Happy Lunar New Year!

Transcription

1 Happy Lunar New Year! (optional) To keep track of time, humans have created calendars based on the Sun (solar) the Moon (lunar) or both! Today is a New Moon Some Asian countries start the year on the second New Moon after the winter solstice. Some New Years Greetings བ" ཤ ས བད ལ གས ལ གསར Happy Losar (Tibet) 恭喜發財 Gung Hay Fat Choy (China) Chúc Mừng Năm Mới (Tết in Vietnam) (Sŏllal in Korea) ᠴᠠᠭᠠᠨ ᠰᠠᠷᠠ (Tsagaan Sar in Mongolia) (Shōgatsu in Japan )

2 More New Years! (optional) Solar calendars (like ours) use the position of the Sun, not the Moon. For example, New Year is celebrated: April 13 in Thailand, Cambodia, Burma, Laos & Sri Lanka March 21 in Iran (Persian Nowruz) The Jewish calendar celebrates Rosh Hashanah (a New Moon, usually in Sept.) The Islamic calendar is purely lunar, so New Year (1st day of Muharram) can be in any season.

3 In Class Voting Sheet Print out from: physics.sfsu.edu/~chris/astro115 A B Bring your voting sheet to EVERY class. Its mandatory... and fun! C D

4 The Annual Motion of the Earth Earth revolves around the Sun The Sun appears in front of just 13 constellations. (Note: You can t see a constellation when the Sun is in front of it)

5 Ecliptic hroughout the year, the Sun moves from one constellation f the Zodiac to another. his path in the sky is called the ecliptic. ut...the dates when this happens have slowly changed.

6 What s Your (Real) Sign? his is where the Sun is found at different times of the year Capricorn - Jan 21 to Feb 17 Aquarius - Feb 17 to Mar 12 Pisces - Mar 12 to Apr 19 Aries - Apr 19 to May 14 Taurus - May 14 to Jun 21 Gemini - Jun 21 to Jul 21 Cancer - Jul 21 to Aug 11 Leo - Aug 11 to Sep 17 Virgo - Sep 17 to Oct 31 Libra - Oct 31 to Nov 21 Scorpius - Nov 21 to Nov 30 Ophiuchus - Nov 30 to Dec 18 Sagittarius - Dec 18 to Jan 21 Note: These dates are based on the true position of the Sun and don t agree with most astrological dates! due to Precession of the Earth s axis.

7 Sun s Annual Cycle The Sun s path through the sky varies annually. The day it reaches greatest height (at noon) is called the Summer Solstice The day it reaches the lowest height (at noon) is called the Winter Solstice Its rising and setting directions also change. anim

8 Seasons Discussion EVERYONE Pair up with a person near you. Introduce yourself. Person whose name comes first alphabetically goes first. 1st person begins by completing this sentence: Seasons on Earth are caused by... 2nd person must either agree or disagree: If you disagree, politely begin: I think the seasons are caused by... If you agree, you must ADD something further that wasn t said by #1 1st person also gets to respond.

9 The Reason for the Seasons Hypothesis: The seasons are caused by the Earth s proximity to the Sun. In Summer, the Earth must be closer to the Sun. Data: When things are closer to a light source (like the Sun) they get hotter. Data: In most of the Northern hemisphere it is warmer in summer (ie June July and August), But in the Southern Hemisphere, just the opposite is true. Data: Earth s distance from the Sun hardly changes in the course of a year. (about 1%) In fact, the Earth is closest to the Sun each year on January 4. Conclusions?

10 Reason for the Seasons The seasons are caused by the tilt of the Earth s Axis In Summer, the Sun s rays are more direct The days are also longer. In Winter, the days are shorter and the Sun s light is slanted, and less powerful The Seasons do NOT occur because the Earth gets closer or farther from the Sun!! tilt? NASA vid.

11 Earth s rotation axis is tilted with respect to: The Ecliptic Plane in which Earth orbits the Sun

12 The other planets also orbit in the Ecliptic Plane.

13 A direct beam of light intercepts a smaller area than a glancing beam. So a direct beam is more intense Spring Winter Fall Summer

14 Summer p.28b

15 Winter p.29c

16 Sun s Path Throughout the Year

17 Seasons: Northern Hemisphere On March 20, the days are as long as the nights & the Sun rises Due East & sets Due West March 20 is the Vernal Equinox, the 1st day of Spring As the Earth orbits, the Sun appears further and further North, and the days get longer until June 20, the Summer Solstice, is the longest day of the year. The Sun rises in the Northeast and sets in the Northwest The days begin to get shorter again.

18 Seasons: Northern Hemisphere On Sept 22, the days and nights are both 12 hours long. Sept 22 is the Autumnal Equinox, the 1st day of Fall The Sun rises Due East & sets Due West As the Earth orbits, the Sun appears further and further South, and the days get shorter until Dec 21, the Winter Solstice shortest day of the year. The Sun rises in the Southeast and sets in the Southwest The days begin to get longer

19 Two Planes in the Sky: Celestial Equator and Ecliptic Plane Earth s axis is not perpendicular to the ecliptic. It is tilted by 23.5 º. The Celestial Equator is determined by Earth s daily rotation The Ecliptic Plane is determined by the Earth s annual orbital motion. These two planes in the sky intersect at the Equinoxes.

20 From Earth s Perspective, the Sun appears to move along the Ecliptic

21 Sun s Apparent Annual Motion

22 Motions of the Moon In the course of one night, the Moon rises & sets just like the Sun However, in the course of one month the Moon appears in different parts of the sky. It also changes its shape

23 Phases of the Moon The Moon goes through a set of phases approximately once every month. In fact, the name month comes from the word moon. The period of the phases, (from Full Moon to Full Moon) is 29.5 Earth days. The different phases have different names

24 Phases of the Moon If the Moon appears to be getting larger each night it is said to be waxing But if its getting smaller, then it s: waning If less than half is visible, it is called crescent More than half: gibbous. When the Moon s face is completely visible, it is a Full Moon If none of the Moon is visible, it is a New Moon

25 Fig. 3-3a, p.31

26 Fig. 3-3b, p.31

27 Fig. 3-3c, p.31

28

29 One month in 5 seconds!