Why did it take astronomers until 1838 to measure the parallax of the stars?
A) because most stars are too faint to see without a good telescope
B) because the stars are so far away that their annual shift of position in the sky is too small to see without a good telescope
C) because detecting parallax requires measuring a spectrum, which only became possible in the 1830's
D) because cepheid variable stars had not been discovered earlier
E) because no one before then could conceive of the Earth moving around the Sun

Question

Quizplus · Accepted Answer

The parallax of a star is the apparent shift in its position against the background of more distant stars as seen from two different points in Earth's orbit around the Sun, six months apart. This shift is very small, and therefore, it requires careful measurement by telescopes. Until the mid-1800s, telescopes were not powerful enough to measure the small parallax angles of most stars, as they are too far away. Therefore, it took until 1838 for astronomers to measure the parallax of a star, which was done by Friedrich Bessel for the star 61 Cygni.

Why Did It Take Astronomers Until 1838 to Measure the Parallax