Posted on March 9, 2019
Occupation: Pastor
Known for: discovery of variable stars and of sunspots
Whhhaaattt?
How does a pastor make two major discoveries in astronomy?
David Fabricius was born on this date in 1564 and lived until 1617, so he lived during England's Elizabethan Era, at the same time as Shakespeare (1564-1616). Back then, there were few "professional" astronomers, so amateur astronomers were able to make substantial contributions to the science.
Actually, David Fabricius made these discoveries with his oldest son, Johannes Fabricius (1587 - 1615). He is listed in Wikipedia as an astronomer, possibly because he didn't live very long after his university studies and, perhaps, never had to earn a living.
By the way, both father and son are considered German; they were born in a coastal area known as Frisia, which is now part of the Netherlands and northern Germany. The last name, Fabricius, is the Latinized version of the last name Faber, but they are also listed as Goldschmidt or Goldsmid, which might be Hebrew names. It's all very confusing!
Variable stars
We now know that variable stars, whose brightness changes regularly and dramatically (most stars have at least a little variation in brightness!) fall into two categories:
Some stars brighten and dim because they swell and shrink, or pulsate; others regularly lose stellar material or regularly gain stellar material from a companion or nebula.
Other stars don't actually change in brightness, but they seem to from us watching on Earth. This is often because the star has an orbiting companion that sometimes blocks some of the light from our view.
Mira happens to be one of the pulsating variables. The entire class of pulsating stars that share certain characteristics are called Mira variables.
Sunspots
Johannes Fabricius returned from university with telescopes. David decided to use it to observe the Sun - but of course that's hard on the eyes. The pair invented camera obscura telescopy in order to study the Sun, and in 1611 they were able to see sunspots and observe that the spots moved - and the manner of that movement provided evidence that the Sun rotated on its axis. (Some scientists had speculated that the Sun, like so many other celestial objects, rotated, but until evidence backed it up, those were just educated guesses.)
Johannes published these findings in June of 1611. His paper and the discovery remained relatively unknown, however, and astronomers from Southern Germany, Christoph Scheiner, and from Italy, Galileo Galilei, both independently discovered sunspots.
I should mention that there had been mentions of possible sightings of sunspots by Ancient Greek and especially Ancient Chinese astronomers. However, those naked-eye sightings - and even the careful telescopic studies of sunspots - were very controversial to those who insisted that the heavens were unchanging or that the Sun was perfect, without flaws.
What are sunspots? These temporary spots look dark because they are so much cooler than the surrounding area. They're caused by concentrations of the Sun's magnetic field, and they accompany other magnetic activity like solar flares, coronal loops, and prominences on the Sun and auroral displays in the Earth's atmosphere. 
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| Coronal loops, above. Solar prominences, below. |
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| Auroras appear in Earth's skies when there is a lot of activity on the Sun, including sunspots. |
Also on this date:
Genealogy Day
(Saturday of the first full week of March)
(Second Saturday in March)
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