Lesson: How Far Away Is SOHO ? (Grades 9-12)

Teacher Information

SOHO was launched into an orbit around the Sun, rather than an orbit around the Earth, to assure that SOHO would provide solar data 24 hours a day. At no time would the Sun be hidden from SOHO by the Earth. Its position is around a point called the L1 Lagrangian point, a rather stable location at which the gravitational pull from Earth equals the gravitational pull from the Sun. L1 lies on the direct line between the Earth and the Sun, approximately 0.01 the distance from the Earth to the Sun. This allows SOHO to travel with the Earth as it revolves around the Sun, but at a distance of 1,500,000 km closer to the Sun.

SOHO is tracked and data is collected by the Deep Space Network (DSN), a series of three deep space communications facilities strategically placed on three continents, approximately 120 degrees apart around the world: Goldstone, CA (USA); Madrid, Spain; and Canberra, Australia. As the Earth rotates on its axis, DSN observes SOHO continuously from one of its sites.

Activity: How far away is SOHO?

Materials:

• Meter sticks, or meter tape
• Cut-outs of Sun, Earth, Moon, SOHO, Mercury, Venus (A blow-up Earth ball, showing locations of California, Spain and Australia, would be ideal to show why SOHO is always in view.)
• Individual student science notebooks or paper.

Type of Activity:

• Student-centered: Students measure distances and position classmates.
• Out of doors: Students use football field or parking lot
• Measurement: Use of metric system and scaling

Procedure:

1. Using a football field (size is approximately 100 meters) or 100 meters of string, place a student with the "Sun" at one goal line and the "Earth" at the other goal line.
2. Place student with "SOHO" at 0.01 of the distance (1 meter) from the Earth to the Sun.(These distances can be calculated by students prior to the activity. See Pre-activity sheet.)
3. Place student with Moon at 0.00256 of the distance to the Sun (0.25 meters).
4. Place student with Venus at 0.28 of the distance to the Sun (28 meters).
5. Place student with Mercury at 0.61 of the distance to the Sun (61 meters).
6. Mercury, Venus, Earth and SOHO slowly orbit the Sun while the Moon orbits Earth. Remember, Moon is always facing Earth!
7. Writing Component: Students stop and sketch on paper what they've portrayed on the football field and write a paragraph describing the event.
8. Allow 45 minutes for this activity.
9. For Pre-activity Sheet(see below), allow 15 minutes prior to the activity.

Pre-Activity Sheet:

Scaling

Purpose:

To create a scale model of the relative distances from Earth to the Moon, SOHO, Venus, and Mercury, using the length of a football field (100 meters) as the distance from the Earth to the Sun.

Complete the following table:

Connections to National Standards:

• National Science Education Content Standard D:
  • All students should develop an understanding of Earth in the solar system, of gravity as a force that holds all parts of the solar system together, and of orbits.
• Benchmarks for Science Literacy:
  • Students should know that planets move around the sun in orbits, that laws of gravitational force and motion show that planetary orbits are elliptical, and that increasingly sophisticated technology is used to learn about the universe.
• Standards for School Mathematics:
  • Students should estimate, make and use measurements to describe and compare phenomena; select appropriate units and tools to measure to the degree of accuracy required in a particular situation; develop formulas and procedures for determining measures to solve problems.

Created by: Ginger Sutula
Direct Comments to: vsutula@umd5.umd.edu