Early Astronomy

1. Early Astronomy

2. The Geocentric Model Geo = Earth Centric = Centred

3. Geocentric Model • First described by Aristotle around 300 B.C. • All celestial bodies seem to move across sky from East-West • Earth must be at the centre, with everything moving around us • Moon, Mercury, Venus, Sun, Mars, Jupiter, Saturn – all fixed on circular spheres orbiting the Earth.

4. About 400 years later, new discoveries in mathematics showed problems with the Geocentric model • Ptolemy (around 100 A.D.), updated the model, adding “epicycles” to the orbits of the planets • This helped to explain the retrograde motion of some planets • In total this model lasted for about 2000 years!

5. The Heliocentric Model • Helio = Sun Centric = Centred

6. Copernicus (1500) devises a new model, with the Sun at the centre Many new discoveries were being made at this time to help prove this model Kepler (1600) improved the model by using ellipses for the orbits instead of circles

8. Formation of the Universe • Because it is believed that the Universe is expanding, it must have started off as something small • The Big Bang occurred around 15-20 billion years ago • Formation of stars and galaxies shortly after

9. We are all Made of Stars • An average star (like our Sun) lives for about 10 billion years • Therefore, many stars have died out since the Big Bang • When a star explodes and dies, it is called a super nova These explosions supply the energy to make the elements which everything is made up from

10. The Solar System • The Sun, and anything orbiting the Sun including the planets & their satellites, comets, meteors, and asteroids. • First existed as a solar nebula (a huge cloud of gas and dust) • Gravity pulls the nebula inward, and it begins to rotate • As the nebula rotates, it forms a flat disk

11. A Rotating Solar Nebula

12. The material in the disk is what formed the planets • This is why all the planets are on the same plane, and all orbit in a CCW direction • The material in the centre is what formed the Sun

13. Galaxy • A large group of stars, gas, and dust bound together by gravitational attractions • The Milky Way is our galaxy • There are approx 200 billion stars in the Milky Way • Scientist estimate that there are 100’s of billions of galaxies

14. The Universe • All space, along with all the matter and radiation in space • Anything and everything!

19. Solar Distances • Distances on Earth are measured in a variety of units, depending on the distance • If really small: Micrometers • Size of a school: Meters • From WPG to VAN: Kilometres

20. Units must change, because it would not make sense to measure the distance from Winnipeg to Vancouver in millimetres! • If this distance was 1900 km, how many mm? • Almost 2 billion! • 1900 km = 1, 900, 000, 000 mm

21. Solar System Measurements • The distance from the Sun to the Earth is 155 million km • This is too large of a number to use, therefore when measuring distances in the Solar System we use Astronomical Units • Each AU = 155 million km

22. Outside the Solar System • For any measurements outside the Solar System, the AU is not very useful • Closest star (Proxima Centauri) is 270 000 AU away • Therefore we need to use a new unit

23. Light Year • A light Year is the distance light can travel in one year • Light moves at 3 X 108 m/s • Earth is 155 million km away • How long does it take light to reach the Earth?

24. 1) Change km to m 1.55 X 108 km = 1.55 X 1011 m • 2) Divide this distance by the speed of light 1.55 X 1011 m / 3 X 108 m/s = 516.75 s

26. The Third Rock From The Sun A geologically active planet - earthquakes, volcanoes - erosion from wind & water Large amounts of liquid water - 70% of Earth’s surface Unique atmosphere among the planets - 80% nitrogen, 19% oxygen

27. When the Earth first formed (4.6 billion years ago) it was entirely molten • Heavier elements sank towards the centre • Lighter elements rose towards the surface • Solid inner core (iron), molten outer core, mantle, crust

28. Earth in Space • The Earth revolves around the Sun once every 365 days • The Earth rotates on it’s axis once every 24 hours • The axis is tilted 23.5 degrees • Always pointed in the same direction (North Star)

29. Reasons for the Seasons • For half the year the Northern Hemisphere is tilted toward the Sun (Summer!) • For half the year the Northern Hemisphere is tilted away from the Sun (Winter) • This is the cause of the seasons!

30. Important Dates • June 21: Summer Solstice • Arctic circle 24 hours daylight • March 21, Sept. 21: Spring & Fall Equinox • Everywhere receives 12 hours of day & night • Dec 21: Winter Solstice • Arctic circle 24 hours of darkness

32. The Moon • The most visible object in the night sky • Can see surface features with the naked eye (Light grey/dark grey areas) • Dark grey areas called “Maria” • Latin for sea (People used to think these areas were large bodies of water)

33. Characteristics • The Moon has many craters • Most small, but some up to 100 km • No water on the moon • No atmosphere • Surface covered with a fine powder and rock fragments

34. How did the Moon Form? • Early Earth struck by Mars sized object • Tons of debris flown into space, orbits around the Earth • This debris later condensed together to form the Moon • Proof for this is in the composition of the Moon

35. Moon Movements • The Moon revolves around the Earth every 27 days • The Moon revolves at the same rate it rotates on its axis (1 moon day = 27 days!) • Because of this, we never see the far side of the Moon • New moon to full moon: Waxing • Full moon to new moon: Waning

37. The Sun • The only star in our SS • Makes up 99.9% of all the mass in the SS • The source of almost all the energy on Earth. • Where does this energy come from?

38. Thermonuclear Reactions • The Sun is made up of mostly Hydrogen and Helium atoms • It is so hot at the core that 2 hydrogen atoms can fuse together to form helium • This is called nuclear fusion • Power plants use nuclear fision (opposite)

39. Sun Atmosphere • The photosphere is the visible layer of the Sun • Not really a “surface” • The chromosphere is visible only during an eclipse • The corona is the outermost region of the Sun’s atmosphere

40. Sun Spots • Regions of the photosphere that appear dark because they are cooler than the surrounding areas • Can be about the size of the Earth • Galileo first discovered sunspots • He found they moved across the sun • This proved the sun rotated on its axis

41. Sunspot cycle every 11 years • Last sunspot maximum: 2001 • Last sunspot minimum: 1996 • When there are many sunspots, Earth is usually warmer • When there are fewer sunspots, Earth is usually colder

44. Solar Flares • Huge eruptions from the photosphere • Occur in large sunspot groups • Radiation from these flares hit Earth, interfere with radio communication, create intense northern lights

46. Asteroids • Left over pieces of rock and metal that did not form planets • Large asteroid belt between Mars and Jupiter…………Destroyed planet????? • Some up to 1000 km in diameter • Paths crossing other asteroids, moons, and planets

48. Comets • AKA “dirty snowballs” • Humans have been aware of comets for a very long time, often considered bad omens • Discovered that comets reappear in cycles • Halley’s Comet: Every 76 years. • Last appearance in 1986, next in 2061

49. Comets are made of two parts 1) Head (coma): Small dense nucleus, surrounded by a large gas section 2) Tail: Made of fine particles of dust and gas. Can be very long The tail can only be seen when the comet approaches close enough to the Sun for it to melt the iced gas The tail always points away from the Sun With each pass, the comet loses some of its mass