October 12, 1915. One hundred years ago today, the Scottish-born astronomer Robert Innes, at the Union Observatory in Johannesburg, South Africa announced the discovery of what we now know as the next-nearest star to our sun. That star is Proxima Centauri, one of three known stars in the Alpha Centauri system, with the other two stars being Alpha Centauri A and B. He announced his discovery in a paper dated October 12, 1915 titled A Faint Star of Large Proper Motion.
Prior to this announcement, astronomers believed that Alpha Centauri was the closest star to our solar system.
But Proxima – a relatively small red dwarf star – is closer at about 4.24 light-years away.
SAASTA – the South African Agency for Science and Technology Advancement – is celebrating Proxima’s centenary this year. At its website, SAASTA explained:
Although Alpha had been thoroughly observed by Innes, with his vast experience and passion for observing double stars he suspected that Alpha Centauri might have a companion. While comparing photographic plates that were taken five years apart … Innes observed that a certain faint star had moved. He found that this movement was about the same as that of Alpha Centauri.
After further investigation, he concluded that it was closer to the sun than Alpha. In 1917 he proposed the new star should be called Proxima Centauri, proxima being the Latin word for ‘nearest.’
Today, Proxima remains widely accepted as the closest star to Earth, but it’s still not known for certain whether Proxima is part of the Alpha Centauri system.
Bottom line: October 12, 2015 was the date of the publication of a paper announcing that the little star Proxima – int he Alpha Centauri system – is the next-nearest star to our sun.