Usually, for a couple of months out of every 14 months the variable star $\chi$ (Chi) Cygni is bright enough to rival the brighter stars in Cygnus. I was in the garden the other night and it caught my eye - for a moment I thought it was a satellite changing the appearance of the constellation and then realisation dawned - chi Cygni was back!
At this time of the year Cygnus can be seen in the eastern sky during the late evening. The picture shows the cross-shaped pattern of its brightest stars along with the location of chi Cygni (and my garage).
Mira stars undergo changes in size and temperature - which affect the overall brightness of the star. $\chi$ Cygni is a dramatic example. It is sometimes as bright as 3rd magnitude - see the picture of Cygnus above to get an idea of what that looks like. But it will soon fade by a factor of 20 thousand! The star will drop to 14th magnitude - as faint as Pluto - and only visible through very big telescopes. Despite the big brightness changes the overall energy output doesn't change that much. When the star is near minimum brightness visually it is still shining fairly brightly in infrared.
Although the maximum and minimum of long period variables can be predicted with some confidence up to a year in advance, it is up to amateur observers to spot humps and small standstills in the light curves of some of these stars.