## Searching for Another World: "What Do I Expect to Find?"

In your investigation, you'll attempt to detect an alien world by following the brightness of your star, over a period of time. Use the model below to help you predict what you might expect to find:

• As the planet passes in front of the star, what do you predict will happen to the brightness of the star you observe?
• Will the star's observed brightness depend on the size of the planet? In what way?

### STEP 1: Observe the Model

#### The planet blocks some of the light from its star as it orbits.

If you graphed the star's observed brightness as time passes, what do think it would look like?

Press "Show Graph" on the Orbits Lab to find out. Does this graph make sense?

When you're ready for a challenge, press the "Next" button and go to STEP 2 below.

### STEP 2: Predict...

See if you can predict what the graph will look like for:

#### A Bigger Planet.

Change the size of the planet, using the controls on the orbits lab. In your journal, draw what you predict the graph will look like.

#### A Faster or Slower Planet.

Speed up or slow down the planet. In your journal, draw what you predict the graph will look like? What happens to the time between eclipses? What happens to the duration of a single eclipse?

#### A Tilted Orbit.

Tilt the orbit of the planet so that only part of the planet passes in front of the star (a "grazing transit"). In your journal, draw what you predict this graph will look like? Is the shape of your graph different from the other ones?

When you're ready to check your predictions using the model, click the "Next" button and go to STEP 3 below.

### STEP 3: Check Your Predictions...

Check your predictions using the modeling lab. Try creating a bigger planet, a slower planet, and a tilted orbit. Click "Show Graph" and see how your prediction compares with the model graph in each case.

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