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Parallax is the apparent displacement of an object when it is viewed
different positions.
from two
Earth
A
B
parallax
angle
Moon
apparent image
of the Moon
AB (Montréal, Canada to Selsey, UK)
AC (Montréal, Canada to Montevideo, Uruguay)
BC (Selsey, UK to Montevideo, Uruguay)
ruler
apparent image
of the Moon
Astronomers measure the parallax of celestial bodies to determine how
far those bodies are from Earth.
On October 28, 2004, three astronomers (Peter Cleary, Pete Lawrence,
and Gerardo Addiègo) each at a different location on Earth, took a
digital photo of the Moon during a lunar eclipse at exactly the same
time. The data related to these photos is shown.
Shortest Distance on
Earth's Surface Between
Two Locations
5 220 km
9 121 km
10 967 km
? What is the most accurate method to determine the distance
between the Moon and Earth, from the given data?
Parallax Angle
0.7153⁰
1.189°
1.384°
B.
A. Sketch a triangle with the Moon and locations A and B as the vertices. Label
all the given angles and distances. What kind of triangle do you have?
Determine all unknown sides to the nearest kilometre and angles to the
nearest thousandth of a degree. How far, to the nearest kilometre, is the
Moon from either Montréal or Selsey?
C. Repeat parts A and B for locations B and C, and for A and C.
D. On October 28, 2004, the Moon was about 391 811 km from Earth (surface
to surface). Calculate the relative error, to the nearest tenth of a percent, for
all three distances you calculated.
E. Which of your results is most accurate? What factors contribute most to the
error in this experiment?