2. 1. What’s the difference between astronomy and astrology? 2. What is rotation and revolution? 3. What is a barycenter? 4. Why do we have seasons? 5. What is precession? 6. Draw and label the seasons.

3. Astronomy- the study of space Astrology-predictions about the future based on the stars and planets – Example: horoscopes! – Not a real science, because you can’t prove it, and it’s not based on scientific principals

4.  We’ll be studying ASTRONOMY the next few weeks—not astrology.

5. If you think about a globe of the Earth, it’s tilted The Earth is tilted just like that in space It’s called Earth’s axis It’s the imaginary pole that we spin around on The tilt of the Earth’s axis is 23.5°

6. Rotation- Spinning around on an axis ◦ Does not move the position of the object ◦ Creates days  Revolution- Making a circle around a stationary object, like a star ◦ Physically moves the position of the object  Creates years

7.  Orbit: The same thing as a revolution ◦ Planets, moons, and comets can have orbits, as well as man-made objects

8.  The Earth makes a complete spin on its axis every 23 hours & 56 minutes ◦ 1 day= 1 rotation of the Earth.  It’s daylight when our side of the Earth faces the sun.  It’s nighttime when our side of Earth faces away from the sun.

9. It takes the Earth 365.25 days (or rotations) to travel around the sun once. – This is called a year. – Different planets have different periods of rotations and revolutions

10.  The Earth is rotating (making day and night) at 1,070 mph  The Earth is orbiting around the sun at 67,100 mph

11. PlanetRotation (Length of Day) Revolution (Length of Year) Mercury58.65 days88 days Venus243.01 days225 days Earth24 hours365 days Mars24.62 hours687 days1.89 years Jupiter9.92 hours4,383 days12 years Saturn10.67 hours10,775 days29.52 years Uranus17.23 hours30,681 days84.06 years Neptune16.12 hours60,266 days165.11 years *Pluto6.38 days90,582 days248.17 years

12.  Barycenter: The point between 2 objects where they balance each other ◦ In the case of our sun, the barycenter is located just to the outside of the center ◦ As planets orbit, the sun moves because planets are tugging on it  It just orbits VERY slightly around the barycenter

13. The Earth’s orbit around the Sun is NOT a perfect circle, though it’s very close. – Earth’s orbit is an ellipse Seasons are not caused by how close the Earth is to the sun. In fact, the Earth is closest to the sun around January 3 and farthest away from the sun around July 4. Ellipse

14.  Seasons are caused by the tilt of the Earth's axis. ◦ This tilting is why we have different temperatures in the fall, winter, spring, summer. ◦ The Earth is either leaning towards the Sun, or away from the Sun  This causes parts of the Earth to get either more or less direct sunlight, causing the seasons!

15. Summer: The North Pole tilts towards the sun. Think about reaching out towards a fire. It feels warmer! Winter: The North Pole points away from the sun. Think about leaning back from a fire. It feels colder!

16. ◦ Daylight hours Winter—more hours of darkness Summer— more hours of sunlight Longest day of the year: June 21 st (summer solstice) Shortest day of the year: December 21 st (winter solstice)

17. Depending where you live on the Earth, you are going to have either more or less direct sunlight People living closer to the Equator get more direct sunlight, meaning they have a warmer climate People living closer to the Poles get less direct sunlight, meaning they have a cooler climate It all has to do with the tilt of the Earth’s axis!

18.  Precession: The direction of the Earth’s axis can change, but as long as the tilt stays the same, the seasons stay the same  The Earth's rotation axis is not fixed in space.  Like a rotating top, the direction of the axis changes over a period of 26,000 years ◦ Changes the stars at the Pole  The North Star is no longer the North Star because the axis is no longer pointing at it!  In 3000AD, the star Alra will become our new North Star!

19.  Seasons are caused by the tilt of the Earth’s axis, not how close or far away it is from the Sun ◦ Our axis can change, but as long as the tilt is the same, our season’s are constant

20. Winter Summer Autumn Spring

21.  Work in partners ◦ Keep a constant orbiting speed! ◦ Have the same person orbit each time to keep it equal ◦ Do each distance 3 times, then take the average  On the back, use http://howmanydaysoldami.com/ to figure out how many days old you are! http://howmanydaysoldami.com/