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In 2013, ESA launched a telescope called Gaia that charts the positions, parallaxes, and proper motions of more than one billion stars. That number represents only about 1% of the actual number of stars in the galaxy, but that's enough for astronomers to extrapolate the observations to understand how the Milky Way behaves as a whole.
Using Gaia data, they could, for the first time, create a dynamic movie of the galaxy's life over billions of years, uncovering past events but also projecting what will happen in the future.
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Parallax is the observed displacement of an object caused by the change of the observer's point of view. In astronomy, it is an irreplaceable tool for calculating distances of far away stars.
The night sky appears two-dimensional.
However, it took astronomer...
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A real breakthrough in parallax measurement and therefore in determining distances of stars in our galaxy, the Milky Way, came with a mission called Hipparchos, after the ancient Greek astronomer that first used the method to estimate the distance of the moon.
This mission, launched by ESA...
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The light is spread over an area four times larger, and it will be only one-fourth as bright as when the projector was half as far away. If you move the projector three times farther away, the light will cover 9 square feet and appear only one-ninth as bright.
If a star measured in this ma...
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The first known astronomical measurement using parallax didn't involve a star but the moon. The ancient Greek astronomer Hipparchus reportedly used observations of a solar eclipse from two different locations to calculate the distance of Earth's celestial companion.
In 1672, Italian astrono...
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Another application of parallax is the reproduction and display of 3D images. The key is to capture 2D images of the subject from two slightly different angles, similar to the way human eyes do, and present them in such a w...
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How stars are measured.
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