That distance (line AB in Figure 19.4) is called the baseline. You set up two observing stations some distance apart. Suppose you are trying to measure the distance to a tree across a deep river ( Figure 19.4). Let’s see how surveyors take advantage of the same idea. In order to see the shift of an object a city block or more from you, your eyes would need to be spread apart a lot farther. This is because our depth perception fails for objects more than a few tens of meters away. If your arms were made of rubber, you could stretch the pen far enough away from your eyes that the shift would become imperceptible. Your brain automatically performs such comparisons and gives you a pretty good sense of how far away things in your immediate neighborhood are. If you play with moving the pen for a while, you will notice that the farther away you hold it, the less it seems to shift. Now hold the pen at arm’s length: the shift is less. Note how the pen seems to shift relative to objects across the room. Look at it first with one eye (closing the other) and then switch eyes. To see what we mean, take a pen and hold it a few inches in front of your face. You therefore view the world from two different vantage points, and it is this dual perspective that allows you to get a general sense of how far away objects are. As you are pleased to discover every morning when you look in the mirror, your two eyes are located some distance apart. Triangulation in SpaceĪ practical example of triangulation is your own depth perception. Even so, we can, in principle, survey distances to the stars using the same technique that a civil engineer employs to survey the distance to an inaccessible mountain or tree-the method of triangulation.

1 The nearest star, however, is hundreds of thousands of AU from Earth. As of 2021, Voyager 1 is 152 AU from the Sun. For example, our Voyager 1 probe, which was launched in 1977, has now traveled farther from Earth than any other spacecraft. It is an enormous step to go from the planets to the stars. Discuss astronomers’ efforts to determine the distance of the stars closest to the Sun.Explain why space-based satellites deliver more precise distances than ground-based methods.Understand the concept of triangulating distances to distant objects, including stars.By the end of this section, you will be able to:

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