This 17th-century astronomer made some key discoveries.
The variable star Mira is located in the constellation Cetus the Whale.
credit: Torsten Bronger/WikiMedia Commons
On May 7, 1617, the German astronomer David Fabricius passed away. A contemporary of Johannes Kepler, the two frequently corresponded. I thought about him the other day when I was observing the Sun. And although I’d rather celebrate his birthday (March 9, 1564), I didn’t want to wait another 10 months to do so. Fabricius is famous for making two discoveries in astronomy.
Mira
His first discovery was that the brightness of the star Mira in the constellation Cetus the Whale was variable. This was the first time anyone identified a variable star (that wasn’t a supernova). Earlier observers may have seen Algol in the constellation Perseus change in brightness — noting it as the Demon Star — but they never referred to its variability.
Fabricius noted the brightness of Mira on August 3, 1596. But when he observed it on the 21st of that month, it was a magnitude brighter. He classified it as a nova and it became invisible to him a couple months later. End of story, right? But then, on February 16, 1609, he saw it again.
We now know that Mira is a double star. The main component is a red supergiant whose period varies from 2nd to 10th magnitude every 332 days. A white dwarf orbits this star at roughly 70 times the Earth-Sun distance.
Unfortunately, Mira was at its brightest last month. Start watching its position in February 2026, and you’ll see it brighten again. How bright will it get? I can’t be exact, but somewhere around 3rd magnitude, hopefully brighter.
credit: NASA/SDO
Sunspots
Fabricius made his second discovery along with his son, Johannes, in March 1611. They became the second and third astronomers to see sunspots through a telescope. (The first to view them telescopically was English astronomer Thomas Harriot, three months before Fabricius.)
Such early observations were done one of two ways. Either the astronomer used his telescope to project an image of the Sun onto a light colored surface, or he waited for the Sun to be near the horizon, when some of its blinding rays were blocked by the thicker atmosphere. Obviously, the first method is safe, and the last one is not.
Today, we use approved solar filters that fit on the front end of our telescopes. That’s what I used on my 3-inch refractor the other day. I counted 12 spots, all but one of them were quite small. I love solar observing. Our star’s face changes daily, and differently shaped sunspots and cool spot groups appear all the time.
I encourage you to get an approved solar filter for your scope. We’re all in daylight half the time. Let’s make the most of it.
