Origin of Modern Astronomy

2. Origin of Modern Astronomy

3. Ancient Greeks Early Astronomy  Astronomy is the science that studies the universe. It includes the observation and interpretation of celestial bodies and phenomena.  The Greeks used philosophical arguments to explain natural phenomena.  The Greeks also used some observational data.

4. Ancient Greeks Early Astronomy  Geocentric Model = Ptolemy Greek Astronomer • In the ancient Greeks’ geocentric model, the moon, sun, and the known planets—Mercury, Venus, Mars, and Jupiter—orbit Earth.  Heliocentric Model = Nicolaus Copernicus • In the heliocentric model, Earth and the other planets orbit the sun.

5. Ancient Greeks March Feb. Jan. Dec. April Sept. May June July Retrograde motion of Mars Aug. East West Early Astronomy  Ptolemaic System • Ptolemy created a model of the universe that accounted for the movement of the planets. • Retrograde motion is the apparent westward motion of the planets with respect to the stars.

7. Retrograde Motion

8. 99 Years of Astronomy

9. The Birth of Modern Astronomy Early Astronomy  Nicolaus Copernicus • Copernicus concluded that Earth is a planet. He proposed a model of the solar system with the sun at the center. Heliocentric Model This model explained the retrograde motion of planets better than the geocentric model.

10. The Birth of Modern Astronomy Early Astronomy  Tycho Brahe • Tycho Brahe designed and built instruments to measure the locations of the heavenly bodies. Brahe’s observations, especially of Mars, were far more precise than any made previously.  Johannes Kepler • Kepler discovered three laws of planetary motion: 1. Orbits of the planets are elliptical. 2. Planets revolve around the sun at varying speed. 3. There is a proportional relationship between a planet’s orbital period and its distance to the sun.

11. The Birth of Modern Astronomy Early Astronomy German astronomer Johannes Kepler (1571-1630) helped establish the era of modern astronomy by deriving three laws of planetary motion.

12. Johannes Kepler • 1599 – Kepler hired by Tycho Brahe • Work on the orbit of Mars • 1609 – Kepler’s 1st and 2nd Laws • Planets move on ellipseswith the Sun at one focus • The radius vector sweeps out equal areas in equal times • 1618 – Kepler’s 3rd Law • The squareof a planet’s orbital period P is proportional to the cubeof its semi-major axis R. • P2 = a3 where P is measured in years and a is measured in AU

13. Earth’s orbit January 15th Equal areas June 15th (30 days) (30 days) Sun July 15th December 15th KEPLER’S EQUAL AREA LAW states that a line connecting Earth to the sun will pass over equal areas of space in equal times. Because Earth’s orbit is elliptical, Earth moves faster when it is nearer to the sun. Early Astronomy Johannes Kepler used Tycho Brahe’s data to develop three laws that explained the motions of the planets.

14. Early Astronomy KEPLER’S EQUAL AREA LAW states that a line connecting Earth to the sun will pass over equal areas of space in equal times. Because Earth’s orbit is elliptical, Earth moves faster when it is nearer to the sun. Equal areas law Faster Slower

15. Early Astronomy  Galileo Galilei Italian scientist Galileo Galilei (1564—1642) used a new invention, the telescope, to observe the Sun, Moon, and planets in more detail than ever before.

16. The Birth of Modern Astronomy Early Astronomy  Galileo Galilei • Galileo’s most important contributions were his descriptions of the behavior of moving objects. • He developed his own telescope and made important discoveries: 1. Four satellites, or moons, orbit Jupiter. 2. Planets are circular disks, not just points of light. 3. Venus has phases just like the moon. 4. The moon’s surface is not smooth. 5. The sun has sunspots, or dark regions.

18. Early Astronomy  Sir Isaac Newton English scientist Sir Isaac Newton (1642—1727) explained gravity as the force that holds planets in orbit around the Sun.

19. The Birth of Modern Astronomy Early Astronomy  Sir Isaac Newton • Although others had theorized the existence of gravitational force, Newton was the first to formulate and test the law of universal gravitation. The universal law of gravitation, helped explain the motions of planets in the solar system.  Universal Gravitation • Gravitational force decreases with distance. • The greater the mass of an object, the greater is its gravitational force.

20. Gravity’s Influence on Orbits

21. Newton’s Laws of Motion • 1st Law • A body at rest, or in uniform motion, will remain so unless acted upon by an unbalanced force. • 2nd Law • The change in motion (acceleration) is proportional to the unbalanced force • 3rd Law • For every action there is an equal and opposite reaction

22. Gravity • Gravity is the force that • holds us to the Earth • causes a rock to fall towards the ground • causes the Earth to go around the Sun • causes the Sun to be pulled towards the center of the Milky Way galaxy • Gravity acts between any two objects even if they are far apart. • “action at a distance”

23. Summary • Kepler’s and Galileo’s Laws provided Newton with important clues that helped him formulate his laws of motion • Newton arrived at 3 laws that govern the motion of objects • The law of inertia • The law of force • The law of action and reaction • Newton also arrived at a law of gravity • But it seemed to require action at a distance!

24. Earth Science Light and Astronomical Observations

25. Important Astronomical Measurements • An ellipseis an oval-shaped path. An astronomical unit (AU)is the average distance between Earth and the sun; it is about 150 million kilometers. Light-year The distance that light travels in one year, about 9.5 trillion kilometers. Parsec: A unit of measurement used to describe distances between celestial objects, equal to 3.258 light-years.

26. The study of light Electromagnetic radiation • Visible light is only one small part of an array of energy • Electromagnetic radiation includes • Gamma rays • X-rays • Ultraviolet light • Visible light • Infrared light • Radio waves *Energy radiated in the form of a wave, resulting from the motion of electric charges and the magnetic fields they produce.

27. The study of light • Electromagnetic radiation • All forms of radiation travel at 300,000 kilometers (186,000 miles) per second • Light (electromagnetic radiation) can be described in two ways • Wave model • Wavelengths of radiation vary • Radio waves measure up to several kilometers long • Gamma ray waves are less than a billionth of a centimeter long • White light consists of several wavelengths corresponding to the colors of the rainbow A continuum depicting the range of electromagnetic radiation, with the longest wavelength at one end and the shortest at the other.

28. Light (electromagnetic radiation) can be described in two ways • Particle model • Particles called photons • Exert a pressure, called radiation pressure, on matter • Shorter wavelengths correspond to more energetic photons

29. The study of light • Spectroscopy • The study of the properties of light that depend on wavelength • The light pattern produced by passing light through a prism, which spreads out the various wavelengths, is called a spectrum (plural: spectra)

30. The study of light A spectrum is produced when white light passes through a prism

31. The study of light • Spectroscopy • Types of spectra • Continuous spectrum: A spectrum that contains all colors or wavelengths. • Produced by an incandescent solid, liquid, or high pressure gas • Uninterrupted band of color • Dark-line(absorption) spectrum • Produced when white light is passed through a comparatively cool, low pressure gas • Appears as a continuous spectrum but with dark lines running through it

32. Formation of the three types of spectra

33. Emission spectrum of hydrogen Absorption Spectrum of Hydrogen Emission Spectrum Absorption Spectrum A continuous spectrum crossed by dark lines produced when light passes through a nonincandescent gas. A spectrum consisting of individual lines at characteristic wavelengths produced when light passes through an incandescent gas; a bright-line spectrum.

34. The study of light • Doppler effect • The apparent change in wavelength of radiation caused by the relative motions of the source and observer • Used to determine • Direction of motion • Increasing distance – wavelength is longer ("stretches") • Decreasing distance – makes wavelength shorter ("compresses") • Velocity – larger Doppler shifts indicate higher velocities

35. The Doppler effect Originally discovered by the Austrian mathematician and physicist, Christian Doppler (1803-53), this change in pitch results from a shift in the frequency of the sound waves.

36. The Doppler effect The electromagnetic radiation emitted by a moving object also exhibits the Doppler effect. • Redshift, a phenomenon of electromagnetic waves such as light in which spectral lines are shifted to the red end of the spectrum.

37. Redshift: This spectrum shows hydrogen shifted to the red end of the spectrum. This star is moving away from Earth. Blueshift: This spectrum shows hydrogen shifted to the blue end of the spectrum. This star is moving toward Earth. The Doppler effect The radiation emitted by an object moving toward an observer is squeezed; its frequency appears to increase and is therefore said to be blueshifted. In contrast, the radiation emitted by an object moving away is stretched or redshifted. Blueshifts and redshifts exhibited by stars, galaxies and gas clouds also indicate their motions with respect to the observer.

38. Astronomical tools • Optical (visible light) telescopes • Two basic types (1) Refracting telescope • Uses a lens (called the objective) to bend (refract) the light to produce an image • Light converges at an area called the focus • Distance between the lens and the focus is called the focal length • The eyepiece is a second lens used to examine the image directly • Have an optical defect called chromatic aberration (color distortion)

39. A simple refracting telescope

40. Astronomical tools • Optical (visible light) telescopes • Two basic types (2) Reflecting telescope • Uses a concave mirror to gather the light • No color distortion • Nearly all large telescopes are of this type

41. A prime focus reflecting telescope

42. Cassegrain focus reflecting telescope

43. Newtonian focus reflecting telescope

44. The 200" (5m) Hale Reflector of Palomar Observatory is shown above. Until recently it was the world's largest optical/infrared telescope.

45. Astronomical tools • Optical (visible light) telescopes • Properties of optical telescopes • Light-gathering power • Larger lens (or mirror) intercepts more light • Determines the brightness • Resolving power • The ability to separate close objects • Allows for a sharper image and finer detail

46. Astronomical tools • Optical (visible light) telescopes • Properties of optical telescopes • Magnifying power • The ability to make an image larger • Calculated by dividing the focal length of the objective by the focal length of the eyepiece • Can be changed by changing the eyepiece • Limited by atmospheric conditions and the resolving power of the telescope • Even with the largest telescopes, stars (other than the Sun) appear only as points of light

47. Astronomical tools • Detecting invisible radiation • Radio radiation • Gathered by "big dishes" called radio telescopes • Large because radio waves are about 100,000 times longer than visible radiation • Often made of a wire mesh • Have rather poor resolution • Can be wired together into a network called a radio interferometer

48. Radio Telescope A steerable radio telescope at Green Bank, West Virginia

49. Astronomical tools • Detecting invisible radiation • Radio radiation • Gathered by "big dishes" called radio telescopes • Advantages over optical telescopes • Less affected by weather • Less expensive • Can be used 24 hours a day • Detects material that does not emit visible radiation • Can "see" through interstellar dust clouds

50. Radio Telescope The 300-meter radio telescope at Arecibo, Puerto Rico