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Distances in Space
From here on earth it is difficult to fathom the huge distances that exist between
the stars and planets. The circumference of the earth (38,500 km) may seem like
a long way to us but is an insignificant distance in space. The nearest celestial
object to earth, the moon, is approximately 400, 000 km away (more than 10
times the earth’s circumference). The sun, which is by far the closest star to
earth, is 150 million km away.
As we leave the solar system, distances become so great that
astronomers no longer refer to them kilometres. Instead they use light years.
Light travels at a speed of 300,000 km/second (that’s 7.5 times around the earth
in one second!). A light year is the distance that light travels in a year
(9,460,800,000,000 km).
The closest star to our solar system, Alpha Centauri, is 4.3 light years
away. There are only 11 stars (not including the sun) that are less than 10 light
years away from earth. Most stars are much farther away than that. Many stars
that we see at night are several thousand light years away. This means that from
earth we can only see these stars as they existed thousands of years ago. It is
possible that some of these stars no longer exist.
The most distant objects that have been detected are approximately 14
billion light years away.
Classroom Triangulation Activity:
In this activity you will use the principle of parallax and the method of
triangulation to determine the distance between two points in the classroom.
You will need:
1) A protractor
2) Paper
3) Pencil
4) Tape measure or meter stick
Working in groups of 2 or 3 you will be given a mark on the wall (an "X")
and a baseline. Follow the steps below to calculate the distance to the "X"
from each end of the baseline.
1) Stand at your baseline and look at the mark on the wall. Estimate the
distance from each end of your baseline.
Estimate: Left side _______
Right side ______
2) At each end of your baseline, look through a tube at your mark. Line
the tube up with your baseline and measure the angle between the tube
and your baseline at each end using a protractor.
3) Get a blank piece of paper and make an appropriate scale (i.e. one that
allows you to use as much of your paper as possible).
4) Accurately draw a scale diagram using the known length (your
baseline) and the two angles you measured.
5) Measure the length of each line on your scale diagram and calculate
the distance from each side of your baseline to your mark
6) Measure the actual distance from each side using a tape measure or
meter stick.
7) Calculate your percent error using the following formula
% error = (estimated distance – measured distance) x 100
Measured distance
To Be Handed In (at the end of class):
1. Estimates of each distance
2. A scale diagram (include your scale)
3. Calculation of the distance based on your scale diagram
4. The actual distances (as measured by a tape measure)
5. Calculation of the percentage error
Answer the following questions in your notebook:
1. Read pages 367-8 and explain what is meant by the word “parallax”.
2. Explain how this method could be used to measure the distances to
stars?
3. What is the largest baseline that astronomers here on earth can use?
4. Explain why this method only works for relatively near stars and not
for stars and galaxies more than 100 light years away.