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39 thousand light-years) per year. *The table shows how the stars will move at various angles to Earth, and this is why we see them moving as if they are orbiting from different distances.* She calculated that 100 disk stars could have a maximum speed of 12 parsecs (39 thousand light-years) per year. *She also noted that there’s no observational evidence for such high speeds in any case where one star can be seen against another background source or group of stars.* Her paper concludes “It seems likely then, on theoretical grounds alone, that most galactic orbits must rotate with respect to each other.” 39 thousand light-years) from the Galactic Center.
*She calculated that a star at 12 parsecs would take about 400 million years to orbit once around, and as an object is farther away its orbital period will get longer.* If she had interpreted the speed of stars as their being closer rather than further away, then it would be possible for her to conclude that they were orbiting faster because they’re nearer! *Her calculations show how orbits could still have variable speeds even if there was no rotation — just from different angles of view.* It does not depend on distance or any other factor besides viewing angle alone.
This sentence introduces what Hildegarde de Sitter’s theory was in 1963: “the rotation of galactic orbits doesThe height of the Milky Way and disk stars has been a question that astronomers have wanted to answer for decades. The most accepted theory is that they are orbiting around the galaxy’s center in an orderly fashion, but there may be another explanation as well!
*The idea that the Milky Way is rotating around its center at a constant speed was first proposed in 1954, and it has been accepted as the explanation for bobbing disk stars.
*In 1963, astronomer Hildegarde de Sitter presented an article to suggest a different theory: “the rotation of galactic orbits does not depend on their distance from the Galactic Center.” She argued that when looking through our galaxy’s plane they seem to be moving at various speeds because we are observing them from different angles.* In her paper she calculated how fast this could be happening. The table shows what would happen if there were 100 stars within 20 kiloparsecs (65 thousand light-years) of Earth at 12 parsecs (