Black Parrot (Slashdot reader #19,622) pointed out a historic anniversary this week: On October 6, 1923, Edwin Hubble got a photo of Andromeda that showed that it contained a variable star, and therefore was an actual galaxy, ending the Great Debate over whether the universe consisted of anything beyond our own galaxy. Unless you're more than 100 years old you grew up with a completely different understanding of the universe than anyone who lived before. Even Einstein did not know about it when he proposed the theory of general relativity. It was later in the decade before Hubble discovered that the universe is expanding. A century later, the European Space Agency was announcing... A very rare, strange burst of extraordinarily bright light in the universe just got even stranger â" thanks to the eagle-eye of the NASA/ESA Hubble Space Telescope. The phenomenon, called a Luminous Fast Blue Optical Transient (LFBOT), flashed onto the scene where it wasnâ(TM)t expected to be found, far away from any host galaxy. Only Hubble could pinpoint its location. The Hubble results suggest astronomers know even less about these objects than previously thought by ruling out some possible theories. Bill Kendrick (Slashdot reader #19,287) writes: Edwin Hubble's discovery — thanks to a Cepheid Variable star — that the "Andromeda Nebula" was actually an entire galaxy 2.5 million light years away... NASA's Astronomy Photo of the Day for today celebrates this with an image of the original photo plate from October 6, 1923. Notice the "N" (for nova) crossed off, and "VAR!" (for variable) next to the star! The discovery of Cepheids, and the important fact that their brightening and dimming was regular, and could be used to determine a star's intrinsic brightness, was thanks to Henrietta Swan Leavitt about a decade earlier. David Butler's "How Far Away Is It?" series has an excellent episode on Andromeda on YouTube.

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