Maggie and Me (a philosophical dialogue): On Huygens, Cassini, and Messier

Maggie:  I am still working out my thoughts about Newton.

John:  Yeah, he’s tough.  Do you want to stick with him for now or move on to the next astronomers on our historical list?

Maggie:  Let’s move on.  I have the feeling that I’m going to be thinking about Isaac for the next ten years.

John:  That probably right. 

In this discussion, let’s tackle three astronomers that made some significant observational contributions: Huygens, Cassini, and Messier.

Maggie:  Okay, but let’s not bite off too much. 

John: Agreed.  But I think we can do all three due to the nature of their contributions.  Astronomy took a different path after Newton, and two important things happened.  First, as a result of improvements to the telescope, astronomers were spending more and more time observing the stars and planets.  This led to many new discoveries, which we will talk about. Second, the field of astronomy became more professionalized, meaning more and more scientists were turning to the field. 

Maggie:  So astronomy was becoming a viable career?

John: Exactly! 

Christiaan Huygens

Maggie: Who are we talking about first?

John: Christiaan Huygens.   Huygens

This guy was another Isaac Newton, a genius in many different fields.

Maggie:  Give me the dry facts first, before we get into the cool stuff.  I like to know dates and things like that before we talk about ideas.

John: Okay.  Huygens was born in 1629 to a very rich Dutch family. He was educated at home until he was 16, learning mathematics, geometry, rhetoric, languages, music, geography, fencing, and dancing.  He had a great education, but he also had a huge brain that allowed him to absorb, understand, and excel at all these different subjects.

Maggie:  Did his father teach him?

John:  No, no.  He hired tutors to teach Christiaan.  That is how the rich did it back then.

Maggie:  So then what happened to him?

John:  When he was 16, he went to the University of Leiden to study mathematics and law.  But he had to leave the college after two years because his brother got into a duel with another student.

Maggie:  Wait, wait, wait.  Christiaan had to leave because his brother got into a duel?

John: Exactly.  Leaving prevented retaliation against Christiaan.  So he transferred to a school called Orange College.  But it worked out well because he was able to take math classes from a famous mathematician, John Pell.  And he finished his schooling two years later, in 1649. 

Maggie:  What did he do after college?

John:  This guy was amazing.  He corresponded with all the leading intellectuals of the time about many different subjects.

Maggie:  Like who?

John: Mersenne, Newton, and John Locke, are just a few.  And Huygens could go toe-to-toe with each of them on any given subject. You can still read some of the correspondence. 

Maggie:  Did he do any great work in math?  I love these math geniuses.

John:  Yes, he did.  He wrote the very first treatise on probability theory, called “On Reasoning in Games of Chance.”

Maggie:  Wow.  What is he most famous for?

John:  He invented the pendulum clock in 1656, which became the most accurate way of telling and keeping time for the next 300 years.

Maggie:  I suppose it made him lots of money?

John:  You would think, but not really.  His idea was quickly stolen by others, who themselves made a lot of money.

Maggie:  It sounds like Huygens was a Renaissance man, an expert in many things.

John:  That’s exactly right.  He was amazing.  But we want to focus on his contributions to astronomy here.

Maggie: I get caught up in the way these guys could do almost anything.  But you’re correct.  Back to astronomy.

John:  Huygens became interested in telescopes in the 1650s, especially the lenses used in the telescopes.  So he started studying lens grinding. 

Maggie:  Nerd!

John:  Total nerd.  In 1662, he invented the Huygenian eyepiece, which is made of two lenses, and which solved some visual aberration problems in some telescopes.

But his greatest contribution to astronomy came from observation, not invention. 

After viewing Saturn through telescopes greatly improved upon since Galileo’s time, Huygens observed that Saturn was actually surrounded by a flat ring. 

Maggie:  So he was the first to see the ring?

John:  No, not quite.  Others had noticed an anomaly about Saturn, that it had an odd shape.  But it was Huygens who figured out that the odd shape was a result of a ring around Saturn.

Maggie:  That’s so cool.  I love looking at Saturn.

John:  Me too.  It’s my favorite planet.

Maggie:  What else did Huygens discover?

John:  You will love this.  Using a refracting telescope, he discovered Titan, Saturn’s most famous moon. 


Maggie:  So cool. Titan is most like Earth, and it might actually have life on it.  I can’t wait to find out.

John:  And he also discovered the Orion Nebula, publishing a sketch of the nebula in 1659.

Maggie:  I understand now what you said earlier. Astronomy took a new turn with the invention of the telescope.  Astronomers spent more time looking into the sky and discovering all the objects we now take for granted.

John:  That is a perfect way of putting it.

Giovanni Domenico Cassini

Maggie:  Who is next in our discussion?

John:  Giovanni Cassini.   Cassini

He played a key role in the professionalization of astronomy, and he made some great discoveries.

Maggie: Why do these guys all have the same hair?  Look at it.  It’s the wigs, isn’t it?

John:  Exactly right.  Slaves to fashion, I guess.

Maggie:  Funny!  

Tell me about the professionalization of astronomy first.

John:  Because of the discoveries of Galileo and Newton, there was a growing interest in astronomy, especially by individuals with political power.  That interest led to more funding for astronomical ventures, including the construction of observatories and support for professional astronomers.

Maggie:  Okay, I get it: more funding equals more work in astronomy.  With more work, more scientists were entering the field.

John:  You just get things.

Maggie:  Thanks.  So what about Cassini?

John:   He was born in 1625 to Italian parents.  Like Huygens, his brain was humongous.  In addition to being an astronomer, he was also a mathematician and an engineer. 

Maggie:  It is amazing to me how people like Huygens, Cassini, and Newton could do so many different things.  Where did they find the time?

John:  I don’t really know, but I imagine it has a lot to do with not having television and cell phones and all the other things we have today that waste our time.

Maggie:  That makes sense to me.  I know I waste a lot of time on social media.

John:  Me too.  Most of us do. 

Maggie:  Okay, back to Cassini.

John:  Cassini started his professional astronomy career in 1648, when he obtained a position at the Panzano Observatory, near Bologna, Italy.  He worked with some accomplished scientists there, furthering his education and knowledge of the solar system.  In fact, he made such great progress that he was appointed to the Chair of Astronomy at the University of Bologna in 1650.

Maggie:  How long did he stay at the university?

John:  For almost 20 years, until he left for France in 1669.

Maggie:  Why did he move to France?

John:  Do you know who Louis XIV was?

Maggie: Sure.  He was the longest reigning king of France.  He consolidated political power under the monarchy and forced French citizens to become Catholic. 

John:  You’ve been reading, I see.

Maggie:  Just a little French history.  I like it.  But do you want to know what I really like?

John:  What?

Maggie:  French literature.  Mostly Alexandre Dumas.  He is such a great writer.  Most people probably know Louis XIV as a character in The Man in the Iron Mask, based on a book by Dumas.  Did you know that Leonardo DiCarprio played Louis in a recent version of the movie?  Leo is so great!

John:  Yeah, I agree, Leo is great. 

Maggie:  But what does Louis XIV have to do with Cassini?

John:  The king was interested in science, including astronomy.  He helped fund the building of the Paris Observatory, which opened for business in 1671. Cassini was hired to help set up the Observatory, so he moved to Paris in 1669.  When the Observatory opened, he became its director, and he kept this position until his death in 1712.  He also served as the official astronomer to the king.

Maggie:  Is he famous because he directed the Paris Observatory?

John:  Yes, in part.  He set it up and helped it become a great platform for future scientific advancement.  But he also made some pretty significant discoveries of his own.

Maggie:  Like what?

Cassini DivisionJohn:  While Huygens was the first to discover Titan, Cassini discovered the next four moons: Iapetus, Rhea, Tethys, and Dione. And he also discovered that Saturn’s A ring and B ring have a 3,000-mile gap between them, now called the Cassini Division.   If you look at it through a telescope, the gap appears like a thin, black band between the two rings.  It wasn’t until the Voyager spacecraft was able to investigate the gap that scientists discovered that the gap is in fact filled with material.

Maggie:  Is that why NASA named one of its space probes after Cassini, for his discoveries about Saturn?

John:  Yes, exactly.  The Cassini probe was the fourth probe to visit Saturn, but the first to actually orbit the planet.  It spent 13 years exploring the planet, its rings, and its moon Titan. Much of what we know about Saturn comes from this probe.

Maggie:  So cool.

John:  It is.  You can look at some of the pictures taken by the Cassini probe on the NASA website.

Maggie:  I am going to do that.

John:  Well, that’s it for Cassini.

Charles Messier

Maggie:  Who’s next?


John:  Our last astronomer is Charles Messier.  He was born in France in 1730.

Messier became interested in astronomy when he was a teenager.  At 14, he saw a comet in the sky, and then when he was 18 he saw a solar eclipse.  These two events freaked him out, causing him to dedicate his life to astronomy.

Maggie:  How did he get started?

John:  At the age of 21, he took a job with a French astronomer named Joseph Delisle.  Delisle gave him a piece of advice that stuck with Messier his entire career. He told Messier to keep detailed records of everything he observed in the sky, which Messier did.

Maggie:  Oh, I get it.  That is how the Messier Catalogue came about.  He kept detailed records of what he saw.  That’s so interesting.

John:  It is.  Messier started out observing comets and writing down his observations.  As he was looking for comets, he saw other things in the sky, and recorded these also. 

Maggie:  Like what other things?

John:  Galaxies, nebulae, and star clusters.

Maggie:  And the things he recorded are called Messier Objects?

Messier CatalogueJohn: Right!  The Messier Objects are what got recorded into the Messier Catalog, which is more or less a listing of the objects.

Maggie:  How many are there?

John:  The first list was published in 1774, and included 45 objects.  The final list published during Messier’s lifetime came out in 1784, and included 103 objects, but many of these were objects discovered by other astronomers. The modern list now has 110 objects on it, with the designations M1 to M110.

Maggie:  I think it is so cool that he took the advice of a mentor and carved out a career observing the night sky.

John:  Yeah, me too.

As a result of his work, Messier has a crater on the moon named after him. 

Maggie:  I wish I had a crater named after me.  Maybe in the future.

John:  Well that does it for today.

Maggie:  Can I summarize what we learned?

John:  That would be great.

Maggie:  Once enough advancements were made to the telescope, astronomy took a different turn.  Observation became very important, and astronomers started to make many significant discoveries about the planets and the stars.  Astronomy was also becoming a serious profession for new scientists, in part due to the development of observatories.

Is that it?

John:  That is a perfect summary.

Maggie.  Thanks. I look forward to our discussion next month.

2 thoughts on “Maggie and Me (a philosophical dialogue): On Huygens, Cassini, and Messier

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