How Do Astronomers Know How Far Away or How Big the Objects on the Cards Are?
Measuring distances to objects out in space is one of the most challenging parts of modern astronomy. After all, you can’t just send a graduate student out there with a tape measure. Most of the objects astronomers are interested in are, in fact, so far away that we may never be able to visit them. Nevertheless, if we want to figure out how big they are, how much energy they give off, or what groups of objects they are part of, we first need to know how far away they are located. One way to measure distances is to look at relatively nearby objects in space from opposite sides of the Earth’s orbit. (In the same way, surveyors can measure distances across a wide river, by sighting from two different locations along the river’s bank.) One nice bonus we get from living on Earth is a free trip around the Sun every year. This means that the Earth’s position in its orbit in the spring is roughly twice the distance between the Earth and the Sun, or 186 million miles from its position in the fa
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