This 11-minute video lesson works through a calculation for K-Ar dating (it is good to have some prior experience with e and logarithms to understand). [Cosmology and Astronomy playlist: Lesson 80 of 85]

Khan Academy learning modules include a Community space where users can ask questions and seek help from community members. Educators should consult with their Technology administrators to determine the use of Khan Academy learning modules in their classroom. Please review materials from external sites before sharing with students.

This 7-minute video lesson looks at the lifecycle of massive stars (stars with masses greater than 9 times the sun). [Cosmology and Astronomy playlist: Lesson 27 of 85]

Khan Academy learning modules include a Community space where users can ask questions and seek help from community members. Educators should consult with their Technology administrators to determine the use of Khan Academy learning modules in their classroom. Please review materials from external sites before sharing with students.

This 13-minute video lesson looks at how changes in Earth's rotation can effect Earth's seasons and climate. It discusses Milankovitch Cycles, Precession, and Obliquity. [Cosmology and Astronomy playlist: Lesson 71 of 85]

Khan Academy learning modules include a Community space where users can ask questions and seek help from community members. Educators should consult with their Technology administrators to determine the use of Khan Academy learning modules in their classroom. Please review materials from external sites before sharing with students.

This 6-minute video lesson looks at the idea of Pangaea and some of the evidence behind it. [Cosmology and Astronomy playlist: Lesson 56 of 85]

Khan Academy learning modules include a Community space where users can ask questions and seek help from community members. Educators should consult with their Technology administrators to determine the use of Khan Academy learning modules in their classroom. Please review materials from external sites before sharing with students.

This 7-minute video lesson explains what parallax is and how it is used to determine distances between stars. [Cosmology and Astronomy playlist: Lesson 21 of 85]

Khan Academy learning modules include a Community space where users can ask questions and seek help from community members. Educators should consult with their Technology administrators to determine the use of Khan Academy learning modules in their classroom. Please review materials from external sites before sharing with students.

This 8-minute video lesson defines parsec a unit of distance used in astronomy. [Cosmology and Astronomy playlist: Lesson 25 of 85]

Khan Academy learning modules include a Community space where users can ask questions and seek help from community members. Educators should consult with their Technology administrators to determine the use of Khan Academy learning modules in their classroom. Please review materials from external sites before sharing with students.

This 8-minute video lesson looks at plate tectonics and the difference between crust and lithosphere. [Cosmology and Astronomy playlist: Lesson 43 of 85]

Khan Academy learning modules include a Community space where users can ask questions and seek help from community members. Educators should consult with their Technology administrators to determine the use of Khan Academy learning modules in their classroom. Please review materials from external sites before sharing with students.

This 13-minute video lesson looks at plate tectonics and the evidence of plate movement. [Cosmology and Astronomy playlist: Lesson 45 of 85]

Khan Academy learning modules include a Community space where users can ask questions and seek help from community members. Educators should consult with their Technology administrators to determine the use of Khan Academy learning modules in their classroom. Please review materials from external sites before sharing with students.

This 12-minute video lesson continues to explore plate tectonics. It covers the geological features of divergent plate boundaries. [Cosmology and Astronomy playlist: Lesson 46 of 85]

Khan Academy learning modules include a Community space where users can ask questions and seek help from community members. Educators should consult with their Technology administrators to determine the use of Khan Academy learning modules in their classroom. Please review materials from external sites before sharing with students.

This 6-minute video lesson continues to explore plate tectonics. It covers the geological features of convergent plate boundaries. [Cosmology and Astronomy playlist: Lesson 47 of 85]

Khan Academy learning modules include a Community space where users can ask questions and seek help from community members. Educators should consult with their Technology administrators to determine the use of Khan Academy learning modules in their classroom. Please review materials from external sites before sharing with students.

This 6-minute video lesson coninues to look at plate tectonics. It discusses plates moving due to convection in mantle. [Cosmology and Astronomy playlist: Lesson 48 of 85]

Khan Academy learning modules include a Community space where users can ask questions and seek help from community members. Educators should consult with their Technology administrators to determine the use of Khan Academy learning modules in their classroom. Please review materials from external sites before sharing with students.

This 11-minute video lesson looks at Potassium-Argon (K-Ar) dating and it can be used to date very old volcanic rock and the things that might be buried in between. [Cosmology and Astronomy playlist: Lesson 79 of 85]

Khan Academy learning modules include a Community space where users can ask questions and seek help from community members. Educators should consult with their Technology administrators to determine the use of Khan Academy learning modules in their classroom. Please review materials from external sites before sharing with students.

This 12-minute video lesson clarifies the effect of axial precession on the calendar and the date of perihelion and aphelion. [Cosmology and Astronomy playlist: Lesson 73 of 85]

Khan Academy learning modules include a Community space where users can ask questions and seek help from community members. Educators should consult with their Technology administrators to determine the use of Khan Academy learning modules in their classroom. Please review materials from external sites before sharing with students.

This 2-minute video lesson provides a correction to the previous video about quasars. [Cosmology and Astronomy playlist: Lesson 36 of 85]

Khan Academy learning modules include a Community space where users can ask questions and seek help from community members. Educators should consult with their Technology administrators to determine the use of Khan Academy learning modules in their classroom. Please review materials from external sites before sharing with students.

This 9-minute video lesson discusses quasars. [Cosmology and Astronomy playlist: Lesson 35 of 85]

Khan Academy learning modules include a Community space where users can ask questions and seek help from community members. Educators should consult with their Technology administrators to determine the use of Khan Academy learning modules in their classroom. Please review materials from external sites before sharing with students.

This 17-minute video lesson discusses the radius of the observable universe. [Cosmology and Astronomy playlist: Lesson 8 of 85]

Khan Academy learning modules include a Community space where users can ask questions and seek help from community members. Educators should consult with their Technology administrators to determine the use of Khan Academy learning modules in their classroom. Please review materials from external sites before sharing with students.

In this 11-minute video lesson Sal makes random predictions for the year 2060. [Cosmology and Astronomy playlist: Lesson 85 of 85]

Khan Academy learning modules include a Community space where users can ask questions and seek help from community members. Educators should consult with their Technology administrators to determine the use of Khan Academy learning modules in their classroom. Please review materials from external sites before sharing with students.

This 10-minute video discusses redshift and the Doppler Effect. [Cosmology and Astronomy playlist: Lesson 10 of 85]

Khan Academy learning modules include a Community space where users can ask questions and seek help from community members. Educators should consult with their Technology administrators to determine the use of Khan Academy learning modules in their classroom. Please review materials from external sites before sharing with students.

This 9-minute video lesson looks at refraction and focuses on refraction in seismic waves. [Cosmology and Astronomy playlist: Lesson 53 of 85]

Khan Academy learning modules include a Community space where users can ask questions and seek help from community members. Educators should consult with their Technology administrators to determine the use of Khan Academy learning modules in their classroom. Please review materials from external sites before sharing with students.

This 8-minute video lesson examines the scale of distance from the solar system to the closest stars. [Cosmology and Astronomy playlist: Lesson 3 of 85]

Khan Academy learning modules include a Community space where users can ask questions and seek help from community members. Educators should consult with their Technology administrators to determine the use of Khan Academy learning modules in their classroom. Please review materials from external sites before sharing with students.