Welcome to Ned Wright's Cosmology Tutorial

News of the Universe
Frequently Asked Questions
Enter the tutorial or the Italian version    or the French version   
Cosmological fads and fallacies

Cosmology and art

CMB Spectrum
CMB Anisotropy
Big Bang Nucleosynthesis
Supernova Observations
Cosmology, Religion & Kansas
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New on the tutorial:

• A discussion of the history of the CMB dipole discovery.
• A history of COBE, the COsmic Background Explorer, in pictures.
• A cool rollover page that blinks between a color image contructed from 3 WMAP bands and the WMAP ILC reduced galaxy map
• A calculator that takes light travel time and computes the redshift. There is also an advanced version of my Cosmology Calculator.

Cosmology is the study of the origin, current state, and future of our Universe. This field has been revolutionized by many discoveries made during the past century. My cosmology tutorial is an attempt to summarize these discoveries. It will be "under construction" for the foreseeable future as new discoveries are made. I will attempt to keep these pages up-to-date as a resource for the cosmology courses I teach at UCLA. The tutorial is completely non-commercial, but tax deductible donations to UCLA are always welcome.

Astronomy and cosmology are very much mathematical sciences, but I have attempted to avoid higher math in these pages. I do use high school algebra and geometry - courses required for admission to UCLA - but I have also included some animations [1, 2, 3, 4, 5, 6, 7], some Java applets [1, 2], and many illustrations in the tutorials, the ABC's of Distances, and the answers to some of the Frequently Asked Questions.

In addition to the cosmology tutorial, there is also a relativity tutorial and extensive discussions on the age, density and size of the Universe. There is also a bibliography of books at a range of levels, and a Javascript calculator of the many distances involved in cosmology.

Slides for recent talks:

• Slides for the 105^th Faculty Research Lecture at UCLA, 28 Oct 2008.
• Colloquium at the Geneva Observatory, 10 Nov 2006.
• Public talk at the 20 Oct 2006 meeting of the Ventura County Astronomical Society
• 27 Sep 2006 colloquium at the Arizona State University School of Earth and Space Exploration.
• 24 Sep 2006 Talk at the Mt. Wilson Observatory Association
• Invited talk at Einstein's Legacy: Relativistic Astrophysics and Cosmology, 7-11 Nov 2005.
• Presentation at the International Symposium on Particle Physics, Astrophysics and Cosmology
• Lectures at the International Summer Institute on Particle physics, Astrophysics and Cosmology, Hangzhou China, 2005 August 15, 16, 18.
• "Fact and Fiction in Cosmology", a public lecture at the Cal State Northridge planetarium.
• 13 March 2005 AFHU Einstein Symposium Talk
• 3 March 2005 Director's Distinguished Lecture at LLNL
• 27 May 2004 Ohio State Colloquium
• 11 Oct 2003 UCLA Extension Course
• September, 2003 NATO ASI in Cargese lectures (1, 2, 3)
• lectures at the July, 2003 winter school in Argentina
• "Are We Likely to Be Alone" at the 4 April 2003 CSEOL Symposium
• Astrophysics Fact Sheet

The course notes (130 pages, 398 equations, 51 figures) for the upper division undergraduate Stellar Systems and Cosmology course, Astronomy 140, that I last taught in spring 2008 are available on the Web. And for a much more technical discussion of cosmology see my graduate course Astro 275 lecture notes (126 pages, 381 equations, 42 figures). This course was last taught in the spring of 2009. If this course Web site gets closed, you can use a backup copy of the A275 notes.

28 Nov 2010 - There has been a lot of discussion about a preprint by Gurzadyan & Penrose entitled "Concentric circles in WMAP data may provide evidence of violent pre-Big-Bang activity". I find this very unlikely, and Peter Coles also has his doubts. It is important to remember that this is a Gurzadyan paper, and not a Penrose paper. Update 6-Dec-2010: Moss, Scott & Zibin and Wehus & Eriksen both show that Gurzadyan & Penrose made an error, and that simulated maps using the standard ΛCDM model are fully consistent with the actual WMAP data.

15 Nov 2010 - Word came that Allan Sandage has died. He worked under Hubble as a student. He continued Hubble's work in determining the Hubble constant by measuring the distance and redshift of galaxies. He corrected the Hubble constant from the 500-600 km/sec/Mpc value first found by Le Maitre and Hubble to about 50 km/sec/Mpc. Sandage was then part of a controversy between the "50" camp and the "100" camp led by de Vaucouleurs, which has ultimately been settled in favor of the middle ground, with the best current value of H₀=70.4±1.4 km/sec/Mpc.

19 Aug 2010 - WMAP has completed its end of mission calibration observations.

10 Aug 2010 - WMAP has stopped taking cosmology data after nine full years of observations, with one extra day to finish the last season of Jupiter observations. There will be a few days of calibration data taken at different precession angles and then WMAP will be done. However, observations of the CMB will continue with the Planck mission which has more frequencies, better sensitivity, and better angular resolution than WMAP.

The thumbnail to the right is a map from Planck released in July 2010. Click to get a larger version.

Geoff Burbidge, 1925-2010

26 Jan 2010 - Geoff Burbidge, a cosmologist famous for working out how all the elements heavier than helium are made in stars, and noted Big Bang skeptic, died today in La Jolla. The high point of his career was the massive paper B²FH, "The Synthesis of the Elements in Stars". The low point of his career was its end, devoted to promoting the Quasi-Steady State Cosmology by publications that verged on fraud. Obituaries in the LA Times, the Wall Street Journal.

25 Jan 2010 - The seven year datasets and papers from WMAP are posted on LAMBDA. Luckily for me, the default parameters in my Cosmology Calculator taken from the first year results are still a good fit to all the data. The image on the right shows a map of the anisotropy of the Cosmic Microwave Background in the three highest frequency bands measured by WMAP: 41, 61 and 94 GHz. Click on the thumbnail for a larger version.

22 Jan 2010 - Andrew Lange, a principal in the BOOMERanG experiment and Planck, died today, an apparent suicide. He was very influential in pushing the development of extremely sensitive bolometer detectors in CMB experiments. Update 27 Jan 2010: New York Times obituary.

The legend that BOOMERanG showed the Universe is flat is actually not quite correct, since the results published in 2000 had a serious systematic error. The position of the peak in the angular power spectrum of the anisotropy of the CMB was known to be ell_pk = 210 ± 15 in 1999, and BOOMERanG found ell_pk = 197 ± 6 in 2000, while the correct value is ell_pk = 220. Thus while BOOMERanG provided improved precision, it actually gave a less accurate value for the flatness of the Universe. Since a flat Universe requires Ω=1, and Ω goes like 1/ell_pk², the 10% error in the BOOMERanG value for ell_pk really implied a closed Universe. The de Bernardis et al. paper correctly claimed a flat Universe by using strong priors from non-CMB measurements.

Note that Andrew Lange also worked on the MAXIMA experiment which did not have the systematic error, and the systematic error was corrected in 2001. He always worked on the bleeding edge of the possible, and really extended our capabilities in observational cosmology.

11 Nov 2009 - Fixsen has combined velocity maps from the WMAP satellite with the CMB spectra measured by the instrument on the COBE satellite to come up with a quite precise value for the T_o of the CMB. FIRAS has measured the difference in total CMB power associated with the dipole pattern to an accuracy of 1 part in 700, and since this power varies like (v/c)T_o⁴, the well determined velocity measured by WMAP gives a 1 part in 2000 determination of T_o.

29 Oct 2009 - Today's Nature includes the papers about the high redshift (z = 8) gamma-ray burst GRB090423 mentioned earlier. News coverage today: NPR, USA Today, and Universe Today,

27 Oct 2009 - Andreon et al. (2009) claim that the cluster JKCS041 is the most distant known cluster of galaxies. Unfortunately they have no spectrographic redshifts so this distance claim must be treated with skepticism until confirmed.

17 Sep 2009 - Today's Nature has a letter explaining the anomalous precession of the orbit of DI Herculis by Albrecht et al. 2009, Nature, 461, 373. A preprint is also available. It turns out that the spin axes of the stars are quite mis-aligned with the orbit, leading to tidal torques that explain why the precession was slower than the prediction of General Relativity.
MIT Press Release.
The Cat Herder.

11 Sep 2009 - Bouwens et al. (2009) have posted a preprint describing a set of 5 redshift 8 to 8.5 galaxies in the Hubble Ultra Deep Field. My cosmology calculator gives an age for the Universe of 625 million years for these objects. While these are redshifts based on colors, they appear to be reasonable. A press release is promised for when the paper is accepted, and I expect spectacular new images of the HUDF will be released, but for now admire the HUDF in optical vs infrared from 2004. In 2004 the Hubble had a small IR camera, but even so it could see distant galaxies better in the IR than in the optical. Now it has a big IR camera in the WFC3, and can observe more distant galaxies than before.

02 Sep 2009 - Fomalont, Kopeikin, Lanyi & Benson report on an improved measurement of the deflection of starlight using radio waves and the VLBA. The result agrees quite well with General Relativity. Oddly enough, the press coverage is dated 2 Sep 2009 although the paper was published in the 10 July 2009 ApJ. Also odd is that there was a press release at all, since the previous work using the delay of radio signals from Cassini is 13 times more accurate. But it is nice to know that the deflection of starlight, the experiment that made Einstein famous, agrees with the prediction of General Relativity to one part in 6000. The claim in the press release of 1 part in 30,000 accuracy is just bad arithmetic. [Update 2-Sep-2009 19:28 PDT: I E-mailed Dave Finley at NRAO about the arithmetic problem and he fixed it.]

UPDATE: 17 Sep 2009 - Planck has released first light images.

15 May 2009 - After 2090 days of crygenic operation in space, the Spitzer Space Telescope has used up its entire stock of liquid helium and is warming up. I first worked on Spitzer when it was the Shuttle Infrared Telescope Facility in 1976.

14 May 2009 - Herschel and Planck have launched! ESA has a page listing the latest press releases. Herschel is a 3.5 meter diameter far-infrared telescope. The BLAST balloon-borne large sub-millimeter telescope was a test of one of the Herschel intruments. I first heard about Herschel when it was called FIRST and was an 8 meter telescope, back in the early 1980's. At that time NASA was planning to build a a 20 meter far-infrared telescope call the Large Deployable Reflector. In 1980 this NASA project was called LADIRT. Planck is a new CMB anisotropy mission many times more sensitive than WMAP and also covers a larger range of frequencies with better angular resolution. It should do very good work on small angular CMB anisotropy and the Sunyaev-Zeldovich effect. And the first of many planned spacewalks during the STS-125 mission to repair the Hubble Space Telescope is going well today.

07 May 2009 - Riess et al. report a new value for the Hubble constant of H_o = 74.2 +/- 3.6 km/sec/Mpc based on Cepheid measurements in galaxies that have hosted Type Ia supernovae, including the nuclear ring maser galaxy NGC 4258 which has a very precise distance determined by geometric means.

28 Apr 2009 - NASA and the CfA issued press releases about a gamma-ray burst that went off on 23 April 2009, known as GRB 090423. The burst showed a fading infrared transient but no flux in the optical. In fact there was no flux shorter than 1.1 microns. If this edge is assigned to the Lyman α forest edge at 122 nm, then the redshift is z = 8. No paper has been submitted to the preprint server, but a collection of GCN Circulars is available. Update 8 Jun 2009: Tanvir et al. and Salvaterra et al. have been posted.

09 Apr 2009 - BLAST has published results in today's Nature: Devlin et al (Nature, 2009, 458, 737) showing that half of the CIRB at 250 to 500 micron wavelengths comes from redshifts less than 1.2, and half comes from redshifts greater than 1.2. The arXiv version includes the supplemental information. A more complete paper discussing these results is Marsden et al.

24 Feb 2009 - The Reid et al. paper describing the press announcment is finally on the preprint server. The value for the distance from the Sun to the Galactic Center is 8.4 +/- 0.6 kpc. The rotational speed at this distance from the Galactic Center is 254 +/- 16 km/sec. Allowing for the 5.3 km/sec peculiar velocity of the Sun in the direction of Galactic rotation, a predicted proper motion for the Galactic Center of 6.50 +/- 0.20 milli-arcseconds/year is found compared to the observed proper motion 6.379 +/- 0.024 milli-arcseconds/year. This rotation speed is very similar to the rotation speed of Andromeda at the same radius, implying that the Milky Way and Andromeda are very similar in mass. This represents an increased mass for the Milky Way.

07 Jan 2009 - The ARCADE experiment reported ( NYT, Science News, GSFC press release) the existence of an extragalactic radio background. But this signal has the same spectrum as the radio emission from the Milky Way, and could well be due to an error in determining the galactic contribution to the total signal. The papers are available here, here, here and here. The ARCADE data are beautiful but mainly cover higher frequencies where the extragalactic radio background is not detectable, so the "ERB" depends on a debatable assumption about the lower frequency data, which are all tied to the Haslam 408 Mhz map, published in 1981, but with a zero point set using Pauliny-Toth & Shakeshaft, published in 1962! Pauliny-Toth & Shakeshaft certainly did not see an ERB or even the CMB in their data. Update 26 Nov 2010: Guzman et al. give a much smaller ERB estimate.

05 Jan 2009 - Mark Reid reported at the AAS meeting on very precise distances to radio masers that have led to an increase in the estimated size and rotation velocity of the Milky Way (NYT, BBC). The distance scale scale and velocity both increase by 15 percent so the angular velocity stays about the same. This leads to a 50 percent increase in the estimated mass of the Milky Way.

24 Sep 2008 - Kashlinsky et al. (2008) have claimed a detection of a bulk flow in the motion of many distant X-ray emitting clusters of galaxies. Unfortunately this paper and the companion paper have several errors so their conclusions cannot be trusted. A technical discussion of these errors can be found here.

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