We will return to our usual programming shortly. But first, a few words on the eclipse experience last Monday. It. Was. Awesome. That’s a few words, so Mission Accomplished. That’s really all I had planned to say. However, I find I am still giddy from this momentous event, so will share my experience of the day, such as words can humbly convey. Prelude We had good weather here in Cleveland, with the temperature reaching the upper 60s Fahrenheit. It was cloudy in the morning and many people were concerned about the prospects to see the eclipse. I was not. Having spent a lifetime as an observer ..read more

The day of doom approaches, and the moon is cleft in half! Ayah al-Qamar 54:1 Perhaps the most compelling astronomical phenomenon accessible to a naked-eye observer is a total eclipse of the sun. These rare events have always fascinated us, and often terrified us. It is abnormal and disturbing for the sun to be blotted from the sky! A solar eclipse will occur on Monday, 8 April 2024. A partial eclipse will be visible from nearly every part of North America. The path of totality will sweep from Mexico through Texas, the Midwest, New England, and across the maritime provinces of Canada. If you ..read more

I just got back from a visit to the Carnegie Institution of Washington where I gave a talk and saw some old friends. I was a postdoc at the Department of Terrestrial Magnetism (DTM) in the ’90s. DTM is so-named because in their early days they literally traveled the world mapping the magnetic field. When I was there, DTM+ had a small extragalactic astronomy group including Vera Rubin*, Francois Schweizer, and John Graham. Working there as a Carnegie Fellow gave me great latitude to pursue whatever science I wanted, with the benefit of discussions with these great astronomers. After my initial ..read more

The results from the high redshift universe keep pouring in from JWST. It is a full time job, and then some, just to keep track. One intriguing aspect is the luminosity density of the universe at z > 10. I had not thought this to be problematic for LCDM, as it only depends on the overall number density of stars, not whether they’re in big or small galaxies. I checked this a couple of years ago, and it was fine. At that point we were limited to z < 10, so what about higher redshift? It helps to have in mind the contrasting predictions of distinct hypotheses, so a quick reminder. LCDM pred ..read more

A common refrain I hear is that MOND works well in galaxies, but not in clusters of galaxies. The oft-unspoken but absolutely intended implication is that we can therefore dismiss MOND and never speak of it again. That’s silly. Even if MOND is wrong, that it works as well as it does is surely telling us something. I would like to know why that is. Perhaps it has something to do with the nature of dark matter, but we need to engage with it to make sense of it. We will never make progress if we ignore it. Like the seventeenth century cleric Paul Gerhardt, I’m a stickler for intellectual honesty ..read more

As predicted, JWST has been seeing big galaxies at high redshift. There are now many papers on the subject, ranging in tone from “this is a huge problem for LCDM” to “this is not a problem for LCDM at all” – a dichotomy that persists. So – which is it? It will take some time to sort out. There are several important aspects to the problem, one of which is agreeing on what LCDM actually predicts. It is fairly robust at predicting the number density of dark matter halos as a function of mass. To convert that into something observable requires understanding how baryons find their way into dark mat ..read more

To start the new year, I provide a link to a discussion I had with Simon White on Phil Halper’s YouTube channel: In this post I’ll say little that we don’t talk about, but will add some background and mildly amusing anecdotes. I’ll also try addressing the one point of factual disagreement. For the most part, Simon & I entirely agree about the relevant facts; what we’re discussing is the interpretation of those facts. It was a perfectly civil conversation, and I hope it can provide an example for how it is possible to have a positive discussion about a controversial topic+ without personal ..read more

Last time, I expressed extreme disappointment that fossil fuel executives had any role in leading the climate meeting COP28. This is a classic example of putting the the fox in charge of the hen house. The issue is easily summed up: It’s difficult to get a man to understand something when his salary depends on not understanding it. Upton Sinclair Setting aside economic self-interest and other human foibles, it is clear from the comments that the science is not as clear to everyone as it is to me. That’s fair; I’ve followed this subject for half a lifetime, and it is closely related to my own ..read more

In 1986, I was a grad student at Princeton, working in the atomic physics lab of Will Happer. It was at a department colloquium that I first heard a science talk that raised serious concerns about our use of fossil fuels potentially impacting the climate. This was not received well. People asked all sorts of questions, with much of the discussion revolving around feedback effects. Perhaps warmer weather from CO2 will result in higher humidity, making more clouds*, and reflecting more sunlight into space. It does not. What about ice cover? This is actually a positive feedback – as the globe war ..read more

I have tried very hard to remain objective and even handed, but I find that I weary of the wide binary debate. I don’t know what the right answer will turn out to be. But I do have opinions. For starters, it is a big Galaxy. There is just too much to know. When I wrote about the Milky Way earlier this year, the idea was to set up an expectation value for wide binaries in the solar neighborhood. That devolved into at least eight other posts on the Milky Way itself, because our Galaxy is too damn interesting, and has its own controversies. So it occurs to me that I never really got on with the r ..read more