While Rigel is not technically the fourth brightest star in the sky (that honor goes to Arcturus), it is a very bright star and known for its blue-white color, indicating a high temperature. However, it's important to note that:
* Temperature is measured in Kelvin or Celsius, not Fahrenheit. 20,000 degrees Fahrenheit is approximately 11,093 degrees Celsius or 11,366 Kelvin.
* The exact temperature of Rigel is estimated to be around 11,000 Kelvin. This is still extremely hot, but not exactly 20,000 degrees Fahrenheit.
It seems you might be combining information about different stars. Remember that while Rigel is a bright star with a high temperature, its exact position on the "brightest stars" list and its temperature can vary depending on the source.
