Name: ______Date: ______
Student Activity 6—Sheet 2
The Search for Exoplanets
Science Background
An exoplanet is a planet that orbits a star in the way that Earth orbits the Sun. When scientists look for exoplanets, they set their telescopes on a small piece of sky for a very long time and look for small changes in the amount of light that is received from stars that they are tracking. When an exoplanet moves across the face of the star, the light that the telescope receives dims slightly. When an exoplanet crosses in front of a star, we say that it has transited the star.
In this activity, you will simulate an exoplanet transiting a star. By performing some calculations, you will be able to graph the data and see the characteristic dip in light intensity that helps scientists find exoplanets.
Draw
1.On the large piece of paper your teacher provides, draw a line segment that is 30 cm long with the line centred across the length of the paper. At the midpoint of the line segment, construct a circle of radius 6cm. This is the “star.”
2.At the centre of the star, construct a circle of radius 3 cm. This is the “exoplanet” in the middle position, which we will call position 4.
3.Every 3 cm along the line on each side of the centre of the star, construct a circle of radius 3 cm so that there are four circles on each side of the circle at position 4. These circles represent eight more positions for the exoplanet. Label all nine smaller circles with the position numbers 0 to 8.
Calculate
4.Knowing the radius of the larger circle and the radius of the smaller circles, calculate the area of the star and the area of the exoplanet, each accurate to 1 decimal place.
Area of star: ______Area of exoplanet: ______Units: ______
5.In position 0, what percent of the star’s light is blocked by the exoplanet?______
In position 0, what percent of the star’s light is being received by the telescope?______
What other position(s) will result in the same percent of light being received by the telescope?______
6.In position 4, what percent of the star’s light is received by the telescope?______
What other position(s) will have the same percent of light being received by the telescope?______
7.In position 2, let us assume that the exoplanet is half over the star and half not.
In position 2, what percent of the star’s light is being received by the telescope?______
What other position(s) will result in the same amount of light being received by the telescope?______
Summarize Your Learning
1.Fill in the table of values on the next page. In the first column, write the position number for the exoplanet (0 through 8) and in the second column, write the percent of the star’s light that is received by a viewing telescope. Give the table a title and label the columns appropriately.
2.Graph the data from your table of values. Label both sets of axes and give the graph a title.
3.In this activity, the radius of the exoplanet is half the radius of the star. (The area of the exoplanet is one-quarter the area of the star.) Typically, however, an exoplanet is tiny compared to its star.
(a)If the exoplanet is much smaller than the star, how will the amount of light blocked be different than in our activity?
______
______
(b)How will the percent of light received by a viewing telescope be different?
______
______
(c)How would your graph be different if the exoplanet were tiny compared to the star?
______
______
Post-Activity Assessment
Answer the following questions to check your understanding of modelling the transit method two-dimensionally.
1.Exoplanets are very small compared with the star that they orbit. If the radius of the star is known and the percent light drop is known, the radius of the exoplanet can be calculated.
To calculate the radius of the exoplanet, scientists use the formula % drop where R is the radius of the star and r is the radius of the exoplanet.
In our activity, the star has a radius of 6 cm. If an exoplanet transits the star and the percent drop in light intensity is 1%, what is the radius of the exoplanet in centimetres?
2.Recall that in the activity, the star has a radius of 6 cm.
(a)If the percent drop in light intensity is 0.5%, calculate the radius of the exoplanet in centimetres.
(b)If 1 cm represents 100 000 km, what is the real radius of the exoplanet?
3.The star Kepler-452 has a radius of about 386 000 km. When its exoplanet, Kepler-452b, transits the star, the percent drop in light intensity is 0.06%. Calculate the radius of exoplanet Kepler-452b in kilometres.
Permission to reproduce this page is granted for student use.1