HR+Diagram

=2 lesson plans on the HR diagram:= = = =I. Looking for Correlations in Data: Star Classification=


 * Author:** Ben Farr, 2011

Through the use of various tools and techniques, astronomers are capable of measuring many properties of a star. Once collected, astronomers must then look through all of this data and search for properties of stars that seem to be connected to one another. When two types of data seem to be connected to one another, these parameters are said to be //correlated//. By finding and studying these correlations, we can better understand the physics governing stars’ behavior.

Students first familiarize themselves with this idea by analyzing data about themselves (height, weight, gender, # of siblings, GPA, time spent doing homework, etc.) and searching for correlations. They then apply this same method to understanding and characterizing stars.


 * Materials:**

[|HRdiagramActivity.pdf]

[|ppt.ppt] [|BlankHRdiagram.pdf]

[|HRclass.nb] [|HRsurvey.nbp] [|HRsurvey.nb]

= = =II. Understanding Star Clusters and the HR Diagram=


 * Author:** Meagan Morscher, 2012

2 day lesson plan.


 * Pre-reqs:**

Over the previous month or so, they'd been learning about stars. What powers them, how they evolve, and what the HR diagram is all about.


 * Vocabulary:**

HR diagram: this is a diagram you can make by plotting the luminosity [brightness] versus the temperature, for a bunch of stars. There are certain correlations that pop out when you do this - the main sequence [where most stars spend the majority of their lives], the giant branch, etc. The HR diagram is a useful tool for learning about the evolution of stars].

Star clusters: star clusters are groups of stars held together by the mutual gravitational attraction among all the stars.


 * Day 1: Star cluster trivia**

List of topics/questions about star clusters: [|star_cluster_trivia.pdf] We gave them 15 minutes to work on the computers doing their own research on star clusters. They worked in groups of 5-6, but we suggested that they split up the work among two smaller groups (2-3 people) to try to get to all of the topics.

We told them that after doing the research, we would play a game of trivia based on the questions on the sheet, and we'd give treats for correct answers. Most teams were able to address all the points in the time we gave them.

[|globular_cluster_trivia.key] - We used these slides for the trivia game. What we did was have four cards representing the four groups (each had a suit, hearts, diamonds, clubs, and spades). After asking a question, we'd draw one of the cards, and that team would have the first stab at answering the question. If they got it right, they'd all get treats. If not, then another team would have the chance to give the correct answer. That team's card was removed from the set, and for the next question, one of the other three teams would be drawn to try to answer it first. All teams got candy in each class (the candy included starburst, hershey kisses, and jolly ranchers, in case you were wondering!) Since I knew they'd find a range of answers to the questions by searching the internet (and in some questions, the answer really was a range, sometimes quite large), I accepted answers that were reasonable. Prior to this activity, I did a lot of googling my self and looked through all the resources that they were likely to encounter, so I kind of knew what to expect. After a group answered each question reasonably well, I'd show them the answer that I had, talked briefly about it, if necessary. We finished about 3/4 of the trivia that day, and the next day we finished off the trivia before starting on the next activity.

This was the first time that I used candy to bribe them. I was very happy with the outcome. They had energy, they seemed engaged, they participated, they seemed to have fun. Andy suggested to them that they take notes on the material, because it was all fair game for their test, and many of them did. I got some good questions along the way too.


 * Day 2-3: Hands on HR diagram "simulation" with coins**

One of the most important uses of the HR diagram is measuring the ages of star clusters. When stars evolve (start on the main sequence, run out of Hydrogen to burn, start burning Helium, become a giant star, later on burn out and die...), their luminosities and temperatures change, so their position on the HR diagram changes as well. The idea is that we can observe a star cluster, and using the properties of all the stars, we can make an HR diagram. Then, we can analyze the HR diagram, noting the structure, where stars lie on the diagram. If we know how stars evolve over time, and thus how the HR diagram will change over time, then by looking at the HR diagram for the cluster of interest, we can estimate how long the stars in the system have been evolving, or the age of the cluster. This relies on the assumption that the stars were all born at approximately the same time.

Students had learned a bit about the HR diagram prior to this. I wanted them to understand how they could use it to get the ages of clusters.

We started off with this visual - [|making_an_HR_diagram_slideshow.pdf]

With the HR diagram on the screen, we talked briefly about the different parts of the diagram (What is this line where most of the stars are? -the Main sequence). What about this part up here? -The giant branch. We asked them questions about how stars evolve, and why a main sequence star becomes a giant, etc. We found out at this point that they didn't know as much as we thought they should having just finished a unit on stellar evolution.

Ok, so after that brief review, they started with the coin HR diagram activity. They worked in groups. We gave them each 10 pennies and 5 nickels, and a big sheet of paper. The coins represented stars: the pennies had lower mass than the nickels.

They followed this worksheet: [|HR_diagram_model_with_coins.pdf] to guide them to an understanding of how the HR diagram could be used to measure the ages of clusters and "simulate" the evolution of an HR diagram, by hand. The timesteps were big - big enough that a major qualitative change occur in each timestep. At the end they have three sketches of the SAME cluster, at three different times/ages.

There were many questions interspersed throughout the instructions, so that they had to do some thinking about the "why", rather than just going through the movements (which would be really difficult without some understanding of what it was all about). By the end they had to explain how the age could be estimated by observing the HR diagram for a cluster.

Since they turned out to not be fully prepared for the activity, we didn't finish that day. I really think the activity can be done in a single class period, but they need to have a better understanding of stellar evolution before starting on this activity. We decided that for the remaining periods, we would give a longer review of the HR diagram and stellar evolution, and assume that the activity would take 2 days. That seemed to work well.

When they completed this, they were given a handout which had three sketches of HR diagrams at three different ages, and were told to go to a website that would show a computer simulation of how an HR diagram evolves.

[] (initialize, then add stars, then evolve).