Distance[edit]
In his 1698 book Cosmotheoros, Christiaan Huygens estimated the distance to Sirius at 27664 times the distance of the earth to the sun (about 0.437 light years).[53]
The parallax of Sirius was measured by Thomas Henderson using his observations made in 1832-1833 and Maclear's observations made in 1836-1837, and was published in 1839. The value of the parallax was 0.23 arcseconds, and error of the parallax was estimated not to exceed a quarter of a second.
Also, there were earlier attempts to measure the parallax of Sirius: by the second Cassini (6 seconds); by some astronomers (including Nevil Maskelyne)[54] using Lacaille's observations made at the Cape of Good Hope (4 seconds); by Piazzi (the same amount); using Lacaille's observations made at Paris, more numerous and certain than those made at the Cape (no sensible parallax); by Bessel (no sensible parallax).[55]