The Life of Super-Earths by Dimitar Sasselov Read Free Book Online

father had shown me how to use it, mostly during the day; I was on my own at night, spending hours out in the backyard. The place where I grew up was small, no telescope or observatory at school, no planetarium to visit nearby. So I had almost no idea what I would see through my small telescope. Sure, I had read books, some with pictures, but the view
through the telescope was something else. The experience was truly visceral—shivers would run up and down my spine every time I pointed the telescope at a patch of stars. Eventually the feeling went away, but I still remember it. As I looked at the darkness between the stars, I felt as if I could fall into it. Like a fear of heights in reverse. Like an upside-down vertigo.
    Perhaps I had read one book too many, and I was imagining things too vividly. After all, I had read about the vastness of the empty space between the stars in my books. But if we had a feel for how big the Universe is, we would have permanent shivers up our spines. To stay sane, astronomers use math, lots of it, and this can ruin even the best party. c Seriously, though, this is a way to deal with the problem. Since the time of Eratosthenes in ancient Greece, who measured the size of the Earth, humans have used math (and geometry) to take the measure of the Universe. Almost always the new knowledge increases our feeling of wonder. Many scientists (and I am one of them) will tell you that this is why they do what they do.
    Ironically, this vastness—as unfit as it may be to our tiny scale d —may be essential for life to emerge and survive. So
let us explore it some. I will use the word “scale” often from now on; it means the extent or relative size of something, whether space or time. When it applies to time, I use “timescale.” Let’s deal with space first.
    We live in a galaxy—the Milky Way—an “island” of stars and gas swirling in spiral arms around a center. The Universe, as seen through telescopes, is filled with galaxies. The current estimate is that there are at least 200 billion of them.
    My night sky exploits as a high school youth included viewing different galaxies. It was a challenge, since most galaxies require dark, clear skies and a sizable telescope. However, there is one galaxy that can be seen with an unaided eye, and, unlike most galaxies, it even has a name: Andromeda. If you live north of the equator, you can try to see it—a faint nebulous smudge in the constellation of Andromeda—rising in the east during the late summer nights, and overhead during the fall and winter evenings. I recommend you try hard because this is—by far—the most distant object a human can ever see unaided, with no help from telescopes or any technology. The Andromeda galaxy is 2.5 million light-years away, about 10,000 times farther than the average stars you see at night.
    The Andromeda galaxy is very similar to our own Milky Way. Andromeda is a similar flattened disk of stars and gas, most of them bunched in spiral arms, and it’s roughly the
same size. If you are blessed with a dark, clear sky, you will notice that the “smudge” of the Andromeda galaxy appears to be an elongated ellipse. This is because its disk is oriented sideways to us.
    Galaxies are mostly close to each other; you could build a scale model of our Milky Way Galaxy neighborhood in your living room. If we were to take our Galaxy to be a dinner plate, then the Andromeda galaxy would be a dinner plate about twelve feet away, and the Triangulum galaxy (another neighboring galaxy, known as M33) would be a salad plate about ten feet away from the Milky Way and a bit to the side of Andromeda. A dozen M&Ms could stand in for the multitude of dwarf satellite galaxies. This is common for our Universe. The galaxies that fill it wall to wall are separated from each other by distances that are comparable to their sizes. You can visualize how this would go in all