Which was discovered first Betelgeuse or Rigel?
Betelgeuse and Rigel are both in the top 10 brightest stars in the sky. They have been seen bright in the sky even since cavemen looked up. So, they were discovered about the same time.
Betelgeuse and Rigel are the two brightest stars in the constellation of Orion. They are very easy to spot, with Betelgeuse being at the top left and Rigel at the bottom right. Comparing the two it is also easy to notice the difference in colour as Betelgeuse is a red supergiant and looks reddish in colour, very different to Rigel.
Betelgeuse is much bigger, in size than Rigel - about 12 times. but only just smaller in terms of mass. Betelgeuse has a radius of about 936 times that of our Sun Rigel has a radius of about 78 times that of our Sun Betelgeuse has a mass of 18 times that of our Sun Rigel has a mass of 17 times that of our Sun
Answer When Bayer prepared his catalogue, there was no way to measure stellar brightness precisely. Traditionally, the stars were assigned to one of six magnitude classes, and Bayer's catalog lists all the first-magnitude stars, followed by all the second-magnitude stars, and so on. However within each magnitude class, there was no attempt to arrange stars by relative brightness. For example, in the Orion constellation, Bayer first designated the two 1st-magnitude stars, Betelgeuse and Rigel, as…
Orion is the most prominent constellation in the sky, so it has lots of prominent stars. Two in particular stand out. They are Rigel and Betelgeuse. Rigel is a very bright star in the bottom right corner, the brightest star in Orion. In the top left is Betelgeuse, also very bright but noticeably different in colour to Rigel, as it is a red giant star.