Archive for Vesto Slipher

My talk at “The Origins of the Expanding Universe”

Posted in Books, Talks and Reviews, The Universe and Stuff with tags , , , , , , on October 9, 2012 by telescoper

You may recall that I gave a talk recently at a meeting called The Origins of the Expanding Universe in Flagstaff, Arizona. I put the slides up here. Well, the organizers have now put videos of the presentations online so you have the chance to see mine, warts and all.

I was relieved when I saw this on Youtube that the organizers were kind enough to edit out the embarrassing bit at the start when my laptop refused to talk to the data projector and I had to swap to another one. Sorting all that out seemed to take ages, which didn’t help my frame of mind and I was even more nervous than I would have been anyway given that this was my first public appearance after a rather difficult summer. Those are my excuses for what was, frankly, not a particularly good talk. But at least I survived. Better is the end of a thing than the beginning thereof.

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Origins of the Expanding Universe Conference – My Contribution

Posted in History, The Universe and Stuff with tags , , , , , on September 19, 2012 by telescoper

For those of you interested in such things, here are the slides I used in my talk at the Origins of the Expanding Universe conference. I spoke about the events on and after 29th May 1919, when measurements were made during a total eclipse of the Sun that have gone down in history as vindicating Einstein’s (then) new general theory of relativity. I’ve written quite a lot about this in past years, including a little book and a slightly more technical paper. This was a relevant topic for the conference because it wasn’t until general theory of relativity was established as a viable theory of gravity that an explanation could be developed of Slipher’s measurements of galaxy redshifts in terms of an expanding Universe.

The Lowell Observatory

Posted in History, The Universe and Stuff with tags , , , , on September 17, 2012 by telescoper

Well, here I am back in Blighty after the  conference celebrating  Vesto M. Slipher. The return trip went remarkably smoothly – no hassles at the airport at either end, and all pretty well on time. When I arrived in Flagstaff last Thursday evening I missed the reception that took place in the Lowell Observatory, but fortunately had time on Sunday morning to have a look around the site, on “Mars Hill”, and take a few pictures.

First and foremost with regard to the topic of the conference, here is  a picture of the actual spectrograph used by Vesto Slipher to measure the radial velocity of the Andromeda Nebula (M31), which he actually did 100 years ago today, on 17th September 1912. I had a bit of a struggle with the reflection on the case, but you can see  it’s a beautiful piece of kit:

Here’s one of me standing outside the dome that houses the 24″ Clark Refractor that Slipher used for his spectrographic studies:

And just to remind you that the site isn’t famous only for Slipher’s work, here is the dome housing the 13″ astrographic telescope that was used in 1930 by Clyde Tombaugh to discover Pluto.

Here’s my chauffeur for the day, Prof. Peacock, with the rusting remains of a 42″ telescope:

Of course the Lowell Observatory is named after Percival Lowell (known to his friends as “Percy”) a flamboyant character who founded it in 1894. Lowell did many great things for astronomy, but unfortunately he is mostly remembered these days for his erroneous observations of “canals” on Mars.

Hubble versus Slipher

Posted in History, The Universe and Stuff with tags , , , , , on September 15, 2012 by telescoper

Since I’m here at a conference celebrating the scientific achievements of Vesto M. Slipher, I thought I’d take the opportunity to make a few remarks about Slipher’s work and legacy.

I often use this picture in popular talks to illustrate the correlation between distance (x-axis) and apparent recession velocity (y-axis) that has become universally known as Hubble’s Law. This is an early version of such a plot published by Edwin Hubble in 1929.

In public talks I rarely have time to go into the details of this, but it is worth saying that only the results on the x-axis were Hubble’s own measurements. Hubble only contributed half of the above plot, i.e. the distance measurements, and these turned out to be wrong by a factor of about 10 owing to an incorrect identification of the stars used as standard candles. All the recession velocities on the y-axis – obtained by looking at the displacement of lines in the target galaxy’s spectrum – were in fact obtained by Vesto Slipher at the Lowell Observatory here in Flagstaff, Arizona. Hubble used these data from Slipher with permission, but gave no credit to Slipher in the references to his 1929 work. A later, and more convincing, version of this plot published in 1931 by Hubble and Humason, was accompanied by a generous acknowledgement to Slipher’s contribution. However, by then, Hubble’s name was firmly associated with the plot and Slipher’s contribution was largely forgotten for many years subsequently.

This episode isn’t at all atypical of Hubble’s behaviour. He was an extremely ambitious man who was an expert in the art of promoting himself and the Mount Wilson Observatory where he worked. Slipher was a very different type of man: quiet, self-effacing, and very much a team player, dedicated to scientific accuracy rather than his own reputation.

It’s worth saying further that the key observation that led to the understanding that the Universe is expanding is the fact that most of the spectra obtained by Slipher, over the years subsequent to his first measurement of the spectrum of the Andromeda Nebula (M31) celebrated by this conference, showed a redshift indicating velocity away from the observer. Even without distance measurements this leads directly an interpretation in terms of cosmic expansion. Ironically, the first spectrum he obtained, M31 shows a blue shift, as do a few others plotted with negative velocities in the above diagram, but the more distant sources exclusively show a redshift.

As a scientist should be, Slipher was very careful about the interpretation of this result. The more distant objects are fainter and thus more difficult to observe. Could it arise from some systematic artifact? Or could there be an unknown physical effect that produces a redshift dependent on the size of the source? These questions could only be answered when accurate distances to the nebulae were established, so Hubble’s contribution was by no means negligible. It’s completely untrue, however, to say that Hubble discovered the expansion of the Universe, so there’s yet another example of Stigler’s Law of Eponymy whenever anyone talks about the Hubble expansion.

One of the great things about coming to this meeting was the chance to meet Alan Slipher, grandson of Vesto Slipher. He and other members of his family refer to Vesto as “VM”, by the way, which I hadn’t realised before. VM lived a long life, dying in 1969 just short of his 94th birthday, so Alan knew him well until age 17 or so. He spoke most warmly and movingly after yesterday’s conference dinner about his memories of his grandfather, who he clearly looked up to. His words confirmed the impression I’d already formed, that Slipher was an extremely cautious and serious scientist as well as a kindly and humble man.

The contrasting personalities of Slipher and Hubble are further illustrated by correspondence between the two that is archived at the Lowell Observatory. Slipher comes across as kindly and cooperative, Hubble as pompous and self-regarding. I know which of the two I admire the best, both and scientist and human being.

The Origins of the Expanding Universe

Posted in Books, Talks and Reviews, The Universe and Stuff with tags , , , , on July 30, 2012 by telescoper

Not having much time to write anything particularly original, I thought I’d use this blog to advertise a forthcoming centenary celebration which I hope to attend and speak at, if my recovery goes to plan.  The text below is taken from the conference website for a meeting due to take place at the Lowell Observatory in Flagstaff, Arizona from September 13-15. I’m sure they won’t mind me borrowing it, as it helps promote the event.  Registration is open until 10th August…

On September 17, 1912, Vesto Slipher obtained the first radial velocity of a “spiral nebula” – the Andromeda Galaxy. Using the 24-inch telescope at Lowell Observatory, he followed up with more Doppler shifts, and wrote a series of papers establishing that large velocities, usually in recession, are a general property of the spiral nebulae. Those early redshifts were recognized as remarkable by Slipher, and were critical to the discovery of what came eventually to be called the expanding Universe. Surprisingly, Slipher’s role in the story remains almost unknown to much of the astronomical community.

The nature, and especially the distance, of spiral nebulae was fiercely argued – most famously in the 1920 Shapley-Curtis debate. Hubble’s 1923 discovery of Cepheids in Andromeda, along with Henrietta Leavitt’s period-luminosity relation for Cepheids, led to a distance scale for the nebulae, enabling Lemaitre (1927) to derive a linear relation between velocity and distance (including a “Hubble constant” and, by 1931, a Primeval Atom theory).

Meanwhile, a new concept of space and time was formulated by Einstein, providing a new language in which to understand the large-scale Universe. By 1932, all the major actors had arrived on stage, and Universal expansion – the most general property of the Universe yet found – acquired a solid basis in observation and in the (relativistic) concept of space. “Space expands”… or does it? How did Lemaitre and Hubble interpret this concept? How do we interpret it? It continues to evolve today, with cosmic inflation and dark energy presenting new challenges still not fully assimilated.

This conference is in honor of Vesto Melvin Slipher and is timed to coincide with the 100th anniversary of the first measured Doppler shift in a Galaxy (then known as a Spiral-Nebula) on September 17, 1912:Slipher 1913 Lowell Obs 2, 56

We are bringing together astronomers and historians of science to explore the beginnings and trajectories of the subject, at the place where it began.