Transcript Seasons
Aim: What are some celestial and terrestrial observations? I. Celestial Motions A. Celestial Object – any object observed in the sky during the day or night (ex: stars, moon, planets, sun) 1. Apparent Motion – the motion an object appears to move, but does not actually move in that direction or does not move at all. WHAT DIRECTION DO OBJECTS APPEAR TO MOVE IN THE SKY? From east to west. WHY????? 2. Earth rotates from west to east, causing objects in the sky to appear to be moving from east to west. a. Arc (part of a circle) – shape that an object appears to make in the sky. b. The apparent center of the arcs is Polaris (north star) WHY? i. Since Polaris is located above the Earth’s axis of rotation, the stars and planets seem to rotate counterclockwise around Polaris at approximately 15o per hour. WHY 15o per hour? ii. The apparent daily motion of stars, moon, and planets is due to Earth’s rotation toward the east at a rate of 15o per hour. How long does it take the earth to rotate 360o? 3. Solar Day – the amount of time it takes for the earth to rotate once (24 hours). WHY 24 HOURS? II. Terrestrial Observations A. What are the two main motions of the earth? That is correct!!!! Revolution (orbit) and rotation (spin) on its axis. 1. Evidence of rotation – How do we know that the earth rotates? a. Coriolis Effect – observed path of an object (or fluid) at the surface of the earth undergoing a predictable horizontal deflection. (Rightward deflection in the Northern Hemisphere and leftward deflection in the Southern Hemisphere. b. Focault Pendulum – a free swinging pendulum. When it is allowed to swing freely, it appears to change direction. Focault Pendulum B. Apparent Motion of the Sun 1. Moves from east to west _____ degrees per hour. a. Rises in the ___________ and sets in the _________. http://www.classzone.com/books/earth_science/terc/content/visuali zations/es0408/es0408page01.cfm?chapter_no=visualization C. SEASONS 1. Seasons are a direct result of the relative position of the sun in the sky at different times of the year and also due to Earth’s tilt (23.5o) 2. 1st day of Summer (Summer Solstice) June 21st a. Longest day in Northern Hemisphere b. 23.5o N (Tropic of Cancer)has sun directly overhead (90o) 3. 1st day of Winter (Winter Solstice) December 21st a. Shortest day of year in Northern Hemisphere b. 23.5o S (Tropic of Capricorn) has sun directly overhead 4. The Equinoxes (Autumnal Equinox and Vernal Equinox) September 21st and March 21st a. 12 hours of daylight and 12 hours of darkness b. Sun is directly overhead at the equator