1. Light and Astronomical Observations
Earth Science
Light and Astronomical Observations

2. Important Astronomical Measurements
• An ellipse is 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 light-years.

3. 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.

4. The study of light Electromagnetic radiation Wave model
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.

5. 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

6. 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)

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

8. 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

9. Formation of the three types of spectra

10. Emission Spectrum Absorption Spectrum
Emission 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.
Absorption Spectrum of Hydrogen

11. 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

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

13. 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.

14. The Doppler effect
Blueshift: This spectrum shows hydrogen shifted to the blue end of the spectrum. This star is moving toward Earth.
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.
Redshift: This spectrum shows hydrogen shifted to the red end of the spectrum. This star is moving away from Earth.

15. 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)

16. A simple refracting telescope

17. 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

18. A prime focus reflecting telescope

19. Cassegrain focus reflecting telescope

20. Newtonian focus reflecting telescope

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

22. 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

23. 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

24. 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

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

26. 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

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

28. The Big Bang Theory
The theory holding that the universe originated from the instant expansion of an extremely small agglomeration of matter of extremely high density and temperature.

29. Photons converted into particle-antiparticle pairs and vice-versa
E = mc2
Early universe was full of particles and radiation because of its high temperature

31. The Big Band Theory Evidence for Big Bang
This is the theory of the universe’s earliest moments.
It presumes that the universe began from a tiny, hot, and dense collection of matter and radiation.
It describes how expansion and cooling of particles could have led to the present universe of stars and galaxies.
It explains several aspects of today’s universe with a very good accuracy.

32. The Big Band Theory
The Big Bang theory is a model, which explains some facts (observations).
It should be able to make predictions that can be verified through observations or experiments.
Two important predictions:
Cosmic microwave background radiation.
2. Fusion of original hydrogen into helium.

33. The Cosmic Background Radiation (Microwaves)
Evidence for the Big Bang
The Cosmic Background Radiation (Microwaves)
Penzias & Wilson (1962) discovered an isotropic background microwave signal during testing a microwave antenna at Bell Labs in The noise was found to be coming from every direction.
At the same time, physicists from Princeton calculated the expected radiation from the initially hot universe.They suggested that this radiation could be detected with a microwave antenna.
The result was a Nobel Prize in physics for 1978.

34. The Cosmic Microwave Background

35. The Cosmic Background Radiation (Microwaves)
Background radiation from Big Bang has been freely streaming across universe since atoms formed at temperature ~ 3,000 K: visible/IR

36. The Cosmic Microwave Background
The background consists of photons (radiation) arriving at Earth directly from the end of the era of nuclei (when the Universe was about 380,000 years old).
Neutral atoms captured most of the electrons.
Photons were released and have flown freely through the universe ever since.
This background radiation can be detected with a small TV antenna as part (1%) of static “snow”. The redshifted spectrum of the background radiation has now a temperature of 2.73 K.

37. Cosmic Background Explorer
The first satellite built dedicated to cosmology. Its goals were to investigate the cosmic microwave background radiation (CMB) of the universe and provide measurements that would help shape our understanding of the cosmos.

38. Cosmic Background Explorer
This work helped cement the big-bang theory of the universe. According to the Nobel Prize committee, "the COBE-project can also be regarded as the starting point for cosmology as a precision science". Two of COBE's principal investigators, George Smoot and John Mather, received the Nobel Prize in Physics in 2006.

39. Cosmic Background Explorer

40. Cosmic Background Explorer
The "famous" map of the CMB anisotropy formed from data taken by the COBE spacecraft.

41. Evidence for the Big Bang
In 1927, the Belgian priest Georges Lemaître was the first to propose that the universe began with the explosion of a primeval atom.

42. Evidence for the Big Bang
Edwin Hubble found experimental evidence to help justify Lemaître's theory. He found that distant galaxies in every direction are going away from us with speeds proportional to their distance (the redshift).
The big bang was initially suggested because it explains why distant galaxies are traveling away from us at great speeds. The theory also predicts the existence of cosmic background radiation (the glow left over from the explosion itself). The Big Bang Theory received its strongest confirmation when this radiation was discovered in 1964 by Arno Penzias and Robert Wilson, who later won the Nobel Prize for this discovery.

43. Hubble’s Evidence
Doppler shifting - wavelength emitted by something moving away from us is shifted to a lower frequency
Sound of a fire truck siren - pitch of the siren is higher as the fire truck moves towards you, and lower as it moves away from you
Visible wavelengths emitted by objects moving away from us are shifted towards the red part of the visible spectrum
The faster they move away from us, the more they are redshifted. Thus, redshift is a reasonable way to measure the speed of an object (this, by the way, is the principal by which radar guns measure the speed of a car or baseball)
When we observe the redshift of galaxies outside our local group, every galaxy appears to be moving away from us - universe is expanding.

44. Expansion of universe has redshifted thermal radiation from that time to ~1000 times longer wavelength: microwaves

45. Evidence for the Big Bang
Big Bang Theory - Evidence for the Theory What are the major evidences which support the Big Bang theory?
First of all, we are reasonably certain that the universe had a beginning.
Second, galaxies appear to be moving away from us at speeds proportional to their distance. This is called "Hubble's Law," named after Edwin Hubble ( ) who discovered this phenomenon in This observation supports the expansion of the universe and suggests that the universe was once compacted.

46. Evidence for the Big Bang
Third, if the universe was initially very, very hot as the Big Bang suggests, we should be able to find some remnant of this heat. In 1965, Radioastronomers Arno Penzias and Robert Wilson discovered a degree Kelvin ( degree Fahrenheit, degree Celsius) Cosmic Microwave Background radiation (CMB) which pervades the observable universe. This is thought to be the remnant which scientists were looking for. Penzias and Wilson shared in the 1978 Nobel Prize for Physics for their discovery.

47. Evidence for the Big Bang
Finally, the abundance of the "light elements" Hydrogen and Helium found in the observable universe are thought to support the Big Bang model of origins.

48. Synthesis of Helium
The current CMB temperature tells us precisely how hot the universe was when it appeared.
It tells us how much helium was initially produced.
A helium nucleus contains 2 protons and 2 neutrons.
At T > 1011 K, nuclear reactions converted protons into neutrons and back, keeping their numbers nearly equal.
Between 1010 and 1011 K, neutron – proton reactions favor protons, because neutrons are heavier than protons.

49. Synthesis of Helium Energy is required to convert protons to neutrons.
At T < 1010 K, only neutrons can be changed into protons.
However, fusion continued to operate
and protons and neutrons combined into deuterium.
Then deuterium fused into helium.
During the early era of nucleosynthesis, helium nuclei were being destroyed by gamma-rays.
At ~1 minute, gamma-rays were gone and the proton – neutron ratio was set to 7:1.

50. Synthesis of Helium
Big Bang theory prediction: 75% H, 25% He (by mass)
Matches observations of nearly primordial gases

51. Synthesis of Helium
Abundances of other light elements agree with Big Bang model having 4.4% normal matter – more evidence for WIMPS!

53. Nebular Hypothesis of Solar System Formation.
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