(Roughly) Daily

If you want to see a black hole tonight, just look in the direction of Sagittarius, the constellation. That’s the center of the Milky Way Galaxy and there’s a raging black hole at the very center of that constellation that holds the galaxy together.

– Michio Kaku

So, which came first:  the galaxies spread through the universe, of the black holes that hold them together? Ethan Siegel answers and explains.

* Philip Plait, Death from the Skies!: These Are the Ways the World Will End…

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As we raise our eyes, we might send star-struck birthday greetings to Johann Rudolf Wolf; he was born on this date in 1816.  A distinguished astronomer and mathematician, Wolf wrote on prime number theory, geometry, probability, and statistics; but he is best remembered for his work on sunspots.  Working from Heinrich Schwabe’s suggestion that sunspot activity was cyclical, Wolf calculated the period of the cycle at 11.1 years; he was among the first to establish the connection of sunspot activity to geomagnetic activity on Earth; and he developed a way of quantifying sunspot activity– the Wolf number, as it is known– that remains in use.

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