A very special star
Edwin Hubble was neither the most accomplished astronomer on Earth nor the most well-liked by his colleagues. Yet, in the fall of 1923, he discovered a special star that turned our understanding of the cosmos on its head. On the night of October 5/6, using the 100-inch Hooker Telescope at Mount Wilson Observatory outside Los Angeles, Hubble recorded a deep exposure of what was then called the Andromeda Nebula. He was intensely curious about so-called spiral nebulae: Were they clouds of gas and stars within our galaxy, or very distant, mysterious objects?
Hubble was elated with his glass-plate negative. He believed he had found a nova, an exploding star, within the nebula, and he marked it with an N. Subsequent checking back at his office, however, nearly made him fall out of his chair. The star demonstrated a regular and well-known pattern of dimming and brightening: It was a Cepheid variable. He changed the marking to “VAR!” The star’s incredibly faint nature, at around 19th magnitude, meant the “nebula” was immensely far away. In his landmark observation, Hubble had discovered the nature of galaxies and the first clues to the huge cosmic distance scale. Hubble thought what could then be renamed the Andromeda Galaxy was a million light-years off, three times larger than the previously imagined size of the whole universe. (We now know it lies 2.5 million light-years away.)
This legendary star has received scant attention since the days of Hubble, but astronomy enthusiast Rod Pommier, a frequent contributor to Astronomy, set out to hunt for the star, succeeding in imaging it with his 14-inch scope. I know that a few others, notably Tony Hallas, have also imaged this star, which has come to be known as M31-V1.
Rod’s story of cosmic discovery (page 54), retracing the steps of Hubble’s great discovery, will open your eyes to the amazing capabilities amateur astronomers now have with their telescopes and digital equipment, ready to be unlimbered on any given dark night.
Yours truly,