While the number of stars in the universe is very large - some 300,000,000,000 in the Milky Way Galaxy alone - there are only a relatively small number which could provide life-supporting heat for a habitable planet The primary restriction is the necessity of being in the Galactic Habitable Zone. This is followed by the secondary restriction of being in one of the few arms of the galaxy. These two restrictions reduce the number of possibilities to just a few million. Next the star must be 'hot'. Red Dwarfs will not do as they are 'relatively-speaking' cool, which necessitates that any planet be quite close in order to be in their 'habitable zone'. However 'close' means that the gravity of the star would distort the planet causing it to lock up with one side always facing the star. While numerous planets have been discovered near Red Dwarf stars those in the habitable zones are always very close to the star and are commonly understood to be orbiting the star in just a few days. If a person could stand on one of these planets the star would take up a large portion of the sky and because the planet would be 'locked up', the hot side would be much too hot and the other side would be much too cold. In fact it would be so cold that even CO2 would be frozen on the cold side along with whatever water had been present. Therefore even being in the twilight zone would not enable habitability. Furthermore the proximity of the star and the overpowering pull of its gravity would eliminate any possibility of there being a moon. However we understand from the way that the Earth operates that an axial tilt is necessary and of course the Moon is the factor that sets up and maintains the Axial Tilt. Without a properly-sized Moon there would not be any axial tilt meaning that even the Earth would be barely habitable and possibly not habitable at all. So Red Dwarfs are out which eliminates 95% of all of the stars in the universe including those within the Galactic habitable Zone. The next factor of interest relates to singularity. A star must be singular in order for any potentially-habitable planet to enjoy a circular orbit. The only way to eliminate this restriction is for the planet to be so close to its host star that the other stars in the group will not cause its orbit to deviate from circularity. However as we have already seen 'close' will not work.Getting setup for habitability is not a trivial affair with temperature control being paramount. In the case of the Earth, there are numerous factors involved with temperature control and being properly distanced from the host star is at the top of the list. Mars is not habitable and any idea that it can be colonized is bizarre. While the temperature range is similar to Antarctica - which is certainly not habitable - neither is there a magnetic field. Hence there is no protection from cosmic radiation. The Earth has a magnetic field but even in this case it is a transient and will not be able to provide protection for very much longer. However it will probably be longer than the Greenhouse Effect will be able to regulate the temperature on the Earth's surface to within the habitability range. This would seem to necessitate that any far-away planet must also have a Greenhouse Effect in place to regulate temperature but as we observe what is happening on Earth there is a limit to what the Greenhouse Effect can accomplice. The Earth is warming up and will continue to warm up. While a few degrees does seem trivial, our scientists recognize that warming up will have major consequences.The Earth is barely habitable and will not be habitable for very much longer. What can we possibly expect from a far-away planet? It all boils down to the conclusion that 'Extraterrestrial Life is Impossible'.