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?

(A measuring activity, appropriate for grades 9-12)


Type of Activity:

Activity Data
ObjectDistance from Earth*
Sun150,000,000 km (1.5 x 108 km)
Moon384,000 km (3.84 x 105 km)
Venus 42,000,000 km (4.2 x 107 km)
Mercury92,000,000 km (9.2 x 107 km)
SOHO1,500,000 km (1.5 x 106 km)

* Distances at conjunction.


  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:



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:

ObjectDistance from Earth Scaled Distance
Sun150,000,000 km100 m
Moon364,000 km ____m
Venus42,000,000 km ____m
Mercury92,000,000 km____ m
SOHO1,500,000 km____ m
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Connections to National Standards:

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