Interdisciplinary Space: Studying the Universe for IJSO Training Course

1. Interdisciplinary "Space" Studying the Universe for IJSO training course

2. Content • Solar system – an overview • Order of the planets • Key features of each planet • Asteroids, comets and meteoroids • Stars and their colors • Constellations • Galaxy • Space exploration • Scale model of planets

3. 1. Solar system • Sun: itsmass is about 300,000 times more massive than the Earth. Its radius is 700,000 km, about 110 times that of the Earth. • Energy source: thermonuclear reactions (熱核反應)at the core. • Its atmosphere is divided into 3 layers: • Photosphere (~ 500 km thick) (光球層) • Chromosphere (色球層) • Corona (日冕)

4. 1. Core 2. Radiative zone 3. Convective zone 4. Photosphere 5. Chromosphere 6. Corona 7. Sunspot 8. Granules 9. Prominence (Wikimedia Commons)

5. Sunspots (太陽黑子): cool, dark areas of the solar surface, each consists of a darker, cooler (~ 4,000 K) region called umbra (本影), surrounded by a less cool regioncalled penumbra (半影). A large group of sunspots in year 2004. The grey area around the spots can be seen very clearly, as well as the granulation of the sun's surface. (Wikimedia Commons)

6. Planets (行星): 8 planets and their satellites • lie close to a common plane. • Planets move in nearly circular orbits around the sun in counter-clockwise sense as seen from “above”. • The average distance between the sun and the earth is about 1.5  1011 m, which is also called 1 AU (Astronomical unit).

7. Self-rotation is also in the counter-clockwise sense as seen from “above”, except for Venus and Uranus. • Orbits of planets are not evenly spaced - distances between successive planets increase with their distances from the sun.

8. (Wikimedia Commons)

9. Scale model of planets • Earth: a grain of table salt (0.3 mm in diameter) • Moon: A speck of pepper 1 cm away • Sun: A plum 4 m away • Mercury, Venus, Mars: grains of salt • Jupiter: Apple seed 20 m from the sun • Saturn: Smaller apple seed 36 m from the sun • Uranus: lighter than salt grain • Neptune: lighter than salt grain, 115 m from the sun

10. Dwarf planets (矮行星): “Minor” planets. The first three members are • Ceres (穀神星) --- in the Asteroid Belt • Pluto (冥王星) • Eris [formerly known as 2003 UB313 or Xena (齊娜)]

11. The orbit of Eris (blue) compared to those of Saturn, Uranus, Neptune, and Pluto (white/grey). The arcs below the ecliptic are plotted in darker colours, and the red dot is the Sun. The diagram on the left is a polar view while the diagrams on the right are different views from the ecliptic.

12. Small solar-system bodies: include • Asteroids (小行星):Most can be found in the Asteroid belt (小行星帶) that lies between the orbits of Mars and Jupiter. • Comets (彗星): “Dirty snow balls” moving in highly elliptical orbits around the sun In the solar system, there are the sun, the planets, the dwarf planets and small solar-system bodies.

13. Universal gravitation (萬有引力) • In hammer throw (投鏈球), the tension in the chain keeps the ball moving around a centre. Without the tension, the ball will fly straight away. (Wikimedia Commons)

14. The gravitational force from the sun is just like the tension in an invisible chain that keeps a planet in its orbit around the sun.

15. Inverse square law: The attractive force (F) between any two bodies is directly proportional to the product of their masses (M1 and M2) and is inversely proportional to the square of their separation (r). G = 6.674  10-11 Nm2kg-2

16. Circular motion (圓周運動) • An object is moving in a circle of radius r. Its speed is v. • What is the acceleration of the object? r v

17. Time for the particle to travel from A to B is given by To find the acceleration, we have to know the change in velocity.

18. Magnitude of acceleration a is then

19. To find the instantaneous acceleration at A, we let Dq tend to 0. We also note that sin(x) = x when x is very small, hence Acceleration is Direction: Perpendicular to the velocity and towards the centre, hence centripetal.

20. Example 1 • It is given that the gravitational acceleration on the Earth is 9.81 ms-2 and the radius of the Earth is 6373 km. • Find the mass of the Earth. Solution: Let m be an object on the Earth, M the mass of the Earth, R the radius of the Earth, the weight of the object is

21. Hence From table: 5.97  1024 kg

22. Example 2 • It is given that the mean radius R of the Earth’s orbit is 149600000 km. Mass of the sun M is 1.98911030 kg. Find the period of revolution of the Earth around the sun. Solution: The centripetal acceleration of the Earth is caused by the gravitational attraction from the sun. v: speed of the Earth m: mass of the Earth

23. The period T is therefore

24. 2. Order of the planets

25. Two kinds of planets: Terrestrial (類地行星) • Mercury, Venus, Earth, Mars, all lie in the inner solar system • Relatively dense (~3-5 g cm-3), with cores of iron and nickel surrounded by a mantle of dense rocks. • Small in size and mass • weak gravity • have a few satellites (e.g., one for Earth, two for Mars) and thin atmospheres, no ring systems • Their surfaces are scarred with craters.

26. Two kinds of planets: Jovian (類木行星) • Jupiter, Saturn, Uranus, Neptune, all lie in the outer solar system • Gaseous-like, mainly made up of hydrogen and helium, low-density (1 g cm-3) • They do not have solid surfaces, but have thick liquid layers inside, possibly with small rocky core of Earth’s size.

27. Large in size and mass • strong gravity • all have ringsystems (光環系統), many satellites and thick atmospheres of hydrogen, high atmospheric pressure and a lot of weather activities.

28. 3. Key features of each planet A. Mercury (水星) • Too hot and gravity too weak to hold a thick atmosphere. • Results: • retains a lot of craters • No thick atmosphere to retain heat, large temperature difference between day and night (-173oC – 430oC) (NASA)

29. Mercury in fact has a thin layer of atmosphere, which is mainly made up of sodium and a little helium. The atmospheric pressure is almost zero. The presence of gaseous sodium means the temperature is high enough to allow sodium in rock be released. This is expected as Mercury is so near the Sun. (NASA)

30. Rotation of Venus B. Venus (金星) • Firstly, its self-rotation is in the clockwise sense. (NASA)

31. Secondly, the axis of rotation is almost perpendicular to the orbital plane. (For the Earth, the rotational axis tilts 23.5o.) As a result, there is no seasonal change on Venus. (NASA)

32. The atmosphere of Venus • Venus has a thick atmosphere. The pressure is 90 times that of the Earth. The atmosphere consists of 90% of CO2 , 3% of N2 , and some SO2 . The whole planet is completely covered by clouds made up of sulphuric acid (H2SO4). As a result, the rain on Venus is acidic.

33. Much carbon dioxide • Greenhouse effect (溫室效應) : CO2 traps the heat of solar radiation • very hot surface (470C); the atmosphere is full of vapour of chemical compounds. A schematic representation of the exchanges of energy between outer space, the Earth's atmosphere, and the Earth surface. The ability of the atmosphere to capture and recycle energy emitted by the Earth surface is the defining characteristic of the greenhouse effect. (Wikimedia Commons)

34. Volcano Eista (NASA) Crator Cunitz: diameter ~ 48.5 km (NASA)

35. C. Mars (火星) • Like Earth, the axis of rotation tilts 24o. Hence, there are seasonal changes on Mars. • Mars looks red because its soil contains minerals of iron (like rust). (NASA)

36. The atmosphere of Mars • Mars has a mass less than 11% of Earth’s, its gravity is weak • the atmosphere was much denser billions of years ago, but volatile gases escaped, leaving a thin atmosphere (1% of Earth’s). The chemical composition is mainly carbon dioxide (95%) and nitrogen (3%). • Long ago water was dissociated by the solar radiation (unlike the earth, Mars has no ozone layer to shield the solar ultraviolet radiation) • no liquid water on surface, a little water combined with minerals in soil; polar caps (極冠) contain layers of frozen CO2 (dry ice) with frozen water beneath.

37. (NASA)

38. Although the atmosphere consists mainly of carbon dioxide, it is too thin to trap heat. So, the surface temperature varies enormously, from -100oC to -10oC. Moreover, owing to the long distance from the Sun, the temperature is quite low on average.

39. Features on the surface • Mars is a cratered world having gigantic volcanoes (e.g. Olympus Mons 奧林匹斯山), deep canyons (e.g. Valles Marineris 水手谷), dry channels, and vast dust storm. 5000 km long, 200 km wide and 7 km deep 25 km above the surface and is 600 km in diameter (NASA) (NASA)

40. Large bodies of liquid water may have existed on Mars (NASA)

41. Evidence of old channels and signs of erosion, seemingly carved by running liquid • billions of years ago Mars was much warmer (with a thicker atmosphere) • Large bodies of liquid water may have existed (NASA)

42. Its two satellites (NASA) Deimos Phobos

43. D. Jupiter (木星) • The largest and most massive planet in our solar system. The mass of Jupiter is about 300 times that of the Earth, however its density is low. In fact, these are general features of Jovian planets. • Almost completely made up of gases. (NASA)

44. The rotational period of Jupiter is about 10 hours, and such a high velocity flattens Jupiter at the two poles. • Mainly made up of hydrogen, helium, and a small amount of methane and ammonia. • The atmospheric pressure is extremely high, over 1000 times than that of the Earth. Because of the great pressure, the core of Jupiter is made up of metallic hydrogen. The rapid rotation of such metallic core explains the strong magnetic field of Jupiter.

45. Feature I: Dark belts and light zones (NASA)

46. Feature II: Great Red Spot • A great cyclone lasting for at least 300 years. • 3 times the size of the Earth. • Red: presence of sulphuric compounds. (NASA)

47. (NASA)

48. Feature III: Ring system • The dark and thin ring of Jupiter. It is composed of small particles. (NASA)

49. Satellites • Jupiter has 63 satellites, the four largest ones were discovered by Galileo. (NASA)

50. Io (木衛一) • Famous for its active volcanic activity that emits sulphuric compounds, and has a geologically young surface. (NASA)