Stellar Parallax Interactive (126.0K)
If Earth really orbited the Sun, early astronomers reasoned, we’d be able to observe stellar parallax, or the apparent motions of stars created by our changing vantage point, as Earth orbited the Sun. The flaw in that reasoning was that stars were so far away, that those motions were unobservable. Now, with today’s technology, astronomers do measure these motions, and you can observe it with this Interactive. Some simple trigonometry is the basis for stellar parallax. Try it out here, and see how different sized Earth orbits, the distance to the star, and the quality of the telescope impact your observations.
It was not until jsut before the American Civil War that observers at last telescopically detected the tiny parallax shifts of even the closest of the stars, such as alpha Centauri at 4.3 light years distance.
Let's explore the limits of the resolution of the Hipparcos data to see just how much of the universe we are still missing good distance data for.
To understand what a revolution in our accurate distance measurements Hipparcos discovered, consider that our best Earth based observations were only about a tenth the resolution of Hipparcos.
While Hipparcos was in orbit about the Earth, with a base line of 2 A.U., just like Earth based observers, its great increase in accuracy came from its sharp optics working above the turbuence of our atmopshere. But why not put the new "Long Baseline Telescope" into an even more distant orbit, and give it even sharper optics to boot!