Re:How Do We Measure the Distance to a Star?
by eesmith on Monday August 20, 2018 @02:49PM
(#17802681)
https://en.wikipedia.org/wiki/Cosmic_distance_ladder - "At the base of the ladder are fundamental distance measurements, in which distances are determined directly, with no physical assumptions about the nature of the object in question. ... The most important fundamental distance measurements come from trigonometric parallax."
Re:How Do We Measure the Distance to a Star?
by xtacy on Monday August 20, 2018 @02:50PM
(#17802694)
Also highly recommend Terry Tao's talk on the cosmic distance ladder:
https://terrytao.wordpress.com/2010/10/10/the-cosmic-distanc...
Re:How Do We Measure the Distance to a Star?
by mannykannot on Monday August 20, 2018 @06:01PM
(#17804404)
In addition to the annual parallax of the star being measured, you also need the diameter of the Earth's orbit, which was also first measured by parallax (together with Kepler's laws, giving the ratio of planets' orbital sizes from their periods): When Mars came close to Earth in 1672, simultaneous observations by Giovanni Cassini (in Paris) and Jean Richer (in French Guiana), comparing where Mars appeared relative to background stars, yielded a value of an astronomical unit that was about 7% higher than the modern value. [1]
Subsequent measurements of the dual transits of Venus in 1761 and 1769 refined the figure (Lalande, 1771), again using parallax, in a method proposed by Halley. Current measurements are based on radar.
[1] http://curious.astro.cornell.edu/physics/62-our-solar-system...
Re:How Do We Measure the Distance to a Star?
by antognini on Monday August 20, 2018 @03:33PM
(#17803117)
Former astronomer here. Yes, parallax measurements are absolutely the foundation of almost all distance measurements in astronomy.
The obvious advantage of using parallax is that you effectively use for the measurements an "instrument" of the size of 300 million kilometers (190 million miles). Which is really needed when the nearest star is 41 trillion(!) km away.
From class I remember that you can also determine the distance by measuring the coherence of the light coming from the star at two distant points on the order of 100m. In theory this would require more equipment, but has the obvious advantage of taking less than 6 months to get the results.