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## The Penzias & Wilson CMB discovery paper

For the final part of my series to commemorate the 50th anniversary of the discovery of the Cosmic Microwave Background (CMB), today I’m going to show the original papers announcing this momentous discovery to the scientific community. I should point out that I have taken these photographs to portray the historical context, even though it is not easy to read what they say. The papers have been scanned and are available online for free in both gif and pdf format, follow this link to get them.

The announcement of the CMB’s discovery came in two back-to-back papers in the July 1st edition of The Astrophysical Journal (see the front page below). On pages 414 to 419 Robert Dicke and his team from Princeton (Dicke, Peebles, Roll and Wilkinson, 1965, ApJ, 142, pp414-419) described the theoretical work they had been doing which predicted a relic radiation from a hotter denser early Universe.

The front page of the July 1st 1965 volume of Astrophysical Journal, in which the Penzias and Wilson CMB paper is to be found.

Figure 1 from Dicke etal. in which they plot the “possible thermal history” of the Universe. It is due to the high temperatures in the early Universe that blackbody radiation would have been emitted when the Universe changed from being a plasma to being neutral (“re-combination” or “decoupling”) – shown in this figure as happening when the Universe had a radius of $10^{-3}$ (one thousandth of its current size)

The part of Dicke etal’s paper in which they refer to Penzias and Wilson’s observations.

Then, immediately following on from this paper, on pages 419 to 421 is the paper by Penzias and Wilson (Penzias and Wilson, 1965, 142, pp419-421). For the announcement of one of the most important discoveries in the history of science, both the title and content are very understated.
The title is A Measurement Of Excess Antenna Temperature at 4080 Mc/s, hardly a title to grab the attention.

The beginning of Penzias and Wilson’s paper. It possibly has the most understated title of any scientific paper of such importance.

The paper is nearly entirely technical, detailing their experiment and the steps they had taken to ensure that they accounted for the origin of every signal detected, apart from the “excess antenna temperature” of the title. At the end of the first paragraph of the paper is the following sentence – their only reference to its possible origin.

The only reference to the possible explanation for Penzias and Wilson’s “excess antenna temperature” (i.e.. signal) is the line “a possible explanation for the observed excess noise temperature is the one given by Dicke, Peebles, Roll and Wilkinson (1965) in a companion letter in this issue.”

The paper was submitted on the 13th of May 1965, as can be seen below.

The end of Penzias and Wilson’s paper, which was submitted on the 13th of May 1965.

Although the paper appeared in the July 1st volume of Astrophysical Journal, the New York Times had picked up on the story and ran its discovery as headlines in their issue on the 21st of May 1965. Although press releases of major discoveries are now often made when the paper is submitted, I would imagine it was rather unusual in the 1960s for scientific discoveries to be published in the popular press before the journal article had appeared. Does anyone now of other examples from this time and before?

A rather fuzzy screen capture of the front page of the New York Times from the 21st of May 1965

And this is the actual article, from the New York Times archives (one has to pay to get such articles, but it is not much).

The actual article as it appeared on the front page

The remainder of the article from the 21 May 1965 edition of the New York Times on the CMB’s discovery

That concludes my series to mark the 50th anniversary of this most important of discoveries. If you want to read far more about the history of the CMB’s discovery, as well as its 1948 prediction and what we can learn from it, then check out my book by following this link.

My book “The Cosmic Microwave Background – how it changed our understanding of the Universe” is published by Springer and can be found by following this link.

## The greatest astronomer of the 20th Century?

In November of last year (2011), I have a talk to Swansea Astronomical Society on the early history of Yerkes Observatory. I blogged about that talk here.

Last night (Thursday 8th of November) I gave a talk to the same society with the title “ George Ellery Hale : The greatest Astronomer of the 20th Century?“. The title is deliberately provocative. In the talk I attempted to show Hale‘s main achievements in his productive life. There were many, but this slide summarises the main ones :

A summary of Hale’s main achievements in his astronomical career

Here is a gallery of all the 32 slides in the talk.

My conclusion, in the last slide, is that maybe Hale wasn’t the greatest astronomer of the 20th Century, but probably the most important. Without Hale, Yerkes Observatory would never have existed, nor Mount Wilson Observatory.

Who do you think was the greatest astronomer of the 20th Century?

## The birthplace of modern astrophysics

Last Thursday (10th of November) I gave a talk to Swansea Astronomical Society. This is the 3rd or 4th time I have talked to them, and I was asked by Dr. Steve Wainwright to talk about the early history of the Universty of Chicago‘s Yerkes Observatory.

The great 40-inch refractor at Yerkes Observatory

I worked at Yerkes from 1995 to 2001, during my time there as a post-doctoral researcher I worked with Professor Al Harper on Airborne astronomy, initially on the Kuiper Airborne Observatory. In 1997 I started working on the HAWC far-infrared instrument for the Stratospheric Observatory For Infrared Astronomy (SOFIA). I feel very privileged to have worked at such an amazing place, so steeped in the history and development of 20th Century astrophysics.

Yerkes Observatory, which was founded by the University of Chicago, was home to the World’s largest telescope when it opened in 1897. This is the famous 40-inch refractor, which is still today the largest refracting (lens) telescope in the World. The Observatory gets its name from Charles Tyson Yerkes, the man who paid for the Observatory and the telescope. Its first Director was George Ellery Hale, a remarkable man who went on to establish Mount Wilson Observatory. I am giving a talk about Hale in a few months, so will write a longer blog about him then.

George Ellery Hale as a young man

Hale left Yerkes in 1903 to try to set up Mount Wilson Observatory. Initially he wanted the University of Chicago to establish it as a remote observing station, but they refused. So, he resigned his position and struck out on his own. Mount Wilson became the premier observing site in the World for the best part of 50 years, being home to the 60-inch and then the 100-inch telescopes. It was the 100-inch which Edwin Hubble (who did his PhD at Yerkes in 1919) used to show in 1923 that the Andromeda Nebula was external to our Milky Way galaxy, and in 1929 that the Universe was expanding.

My talk was on the early history of Yerkes, from 1891 to 1903. I stopped at 1903 as this is when Hale left to establish Mount Wilson. I chart the appointment of Hale as Associate Professor of Astro-physics at the University of Chicago by its first President William Rainey Harper, the meetings they had with Yerkes to persuade him to fund the building of the Observatory and its massive telescope, and the trials and tribulations in bringing the dream to fruition.

Here is the first few minutes of my talk – filmed by my daughter Esyllt.

Here is a link to a PDF file of the slides I presented. There are 46 slides in the presentation, but many of them are just photographs from the Observatory’s early days.

I will also try and put them up as a slideshow, but so far I have not had much success in getting this to work on my blog.