Several things to consider:
-- Because of its ENORMOUS size. We believe that Betelgeuse is about as large
as the orbits of the Asteroid Belt. So if Betelgeuse sat exactly where the sun sits,
then Mercury, Venus, the Earth, and Mars would all be inside of it.
-- Because it's so close to us. Betelgeuse is roughly 800 light-years from us. That's
an enormous distance, but actually pretty close as stars go.
-- Because it's so hot. The surface temperature of Betelgeuse is estimated at 3,600 K,
which is roughly 3,325° Celsius and 5,960° Fahrenheit. That's pretty cool for a star,
but you still wouldn't want to touch it.
The red giants like Betelgeuse and Antares are bright and - relatively - cool.
The red giants like Betelgeuse and Antares are bright and - relatively - cool.
The red giants like Betelgeuse and Antares are bright and - relatively - cool.
It isn't the brightest star - at least, usually Rigel is brighter. However, Betelgeuse is variable, and can sometimes be brighter than Rigel. Wikipedia lists its luminosity as 105,000 times the luminosity of our Sun; and the distance, as 640 light years. Assuming these numbers, this would make it as bright as a star that is 10.5 times as bright as our Sun, at a distance of only 6.4 light years. In other words, the extreme luminosity compensates for its distance.
When talking about stars, "cool" is a relative term. Betelgeuse has a variable surface temperature of 5,200 to 6,100 degrees Fahrenheit. Such a temperature may seem extremely hot to us and is easily hot enough to emit bright light but it is fairly cool as stars go. The comparatively low temperature of Betelgeuse means that it gives off less light per square meter than a hotter star would, but it makes up for it with its massive size, more than 900 times the diameter of the sun. As massive size means a large surface are and thus a huge output of light.
To be bright you need to be hot, close or have a large surface area. The brightest coolest stars are red super giants. They have such a large surface area, that even though their surface temperature is cool - in star terms - their large surface area makes them appear bright.
It is a cool star.
Betelgeuse is a red giant star and comparatively cool.
The red colour means that it's surface temperature is cool < 3,700K. At that temperature, the spectrum of light is red.
They do not necessarily have greater luminosity, it depends on their size. Betelgeuse is cooler and brighter; a red dwarf is cooler and less bright.
Betelgeuse is a large cool star
To be bright you need to be hot, close or have a large surface area. The brightest coolest stars are red super giants. They have such a large surface area, that even though their surface temperature is cool - in star terms - their large surface area makes them appear bright.