It's considered to the habitable zone around the stars were the temperature is just optimal for the existence of the life to develop. They are the part of the system that is nor too hot nor too cold for the survival and germination of bacteria that needs liquid moisture to grow.
Consider a time when mars is in the middle of one of its periods of apparent retrograde motion. during this time, mars appears <u>brightest</u> in our night sky and crosses the meridian around <u>midnight</u>.
