If you will notice this star is probably close to the horizon. It is probably Sirus (the dog star) in the constellation Canis Major, it is the eye of the big dog. This star rises and sets during the last weeks of July and the first days of August and the people in acient times believed that the combination of this star and the Sun being in the sky at the same time caused the extra warm weather during this part of the year which is the origin of the saying "The dog days of summer". The cause of the twinkle is the Earth atmosphere defracting the light as it passes through, you will notice that when the star is higher it will not twinkle as much. : I often see a star in the sky that changes colors. : It twinkles red and blue. What causes this?