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This date in science: Discovery of Proxima Centauri

Happy anniversary, Proxima Centauri! Today is the 100th anniversary of the announcement that this star is next-nearest to our sun.

Hubble Space Telescope image of Proxima Centauri, the closest known star to the sun.  Read more about this image.

Hubble Space Telescope image of Proxima Centauri, the closest known star to the sun. Read more about this image.

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.

Read more: Proxima Centauri’s awesome new planet

Alpha, Beta, and Proxima Centauri

The two bright stars here are Alpha and Beta Centauri. The circle shows the location of Proxima. At just over one parsec away, it is the closest star to our sun. Sitting in the southern constellation Centaurus, the Centaur, it is most likely gravitationally bound to the bright star on the right: Alpha Centauri. The other bright star, Beta Centauri, is about 100 parsecs (300 light-years) from Earth. Image via Wikipedia user Skatebiker.

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.

Deborah Byrd