The variable star Mira is high in the northern sky. It is a red giant star with a bloated atmosphere that is 200 times the width of our Sun. When the star is at its faintest its temperature is only (!) 2000 degrees Celsius. At those times Mira is one of the coolest stars known.
A Hubble Space Telescope close up of MIRA. Courtesy Margarita Karovska (Harvard-Smithsonian Center for Astrophysics) and NASA