Overview
This lecture explains how to determine your latitude using the North Star (Polaris) and introduces the concept of time zones and how they relate to Earth's rotation.
Determining Latitude with Polaris
- Polaris, also called the North Star, is not the brightest star but is important for navigation.
- The Earth's axis points nearly directly at Polaris, making it a stable reference in the night sky.
- The angle between Polaris and the horizon equals your latitude if you are in the Northern Hemisphere.
- To find Polaris, locate the Big Dipper; use its "pointer stars" to trace a line to Polaris.
- Polaris is the last star in the handle of the Little Dipper, but the Little Dipper is harder to find.
- Measuring the angle (in degrees) from the horizon to Polaris gives your latitude north (e.g., 52° above the horizon = 52°N latitude).
Polaris in Culture
- Alaska's state flag features the Big Dipper and Polaris due to the state's northern location.
- Polaris is used for orientation—wherever Polaris is in the sky, that direction is North.
Understanding Time Zones
- The apparent movement of the sun (sunrise/sunset) is due to Earth's rotation on its axis.
- Earth rotates 360° in 24 hours, so each hour corresponds to 15° of longitude.
- Time zones are approximately 15° wide, but boundaries are adjusted for state/country borders.
- As Earth rotates eastward (counterclockwise when viewed from above the North Pole), places east experience sunrise and time earlier than those to the west.
- The United States has several time zones: Eastern, Central, Mountain, Pacific, Alaska, and Hawaii, each typically one hour apart.
Time Zone Examples & Calculations
- The time difference between adjacent time zones is one hour.
- To find the local time in another time zone, count the number of time zones between locations and adjust the hour accordingly.
- When traveling west, subtract hours; when traveling east, add hours (e.g., 3 p.m. in Eastern = 12 p.m. in Pacific).
Key Terms & Definitions
- Polaris (North Star) — The star located nearly above Earth's North Pole, used to determine latitude.
- Latitude — The angular distance north or south of the equator, measured in degrees.
- Horizon — The line where the sky appears to meet the ground.
- Pointer Stars — The two stars at the end of the Big Dipper used to locate Polaris.
- Time Zone — A region where the local time is set to the same standard; typically 15° of longitude wide.
- Longitude — The angular distance east or west of the Prime Meridian.
Action Items / Next Steps
- Practice finding the Big Dipper and Polaris in the night sky.
- Measure the angle between Polaris and the horizon to estimate your latitude.
- Copy diagrams and time zone calculations into your notes.
- Complete the remaining time zone practice questions on your own.