Timeline of the Universe

Four days ago on the 26th of April, it was the 100th anniversary of the Great Debate, which is also known as the Shapley-Curtis Debate. The debate was held at the Smithsonian Museum of Natural History and it concerned the nature of the so-called nebulae (i.e. a giant cloud made out of gas and dust in space) and the size of the Universe. Shapley had the belief that the distant nebulae are relatively small and lay within our Galaxy, while Curtis that they are independent galaxies, which implies that they are large and distant. Before checking what happened in the Great Debate, it is worth having a look at the evolution of Astronomy as a science which led to the Great Debate, through the timeline of the Universe.

History of the Milky Way Galaxy

The establishment of the heliocentric model (i.e. the Sun is the center of the world) for what it was believed back in the 16th century to be the Universe, was the beginning of the evolution of Astronomy. Already in the early 17th century the famous Italian astronomer Galileo Galilei used a telescope to observe the night sky and discovered that it is composed of a huge number of faint stars. Additionally, during this period, many astronomers reported they were also able to observe faint nebulae in the sky, but they could not interpret both their nature and if they are part of our Galaxy, or not.

According to Thomas Wright the Universe is a thin spherical shell, with the Sun located at its centre. The eye at the center of the sphere represents God

In 1750 the English astronomer Thomas Wright in his book An Original Theory, or New Hypothesis of the Universe, by using existing observations suggested that our Galaxy consists of many stars bound by gravity, and that the whole galaxy most likely rotates in a similar way as the Solar System, but on a much larger scale. Based on Wright’s model, the Milky Way Galaxy is a spherical shell of stars, with the Sun on its center. Additionally, according to Wright the faint nebulae are galaxies, thus they were located outside our own. The ideas of Thomas Wright influenced Immanuel Kant and in 1755 he presented his view on the nature of the Universe. According to Kant the stars are a system in order, in the form of a lens-shaped disk, which rotates about its center, following Newton’s laws of motion. The observed nebulae according to Kant are distant galaxies, with the same structure as our own.

 

 

The first attempt to map the Milky Way, was undertaken by William Herschel and his sister Caroline. In 1785, they constructed what was back then the world’s largest telescope (diameter of 1.2 m) and used it for a period of twenty years to observe and count stars along 683 lines of sight. Their observations were made by using two assumptions.

The first map of the Universe, that was made by William and Caroline Herschel. The darker dot near the center shows the location of Sun in Universe.

The first was that stars are distributed uniformly through space and they do not extend beyond our Galaxy, while the second was that their telescope could resolve all stars within the boundaries of the Milky Way. According to their findings the Galaxy has a flattened shape and the Sun is near the center.

 

 

The M51 galaxy as it was seen from the telescope of Lord Rosse.

Towards the end of the 18th century French astronomer Charles Messier, created a catalog with the 109 brightest objects that have nebular structure, while William Herschel published a catalog with 5,000 objects. In 1845 William Parsons, the 3rd Earl of Rosse constructed the largest telescope of its era (diameter 1.83 m). Lord Rosse, was able to observe the known nebulous structures and he was able to distinguish between elliptical and spiral structures. Additionally, he was able to distinguish individual point sources in these structures (i.e. stars in other galaxies).

Half a century later, the Dutch Astronomer Jacobus Kapteyn between 1901 and 1920s, used a similar but refined search method as Herschel and concluded that our Galaxy has an ellipsoid shape with the Sun close to the center. Harlow Shapley based on cataloging star clusters came up with a totally different result, where the Galaxy is a flat disk, with the Sun being far from the center.

The progress of technology led to the construction of spectrographs and in 1912 the American astronomer Vesto Slipher made spectrographic studies of the brightest spiral nebulae to determine their composition. Slipher found that the spiral nebulae move away from us with velocities that were not consistent with star velocities he had measured. In 1917 Heber Curtis observed nova S (i.e. a star that suddenly increases its luminosity tremendously and then fades away to its former obscurity within months, or years.) in the Andromeda galaxy (back then known as M31 or “Great Andromeda” nebula). Curtis found 11 more novae in Andromeda and found that they were much fainter than those observed in our Galaxy. Thus, he became a supporter of the model that suggested that the mysterious observed nebulae are independent galaxies.

The Great Debate in 1920

On April 26, 1920 a debate was held at the Smithsonian Museum of Natural History, with the topics being, how big is the Milky Way and how distant are spiral nebulae. Shapley supported that our Galaxy is 100 Kpc (parsec is a unit to measure distance in Astronomy and it’s equal 3.0857×1016 m) across (three times larger than the actual size), and that the distance to the Andromeda Nebula is only 10 kpc, hence it is part of our Galaxy. Curtis supported that our Galaxy has a size of 10 kpc (three times smaller), while he estimated that the Andromeda nebula is at a distance of 150 kpc (five times smaller), thus it is external.

The Great Debate was actually inconclusive. Even though Shapley had better arguments, he was actually on the wrong side. Curtis on the other hand was on the right side, but his arguments were weak. Also, both got the distance to the Andromeda Nebula wrong (778 kpc) and also they were not able to explain the motion of the nebulae. What actually created confusion on both sides was a report from Adriaan van Maanen, where he claimed that if M101 was outside of our Galaxy then it is moving at speed greater than the speed of light. Actually, no one else was able to reproduce van Maanen’s findings, thus proving that he made something incorrect in his data analysis.

From Hubble to Hubble

The solution to the problem was given three years later, when Edwin Hubble using the new 100-inch Mount Wilson telescope, was able to resolve the outer parts of some spiral nebulae and identified variable stars there. By using these stars he was able to measure the distances to these nebulae, thus finding that they are too far to be part of our Galaxy. Furthermore, in 1936 Hubble produced a classification system for the morphology of the galaxies, a system that is used to this day. In the upcoming decades, with the explosive evolution of technology, our knowledge in Astronomy was at the same pace. Thus, 70 years after the Great Debate, NASA launched into orbit the Hubble Space Telescope (HST) on the 24th of April 1990. Just like Edwin Hubble, HST has broadened our view of the Universe, since we were able to get data from galaxies that are too far away to be observed with ground-based telescopes.

Edwin Hubble’s classification theme of galaxies.

Famous women astronomers and their role in its evolution

So far the only woman that was mentioned, was Caroline Herschel. But the question of, what was the role of women in the development of Astronomy is something that plenty of people ask. In Harvard Observatory Edward Charles Pickering, hired around 80 women, for processing astronomical data and they were known as Harvard Computers. One of the most famous women that was in Harvard during that period was Annie Jump Cannon. During her career in Harvard she classified around 350,000 stars (more than anybody else), she discovered around 300 variable stars and novas and she was also one of the creators of the Harvard classification star system. Henrietta Swan Leavitt was initially hired for cataloging and measuring the brightness of stars. Through her work though she was able to discover a relation between the luminosity and period of a special class of variable stars known as Cepheid variables. This period-luminosity relationship is known as Leavitt’s Law and provided a tool for measuring distances accurately (e.g. Edwin Hubble proved that the Andromeda galaxy is not part of our Galaxy by using Leavitt’s law). It should be mentioned here that all women that were working at Harvard Observatory were getting paid between 0.25-0.50$ per hour (much less than men) and they were criticized for being “out of their place” (i.e. home). Additionally, most of them were for their whole careers assistants, since they were women.

Astronomy fun facts

William Herschel was born in Hannover Germany and he moved to England not as an astronomer, but as a music teacher. Apart from creating the first map of the Universe, he discovered planet Uranus on 13th of March 1781, and on the 11th of January 1787 Uranus’ satellites Oberon and Titania. Furthermore, on the 28th of August and 17th September he discovered two satellites in Saturn, Enceladus and Mimas.

Caroline Herschel discovered many comets and she was the first woman who received the golden medal from the Royal Astronomical Society.

The famous French mathematician, physicist, astronomer and philosopher, Pierre-Simon Laplace, in 1796 suggested that the observed “nebulae”, might be forming planetary systems.

10 thoughts on “Timeline of the Universe”

  1. Those pioneers going back all those years set the benchmark and considering there was no such thing as high-tech or anything to resemble high-tech, they did a remarkable job. In, fact, I don’t really think we have moved on that much with the technology that we do have today.

    I believe they are split on the big-bang theory now. Do you have any theories yourself?

    Science is warming to the possibilities of a multi-dimensional universe and maybe they will come up with the right answers but we are many years away from that.

    The existence of a multi-dimensional universe can be proven, but that is a personal thing and takes a lot of time and dedication, suffice to say that meditation is the key.

    Great post and loved reading it.

    1. Anestis Tziamtzis

      Dear Mick,

      First of all, I would like to thank you for visiting my webpage. Astronomy as a science has evolved at an exponential pace during the 20th century. Also, please consider the amount of data a scientist now days can collect. In the past scientists were performing naked-eye observations, while now days during a night you may store on a hard-drive many gigabytes of data and for the processing and analysis you do not have as much time as people in the past.

      Regarding the creation of the Universe, I believe that at the moment we are on the right way, but still we have a lot of answered questions. The Big-Bang model and our observations from the early Universe are in good agreement, and also our models for the first moments of creation, although they are still in progress, we are also moving ahead.

      Talking for myself here, the multiple Universes is something that is not easy to dig it. Through Mathematics you may prove a lot of things, but reality means physical proof. For example according to the Big-Bang model, the Universe, should be 75% hydrogen and 25% helium and we should be able to detect emission that comes from the early Universe. Both of these are confirmed, thus, when it comes to theoretical cosmology I’m a bit skeptical.

  2. I’ve watched a few documentaries about the beginning of our Universe and I was fascinated with how far we have come in understanding our Solar System and beyond. The story about Hubble and the telescope was the most fascinating thing of them all. It really makes you wonder… Thanks for sharing this awesome article.

    1. Anestis Tziamtzis

      Dear Ivan,

      I would like to thank you for your time. My plan is to cover as many topic as possible. Indeed our Universe is charming and full of surprises. I have read a recent article about the Hubble Space Telescope. NASA’s plan is to keep it operational even beyond 2030. Next the new James Webb Space Telescope will be launched. It will really help us broadening our view on the Universe even further than Hubble Space Telescope.

      Regards,

      Anestis

  3. Interesting article have bookmarked this for the future reference, maybe because I have quite an interest in this topic. Thanks for sharing
    Jason 🙂

    1. Anestis Tziamtzis

      Dear Jason,

      I would like to thank for visiting my page. I am already preparing my next post. It is about the methods that are used for discovering planets outside our Solar System.

      Regards,

      Anestis

  4. Hi there, to think a classification that was created in 1936 is still used today, we are sometimes so stuck on the word technology but it seems that in astronomy we are moving at the same pace. I like the idea that the women were known as “Harvard Computers” and to think that Annie Jump Cannon classified around 350,000 stars is almost unbelievable.

    Very interesting, thank you for sharing.

    1. Anestis Tziamtzis

      Dear Cornelia,

      I would like to thank you for visiting my page. If there is something that does the job finely and without a problem then there is no real reason in replacing in it. Our development in technology is more than incredible. Just consider the following your smart-phone thirty years ago, it would be a super computer!

      Annie Jump Cannon was something more than special. During her career she lost her hearing, but that didn’t stop her from continuing on what she liked. The same applied for Henrietta Swan Leavitt, she also lost her hearing at a young age.

      All these women should be examples of will and determination to everyone.

      Regards,

      Anestis

  5. Dear Anestis,

    I found this absolutely fascinating.

    I think, in part, due to my almost obsessive interest in Astronomy as a child.

    Unfotunately, this turned out to just be a fad or a phase, but your beautiful commentary has definitely taken me back to my childhood.

    I’m especially taken with your explanation of William Herschel , as I remember reading and studying these exact facts.

    Thank you for the trip down memory lane.

    Your website is definitely bookmarked for future reference – and who knows maybe that childhood hobby may well be reignited.

    Keep up the great work.
    Partha

    1. Anestis Tziamtzis

      Dear Partha,

      I would to thank you for visiting my page and your review. Somehow your comments reminded brought me also back to the time I came across William’s Herschel’s name. This is thirty years ago. My plan is to continue delivering material in this way and I promise to do my best to keep everyone satisfied.

Leave a Comment

Your email address will not be published. Required fields are marked *