Chap 4: Bad Astronomy

1. Chap 4: Bad Astronomy Mainly inspired by the book “Bad Astronomy”

2. Contents 4.1 Astrology vs. Astronomy 4.2 Seasons 4.3 Big Moon illusion

3. 4.1 Astrology vs. Astronomy • Astrology (占星術)and Astronomy (天文學)are two different subjects. • Astronomy: a scientific study of all phenomena in the universe • Astrology: a study of the relationship between a man’s fate and the constellations, scientists used to regard it as a pseudo-science (偽科學). Physics Department offers astronomy courses but no Astrology course!

4. Astrology 4.1 Astrology vs. Astronomy • A horoscope 天宮圖 shows the locations of the planets, the sun and the moon among the zodiacal signs in the zodiac 黃道帶 at the moment of a person’s birth. • A person’s personality, life history and fate are revealed in his or her horoscope.

5. The zodiacal signs are the 12 constellations in the zodiac. Each constellation occupies one of the 12 houses in the zodiac (黃道十二宮). Aries: Mar. 21 - April 19 Libra: Sept. 23 - Oct. 23 Scorpio: Oct. 24 - Nov. 21 Taurus: April 20 - May 20 Sagittarius: Nov. 22 - Dec. 21 Gemini: May 21 - June 21 Capricorn: Dec. 22 - Jan. 19 Cancer: June 22 - July 22 Aquarius: Jan. 20 - Feb. 18 Leo: July 23 - Aug. 22 Pisces: Feb. 19 - Mar. 20 Virgo: Aug. 23 - Sept. 22

6. 4.1 Astrology vs. Astronomy • zodiac(黄道帶)is in fact the path of the sun on the celestial sphere(天球)due to the orbital motion of Earth • We shall answer What is the celestial sphere? What happens as a consequence of Earth’s orbital motion? What can be found on the zodiac? What are constellations?

7. Q.1 What is the celestial sphere? 4.1 Astrology vs. Astronomy • Objects very far away from us appear to be of equal distance from us

8. Q.1 What is the celestial sphere? 4.1 Astrology vs. Astronomy Model of the sky • Because stars are extremely far away • Appear to be of the same distance from us • stars seem to be attached on a huge sphere – celestial sphere (天球) • We are at the center of the sphere, geocentric?! Space Museum: http://www.lcsd.gov.hk/CE/Museum/Space/Sitemap/c_index.htm

9. Q.2 consequence of Earth’s orbital motion 4.1 Astrology vs. Astronomy • Earth’ axis 23.5 from perpendicular, so • the earth’s equator (celestial) 23.5with its orbital plane

10. Q.2 consequence of Earth’s orbital motion 4.1 Astrology vs. Astronomy • On the celestial sphere, ecliptic makes an angle of 23.5o with celestial equator • The Sun appears to move along ecliptic 黃道(yearly motion of Sun’s path).

11. Q.2 consequence of Earth’s orbital motion 4.1 Astrology vs. Astronomy SunMotion.mpg

12. Nearly linear arrangement of Saturn, Venus, Jupiter, and Mercury (from top to bottom) on March 3, 1999 demonstrates that the planets lie close to the ecliptic.

13. Q.2 consequence of Earth’s orbital motion 4.1 Astrology vs. Astronomy • Pluto was expulsed from the category of planets in 2006. There are eight planets in our solar system. • Planets orbits lie in nearly the same plane as the earths, except Mercury (7)

14. Q.2 consequence of Earth’s orbital motion 4.1 Astrology vs. Astronomy • move in zodiac (黃道帶): a band of width 18 centered on ecliptic.

15. 4.1 Astrology vs. Astronomy Q.3 What can be found on the zodiac? • The ecliptic passes through 13 constellations (12 constellations in astrology). These are the constellations that can be found on the zodiac.

16. 4.1 Astrology vs. Astronomy Q.3 What can be found on the zodiac? • At night, we can only see constellations at the opposite side of the sun, e.g., in January, we can see Gemini (雙子座)but not Sagittarius (人馬座)

18. Q.4 What are constellations? 4.1 Astrology vs. Astronomy • Constellations:visual groupings of stars • Totally 88 today, some added in modern days, e.g., Telescopium 望遠鏡座. • Names of stars in a constellation: brightest star , then  etc., e.g. Sirius 天狼星known as  Canis Major 大犬座 • Usuallyno correlation among the stars in the same constellations

19. Why would we say astrology is a pseudo-science? 4.1 Astrology vs. Astronomy • Astrology cannot make falsifiable predictions. The predictions are so vague (含糊) that we cannot say they are wrong! Here are some highlights of an online astrological predictions You are more of a poet than a rational scientist, for your mind does not function in a strictly logical, linear fashion. My response: Whose mind can function in a STRICTLY logical, linear fashion? Who can always be unaffected by his own emotions?

20. 4.1 Astrology vs. Astronomy Translating your thoughts and impressions into concrete, everyday language may be difficult for you at times and consequently you may appear less intelligent or at least less quick-witted and verbal than others. My response: Human language is never a perfect tool for expression. Everybody in the world faces the same problem. You can be somewhat absent-minded and you become so immersed in your own thoughts that you overlook things in your immediate, tangible environment. My response: Can be absent-minded? Of course I can be, and everyone can be. The problem is: When will I be absent-minded and how? I indeed can never falsify this astrological prediction.

21. Why would we say astrology is a pseudo-science? 4.1 Astrology vs. Astronomy • Astrology cannot explain how the celestial objects and the events on Earth are related. • Sometimes, astrologers are able to give some seemingly scientific arguments to justify their predictions. Here are two examples: • Gravity • Principle of correspondence

22. A. Gravity In some ways, the forces between the Planets involved in Astrology can be simplified into one word: gravity. The Sun has the greatest gravity and the strongest effect in Astrology, followed by the Moon, the Earth's satellite. The other Planets are not truly satellites of the Earth, but nevertheless, they have gravity and so affect the Earth. The Sun controls the Earth's motion and the Moon controls its tides, but the other Planets have their own effects on the Earth -- and on the people who live on Earth. Sometimes their influences can be so strong that they outweigh the Sun's energy! http://www.astrology.com/aboutastrology/overview/understanding/ My response: The Earth’s gravitational force acting upon us is much stronger than that acted by the sun and planets. Even the nurse or doctor standing near me during by birth had stronger gravitational force on me than the planets.

23. B. Principle of correspondence Mars: The planet of passion (激情之星) Mars is the action Planet of the Zodiac. The 'Red Planet,' after all, should be pretty fiery, and Mars does not disappoint. Energy, passion, drive and determination are all right up Mars's alley. This Planet commands you (and yes, Mars does rule the military) to stand up, be noticed and get things done -- sitting on the sidelines belongs somewhere else in the heavens. Simply put, Mars speaks to the power and confident expression of the individual. http://www.astrology.com/aboutastrology/interpreting/planets/mars.html My response: Mars is red because of the iron oxide dust in its atmosphere. We cannot find any relation between the iron oxide dust on Mars and passion, drive and determination.

24. B. Principle of correspondence Moon: Ruler of the emotions As the ruler of the tides, it is fitting that the Moon should be the ruler of our emotions. Still waters run deep? Making waves? A wellspring of emotion? Yes, our emotions have long been portrayed in terms of the sea: fluid, momentous, churning from within. Mood swings, instinct, how we feel about things and how our feelings affect others are all influenced by the Moon. Whereas the Sun gives us our spirit, it's the Moon which gives us our soul. http://www.astrology.com/aboutastrology/interpreting/planets/moon.html My response: The moon causes tides. The working principle is basically the principle of universal gravitation. That our emotions are like water is just an analogue, which does not rely on any physical principle. We cannot say that the moon can affect emotions just because of an analogue.

25. 4.2 Seasons • Since the orbital of Earth is elliptical, Earth is sometimes nearer to the sun, sometimes farther. • When Earth is near to the sun, it is summer. • When Earth is farther from the sun, it is winter. This explanation is wrong!

26. Why wrong? 4.2 Seasons • If the assertion is correct, the whole Earth should be in summer when it is near the sun. This cannot explain why it is winter in Australia while it is summer in the Northern hemisphere. • From detailed measurements, it is known that it is summer in the Northern hemisphere when Earth is far from the sun. So what is the true reason?

27. 4.2 Seasons Remember: Earth’ axis 23.5 from perpendicular

28. 4.2 Seasons • Vernal equinox(春分) 21/3:Sun crosses the celestial equator moving northward • Summer solstice(夏至) 22/6: Sun isfarthest North, and makes an angle of 23.5 northwards • Autumnal equinox(秋分) 23/9:Sun crosses the celestial equator moving southward • Winter solstice(冬至) 22/12: Sun is farthest South, and makes an angle of 23.5 southwards

29. 4.2 Seasons the Sun at Summer solstice(夏至) • Sun shines nearly overhead in Northern hemisphere • sunlight not spread very much, hence very hot in June in Northern hemisphere

30. 4.2 Seasons the Sun at Winter solstice(冬至) • Sunlight strikes the ground at a steepest angle, receives less energy per unit area in Northern hemisphere • sunlight spread very much, hence cold in December

31. 4.2 Seasons Why does it have a longer daytime in summer?

32. 4.2 Seasons the Sun at Summer solstice(夏至) • Sunlight from north of equatorial plane at 23.5 • Longest daytime in North hemisphere; Shortest daytime in South hemisphere

33. 4.2 Seasons the Sun at Winter solstice(冬至) • Sunlight from south of equatorial plane at 23.5 • Shortest daytime in North hemisphere; Longest daytime in South hemisphere

34. 4.2 Seasons Question: What is the daytime at equator when the Sun travels to summer or winter solstice, vernal or autumnal equinox? No matter where the Sun is, there is 12 hrs daytime and 12 hrs nighttime at equator

35. 4.3 Big Moon illusion • It has long been found that the moon looks bigger when it rises or sets. • Tests indicate that the Moon appears about 2 or 3 times larger when on the horizon versus overhead.

36. Background 4.3 Big Moon illusion • The effect has been known for thousands of years. • Aristotle wrote of it in about 350 B.C. • A description was found a clay tablet from the royal library of Nineveh that was written more than 300 years earlier than that date.

37. 3 common wrong explanations: 4.3 Big Moon illusion • The moon is physically nearer to the viewer on the horizon, making it look bigger. • Earth’s atmosphere acts like a lens, magnifying the disk of the Moon. • When we view the horizon Moon we mentally compare it to objects like trees and houses on the horizon, making it look bigger.

38. The moon is bigger when on the horizon • The radius of the moon’s orbit is about 380,000 km. • Earth’s radius is about 6,400 km. The overhead Moon is physically nearer than when on the horizon by 6,400/380,000  2%. Therefore the overhead Moon should appear 2% larger.

39. The atmosphere acts like a lens • Light rays from different parts of the Moon strike at the atmosphere at different angles. • Some bend less and some bend more. • As a result, the atmosphere only flattens the moon instead of making it larger.

40. Wave nature of light: Refraction See tricks of light http://www.youtube.com/watch?v=8ZxG_vyZWCw&feature=related

41. Refraction of light Light ray bends at the interface of two media

42. Refraction of light due to the fact that light speed changes as it enters into another medium.

43. The atmosphere acts like a lens The image seems squeezed!

44. We mentally compare it to objects like trees and houses on the horizon, • The illusion persists when the horizon is clear, as when the Moon is viewed from ships at sea or out airplane windows. • If we position ourselves so that we can see the overhead Moon between tall buildings, it does not look larger.

45. 4.3 Big Moon illusion • A simple measurement by finger: • Wherever the Moon is, the moon always subtends about 0.5o. The angle never becomes 2 or 3 times larger. • That means, the Moon is actually the same size.This is indeed an illusion! Why do we perceive it bigger at horizon?

46. 4.3 Big Moon illusion • In fact, no one knows exactly why it happens • There are two factors, which areBELIEVEDto be most important: • how we judge the size of distant objects • how we perceive the shape of the sky

47. Judgment of the size of distant objects 4.3 Big Moon illusion • The apparent size of an object is inversely proportional to its distance, e.g., someone standing 5 m away might look to be 30 cm tall, but someone twice as far away would look only 15 cm tall. • You certainly don’t think the farther one is half the height of the nearer one, but you perceive them to be the same size. • This effect is called “size constancy”.

48. A B C D E Almost the same, agree? Which pole is longer?

49. Box 4.1Size constancy (大小恆常性) • Size constancy is in fact a survival factor. • If we perceive a predator far away as being smaller, the sense of depth perception would have been messed-up, and we would be caught up easily! • However, we can be fooled by size constancy sometimes. See the following examples.

50. Box 4.1Size constancy (大小恆常性) Which line is longer? 天龍座 a