Universe. It can have at least 2 Trillion Galaxies. That is 2 followed by 12 zeroes - 12,000,000,000,000. By the way, this estimate was 100 - 200 Billion Galaxies just until a few years ago. A Billion has 9 zeroes. 200 Billion is 2 followed by 11 zeroes. So, a 10 fold increase in estimated galaxies just in a few years. Shouldn't be surprised if this estimate increases again.
Galaxies. Our home which is in Milky Way galaxy has an estimated 250 Billion stars. Few other known Galaxies in the known Universe, for example Andromeda galaxy has as many as an estimated 1 Trillion stars in it. Again, that is 1 followed by 12 zeroes.
Stars. There seem to be countless Stars if we were to consider the known and unknown Universe but if we were to extrapolate, there could be as many as 1 Septillion stars i.e., 1 followed by 24 zeroes - 1,000,000,000,000,000,000,000,000. If you are unable to wrap your head around the enormity and magnitude of the number of stars, think of it this way - there are an estimated 10,000 stars for each grain of sand on Earth. Yes, there are a lot more stars out there than the grains of sand you can count on our planet. That's our cosmos folks. It's GIGANTIC.
Get this - the number of stars in the heavens is an unbelievably large number, but then you will find the same number of molecules in just ten drops of water. 1,000,000,000,000,000,000,000,000 molecules in 10 drops of water! Whoa! Pause and process it. Just mind boggling as to how the nature and creation works!!!
Planets. Yes, we live on planet Earth which is just one of the eight planets within the Solar system i.e., planets that go around the Sun, our own super Star. Mercury, Venus, Mars, Jupiter, Saturn, Uranus, and Neptune being the rest of the planets in our solar system. Sorry to disappoint but Pluto isn't a planet. Wish, I could have said that to my Elementary teacher and didn't have to memorize it as a planet in school and through the years. May be it will become a planet again one day (or may be not) but for now Pluto has to be happy with its status of Dwarf Planet. Good luck, Pluto!
Now imagine this. Each Star in the Universe could have its own solar-like system with multiple Planets going around each star. Sure, there might be stars with no planets but again per estimates, the number of planets in the entire Universe could equal the total number of stars. In other words, we possibly have 1 Septillion planets in the entire Universe i.e., 1,000,000,000,000,000,000,000,000 planets in Universe. Let's not talk about Satellites going around these planets, like Moon is to Earth.
If that's not enough by itself, some astro physicists say that our universe may be one of many. For now, even if we were to believe there is just one Universe, the point is our Cosmos (and even known Universe) is vast. How smart is it for us to think that the Earth is the only habitable planet out of 1,000,000,000,000,000,000,000,000 planets that could exist out there?