![]() Let's call the angle to the object AC, and agree to measure it from the direction to the Sun. It's easy to see from this figure that the size of the angles tells us the distance B since we know that A, one astronomical unit, is 150,000,000 km. Triangulation: The larger the angle AC and the smaller the angle BC, the more distant the object You could use it for something as simple as finding the height of a telephone pole without climbing it, tape measure in hand.Ī simple example in astronomy occurs when we measure the direction to an object seen when the Earth is first on one side of its orbit, and then again six months later when Earth is on the other side. Surveyors use it to locate to locate property boundaries and plan construction. Kepler used it to find distances to the planets. ![]() Greek astronomers used it to try to determine distances of the Moon and Sun. Triangulation has been used to measure distances for thousands of years. Or about 150 million km, 93 million miles, 8.3 light minutes. It is preciselyġ Astronomical Unit = 149,597,871.5 kilometers For most purposes this means that the AU is the average distance from the Earth to the Sun. Since the Earth's orbit is an ellipse, astronomers prefer to define the "AU" for an imaginary planet that would orbit in the Sun in a circle in the same time it takes for Earth to orbit in its ellipse. Within the solar system we measure distances by comparison to the Earth-Sun distance, and use the Astronomical Unit as the measuring stick. The images of Saturn returned by the Cassini satellite take about 1 hour and 23 minutes to travel 1,300,000,000 kilometers to reach us. McDonald Observatory sending a laser beam to bounce back from mirrors on the Moonĭistances to Sun and planets are measured by timing radio signals from man-made satellites orbiting around those planets. ![]()
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