This 12-minute video lesson looks at how to measure stellar distance using parallax. [Cosmology and Astronomy playlist: Lesson 23 of 85]

This 9-minute video lesson provides another introduction to stellar parallax. [Cosmology and Astronomy playlist: Lesson 22 of 85]

This 2-minute video lesson provides clarification on parallax. [Cosmology and Astronomy playlist: Lesson 24 of 85]

This 10-minute video lesson covers the structure of the Earth: The crust, mantle, and core. [Cosmology and Astronomy playlist: Lesson 44 of 85]

This 9-minute video lesson looks at supermassive black holes. [Cosmology and Astronomy playlist: Lesson 34 of 85]

This 2-minute video lesson provides a clarification about supernovae. [Cosmology and Astronomy playlist: Lesson 29 of 85]

This 12-minute video lesson looks at supernovae. [Cosmology and Astronomy playlist: Lesson 28 of 85]

This 6-minute video lesson looks at the Mohorovicic Seismic Discontinuity: the boundary between crust and mantle (or Moho). [Cosmology and Astronomy playlist: Lesson 54 of 85]

This 10-minute video lesson discusses the differences between BC, BCE, AD and CE. It includes a little bit about the birth of Jesus as well. [Cosmology and Astronomy playlist: Lesson 65 of 85]

This 2-minute video lesson looks at the causes precession and other orbital changes. [Cosmology and Astronomy playlist: Lesson 74 of 85]

This 13-minute video lesson looks at the process of stars becoming white and black dwarfs. [Cosmology and Astronomy playlist: Lesson 18 of 85]

This 7-minute video lesson explains why cepheids pulsate. [Cosmology and Astronomy playlist: Lesson 32 of 85]

This 8-minute video lesson looks at why gravity gets so strong near dense objects. [Cosmology and Astronomy playlist: Lesson 33 of 85]

This 4-minute video lesson explains why S-Waves only travel in solids. [Cosmology and Astronomy playlist: Lesson 52 of 85]

This lesson for English Language Learners (ELLs) introduces the trend of dressing up as comic book or anime characters, cosplay. In this lesson, learners will practice reading, listening, speaking and writing. All activities are automatically graded with feedback provided to the learner upon submission.

Students learn about the many types of expenses associated with building a bridge. Working like engineers, they estimate the cost for materials for a bridge member of varying sizes. After making calculations, they graph their results to compare how costs change depending on the use of different materials (steel vs. concrete). They conclude by creating a proposal for a city bridge design based on their findings.

Students design a simple behavioral survey, and learn basic protocol for primary research, survey design and report writing. Note: The literacy activities for the Mechanics unit are based on physical themes that have broad application to our experience in the world — concepts of rhythm, balance, spin, gravity, levity, inertia, momentum, friction, stress and tension.

From the document:
"The Countdown Passages are strictly controlled stories that align with the phonics skills and Heart Words taught in Countdown. Aside from the
Heart Words in the passages, all of the words included are decodable according to the Countdown Scope & Sequence; however, due to the use
of some Heart Words that have not been explicitly taught in Countdown according to the guidelines described below, we consider the passages
to be “strictly controlled” rather than completely “decodable."

There are 12 fiction passages: one for each unit in Countdown, beginning with Unit 17. The passages provide students with longer, connected-text
opportunities to apply the skills they are learning in Countdown. In the Countdown workbook, students practice reading words, phrases, and
sentences. With the Countdown Passages, students extend their practice to longer sections of text. As students develop mastery and automaticity
with the skills taught in Countdown, the Countdown Passages can be used to reinforce these skills, to provide opportunities for practice, and,
ideally, to build fluency. Students will also gain confidence as readers. Reading text controlled for the specific skills students have already
learned allows them to read with success, leading to confidence and the willingness to tackle more difficult text in the future."