## Simple Investigation of Cas A to Identify Interesting Features

**Overview:** Students undertake a simple guided analysis, using tools they've already learned, and share important observations as a starting point for further investigation. In particular, students should notice the strong peaks at certain energies in the spectrum of Cas A.

**Physical resources:** None

**Electronic resources:** X-ray image of Cas A

- Statement of tasks which make up simple analysis: (basic analysis)
- Students share most important observations with a partner group or whole group.
- Possible examples of observations: SNR not all the same color, all parts of the object do not show up in visible
**and**X-ray detectors, etc. - Instructor should guide students to notice and describe the new features in the spectrum: higher intensity at only certain energies, or "peaks".

**Teacher tips/tricks:**

- Timing: can take up to 3 hours, if students still have trouble with basic analysis.
- Emphasize the pieces of analysis that students seem to be having most trouble with, to give them more practice.

- Students should compare linear diameter of remnant to the diameter of the solar system to answer "How many times larger than the diameter of the solar system is the diameter of Cas A?", to apply what they've learned from activity 1.
- With additional time:
- Estimate velocity of expansion, from linear radius and knowing age of remnant ~ 330 years.

**Assessment ideas:**

- Ask students to identify which parts of their simple investigation are observations (spectrum, 3-color image, angular size), which are models (angular/linear size equation) and which are predictions (linear size).