Why do we have different seasons?  This lecture looks at the
consequences of the tilt of the Earth's rotation axis relative to its
orbital plane (the Obliquity of the Ecliptic) combined with the apparent
annual motions of the Sun around the Ecliptic.  The important factor
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 on
the ground.  This, combined with the different length of the day when
the Sun as at different declinations, determines to total amount of
solar heating per day, and drives the general weather.  It has nothing,
however, to do with how far away we are from the Sun at different times
of the year.  Finally, the direction of the Earth's rotation axis slowly
drifts westward, taking 26,000 years to go around the sky.  This
"Precession of the Equinoxes" represents a tiny change that is still
measureable by pre-telescopic observations, and means that at different
epochs in human history there is a different north pole star, or none at
all!  Recorded 2006 Sep 28 in 100 Stillman Hall on the Columbus campus
of The Ohio State University.

Lecture 7: The Four Seasons

Natural Sciences

Science & Medicine

Social Sciences

Medicine

Education

Training

Language Courses

Higher Education

K-12

Educational Technology

A new podcast, Astronomy 141, Life in the Universe, is available
for those interested in continuing an exploration of topics in
modern astronomy.

Astronomy 141 Podcast Teaser

Are there planets around other stars?  Are there Earth-like planets
around other stars?  Do any of those harbor life?  Intelligent life?
We'd like to know the answers to all of these questions, and in recent
years we've made great progress towards at least answering the first.  
To date, more than 200 planets have been found around other stars, most in the
interstellar neighborhood of the Sun, but a few at great distance.  This
lecture reviews the search for ExoPlanets, discussing the successful
Doppler Wobble, Transit, and Microlensing techniques.  What we have
found so far are very suprising systems, especially Jupiter-size or
bigger planets orbiting very close (few hundredths of an AU) from their
parent stars.  The existance of a significant population of so-called
"Hot Jupiters" may be telling us that planetary migration can be much
more extreme that we saw in our own Solar System, or that these
planetary system formed in a very different way than ours.  It seems
appropriate to end this class with more questions than answers, but
that's where the science becomes most exciting.  Recorded 2006 Dec 1 in
100 Stillman Hall on the Columbus campus of The Ohio State University.

Lecture 46: ExoPlanets - Planets around Other Stars

What is a planet?  Is Pluto a planet?  This lecture traces the debate on
the nature of what it means to be a planet by taking an historical approach, 
looking at how the question has arisen with the discovery of the asteroids and
later Pluto and the Kuiper Belt.  Many of the issued raised at the 2006
IAU General Assembly meeting were raised two centuries before after the
discovery of Ceres and Pallas.  We will end with the new definition of a
planet, and why Pluto is better understood as a Dwarf Planet, among the
two largest objects of the class of small icy bodies of the outer solar
system, than as the smallest of the planets.  Recorded 2006 Nov 30 in
100 Stillman Hall on the Columbus campus of The Ohio State University.

Lecture 45: Is Pluto a Planet?

Comets are occasional visitors from the icy reaches of the outer Solar
System.  This lecture discusses the orbits, structure, and properties of
comets, and introduces the "dirty snowball" model of a comet nucleus.
The end of class was a demo where I created a model of a comet nucleus
from common household and office materials.  Imagine a twisted
combination of Alton Brown and Emeril Lagasse with a PhD in Astrophysics
and you get the idea.  We were not able to arrange for a videographer to
come, but we did get some stills before the batteries died on the
digital camera.  The pictures are on the lecture webpage.  The lecture
is slightly abbreviated because we did the student evaluation of
instruction surveys before class started.  Recorded 2006 Nov 29 in 100
Stillman Hall on the Columbus campus of The Ohio State University.

Lecture 44: Comets

Beyond the orbit of Neptune is the realm of the icy worlds, ranging in
size from Triton, the giant moon of Neptune, and the dwarf planets Pluto
and Eris, all the way down to the nuclei of comets.  This lecture
discussed the icy bodies of the Trans-Neptunian regions of the Solar
System, discussing the basic properties of Triton (the best studied such
object), Pluto, Eris, and the Kuiper Belt, introducing the dynamical
families of Trans-Neptunian Objects that record in their orbits the slow
migration of Neptune outwards during the early history of the Solar
System.  The Kuiper Belt is the icy analog of the main Asteroid Belt of
the inner Solar System: both are shaped by their gravitational
interaction with giant gas planets (Jupiter for the asteroids, Neptune
for the KBOs), and are composed of leftover raw materials from the
formation of their respective regions of the Solar System.  Recorded
2006 Nov 28 in 100 Stillman Hall on the Columbus campus of The Ohio
State University.

Lecture 7: The Four Seasons

Download our free app to listen on your phone