Answer:
the temperature of the star
Explanation:
The color of stars usually indicates the temperature of the star. 
A star that is relatively cold usually shows a typical red color. 
The hottest stars have a blue color.  
- These star colors have been used by astronomers to determine their temperature. 
- A broad spectrum between blue, the hottest color,  and red the coldest is used. 
- Class O stars are usually the blue colored ones
- Class M is the coldest with red color
 
        
             
        
        
        
Explanation:
When a carboxylic acid is treated with an alcohol and an acid catalyst, an ester is formed (along with water). This reaction is called the Fischer esterification.