Episodes
What is ordinary matter made of? This lecture reviews the basic
properties of matter from subatomic to atomic scales, introducing atomic
structures, atomic number and chemical elements, isotopes,
radioactivity, and half-life, ending with a brief overview of the four
fundamental forces of nature: gravitation, electromagnetism, and the
weak and strong nuclear forces. Recorded 2007 Oct 23 in 1000 McPherson
Lab on the Columbus campus of The Ohio State University.
Published 10/23/07
What is light? Most astronomical objects are too far away to measure
directly. Light is the messenger of the Universe, carrying with it
information about objects as near as the Moon and as far away as the
most distant objects in the visible Universe. In this lecture we will
review the basic properties of light, the electromagnetic spectrum, the
inverse square law of brightness, and the Dopper Effect. Recorded 2007
Oct 22 in 1000 McPherson Lab on the Columbus campus of The Ohio...
Published 10/22/07
How do objects orbit if more than 2 massive bodies are involved?
Newton's versions of Keplers 3 Laws of Planetary Motion are only
strictly valid for 2 massive bodies. The Solar System, however, clearly
has more than 2 massive objects within it. How do we handle this
many-body problem? This lecture discusses some of the multi-body
gravitational effects seen in our Solar System (and by extension
elsewhere). We will describe Lagrange Points for the restricted 3-body
problem and consequences...
Published 10/18/07
Why are there two high tides a day? This lecture examines tides caused
by the 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 correlate with Lunar Phase. We will also
discuss body tides raised on the Moon by the Earth, and how that has...
Published 10/17/07
Why do Kepler's Laws work? In this lecture I will describe Newton's
generalization of Kepler's Laws of Planetary Motion so that they will
apply to any two massive bodies orbiting around their common center of
mass. I will introduce families of open and closed orbits, the circular
and escape speeds, center-of-mass, conservation of angular momentum, and
Newton's generalized version of Kepler's 3rd Law. The latter is a
powerful tool for using orbital motions as our only way to measure...
Published 10/16/07
What is Gravity? Starting with the properties of falling bodies first
formulated by Galileo, Newton applied his three laws of motion to the
problem of Universal Gravitation. Newtonian Gravity is a mutually
attractive force that acts at a distance 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...
Published 10/15/07
Copernicus, Kepler, Tycho, and Galileo together gave us a new way of
looking at the motions in the heavens, but they could not explain why
the planets move they way the do. It was to be the work of Isaac Newton
who was to sweep away the last vestiges of the Aristotelian view of the
world and replace it with with a new, vastly more powerful predictive
synthesis, in which all motions, in the heavens and on the Earth, obeyed
three simple, mathematical laws of motion. This lecture...
Published 10/12/07
Tycho reached the limits of what could be done with the naked eye. A
new technology was required to extend our vision: the telescope. This
lecture introduces Galileo Galilei, the contemporary of Kepler who was
in many ways the first modern astronomer, and describes his many
discoveries with the telescope. These observations electrified Europe
in the early 17th century, and set the stage for the final dismantling
of the Aristotelian view of the world. Galileo's claims that they
constituted...
Published 10/11/07
In the generation following Copernicus, the question of planetary
motions was picked up by two remarkable astronomers: Tycho Brahe and
Johannes Kepler. Tycho was a Danish nobleman and brilliant astronomer
and instrument builder whose high precision naked-eye measurements of
the stars and planets were to be the summit of pre-telescopic astronomy.
Kepler was the talented German mathematician who was hired by Tycho and
succeeded him after his death who was to use Tycho's data to derive...
Published 10/10/07
Because my voice recorder malfunctioned 15 minutes into my Lecture on
Copernicus on 2007 October 9, I've added this recording of my Copernicus
lecture from Autumn Quarter 2006. It is the same basic material, but
since I generally improvise on a basic outline, there will be some
differences. Personally, I liked this year's lecture better, but this
will at least cover most of the same material. Oh well.
Published 10/09/07
In 1543, Nicolaus Copernicus revived Aristarchus' Heliocentric System in
an attempt to rid Ptolemy's geocentric system of the un-Aristotelian
idea of the Equant. He desired to create a model of the planets that
would please the mind as well as preserving appearances. Rather than
reinstate the ideal of the Aristotelian World View, he was to set the
stage for its overthrow after nearly 2000 years of supremacy, and within
two centuries give birth to the modern world.
This lecture describes the...
Published 10/09/07
What are the origins of the Geocentric and Heliocentric models
put foward to explain planetary motion? This lecture begins a new
unit that will chart the rise of our modern view of the solar system by
reviewing the highly influential work by Greek and Roman philosophers
who elaborated the first geocentric and heliocentric models of
the Solar System. We discuss the various geocentric systems from
the simple crystaline spheres of Anaximander, Eudoxus, and Aristotle
through the Epicyclic...
Published 10/08/07
How do the planets move across the sky? This lecture discusses the
motions of the 5 naked-eye planets (Mercury, Venus, Mars, Jupiter, and
Saturn) as seen from the Earth. We introduce the major configurations
of the planets, and then discuss their apparent retrograde motions. The
apparent motions of the planets are far more complex than those of the
Sun, Moon, and stars, and present a great challenge to understand. The
centuries long effort to understand these motions was to give birth...
Published 10/04/07
How do we make calendars? This lecture explores the astronomical
origins of our calendars. We start by discussing lunar and solar
calendars and their hybrids in history and tradition (for example, the
Islamic Lunar Calendar and the Hebrew Luni-Solar Calendar), and then
describe the Julian and Gregorian Calendar reforms that attempt to align
the calendar with the seasons of the year with greater degrees of
precision. Recorded 2007 Oct 3 in 1000 McPherson Lab on the Columbus
campus of The...
Published 10/03/07
What time is it? Telling time is the oldest practical application of
astronomy. Today's lecture is the first of a 2-part lecture on the
astronomical origins of our methods of keeping time and making
calendars. This lecture reviews the divisions of the year into the
solstices, equinoxes, and cross-quarter days, the division of the year
into months by moon phase cycles, months into weeks, and the division
of the day into hours by marking the location of the Sun in the sky
Recorded 2007 Oct 2...
Published 10/02/07
Among the most amazing sights in the sky, eclipses of the Sun and
Moon have long fascinated us. This lecture describes the eclipses of
the Sun and Moon, their types, and how often they occur.
Recorded 2007 Oct 1 in 1000 McPherson Lab on the Columbus campus
of The Ohio State University.
Published 10/01/07
What are the Phases of the Moon? This lecture introduces the Moon and
describes the monthly cycle of phases. Topics include synchronous
rotation, apogee and perigee, the cycle of phases, and the sidereal and
synodic month. Recorded 2007 Sep 28 in 1000 McPherson Lab on the
Columbus campus of The Ohio State University.
Published 09/28/07
Why do we have different seasons? This lecture explores the
consequences of the tilt of the Earth's rotation axis relative to its
orbital plane combined with the apparent annual motions of the Sun
around the Ecliptic. The most important factor for determining whether
it is hot or cold at a given location at different times in the year is
"insolation": how much sunlight is spread out over the ground. This,
combined with the different length of the day throughout the year,
determines to...
Published 09/27/07
Why do celestial objects appear to rise and set every day? How does this
depend on where you are on the Earth, or the time of year? In today's lecture
we we set the heavens into motion and review the two most basic
celestial motions. Apparent Daily Motion reflects the daily rotation of
the Earth about its axis. Apparent Annual Motion reflects the Earth's
annual orbit around the Sun. We introduce the Ecliptic, the Sun's
apparent annual path across the Celestial Sphere, and note four...
Published 09/26/07
Where are we? Where is someplace else? And how do I get there from
here? These are questions we need to answer both on the Earth and in
the sky to assign a location to a place or celestial object on the
surface of a sphere. This lecture includes a review of angular units
and the terrestrial system of latitude and longitude on the spherical
Earth. We then define the Celestial Sphere, with its Celestial Equator
and Poles, and begin to define an analogous coordinate system on the
sky. An...
Published 09/25/07
What is the shape and size of the Earth? This lecture traces historical
ideas about the shape of the Earth, from ancient ideas of a Flat-Earth
to Aristotle's compelling demonstrations in the 3rd century BC that the
Earth was a sphere. We then discuss two famous classical measurements
of the circumference of the Earth by Eratosthenes of Cyrene in the 3rd
century BC and Claudius Ptolemy in the 2nd century AD. Recorded 2007
Sep 24 in 1000 McPherson Lab on the Columbus campus of The Ohio...
Published 09/24/07
What are the constellations? We will review the most basic feature of
the night sky, the 6000 visible stars sprinkled about the sky, and
introduce the idea of constellations, reviewing their history and uses
by various cultures. Recorded 2007 Sep 21 in 1000 McPherson Lab on the
Columbus campus of The Ohio State University.
Published 09/21/07
What are our units of measure in astronomy? To begin our exploration of
astronomy, we first need to develop a common language for notating large
numbers, and introduce the basic units of length, mass, and time that we
will use throughout the quarter. This lecture is a quick review of
scientific notation and the metric system. For measuring the vast
distances in astronomy, we need to introduce two special units: the
Astronomical Unit for interplanetary distances, and the Light Year...
Published 09/20/07
What is Astronomy? What is Science? What is the course all about?
Brief introductory remarks after going over course mechanics on the
first day of Astronomy 161 for Autumn Quarter 2007. Recorded 2007 Sep
19 in 1000 McPherson Lab on the Columbus campus of The Ohio State
University.
Published 09/19/07
Welcome to the Astronomy 161 Lecture Podcasts. This is a brief message
from me explaining the podcasts, and welcoming new and old listeners.
University. Lectures will begin on Wednesday, 2007 Sept 19, and run
through Friday, 2007 Nov 30. New lectures will appear shortly before
6pm US Eastern Time each day there is a regular class. Recorded 2007
Sep 19 in 4037 McPherson Lab on the Columbus campus of The Ohio State
University.
Published 09/19/07