# Solar Rotation

Overview

In this middle level activity, students work as NASA scientists to make repeated observations of our Sun to determine rotation rates. First, students create a playground model of rotation and create representative diagrams. Students then observe NASA images of sunspots to determine the rotation rate of our Sun. As an extension, students can download NASA movies from the Internet and measure rotation rates for other objects in the solar system.

Learning Outcomes

By completing this activity, the learner will

• describe a scientific model using diagrams
• observe successive images of our Sun
• measure a rotation rate for our Sun
• determine rotation rates for a variety of solar system objects
Materials Needed for Each Group

Each group needs:

• a printed copy of the student activity handout
• 4 construction paper signs & string to hang around students' necks (labed: mountain, lake, crater,and city)
• a stopwatch and regular sheets of paper to roll into simple telescopes for observing students.
Background Information

ROTATION is the length of time for an object to spin once on its axis. Planetary rotation rates are measured by using telescopes or space probes. Scientists carefully pick a particular feature on the planet (a large crater, a mountain, a spot, etc). The task is then to determine how long the feature takes to move from one side of the planetary disk to the other side; this would be one-half of the rotation rate. For example, the animated image of our Sun at right has a rotation rate of about 25 days. After a rotation rate is measured, it can be compared with values found for many objects in the solar system (planets, asteroids, natural satellites, and our Sun). One word of caution is that because Earth's moon is tidally coupled to Earth, determining the rotation rate for Earth's moon is much more problematic using this strategy.

A planet that caused astronomers quite a bit of consternation was the planet Mercury. Because Mercury is located so close to our Sun, it was difficult to observe the planet closely. In 1974, NASA sent the Mariner 10 space probe to investigate Mercury. The plan was to have Mariner 10 orbit our Sun in such a way that it passed by planet Mercury three times for every two orbits. Unfortunately for the astronomers, Mercury has the same rotation of three times every two orbits resulting in Mariner 10 photographing the SAME SIDE of Mercury every time!

Another planet that is difficult to directly observe rotate is our own planet Earth. This is because we live on Earth and rotate with it. Several experiments have been conducted to demonstrate the rotation of Earth; one interesting experiment is Foucault's Pendulum Experiment ( ref ). Recently, NASA scientists were finally able to get great movies of Earth rotating when the Galileo probe flew past Earth on its way to Jupiter in 1994.

On-line Resources

Teacher Lesson Plans - Learning Cycle Format

Anticipatory Set

Using a classroom globe of Earth, ask students how long Earth takes to rotate once (24 hrs). Challenge students about how do they know this. (Many students will suggest that we have movies of it taken by satellites - these movies have not always been around, before that, it was much more difficult). Be certain students know the definition of rotation.

Change the focus of the discussion to the rotation of other planets. Ask students to develop and write out a strategy that they could use determine the rotational period of a distant planet.

Exploration - Creating a playground model for rotation

OUTSIDE PHASE

During this outside phase, students are going to create a playground model for rotation by forming a rotating circle. One half of the class will be part of the circle and one half will observe from a distance - then, of course, they will switch roles.

Create four different colored construction paper signs and label each with a different object: mountain, lake, crater and city. Select four students spread evenly along the circle and hang the signs around their necks with string (or saftey pin the signs to coats).

Challenge the students in the circle to join hands and to make the circle spin as fast as possible while still keeping its cicular shape. It is then the task of the observing students to determine the rotation rate of the circle of students by using a stopwatch and observing through their paper-tube telescopes. It will often help if students work in teams of two where the observer shouts START and STOP for the timekeeper. Make multiple measurements and calculate the average rotation rate before switching teams.

INDOORS PHASE

Students should combine their results on the board for the rotation rate for team one and for team two. The focus of this part of the lesson is on how to determine rotation rates at a distance. First ask students to write down exactly the process they used to measure the rotation rate of the circle using the reference signs. Second, have students create two sketches of the scenario: (1) as viewed from eye level and (2) as viewed from above. See the pictures below as examples. Tell students that they will be using this same observational process to determine the rotation rate of our Sun.

Concept Introduction - Measuring solar rotation rates

View solar image number 001. Notice the location of these spots on the solar surface. Now look at solar image number 002. Where are the spots now? You should note that on the bottom of each image is a time and date mark. These will be very helpful in determining the rotation rate for our Sun. Solar image number 003 appears on a page with lots of additional solar images.

Determine the rotation rate of our Sun by watching sunspots move from one side to the other. It should be close to 26 days. This is how Galileo determined the solar rotation rate in 1610. An animated image of solar rotation is available too!

 solar image number 001 solar image number 002

Concept Application - Studying changing faces in the solar system

Arrange students into 4 member NASA science teams and assign each team one of the following solar system objects. Teams should create a multi-media report that includes six parts:

1. What object was studies?
2. What was the rotation rate of the object?
3. How did you determine this rotation rate?