1. The Earth in Space
Ch 26

2. Astronomy The scientific study of the universe
Scientist who study the universe are called what?
Astronomers
What are some important things astronomers do?
Discover new stars, galaxies, planets, & black holes
Protect Earth against objects that may hit us

3. The Universe
Galaxy – a collection of stars, dust, and gas bound together by gravity.
Our solar system is part of what galaxy?
Milky-Way Galaxy
What are some things found in our solar system?
Earth
Sun
Other planets
Small asteroids and comets

4. Measuring Distances in Space
astronomical unit the average distance between the Earth and the sun; approximately 150 million kilometers (symbol, AU)
Astronomers also use the speed of light to measure distance
Light travels at 300,000,000 m/s. In one year, light travels x 1012 km. This distance is known as a light-year.

5. Earth’s Rotation Rotation – The spin of a body on its axis
Does the Earth rotate from west to east or east to west?
West to east
At any given time, Earth’s hemisphere facing the sun is experiencing daylight and the Earth’s hemisphere away from the sun is experiencing night time.

6. Earth’s Rotation
perihelion the point in the orbit of a planet at which the planet is closet to the sun
aphelion the point in the orbit of a planet at which the planet is farthest from the sun
Earth’s orbit around the sun is an ellipse
An ellipse is a closed curve whose shape is determined by two points, or foci, within the ellipse
Earth is not always the same distance away from the sun

7. Earth’s Orbit

8. The Revolving Earth
Revolution – the motion of a body that travels around another body in space; one complete trip along an orbit
Earth’s revolution around the sun causes seasons to occur.
At what speed does the Earth travel around the sun?
29.8 km/s
How long does it take Earth to orbit the sun? Be specific!
365 ¼ days ~ 1 year

9. The Foucault Pendulum How did we figure out the Earth was spinning?
A brilliant man used a pendulum!
Jean-Bernard-Leon Foucault – scientist who provided evidence of Earth’s rotation by using a pendulum

10. The Coriollis Effect
The rotation of Earth causes ocean currents and wind belts to curve to the left or right.
This curving is caused by Earth’s rotation and is called the Coriolis effect.

11. Earth’s Rotation
Question: What’s one way we can prove the Earth is rotating?
As the night passes, the constellations move in the sky. (Earth’s rotation)
Earth’s revolution around the sun is evidenced by the apparent motion of constellations.
Thus different constellations will appear in the night sky as the seasons change. (Earth’s revolution)

12. Constallation
constellation - a group of stars that are organized in a recognizable pattern.
As the night goes on, constellations appear to change positions in the sky – this is caused by the rotation of the Earth.

13. Measuring Time
Earth’s rotation = one day (about 24 hours)
Earth’s revolution = one year (about 365 ¼ days)
Moon’s revolution = 29.5 days
calendar - a system created for measuring long intervals of time by dividing time into periods of days, weeks, months, and years.
Question: Why do we have a leap year?
Since a year has an extra ¼ day, every 4 years we add a day to the month of February
Who revised the calendar to account for the extra day every four years? – Julius Ceaser

14. Measuring Time con’t.
The modern calendar was created by Pope Gregory XIII – much like the acient ROMANS
Time Zone – 24 different time zones. The zone to the east is an hour later than the zone on the west.
Each time zone is about 15 degrees apart
International Date Line
International Date Line was established to prevent confusion about the point on Earth’s surface where the date changes.
The line runs from north to south through the Pacific Ocean. The line is drawn so that it does not cut through islands or continents.

15. Measuring Time con’t.
Daylight Savings Time - Because of the tilt of Earth’s axis, daylight time is shorter in the winter months than in the summer months

16. Season’s Earth’s axis is tilted at 23.5˚.
Question?? Earth’s axis always points towards what??
– North Star
Changes in the angle at which the sun’s rays strike Earth’s surface cause the seasons.

18. Equinoxes
equinox the moment when the sun appears to cross the celestial equator
- at an equinox, the sun’s rays hit the Earth’s equator at a 90 degree angle.
Night and day light are appx. Equal everywhere on Earth.
The autumnal equinox occurs September of each year and marks the beginning of fall in the Northern Hemisphere.
The vernal equinox occurs on March 21 or 22 of each year and marks the beginning of spring in the Northern Hemisphere.

19. The Season’s con’t
solstice the point at which the sun is as far north or as far south of the equator as possible
The summer solstice occurs on June 21 or 22 of each year and marks the beginning of summer in the Northern Hemisphere.
Most daylight in the summer solstice!!!!
The winter solstice occurs on December 21 or 22 of each year and marks the beginning of winter in the Northern Hemisphere.