Astronomical Observations: Distance & Light 7/2/09. Astronomy 101

Transcription

1 Astronomical Observations: Distance & Light 7/2/09 Astronomy 101

2 Astronomy Picture of the Day Astronomy 101

3 Something Cool: Lasers on the Moon Astronomy 101

4 Outline for Today Astronomy Picture of the Day Something Cool Business Return Lab 2 Q&A session Distance Lecture Light Lecture Minute Writing Break Lab 4 Astronomy 101

5 Questions for Today How big is the Solar System, Galaxy, Universe? How can we use parallax to find distance? What is light? What is the electromagnetic spectrum and how does wavelength relate to energy? What are brightness and luminosity and how do they change with distance? How can we use standard rods and candles to find distance? Astronomy 101

6 Solar System Astronomy 101

7 Solar System Astronomy 101

8 The Sun is One of Many Stars Solar System Milky Way The Local Group of Galaxies

9 htt://xkcd.com/482 Astronomy 101 htt://xkcd.com/482

10 Place in Order from Smallest to Largest: Galaxy, Solar System, Universe, Local Galaxy Cluster A) Solar System, Galaxy, Local Cluster, Universe B) Local Cluster, Galaxy, Solar System, Universe C) Galaxy, Solar System, Universe, Local Cluster D) Solar System, Universe, Galaxy, Local Cluster Astronomy 101

11 Place in Order from Smallest to Largest: Galaxy, Solar System, Universe, Local Galaxy Cluster A) Solar System, Galaxy, Local Cluster, Universe B) Local Cluster, Galaxy, Solar System, Universe C) Galaxy, Solar System, Universe, Local Cluster D) Solar System, Universe, Galaxy, Local Cluster Astronomy 101

12 Parallax

13 Angular Sizes We measure how big objects appear to be in degrees, arcminutes, & arcseconds. 1 degree = 60 arcminutes = 3600 arcseconds

14 Angular Sizes 1 degree = 60 arcminutes = 3600 arcseconds

15 Parallax -> Distance Parallax Angle, Distance distance 1/(parallax angle)

16 The Facts of Light Emission of Light = Radiation Light sometimes acts like a massless particle Light also acts like a wave.

17 Light as Wave & Particle We ll talk about emission and absorption of individual photons. We ll also often assign wave-like qualities to it 1.Wavelengt h 2.Frequency 3.Velocity 4.Energy

18 Wavelength The distance over which the wave pattern repeats is the wavelength.

19 Wavelength The color of light depends upon its wavelength. Short wavelengths are Blue Long wavelengths are

20 Wavelength We see with our eyes only a tiny fraction of the range of possible wavelengths (radio) Size of atomic nucleus! Size of Mt. Everest! Logarithmic scale : each tic mark represents a factor of ten increase.

21 1. Wavelength (radio )

22

23 If you were to design a pair of glasses for seeing animals at night, you would want them to convert A) Infrared photons to X-ray photons B) X-ray photons to optical photons C) Infrared photons to optical photons D) Optical photons to UV photons

24 If you were to design a pair of glasses for seeing animals at night, you would want them to convert A) Infrared photons to X-ray photons B) X-ray photons to optical photons C) Infrared photons to optical photons D) Optical photons to UV photons

25 Frequency The rate at which peaks pass a given location is the frequency.

26 Velocity The speed of light is constant. The speed of light is closely related to its wavelength and its frequency. If you know one, you can calculate the other! Speed of light (c) = distance between peaks = wavelength X frequency time between peaks

27 Light Years How far light travels in a year About 1016 meters About miles The Sun is eight light minutes away

28 Why use light years? Nearest Star: 40,000,000,000,0 00 kilometers (4 X 1013 km) = 4 light years 206,000 times further than the Earth is from the Sun)

29 It takes a green laser 2.5 seconds to reach the surface of the Moon, off and return. Howbounce long does it take a radio wave to complete the same journey? A) Less time because radio waves have smaller frequency B) More time because radio waves have longer wavelengths C) More time because radio waves are less powerful D) The same time

30 It takes a green laser 2.5 seconds to reach the surface of the Moon, off and return. Howbounce long does it take a radio wave to complete the same journey? A) Less time because radio waves have smaller frequency B) More time because radio waves have longer wavelengths C) More time because radio waves are less powerful D) The same time

31 Energy The energy of a photon depends entirely on its frequency (or wavelength) Energy is greater when.. FREQUENCY WAVELENGTH

32 Energy Dangerous!!! Burns you! Goes through you! Mostly Harmless. (Microwaves only hurt because they have a peculiar interaction with water)

33 Energy Watch your intuition here! BLUE Short wavelength High frequency HIGH ENERGY RED Long wavelength Low frequency LOW ENERGY

34 Which has a longer wavelength? A) Ultraviolet light (UV) B) Visible light C) Infrared Light (IR)

35 Which has a longer wavelength? A) Ultraviolet light (UV) B) Visible light C) Infrared Light (IR)

36 How does light interact with matter? Emit Reflect Absorb Transmit

37 Which is an example of reflected light? A) UV Light from the Sun B) The green color of grass C) Heat from a stove D) Gamma ray radiation from Uranium

38 Which is an example of reflected light? A) UV Light from the Sun B) The green color of grass C) Heat from a stove D) Gamma ray radiation from Uranium

39 Brightness he brightness of a star depends on both distance and luminosity

40 Luminosity And Apparent Brightness Luminosity: Amount of power a star radiates (energy per second = Watts) Apparent Brightness or Flux: Amount of starlight that reaches Earth (energy per second per square meter)

41 These two stars have about the same luminosity -which one appears brighter? A. Alpha Centauri B. The Sun

42 These two stars have about the same luminosity -which one appears brighter? A. Alpha Centauri B. The Sun

43 Another Inverse Distance Squared Law Flux = Luminosity 2 Distance

44 How would the apparent brightness of Alpha Centauri change if it were three times farther away? A. It would be only 1/3 as bright B. It would be only 1/6 as bright C. It would be only 1/9 as bright D. It would be three times brighter

45 How would the apparent brightness of Alpha Centauri change if it were three times farther away? A. It would be only 1/3 as bright B. It would be only 1/6 as bright C. It would be only 1/9 as bright D. It would be three times brighter

46 Standard Candles If we know how much light something is emitting (its luminosity) and how much of its light we are receiving (flux) we can tell how far it is

47 The Magnitude Scale Don't Memorize m = apparent magnitude, M = absolute magnitude apparent brightness of Star 1 1/ 5 m1 - m 2 = (100 ) apparent brightness of Star 2 luminosity of Star 1 = (1001/ 5 ) M 1 - M 2 luminosity of Star 2

48 Minute Writing What concept came most easily to you and what concept was the most difficult? Astronomy 101

49 Assignments Read Chapters 5.3, 5.4, 5.5; Send Jeff and me two questions by Tuesday Read Lab 5; Send Jeff and me one question by Tuesday Lab 4 dues Tuesday News article due Tuesday Astronomy 101