by Conor Friedersdorf
Gregg Easterbrook captures how big it is:
Just a century ago, even after people considered themselves advanced owing to developments like powered flight, it was not known that any other galaxies existed. Our Milky Way was considered the totality of creation. In 1923, the existence of galaxies beyond the Milky Way was proven. Initial estimates were that there might be as many as a few dozen additional galaxies a number then viewed as stunning. The latest estimate, from the Sloan Digital Sky Survey, is 100 billion galaxies. The count is expected to rise.
Star estimates have risen in concert. A century ago, even the best-informed believed the Milky Way contained perhaps a few million stars. By the 1960s, astronomers contended the Milky Way held a billion stars, a number many found hard to believe. By the 1980s, the estimate had grown to 40 billion stars. Today it’s thought the Milky Way contains at least 90 billion stars and perhaps as many as 400 billion. Many other galaxies are likely to contain similar numbers. Recently, researchers led by Yale University cosmologists proposed there exists at least three times as many stars as previously thought. The Yale estimate is 200 sextillion stars, a 2 followed by 23 zeroes.