He was the first person to measure the distance to a star using the method of parallax.

Question

BlackTom AI · Accepted Answer

Friedrich Bessel carried out the first successful and published measurement of stellar parallax, so he is the correct answer.

1) Relevant concepts: Stellar (trigonometric) parallax is the apparent shift of a nearby star against distant background stars caused by the Earth's orbital motion. The parallax angle p is defined as half the total angular shift measured six months apart. The distance d (in parsecs) is given by d = 1/p when p is in arcseconds. Using a baseline of 1 astronomical unit (AU) to each side of the Sun (so a total baseline of 2 AU) produces a measurable parallax for nearby stars.

2) Historical reasoning and context: Friedrich Wilhelm Bessel announced in 1838 a precise parallax measurement for the star 61 Cygni. Although Thomas Henderson and others had earlier observations (Henderson measured Alpha Centauri earlier but did not publish promptly), Bessel’s observation was the first reliable, published trigonometric parallax and is credited historically as the first definitive measurement of a stellar distance.

3) Calculation example (showing intermediate steps): Bessel reported a parallax near p = 0.314 arcseconds for 61 Cygni.
- Compute distance in parsecs: d = 1 / p = 1 / 0.314 ≈ 3.1847 parsecs.
- Convert to light years (1 parsec ≈ 3.26156 ly): d ≈ 3.1847 × 3.26156 ≈ 10.4 light years.
(Bessel’s value had measurement error; modern distance differs slightly, but the method and result established the technique.)

4) Why this is correct: Bessel both performed the careful observations with good instruments and published the result first; his measurement established parallax as a practical method for determining stellar distances.

5) Why the other choices are incorrect:
- William Herschel: discovered Uranus and studied stars, but did not make the first parallax measurement.
- Harlow Shapley: early 20th-century astronomer who measured globular cluster distances and galactic structure, not the first parallax.
- Heber Curtis: known for the “Great Debate” about galaxies, not for the first stellar parallax.

Conclusion: The correct and historically credited person is Friedrich Bessel, matching the provided answer.

He was the first person to measure the distance to a star using the method of parallax. Single choice

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