University of Michigan - Department of Astronomy


updated: 04/19/2000

Parallax - Worksheets


Table 1: Tabletop Parallax

a B R (parallax) R (true value)


Table 2: Rooftop Parallax to Parking Structure

Trial   bx     by     a     B   R (parallax) R (map)

Star Name: ______________

Table 3: Parallax to the Moon

βx(Ann Arbor)
B (km)
R (parallax)
R (SN)

% error:


Concluding Questions

  1. What do you think was the leading source of error in your measurements of the distances using parallax?

  2. Why does a parallax measurement become less accurate (higher percent error) as the target object gets to be very distant?

  3. If you wish to use parallax to measure the most distant possible objects, is it better to use a short or long baseline? Why?

  4. For example, in Part 2, we said we couldn't measure the parallax angle of the Moon from the two positions on the rooftop because it would be too small. What would the angle be (using your measurement of the rooftop, and the text value for the distance to the Moon)?

  5. Suppose you wish to measure distances to stars using parallax. The longest baseline that one can possibly have without leaving the Earth is 2 AU (remember that 1 AU = 1.5 x 1011 m). This enormous baseline is attained by measuring in summer, and then again six months later when the Earth is on the opposite side of the Sun. The smallest parallax angle that can reliably be measured from the Earth is 0.01 arcseconds (a = 0.01", remember 1 = 60' = 3600"). How distant is a star with a parallax angle of 0.01"? Show your calculations, and express your answer in light years (1 light year = 9.5 x 1015 m). [Note: if your class is using the Kaufmann book, p.338 of the text uses an alternative definition of parallax angle, called p, which is half the angle a which was used in this lab.]