Chapter 1 Astronomy Today 7th Edition Chaisson/McMillan

1. Chapter 1 Astronomy Today 7th Edition Chaisson/McMillan Grab your text book

2. Charting the Heavens Day 2

3. Celestial Sphere The celestial sphere: Stars seem to be on the inner surface of a sphere surrounding the Earth They aren’t, but they can use two-dimensional spherical coordinates (similar to latitude and longitude) to locate sky objects

4. Celestial Coordinates Right Ascension Declination Like latitude except use +/- instead of north and south • Like longitude • Use units of time-hours instead of degrees • 0 hour is the vernal equinox

5. Terms related to the Celestial Sphere Terrestrial System Celestial System South Celestial Pole North Celestial Pole Celestial Equator Declination 0° at celestial Equator Right Ascension 0 Hours at Vernal Equinox • South Pole • North pole • Equator • Latitude • 0° at the Equator • Longitude • 0° at the Prime Meridian

6. Angular Measure • Full circle contains 360° (degrees) • Each degree contains 60′ (arc-minutes) • Each arc-minute contains 60′′ (arc-seconds) • Angular size of an object depends on its actual size and distance from viewer

7. Earth’s Orbital Motion • Daily cycle, noon to noon, is diurnal—solar day • Stars aren’t in quite the same place 24 hours later, though, due to Earth’s rotation around Sun; when they are once again in the same place, one sidereal day has passed

8. Earth’s Orbital Motion Seasonal changes to night sky are due to Earth’s motion around Sun

9. Earth’s Orbital Motion Twelve constellations (some say thirteen) Sun moves through during the year are called the zodiac; path is ecliptic

10. Sun signs • Are based on which constellation the sun was in on the day of your birth • Moon sign: which constellation is the moon is at the time of your birth • Most astrological signs are Incorrectly shown based on your birth where the sun was During Greek times.

11. Ophiucus • The thirteenth zodiac sign • Sun passes through Ophiucus’ foot • November 30-Dec. 18 • He is the serpent bearer • also used as the medical symbol

12. Seasons • Turn to your elbow partner and discuss why you think we have seasons>WHEN YOU THINK YOU HAVE AN ANSWER < DRAW OR DESCRIBE YOUR ANSWER ON YOUR WHITE BOARD> ALL TABLES WILL BE REPORTING WHAT THEY THINK SO BE PREPARED.

13. Ecliptic • If the sun's path is observed from the Earth's reference frame, it appears to move around the Earth in a path which is tilted with respect to the spin axis at 23.5°. • The angle of earth’s axis=the plane of the angle of the ecliptic to the celestial equator

14. Earth’s Orbital Motion • Ecliptic is plane of Earth’s path around Sun; at 23.5° to celestial equator • Northernmost point of path (above celestial equator) is summer solstice; southernmost is winter solstice; points where path crosses celestial equator are vernal and autumnal equinoxes • Combination of day length and sunlight angle gives seasons • Time from one vernal equinox to next is tropical year

15. Seasons • On the Equinox, the Earth experiences equal amounts of day and night • Summer solstice- the sun is at it’s highest point • Winter Solstice –the sun is at it’s lowest point

16. Local co-ordinate systems • Based on the objects above the plane of the horizon • Altitude is the angle above the horizon star altitude horizon NORTH STAR HAS AN ALTITUDE OF 0° IF YOU ARE ON THE EQUATOR THE ALTITUDE OF THE NORTH STAR=YOUR LATITUDE ON EARTH!!!

17. A ROUGH WAY TO ESTIMATE ALTITUDE • PINKY =1° • 3 FINGERS=3° • FIST = 10°

18. Local Co-ordinate System • Azimuth – starts with north a 0° and south is 180° • Zenith is 90° zenith

19. North Star • Even though Polaris is currently the North star, it doesn’t lie due North –and eventually will move Vega will be our North Star, Why do you think this is happening? Discuss with your elbow partner, write down your thoughts on your white board, be ready to defend them.

20. CIRCUMPOLAR STARS • STARS THAT NEVER GO BELOW THE HORIZON • CAN ALWAYS BE SEEN AT NIGHT • http://upload.wikimedia.org/wikipedia/commons/2/21/Zirkumpolar_ani.gif

21. The North Star • Polaris, our current North Star is the 49th brightest star in the night sky!!!!! • To find it, locate the cup of the Big Dipper to the handle of the Little dipper. • It doesn’t appear to move in the night sky but the other stars rotate around it • North pole and Polaris are about 1° off from one another

22. Earth’s Orbital Motion Precession: rotation of Earth’s axis itself; makes one complete circle in about 26,000 years

23. Precession • Wobbles in a 26,000 year cycle • Wobble is between Polaris, Vega and Thuban • Changes the position of the Vernal Equinox which will also change the co-ordinates of the stars

24. SEASONAL CHANGES IN OUR NIGHT SKY • Summer triangle: Vega, Denab, Altair • Winter: Orion, Sirius (Dog Star) • The change occurs about 1°/night

25. 1.4 Earth’s Orbital Motion Time for Earth to orbit once around Sun, relative to fixed stars, is sidereal year Tropical year follows seasons; sidereal year follows constellations—in 13,000 years July and August will still be summer, but Orion will be a summer constellation