Which group best describes Alpha Orionis (Betelgeuse)?

Alpha Orionis, commonly known as Betelgeuse, is classified as a semi-regular variable red giant. This classification is important because it highlights several key characteristics of the star. As a red giant, Betelgeuse has expanded and cooled, resulting in its distinct reddish hue.

Being semi-regular means that it exhibits variations in brightness that are not entirely periodic, which is typical for stars of this nature. Betelgeuse's brightness fluctuates due to changes in its outer layers and pulsation modes, which can lead to significant brightness changes over weeks or months. This variability is a defining feature of semi-regular variables, which differentiates them from those that display regular, predictable pulsations.

The other categories are not applicable to Betelgeuse. As a type II supernova, it would be an end-of-life stage rather than its current classification, which is that of a star still in the red giant phase. Blue variable stars typically refers to more massive stars that also undergo significant changes but do so in different spectral regions and with different mechanisms. Meanwhile, a dark nebula is a cloud of gas and dust that obscures light from stars behind it, rather than a star itself. Thus, the designation of Betel