Experimenting with Angular Diameter and Distance (study of Outer Space)

Amy Fahey, Oak Crest Elementary, Belle Plaine, MN - based on a experiment from Jancie VanCleave's 204 Sticky, Gloppy, Wacky, & Wonderful Experiments and on unit of study from the Houghton Mifflin Science Series (2007) - Chapter 9 - Our Solar System (Lesson 3 - pages D52-D59).
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Summary

Students will use their prior knowledge about the solar system, including work done with basic telescopes, planetary movements, identification of the inner (terrestrial) and outer (Jovian) planets, and knowing key terms such as the sun, moon, planet, and asteroids from previous studies of Chapter 9 in the Houghton Mifflin science curriculum. Students will be focusing their study on the inner planets and the relative sizes. This lesson will specifically compare the relative sizes of the sun and the moon, and experiment with angular diameter, apparent diameter and distance.

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Learning Goals

This activity is designed for students to:

1) Observe a model of apparent diameter and distance
2) Investigate apparent diameter, angular diameter, and distance by creating own model
3) Apply to investigation results to an orbital model with relative sizes of the inner planets

Process skills used in the investigation include: observing, questioning, comparing, and classifying.

Key vocabulary (concepts):

Prior knowledge - solar system, sun, planet, orbit, moon, inner (terrestrial) / outer (Jovian) planets, asteroid, telescope, & magnify

New knowledge - terrestrial planets, apparent diameter, angular diameter, distance

Context for Use

Grade level - 3-5: Groups of 2 or 4
Class size 24-30; Rural Public School Facility
Lesson in Chapter of study on Space

Materials: sports balls (ping pong, tennis, golf, baseball, softball, basketball, soccer, volleyball, beach ball), 1 meter of roll paper or adding machine tape, paper, construction paper, masking tape, one piece of chalk, pencils, pennies, rulers, tape measure, clock, and science notebook

This activity is for building upon and enriching a student's prior knowledge of outer space, the planets, the sun and moon, by creating a visual model and an understanding that distance affects the apparent size of objects.

Description and Teaching Materials

Introductory Materials:
Masking tape
1 meter of adding machine tape
Piece of chalk
Science notebook / pencils
Rulers

Introductory Activity - Demonstration of apparent diameter and angular diameter-
Begin by sharing with students a 1 meter strip of adding machine tape and asking if they think I can make this the strip of paper look like the width of your thumb. Have students jot down responses in their science notebook under the topic Size (you can add more to the title later - example Apparent Sizes and Space Models). Allow students to share some of their thoughts. Many students might think that it would be impossible for your thumb to be the same size as the paper, while other students may already understand that distance plays a role in allowing objects to look of similar size.
After your discussion, mount the adding machine tape to the wall at about the student's eye level using masking tape. Then from the wall (with the tape on it) measure a distance about 3 m (or 10 feet) away and mark a spot on the floor with masking tape or chalk. Have the students stand at the spot, close one eye, and hold out their thumb in front of themselves. They will have to move their thumb back and forth in front of their open eye until the adding machine tape is blocked from sight. You may want to set up a few stations around the room for students to view the adding tape, to avoid long lines. Students can then write in their science notebooks about what they observed and how close or far they had to hold their thumb out in front of them before the line of tape disappeared. You could also have them measure the size of their thumb and distance from their face that they held their thumb out and write the distances in their science notebook.
When the demonstration is done, discuss with the students why this happened. Explain that we know our thumb is not the same size as the adding machine tape on the wall, yet from a distance they appear to be the same length. This is because the have the same apparent diameter (how large an object's diameter is at a given distance). Angular diameter is another way to describe what happens with the thumb and the adding machine tape. This occurs when the angle of your thumb (from side to side) is held at a distance where the angle matches that of the object further away (the length of the adding machine tape). Scientists use the concept of angular diameter to help approximate the apparent size of objects in space. You may want to draw a diagram of the angle of the thumb and the related angle of the measuring tape. Have students draw this diagram in their science notebooks.


Apparent Size Investigation Materials:
Masking tape or piece of chalk
Sports balls (ping pong, tennis, golf, baseball, softball, basketball, soccer, volleyball, beach ball)
Construction paper
Tape measure
Science notebook / pencils

Apparent Size Investigation-
In this next activity apparent size will be demonstrated briefly again, and students will allowed a chance to experiment with various objects. (The initial part of this activity may also be used to replace the introductory activity). For this demonstration use a ping pong ball and a basketball and bring students into an area with a long hallway (a large gymnasium or outdoors would work also). Ask the students what to objects they usually see in the sky (most will probably say the sun and moon, others may mention planets or stars). Share with them today the will be looking at an example of the sun and the moon from Earth. In this model they are to try and observe how the sun (basketball) is larger than the moon (ping pong ball), yet in the sky they seem to have a similar size. Have students write down in their science notebooks their predictions about what will happen to the size of the sports balls as they are placed at various distances away from the starting point (or Earth). Share with them they can use the previous activity with the thumb and measuring tape to give them some ideas.
Begin the demonstration by marking a starting point (with masking tape or chalk) the represents the Earth. Select one volunteer to take the ping pong ball and walk out a few feet in front of you. Then have a second volunteer take the basketball and stand next to the moon (ping pong ball). Share with the class how the two are different in size at the same distance away from the Earth. Then have the student holding the sun move away from the Earth and moon further down the hallway. Stop at various points to see how the sun and the moon compare in size. Stop the child holding the sun when they have matched the size of the sun. (If your space is not large enough use different sized sports balls to make the comparison). Ask the students to observe the distance between the moon and the sun, yet the have the same apparent size. If possible have some students measure the distance (check with high school sport coaches like track for tape measures). Then ask the students to write a few notes about what the saw and how it related to the thumb and adding machine tape demonstration from yesterday. Remind them about the concept of angular diameter.
Now allow students to experiment with angular diameter and distance. Share with students that you would like them to repeat the demonstration, yet change one thing about it. For example, students may use different sized sport balls, construction paper cut-outs, objects from their desk that are not necessarily round in shape. They may also want to use the same objects as in the demonstration but experiment with distance, or transparency (placing objects of various translucent or opaque qualities in between the spheres). (Other topics to explore may include: comparing posters around the room and distance from where they are viewed, can we calculate the size of an object if we can measure something closer). Give them a chance to write down their experiment (including their prediction) and materials in their science notebooks before beginning. They should also continue to write about the results in their notebooks. Check in with the various groups, and allow a couple of groups to share what they tried (if possible have all groups share or complete sharing during another class period - groups could also write experiment notes on chart paper and post for other groups to read about). When students are finished with their results have them conclude about what they found out and if it matched their predictions.


Culminating the Lesson -
In concluding this activity share with students that scientists use apparent size to help us understand the relative sizes of the planets. It also helps us to know that their distance plays a role in the size we observe in the night-time sky (except Uranus and Neptune which can only be seen with a telescope). Scientists use relative sizes when building or drawing models of the solar system. In our text (pages D52-D53) we will continue our study of planets by making a model of the inner (terrestrial) planets, their relative sizes, and orbits (using masking tape, construction paper, measuring tape, and clock). Note to students that models help us understand what we may not be able to see up close (but even the best model represents our highest level of understanding at the given time).

References and Resources

Books:
Jancie VanCleave's 204 Sticky, Gloppy, Wacky, & Wonderful Experiments. 2002 Jossey-Bass.

Houghton Mifflin Science 2007.

Teaching Notes and Tips

Due to time constraints you may want to omit the introductory activity and use the demonstration at the beginning of the Apparent size experiment instead. Both work on developing the concept of apparent size.

Assessment

Students can be assessed in the follow ways:

Read notes from science notebook
Participation in experiment
Sharing of experiment (either posted, shared with the class, or from reading notebook)

Standards

3.3.3.2.1 - (The Universe) - Objects in the solar system are seen from Earth as points of light with distinctive patterns of motion (Demonstrate how a large light source at a great distance looks like a small light that is much closer).

References and Resources