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It bears mentioning that the Milky Way is only one of 150 billion galaxies visible to our telescopes - and each of these will have its own complement of planets.

There are at least as many galaxies in our observable universe as there are stars in our galaxy.

Astronomers still can't decide what the shape of our universe is. Is it closed and finite, which is to say, is there a countable tally of all the galaxies that exist, even beyond the ones we can see? Or is it infinite? The latter possibility is still on the table.

We've accounted for 95 percent of all the stars in the Milky Way. The other 5 percent are big, bright stars - the kind that dominate the night sky, but are lamentably both rare and short-lived. If biology's your thing, you can forget those guys.

Our galaxy's pretty ordinary, garden-variety. So if we believe our galaxy has a super massive black hole, that tells us that most, if not all, galaxies host such a black hole at their centers.

One of the key differences between galaxies with super massive black holes is whether or not the black holes are lit up, because they are basically bingeing on a lot of material in its surroundings.

Philosophically, the universe has really never made things in ones. The Earth is special and everything else is different? No, we've got seven other planets. The sun? No, the sun is one of those dots in the night sky. The Milky Way? No, it's one of a hundred billion galaxies. And the universe - maybe it's countless other universes.

Estimates are that at least 70 per cent of all stars are accompanied by planets, and since the latter can occur in systems rather than as individuals (think of our own solar system), the number of planets in the Milky Way galaxy is of order one trillion.

I've read that a naked eye can see six thousand stars in the hundred billion galaxies, but I couldn't believe it, what with the sky white with starlight. I saw a million stars with one eye and two million with both.