What is the origin of the letters used in star classification? Why didn't astronomers use ABCD? J. HaldimanChicago, Illinois ...

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Stellar spectral classification utilizes seven main classes (O, B, A, F, G, K, M), ordered by decreasing surface temperature, with each class further subdivided into numerical subclasses (0-9) ...

Transmission spectroscopy during planetary transits is expected to be a major source of information on the atmospheres of small (approximately Earth-sized) exoplanets in the next two decades. This ...