by Rex Parker, PhD
director@princetonastronomy.org

January 13, 2026 Meeting at Peyton Hall.  Despite the unknowns of January weather in central Jersey, let’s aim for a strong turnout in person if possible for the first monthly meeting of the new year. As usual we will run a hybrid meeting via Zoom, so join us virtually (as I will) if you cannot physically attend.  For more on the guest speaker, please see Victor’s section below.  Closer parking update:  While I personally have been parking in the Stadium Drive Garage, be aware that advances in campus construction have made parking closer to Peyton Hall available and walkable.  Here is the university’s official statement:  After 4 PM on weekdays and all day on weekends, University visitors may park in any numbered and non-restricted parking lots, including Theater Drive Garage, Prospect Ave Garage (near Engineering Quad), and Stadium Drive Garage. Motorists must be parked in a legal space between two white lines and adhere to signage.  Prospect Ave Garage seems to be a good choice.  See the map here: https://transportation.princeton.edu/sites/g/files/toruqf611/files/documents/2025-visitor-parking-sp2025.pdf

Hot Topics for 2026?  You are probably the go-to person in your family and circle of friends when it comes to emerging astronomy themes.  The popular press and media have been providing abundant PR for supermoons, planet alignments, and meteor showers, but they don’t usually go into the physics.  I suggest that we start up a regular monthly review to discuss timely and interesting astronomy events during the second half of our meetings at Peyton Hall and via Zoom.  We could go a bit deeper than some of the media do, which might help all of us be ready to prime family and friends about the hot topics.  I am proposing that each month we identify in advance the upcoming astro topics soon to emerge in the popular press and media.  Please send your thoughts and themes for hot topics over the next couple months by email to me at director@princeonastronomy.org. 

Dark Matter Illuminated.  My 2026 resolution is to come to grips with the challenge of better understanding cosmology and astrophysics through reading some of the history of the science.  Here I would like to discuss the intertwined theories of the hot big bang origin and dark matter.  This “standard model of cosmology” is remarkably elegant in its simplicity, but paradoxically highly complex and incomplete.  It relies strongly on the mysterious dark energy (lambda, Λ) and cold dark matter (CDM) that supposedly make up over 90% of the universe.  This keeps me up at night because it is not really so understandable by non-professional physicists. By following the trail of thought from the late 1800’s through early 1900’s, then on to the 1960’s and 70’s, it is possible to trace the emergence of this model, today’s orthodox view in physics. 

Theories and accepted models in science are based on decades of careful observations, experiments, and deductions by the smartest minds.  Yet results can be consistent with more than one interpretation, and solidification of hypotheses into theory and eventually paradigm is not straightforward — a subject for historians and philosophers.  It should be kept in mind that there are other serious alternative cosmologic models beyond the mostly disregarded steady state theory of Hoyle.  These include modified Newtonian Dynamics (MOND) and hybrid variants of the tired light proposal of Zwicky.  Constructing a model explaining physical reality from observations, rather than from hypothesis driven experiments as elsewhere in science, means that alternative explanations are not always completely falsifiable. One may then keep an open mind while still embracing the advances the standard cosmology model provides. 

Alternative models have been developed in our lifetime with the emergence of data that reshaped the hot big bang cosmology model, first proposed by Fritz Zwicky in the 1930s to explain galaxy cluster dynamics.  Vera Rubin (a friend and colleague of Princeton Prof Neta Bahcall) and Kent Ford, starting in 1965 with instruments at Kitt Peak and Lowell Observatory in Arizona, found that the far outer regions of giant spiral galaxies revolve at the same speed as the regions near the center.  Surprisingly the outer region velocity was not slower as predicted by then current gravitational models.  The new data supported the interpretation that there must be vast amounts of invisible mass around galaxies to account for the gravity to produce the faster rotation speed. At this stage, dark matter was a galactic‑scale gravity anomaly. 

During this same period the astounding discovery of the cosmic microwave background (CMB) came serendipitously to Penzias and Wilson at Bell Labs.  The “interference” detected by their antenna in Holmdel NJ was interpreted as relic radiation of the early universe, a signature of the hot big bang origin.  But it was only gradually connected to dark matter in subsequent publications.  It took more precise measurements of the CMB’s thermal anisotropies (big word, here it means variations in temperature in different locations in space) which required major advances in instrumentation, such as the WMAP orbiting microwave telescope championed by David Wilkinson of Princeton (you can see NJ has real claims to fame here).  With these data it eventually became clear that features of the CMB cannot be produced with baryonic matter alone.  Dark matter was seen as the best explanation for the shape of the CMB temperature pattern. In this theory, very early after the big bang event gravitational wells from cold dark matter began “clumping” before electrons and protons combined to form normal (baryonic) matter, shaping the CMB’s measured temperature pattern.  If this is indeed an image of the density fluctuations of early dark matter, it provides a way to calculate precisely the value of the dark matter fraction of the universe.  So dark matter did more than add a new parameter to cosmology, it reshaped the interpretation of the universe’s history. The modern Big Bang model moved from the hot dense early universe picture of the 1960s to today’s ΛCDM model (Lambda–Cold Dark Matter), the standard cosmological model:  roughly 68% dark energy, 27% dark matter, and only about 5% normal matter.  Dark matter provides the gravitational scaffolding for galaxies, while dark energy is even more enigmatic — and for me will require more delving into the history of science to begin to understand.

New AAAP Website.  Just another reminder here, that the new AAAP website will be going on line and the old site being will be turned off this month.  You can access the new site using the same web URL as before (www.princetonastronomy.org).  There are many features of the redesigned site that are much more useful, and we ask that you take some time to get familiar with it.  Stay tuned for emails in January with instructions on setting up your own member account with password for member-exclusive content access.