Stellar Parallax Interactive
Stellar Parallax Interactive

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.

Aristotle realized that is Aristarchus' heliocentric model were correct, we should be able to detect the parallax shifts of nearby stars against the more distant stellar background. In fact, Ptolemy would observe the parallax of the Moon and correctly find its orbitted us at about 30 Earth radii distance.

 1 When would you ideally look for the most stellar parallax? Need a Hint? A) Over twelve hours. B) Over a month. C) Over six months. D) Over a year.

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.

 2 Given at a parsec is 3.26 light years, what was the parallax angle finally measured for this closest of the stars, with the largest observed parallax? Need a Hint? A) 1.31" B) .76 " C) .326 " D) .1 "

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.

 3 The Hipparcos data is good to about .001" in accuracy; just how far out can we expect this parallax data to give us reasonable distances? Need a Hint? A) About 100 light years. B) About 1,000 light years. C) About 3,000 light years. D) About 10,000 light years.

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.

 4 How much larger a volume of space, and how many times more stars, does the Hipparcos data give us access to? Need a Hint? A) 10 X more B) 100X C) 1,000X D) 10,000X

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!

 5 If the LBT were put into a resonant orbit with Jupiter, at 5 A.U from the Sun, what effect would this have on the parallax data it gathered? Need a Hint? A) Twice the accuracy. B) Five times the accuracy. C) Ten times the accuracy. D) 50 times the accuracy.

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