It was first observed to be variable by Sir John Herschel in 1836.

At this period its variations were "most marked and striking." This continued until 1840, when the changes became "much less conspicuous.

In January, 1849, they had recommenced, and on December 5th, 1852, Mr.Fletcher observed [alpha] Orionis brighter than Capella, and actually the largest star in the northern hemisphere." That a star so conspicuous, and presumably so large, should present such remarkable variations, is a circumstance which adds an additional interest to the results which have rewarded the spectrum-analysis of this star by Mr.
Huggins and Professor Miller.

It appears that there is decisive evidence of the presence in this luminary of many elements known to exist in our own sun; amongst others are found sodium, magnesium, calcium, iron, and bismuth.

Hydrogen appears to be absent, or, more correctly, there are no lines in the star's spectrum corresponding to those of hydrogen in the solar spectrum.