Siriometer
The Siriometer is a no longer in use astronomical unit of measurement from the 19th or early 20th century.
The value of the Siriometer has changed over time.
Herschel's Siriometer
Friedrich Wilhelm Herschel defined the Siriometer as the distance from the sun to Sirius at the beginning of the 19th century .
The unit of measurement was created in an effort to measure the distances of visible stars from the earth. Since no methods were known with which the distance could be measured directly, Herschel wanted to at least determine the relative distance between the stars.
Based on the assumption that all stars are more or less equally bright, Herschel took the brightest star in the night sky, Sirius, as a reference. By comparing the brightness of the other stars, he tried to estimate the distance: the brightness decreases with the square of the distance, a star that is a quarter of the brightness of Sirius will be twice as far away.
Due to the inaccurate estimate of the brightness and the fact that the stars have very large differences in brightness, his results were not very accurate.
How big a Siriometer really is was not determined during Herschel's lifetime. The first absolute distance measurements were made by Friedrich Wilhelm Bessel in 1838 , 16 years after Herschel's death. Today we know that Sirius is 8.6 light years away, or about 81 trillion kilometers.
Charlie's Siriometer
In 1911, Carl Charlier proposed setting the Siriometer as 1 million astronomical units . This happened in the course of the debate at the time about the definition of a usable unit of measurement for cosmic orders of magnitude. Ultimately, Parsec emerged victorious from this debate .
The new value corresponds to around 149.5 trillion kilometers, almost twice as large as the original definition.
Individual evidence
- ↑ Simon Singh, Big Bang , ISBN 3-446-20598-5 , pp. 182 ff.
- ↑ James Jeans, Astronomy and Cosmogony , 1929, p. 6, reprinted in 2008, ISBN 978-0-521-74470-6