What Am I Looking At – Part IX

“Kant and Herschel”

     by Aaron Clevenson

 

This is the ninth in a series of interviews with famous astronomers of the ages.  Our ultimate goal is to trace our understandings of the physical universe.  This month we are going to talk to Immanuel Kant and then William Herschel.

 

NORTHSTAR:  Kant, can you tell us a little about how you got your start in astronomy?

KANT:  I was reading a review in a Hamburg journal of a book by Thomas Wright called An Original Theory or New Hypothesis of the Universe.  He was trying to explain why we see the Milky Way in the night sky.  He saw the universe as a great bubble.  The stars are on the surface of this bubble.  When we look along the bubble, we see a swath of stars, elsewhere there are few.

NORTHSTAR:  What did this lead you to conclude?

KANT:  Well there are many nebulae in the sky, some of them are elliptical, such as the great Andromeda nebula.  It occurred to me that if the sun were in one of these disk shaped nebula, then there well could be other ones, and the Andromeda nebula may be one.  I published a book about it called Universal Natural History and Theory of the Heavens.  Unfortunately, right after it was printed, the publisher went out of business

NORTHSTAR:  Kant, thank you very much for helping mankind make this great leap beyond the solar system.  Herschel, would you please tell us a little about yourself?

HERSCHEL:  I was born on November 15, 1738 in Hanover.  I started out pursuing the field of music.  It was not at all satisfying to me.  At the time, people were building bigger and bigger refracting telescopes.  John Flamsteed had constructed a 90 foot long one at the Royal Greeenwich Observatory, and Cassini had built larger and larger ones in France to study Saturn (17 foot, 34 foot, 100 foot, and finally 136 foot).  In fact in 1722 Bradley placed the objective on a pole and was able to measure the angular diameter of Venus with a refractor 212 feet long.  My means were more modest.  I built telescopes that were at first 4 feet long, then 12, 15, and finally 30 feet long.  I still did not get the visibility I was seeking.  I switched to a reflector telescope of Newton’s design.  Problem solved!  I discovered that I was a natural at building telescopes.  I was also a quite respectable observer in my own right.

NORTHSTAR:  How did you do your observations?

HERSCHEL:  I would spend every clear night at the telescope.  I would sweep across the sky, I would then move it slightly in the other dimension and sweep back.  All the while I would note the location of objects that were interesting.

NORTHSTAR:  What was your crowning observation?

HERSCHEL:  Well, I had been studying the sky for so long, that one night, March 13, 1781 I noted a star where it should not have been.  I thought perhaps it was a comet, but when the data was analyzed it was a new planet:  Uranus.  The exciting part was that it was well beyond the orbit of Saturn.  Our solar system just got much bigger.

NORTHSTAR:  What happened after this discovery?

HERSCHEL:  The king gave me money to make a larger telescope.  I was already using a reflector with a mirror that had a diameter of 18.5 inches.   We could now build one that had a mirror with a forty-eight inch diameter.  We were able to discover two more moons of Saturn, but the telescope was difficult to use.  I went back to my own telescopes to study the skies more.

NORTHSTAR:  And did you find anything new?

HERSCHEL:  Well I received a catalog of objects from Messier.  It appeared to me that all of these nebulae were really just groupings of stars.  I believed this for a long time, but on one occasion I found a planetary nebula in Taurus with a distinct star in the center.  The cloud around it could not have been made up of stars.  In fact, in Orion there is also a great nebula that I believe to be gas and dust.  What a wonderful discovery.

NORTHSTAR:  Thank you Herschel.  Your documentation of the many deep sky objects has enriched our understanding of the complexity and beauty of the Universe.