Unit I - Lesson I “Foundations of Astronomy ”

1. Astronomy Unit I - Lesson I “Foundations of Astronomy”

2. S.W.B.A.T. (Students Will Be Able To...) • Identify our place in space • Understand relative sizes of objects in space and discuss constellations • Explain the celestial sphere and how objects are located in space • Discuss how time is measured; precession & the seasons

3. Our Place in Space • Earth: (small) 15 thousand km (12,000 miles) in diameter • Sun: 15 million km in diameter • Solar System: about 6 billion km in diameter

4. Solar System

5. Our Place in Space • Light year – distance that light travels in one year or about 6 trillion miles (10 trillion km) • Local Stellar Neighborhood- 10 light years in diameter or about 60 trillion miles (90 trillion km)

6. Our Place in Space • Milky Way Galaxy- 1000 quadrillion km or 100,000 light years in diameter • It would take a beam of light 100,000 years to cross the entire galaxy!

7. The Milky Way Galaxy

8. Our Place in Space • Local Group-10 million light years in diameter • Includes 35 galaxies with the Milky Way & Andromeda the largest members

9. Our Place in Space • Astronomy – study of the universe • Universe - billions of galaxies (100?) • Includes everything that exists - all space, time, matter & energy • Video (2:34) “Let’s Talk About Size”

10. Hubble Space Telescope (HST) Deep-Field Camera Photo – Every Dot or “Smudge” is a Galaxy!

11. Constellations • Patterns of stars in the night sky • Named after mythological beings, heroes or animals • 88 constellations (mostly Greek) are recognized in the Western world • Different cultures grouped stars differently

12. Constellations • Ecliptic – plane in which the Sun & planets travel • Zodiac – 12 major constellations in the ecliptic

13. Constellations • Astrology (not a science) uses relative positions of stars and planets to attempt to predict the future • Astronomy & astrology were once the same in the distant past

14. Constellations • Celestial Sphere – model of stars & constellations that rotate around an unmoving Earth • Polaris (or the “North Star”) does not move • All other stars move around Polaris in circles due to Earth’s rotation

15. Polaris

17. Polaris is Part of a Triple-Star System – Artist Concept

18. Constellations • Celestial coordinates are used to locate specific stars & constellations on the sphere • Right Ascension (RA) – or “longitude” are the “up & down” lines in the sky • Declination (dec) – or “latitude” are the “side to side” lines

20. Constellations • Azimuth - angle of horizontal deviation from north • Ex. exact North = 0°, exact East = 90°, exact South = 180°, exact West = 270°, exact North = 360° (or 0°)when using a compass • Celestial coordinates uses hours, minutes & seconds (smaller units of degrees)

21. Constellations • 360o / 24 (hours in a day) = 15o • So 15o = 1 hour • Altitude - ranges from 0 to 90 degrees, and measures the angle between the horizon; you and the object • Ex. an object with 0 degrees altitude is right on the horizon; while an object at 90 degrees altitude is directly overhead

22. Telescope Altitude Adjustment Gauge

23. Earth’s Motions • Sidereal Day – takes into account that the Earth is also revolving around the Sun as it rotates • Solar Day – Earth spins once on it’s axis every 24 hours • Sidereal day is only 23 hours & 56 minutes long • Video (0:42)“Sidereal vs. Solar Day”

25. Earth’s Motions • Earth takes 365.24 days to revolve around the Sun • Solstices – farthest north & south that the Sun appears in the sky • Equinoxes – when the Sun appears directly over the equator (equal day & night)

26. Earth’s Motions • Earth’s 23.5 degree tilt along with its orbit around the Sun is the cause of seasons

27. Earth’s Motions • Precession – Earth gyrates like a spinning top (cycle of 26,000 years) • Caused by gravitational forces from the Sun & Moon • In 11,000 years the seasons will be reversed • Video (6:00)“Mechanisms of the Seasons”

28. Classwork Assignment