The " astronomical unit " is used as the baseline of the triangle to measure stellar parallaxes " ( distances in the image are not to scale ) ".
42.
Unlike the stellar parallax method, photometric parallax can be used to estimate the distances of stars over 10 kpc away, at the expense of much more limited accuracy for individual measurements.
43.
Accurate calculations of distance based on stellar parallax require a measurement of the distance from Earth to the Sun, now known to exquisite accuracy based on radar reflection off the surfaces of planets.
44.
The period luminosity relationship for Cepheids made them the first " standard candle " in astronomy, allowing scientists to compute the distances to galaxies too remote for stellar parallax observations to be useful.
45.
"' Stellar parallax "'is parallax on an interstellar scale : the apparent shift of position of any nearby star ( or other object ) against the background of distant objects.
46.
The first successful measurements of stellar parallax ( to determine the distance to a star ) were made by Friedrich Bessel in 1838 for the star atmospheric turbulence in measurements compared to a filar micrometer.
47.
Compared to the FAME accuracy of 50 microarcseconds, the Gaia mission is planning 10 microarcseconds accuracy, for mapping stellar parallax up to a distance of tens of thousands of light-years from Earth.
48.
James Bradley first tried to measure stellar parallaxes in 1729 . The stellar movement proved too insignificant for his telescope, but he instead discovered the aberration of light and the arcsec for the binary star 61 Cygni.
49.
His other topics included a study of atmospheric refraction, stellar parallaxes, drawings of Jupiter, determination of the position of Mars'equator, the amount of its oblateness and the rate of motion of the nodes.
50.
With characteristic kindness, he had volunteered to have the spectra observed for all the stars including comparison stars which had been observed in the observations for stellar parallax which Hinks and I made at Cambridge, and I discussed.
