Measuring the Sun's Diameter

Activity:
Student use a telescope project technique to determine the Sun's Diameter.

Science Standards:
Nature of Science, Energy & Matter, and Scientific Models (Scale)

Objectives:

  • The student will project the Sun's image through a refracting telescope.
  • The student will measure the diameter of the Sun's image.
  • The student will calculate the magnification of the telescope.
  • The student will determine the diameter of the Sun.
  • Materials:

  • refracting telescope with solar projection screen
  • ruler and scientific calculator



  • Introduction:
    Although the Sun and the Full Moon appear to be the same size in the sky, the Sun is many, many times larger than the Moon. The difference in appearance is due to the fact the Sun is 93,000,000 miles from Earth while the Moon is only 240,000 miles away. In order to determine the actual diameter of the Sun, astronomers use the ratio of diameters to the distances as shown below.
     


    Directions:
    1. Never look at the Sun through a telescope . The focused light can permanently blind an observer in 0.1 second. Don't trust solar filters unless they have been looked at by a professional prior to each use. Never use filters that fit on the eyepiece.

    2. Set up the telescope (cover the finder scope with cap or lots of masking tape) and the solar projection screen. Align with the Sun using the shadow of the telescope on the ground (the shadow of the tube should be circular and not cylindrical).

    3. Measure and record the diameter of the Sun's image.

    4. Record the focal length of the objective lens and the focal length of the eyepiece lens.

    5. Determine the magnification by dividing the objective lens focal length by the eyepiece focal length.

    6. Determine the diameter of the Sun using the following relationships: