Motion of the Earth

Motion of the Earth Name: _______________________________________________ Period: ______ Date: ____________ Essential Question: How do I describe the motion of earth in the universe? One of the important characteristics of the Earth is its movement. Seeing the Sun move through the sky is a result of the fact that the Earth rotates on its axis. Earth rotates on its axis: The Earth is an oblate spheroid that rotates, on its axis, passing through the North and South Poles. The rotation is in a counterclockwise direction, looking down at the North Pole. The time it takes for the Earth to make a complete rotation is approximately 24 hours (exactly 23.934 hours). This rotation results in daytime when an area is facing the Sun and nighttime when an area is facing away from the Sun. Since we are on Earth, we do not sense its rotation, but we experience it by observing the relative motion of the Sun. The shape of the Earth is an oblate spheroid, a sphere flattened on the poles and bulging around the equator Revolves around the Sun: The Earth revolves around the Barycenter of the Solar System, in a counterclockwise direction, once every 365.25 days. Its velocity in space in its orbit is about 18.5 miles per second. The shape of the orbit is a slight ellipse, which Kepler’s First law described. All the planets in the Solar system revolve counterclockwise except for Venus. Venus revolves clockwise. I don’t really know why? Leap years: Since a year has been designated as 365 days, a day is added every 4 years to even things out. That year is called a "Leap Year" and occurs on years divisible by 4, such as 2004. The extra day in a leap year is added in February. Actually, the period is slightly less than 365.25 days. Thus a leap year is any year divisible by 4, except for years that are both divisible by 100 and not divisible by 400. Therefore, the year 2000 was a leap year, but the years 1700, 1800 and 1900 were not. Seasons: The axis of the Earth is on a slight tilt with respect to the orbit around the Sun. That tilt is always in the same direction and results in the changing seasons on the Earth. The reason the seasons change has to do with how direct the Sun is shining, as well as the length of a day. Due to the spherical shape of the Earth, there is more daylight in the summer the closer you get to the pole. One you cross the Arctic Circle in the Northern Hemisphere in summer or the Antarctic Circle in the summer in the Southern Hemisphere, a day can be 24 hours long. That is why they can it "the land of the midnight Sun." Solstices: The solstices are days when the Sun reaches its farthest northern and southern declinations. The winter solstice occurs on December 21 or 22 and marks the beginning of winter (this is the shortest day of the year). The summer solstice occurs on June 21 and marks the beginning of summer (this is the longest day of the year). Equinoxes: Equinoxes are days in which day and night are of equal duration. The two yearly equinoxes occur when the Sun crosses the celestial equator. The vernal equinox ( Spring ) occurs in late March (this is the beginning of spring in the Northern Hemisphere and the beginning of fall in the Southern Hemisphere); the autumnal equinox ( Fall ) occurs in late September (this is the beginning of fall in the Northern Hemisphere and the beginning of spring in the Southern Hemisphere). Since the orbit of the Earth around the Sun is an ellipse, surprisingly, the Earth is closer to the Sun for a Northern Hemisphere winter than it is in the summer. That would imply that the Southern Hemisphere has slightly colder winters and warmer summers than the Northern. Other motion: Besides spinning on its axis and revolving around the Sun, the Earth also follows the Sun's movement through the Milky Way galaxy. The Sun and its planets are moving toward the star Vega at a velocity of about 12 miles per second. The Sun and Vega are rotating around the center of the Milky Way at about 150 miles per second. The Milky Way—in turn—is moving through space, as part of the apparent expansion of the Universe. Its estimate velocity is thousands of miles per second depending on which galaxy you compare it. Since the distances are so great, we will never notice these motions with respect to the other stars and galaxies in the immense Universe. Clarifying Questions: counterclockwise direction 1. The rotation is in_____________________________, looking down at the North Pole. The time it takes for the 24 hours Earth to make a complete rotation is approximately ______________(exactly 23.934 hours). This rotation daytime nighttime results in ________when an area is facing the Sun and ___________ when an area is facing away from the Sun. 2. Study the Figure on the top front page. Describe the “Sun’s Path” on December and January. In December, the Sun's path appears lower in the sky, resulting in shorter daylight hours and longer nights. In January, the _____________________________________________________________________________________________ Sun's path gradually starts to rise higher in the sky, leading to slightly longer daylight hours compared to December. _____________________________________________________________________________________________ 3. How does Earth’s rotation result to daytime and nighttime? Earth's rotation causes different parts of the planet to face towards or away from the Sun at different times, creating the _____________________________________________________________________________________________ cycle of daytime and nighttime. _____________________________________________________________________________________________ 4. Why do observe the Sun moving through the sky? Think! We observe the Sun moving through the sky due to the Earth's rotation on its axis, which creates the illusion of the Sun _____________________________________________________________________________________________ moving across the sky from east to west. _____________________________________________________________________________________________ 5. Describe the shape of Earth, which is an oblate spheroid. Earth's shape is an oblate spheroid, meaning it is mostly spherical but slightly flattened at the poles and bulging at the equator. _____________________________________________________________________________________________ _____________________________________________________________________________________________ Sun 6. The Earth revolves around the_______________________________________, in a counterclockwise direction, 365.25 days miles per hourmiles per second. The once every __________________. Its velocity in space in its orbit is about 67,000 _______________ ellipse first shape of the orbit is a slight _______________________, which Kepler’s ____________ law described. All the Venus planets in the Solar system revolve counterclockwise except for _____________. 7. Why do we have leap years? Think! We have leap years to account for the fact that the Earth's orbit around the Sun is not exactly 365 days long. Adding an extra _____________________________________________________________________________________________ day every four years helps to synchronize our calendar with the astronomical year. _____________________________________________________________________________________________ 8. Why do we have seasons (Winter, Spring, Summer, and Fall)? Think! ( 10 pts.) Seasons are caused by the tilt of the Earth's axis relative to its orbit around the Sun. This tilt causes different parts of the Earth _____________________________________________________________________________________________ to receive varying amounts of sunlight throughout the year, resulting in changes in temperature and weather patterns. _____________________________________________________________________________________________ 9. When is it daytime for 24 hours Arctic and the Antarctic Circle? It is daytime for 24 hours in the Arctic Circle during the summer solstice (around June 21st) and in the Antarctic Circle during _____________________________________________________________________________________________ the winter solstice (around December 21st). _____________________________________________________________________________________________ winter December 21st 11. The ______________solstice occurs on __________________and marks the beginning of winter (this is the shortest summer June 21st ____________ day of the year). The _____________ solstice occurs on ____________ and marks the beginning of longest summer (this is the _______________ day of the year). 12. How are the solstices different from the equinoxes? Think! Solstices mark the longest and shortest days of the year, while equinoxes mark the days when day and night are approximately _____________________________________________________________________________________________ equal in length. Solstices also mark the beginning of summer and winter, while equinoxes mark the beginning of spring and autumn. _____________________________________________________________________________________________ 13. Why are winters colder and summers warmer in the Southern hemisphere? Think! ( 10 pts.) Winters are colder and summers are warmer in the Southern Hemisphere because of the tilt of the Earth's axis. When the _____________________________________________________________________________________________ Southern Hemisphere is tilted towards the Sun, it experiences summer, and when it is tilted away, it experiences winter. _____________________________________________________________________________________________ 14. How is Earth moving in relation to the Sun, Vega, Milky Way galaxy, and the Universe? Think! ( 10 pts.) Earth orbits the Sun, along with the rest of the solar system, which is part of the Milky Way galaxy. The Milky Way galaxy is _____________________________________________________________________________________________ also in motion within the universe, but Earth's movement relative to the universe is complex and includes rotation, orbit, and the expansion of the universe. _____________________________________________________________________________________________ 15. Challenge! Multiple Choice Choices: B ______a. A Universe is made up of _______ A. star/s, planets, moons, asteroids C ______b. A Galaxy is made up of _______ B. galaxies A ______c. A Solar system is made up of _______ C. nebulae, clusters, Solar Systems