Star Cards

by Julie Lutz

Department of Astronomy, University of Washington

The Star Cards activity is meant to illustrate some of the physical properties of stars. The cards represent twenty of the brightest stars and twenty of the stars that are nearest to the sun. There is also a card which represents the sun itself. Properties such as distance from the sun, temperature, diameter, and brightness (apparent and absolute) are given on the card.

The twenty brightest stars are quite different from the group of twenty nearby stars. The nearby stars are mostly cool (red), small stars. The brightest stars are a real mixture of colors and sizes (up to 800 times the diameter of the sun, for example).

The Star Cards can be used in several different places during the study of stellar properties: introductory activity to get your students thinking about differences between stars, middle part of unit to reinforce new concepts (for example, the difference between apparent and absolute magnitudes) or at the end of the unit for review.

Whatever size group you have (the activity doesn't work very well with less than 10 participants), give each participant a star card. About half of the cards you distribute should be “nearest stars” and the other half “brightest stars”. I start by asking the students to get in groups by colors. The red stars will dominate. Then I ask them to line up by temperature of the star. You can then easily see the correlation between color and surface temperature. Next you might want to go to diameter of the star: this will destroy the nice color sequence (Why....?). Then distances from the sun. Most (but not all) red stars will be close to the sun and most (but not all) of the other colors of stars will be further away.

Depending on how much detail you are covering on stars, you could delete or add characteristics to the star cards.