Languages: English

The discussion of galaxies continues in this lesson by focusing on a special group of galaxies with very energetic cores called active galaxies. Different types of active galaxies are introduced, from Seyfert galaxies and blazars to quasars.

Some of the most profound questions are asked and discussed in the complex subject of cosmology. What shape is the universe? How did it begin? How will it end? Evidence is presented that supports the big bang theory, and the exciting notion of dark energy is introduced.

Opening with a survey of the solar system and an examination of the solar nebula theory that explains how our solar system was formed, this lesson also reviews how the spinning solar nebula formed a disk of dust particles that eventually became the planetesimals that formed the planets. The actual detection of planets around distant stars is given considerable coverage, with experts describing the newest techniques and the successes achieved.

Using Earth as the archetypical example, this lesson details the stages of differentiation, cratering, flooding, and surface evolution. The impact of plate tectonics is presented as the formation and evolution of Earth is detailed. Comparisons are continuously made to the other terrestrial planets.

Explaining the concept of a scientific model, this lesson introduces the celestial sphere as a model to help describe and organize the night sky. Several specialists explain how different cultures named stars and constellations, and brought the aspects of the sky into their buildings and structures, such as those of Chaco Canyon in the southwestern United States.

This video lesson explains the motion of Earth around the sun and its yearly cycle. Astronomers explain the unique orbital and size relations between the rotation of Earth, the sun, and the moon and how this makes a total solar eclipse possible at predictable intervals, known as the Saros cycle. The lesson concludes with a description of the ecliptic and explains how that differs from constellations that are contained in the zodiac.

A presentation on the foundations of astronomy, The Birth of Astronomy examines the observations, theories, and contributions of Aristotle, Ptolemy, and other ancient scientists and philosophers. Copernicus, Tycho Brahe, Kepler, Galileo, and Sir Isaac Newton’s contributions are discussed throughout this lesson.

Astronomers are the only scientists who do not manipulate the objects they study. Instead, they do two basic things: collect light and analyze it. Accordingly, this lesson answers two basic questions: (1) What is light? and (2) What tools are used to collect it?

Students will discover the interactions of atoms and light and what spectra can tell us about a star. The fascinating history of spectral classes and the intriguing group of women who were responsible for much of our stellar classification system today is also presented.