longitude and latitude.

## Chapter Outline

- 10.1. Latitude
- 10.2. Longitude
- 10.3. About Time: Local and Universal
- 10.4. Local Time (LT) and Time Zones
- 10.5. The Date Line and Universal Time (UT)
- 10.6. Right Ascension and Declination
- 10.7. Exploring Further