Astronomy 161 - Introduction to Solar System Astronomy episodes:

• October 30, 2006Lecture 27: Deep Time - The Age of the Earth

  How old is the Earth? This lecture reviews the idea of cyclic and

  linear time, since how you view time determines whether the question of

  the age of the Earth is even meaningful. We then review various ways

  people have estimated the age of the Earth, starting with historical

  ages that equate human history with the history of the Earth proper, and

  then see how various physical estimates, which do not make an appeal to

  human history, were made. This brings us to the technique of

  radioactive age dating of the oldest rocks, leading to our current best

  estimate of 4.5+/-0.1 Billion years for the age of our planet. Recorded

  2006 Oct 30 in 100 Stillman Hall on the Columbus campus of The Ohio

  State University.

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• October 27, 2006Lecture 26: Telescopes

  Telescopes, equipped with advanced electronic cameras and spectrographs,

  are the primary tools of the astronomer. This lecture reviews the types

  of telescopes and observatory sites, and discusses radio and space

  telescopes, and reviews briefy the observing facilities at Ohio State.

  Recorded 2006 Oct 27 in 100 Stillman Hall on the Columbus campus of The

  Ohio State University.

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• October 26, 2006Lecture 25: Measuring Light - Spectroscopy

  Why does each chemical element have its own unique spectral-line

  signature? How do emission- and absorption-line spectra work? This

  lecture is the second part of a two-part exploration of the interaction

  between matter and light, today discussing how the unique spectral-line

  signatures of atoms are a reflection of their internal electron

  energy-level structure. We will discuss energy level diagrams for

  atoms, excitation, de-excitation, and ionization, and do a short

  demonstration with gas-discharge tubes and slide-mounted diffraction

  gratings. For podcast listeners, the last portion of the class is the

  demo, which we do not, unfortunately, have the resources to videotape.

  Recorded 2006 Oct 26 in 100 Stillman Hall on the Columbus campus of The

  Ohio State University.

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• October 25, 2006Lecture 24: Matter and Light

  How do matter and light interact? This lecture is the first of a

  two-part lecture on the physical basis of spectroscopy. Today we will

  discuss the Kelvin Absolute Temperature scale, which provides a measure

  of the internal energy content of matter, and Kirchoff's empirical Laws

  of Spectroscopy, along with the Stefan-Boltzmann Law and the Wein Law to

  describe the continuous emission from a blackbody. We will end by

  briefly describing the suggestive properties of emission- and

  absorption-line spectra, whose explanation in the details of atomic

  structure will be the topic of the next lecture. Recorded 2006 Oct 25

  in 100 Stillman Hall on the Columbus campus of The Ohio State

  University.

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• October 24, 2006Lecture 23: Worlds Within: Atoms

  What is Matter? This lecture reviews the nature of matter from

  subatomic to atomic scales, and introduces the ideas of atomic

  structure, atomic number (number of protons), the elements, isotopes,

  radioactivity, and half-life. We conclude with a brief overview of the

  four fundamental forces of nature: gravitation, electromatgnetic, and

  the strong and weak nuclear forces. Recorded 2006 Oct 24 in 100

  Stillman Hall on the Columbus campus of The Ohio State University.

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• October 23, 2006Lecture 22: Light the Messenger

  What is Light? This lecture reviews the basic properties of light,

  introducing the inverse square law of brightness and the Doppler Effect.

  Recorded 2006 Oct 23 in 100 Stillman Hall on the Columbus campus of The

  Ohio State University.

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• October 19, 2006Lecture 21: The Rotation and Revolution of the Earth

  How do we prove physically that the Earth rotates on its axis and

  revolves around the Sun? Newtonian physics was so compelling that it

  was mostly accepted before there were ironclad physical demonstrations

  of the Earth's daily rotation about its axis and annual revolution

  (orbit) around the Sun. This lecture reviews three of these

  demonstrations: the Coriolis Effect, the Foucault Pendulum, and Stellar

  Parallaxes. This ties up the last loose-end of the Copernican

  Revolution. Recorded 2006 Oct 19 in 100 Stillman Hall on the Columbus

  campus of The Ohio State University.

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• October 18, 2006Lecture 20: Tides

  Why are there two high tides a day? This lecture examines another of

  the consequences of gravity, the twice-daily tides raised on the Earth

  by the Moon. Tides are a consequence of differences in the gravity

  force of the Moon from one side to the other of the Earth (stronger on

  the side nearest the Moon, weaker on the side farthest from the Moon).

  The Sun raises tides on the Earth as well, about half as strong as Moon

  tides, giving rise to the effect of Spring and Neap tides that strongly

  correlate with Lunar Phase. We also look at body tides raised on the

  Moon by the Earth, and how that has led to Tidal Locking of the Moon's

  rotation, which is why the Moon always keeps the same face towards the

  Earth. We then explore the combined effects of tidal braking of the

  Earth, which slows the Earth's rotation and increases the length of the

  day by about 23 milliseconds per century, and causes the steady

  Recession of the Moon, which moves 3.8cm away from Earth every year.

  Tidal effects are extremely important to understanding the Dynamical

  Evolution of many bodies in the Solar System, as we'll see time and

  again in the second half of the class. Recorded 2006 Oct 18 in 100

  Stillman Hall on the Columbus campus of The Ohio State University.

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• October 17, 2006Lecture 19: Orbits

  Why do Kepler's Laws work? This lecture discusses how Newton applied

  his Three Laws of Motion and the Law of Universal Gravitation to the

  problem of orbits. Newton generalized Kepler's laws to apply to any two

  massive bodies orbiting around their common center of mass. We discuss

  these new, generalized laws of orbital motion, introducing the families

  of open and closed orbits, circular and escape velocity, center-of-mass,

  conservation of angular momentum, and how orbital mechanics is used to

  measure the masses of astronomical objects. Recorded 2006 Oct 17 in 100

  Stillman Hall on the Columbus campus of The Ohio State University.

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• October 16, 2006Lecture 18: The Apple and the Moon - Newtonian Gravity

  What is Gravity? This lecture reviews the law of falling bodies first

  described by Galileo, and then Newton's explanation in terms of his Law

  of Universal Gravitation. Gravity is a mutually attractive force that

  acts between any two massive bodies. Its strength is proportional to

  the product of the two masses, and inversely proportional to the square

  of the distance between their centers. We then compare the fall of an

  apple on the Earth to the orbit of the Moon, and show that the Moon is

  held in its orbit by the same gravity that works on the surface of the

  Earth. In effect, the Moon is perpetually "falling" around the Earth.

  Recorded 2006 Oct 16 in 100 Stillman Hall on the Columbus campus of The

  Ohio State University.

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