Sirius
The brightest star in the night sky, in the Great Dog.
Sirius is bright mostly because it is close: only 8.6 light-years away. It is also about 25 times more luminous than the Sun.
Low in the sky it can flash red, green and blue. That is not the star changing: it's Earth's turbulent air splitting its light like a prism.
Did you know?
Sirius has a tiny companion, a white dwarf the size of Earth but with the mass of the Sun.