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 are anywhere where this event is visible, go out, don a pair of eclipse glasses, and look up. This is especially true in the path of totality. Partial eclipse are cool. Total eclipses are so much more that they have inspired science, art, and literature, with descriptions frequently evincing the deep emotion of profound religious experience*.
The American Astronomical Society has posted lots of useful information, including a map of the path of totality and advice about proper eclipse glasses. These are super-cheap, but that doesn’t preclude bad actors from selling ineffective versions. Simple rule of thumb: don’t look straight at the sun. A proper pair of eclipse glasses enable you to comfortably do so. If it hurts, stop+: close your eyes and look away. Listen to the messages from your pain receptors.
If you can get to the path of totality, it is worth doing so. Expect crowds and plan accordingly. This is a draw of epic proportions, and for many will be the only practical opportunity of their lifetime. Totality is brief, only a few minutes, so be sure to be in the right place at the right time$.
The AAS provides a good list of the phenomena to expect. Most of the action is around and during totality. The partial eclipse is a long (hour+) build up to the brief main show (a few minutes of totality). In addition to seeing the corona, the diamond ring and Baily’s Beads effects, this should be a good time to see solar prominences as the sun is nearing the maximum in its eleven year sunspot cycle. What we will see is unknown, as this is the solar analog of weather phenomena. The forecast calls for a high chance of prominences, but that doesn’t guarantee they’ll show.
One last thing I’ll note is that all the planets are relatively close to the sun on the sky at present, and some might be visible during the eclipse. Venus and Jupiter will be most prominent and easy to spot. Uranus and Neptune, not so much. The others maybe. Also present is Comet 12P/Pons-Brooks (aka the devil comet) in the vicinity of Jupiter. It is quite a temporal coincidence for this comet with a 71 year period to be in the inner solar system during this eclipse. It is unlikely to put on much of a show: comets are notoriously fickle, and the odds are that it will be invisible to the naked eye. But it is there, so keep a weather eye out, just in case.
Now go forth this Monday and witness one of nature’s greatest marvels.
*There are many myths and monsters associated with eclipses. Until the light pollution of recent times, the motions of the sky were very much in our faces. People cared deeply about these things. They were well aware of more than the daily rising and setting of the sun. The phases of the moon, the patterns in the stars, and the wandering of the planets was obvious to everyone who looked up. People learned long ago to keep close track of these events, even those as rare as eclipses. Some of the earliest tablets unearthed from ancient Babylon are elaborate tables of eclipse seasons recognizing lengthy periods like the roughly 18 year Saros cycle. One doesn’t just up and write down this sort of knowledge on a whim one day, as it requires centuries of careful observation and record keeping to recognize the recurrence of events with such long periods, especially for solar eclipses that do not visit exactly the same spot every exeligmos cycle. I suspect there was a strong oral tradition of astronomical record keeping for long ages before we learned to write. Astronomy is the oldest science: this was important knowledge to acquire, preserve, and pass on.
The ancients managed to deduce cycles of eclipse seasons, so they could forecast the chance for eclipses, but only with the same precision as a weather forecast: there is a chance of rain, but we can’t be sure exactly when and where. Now we have measured planetary motions accurately enough and understand the geometry of what is going on so we can forecast exactly when and where eclipses will occur. This is a staggering achievement of human intellect and communal effort.
+There are a lot of misconceptions about the dangers of eclipse viewing. Looking straight at the sun is uncomfortable and dangerous at any time. The only thing special about a total eclipse is that it becomes truly dark for a few minutes, and your pupils start to expand to adapt to the darkness. Consequently, the most dangerous moment is at the end of totality, when your eyes have grown wide and the sun suddenly reappears. Be sure to don your eclipse glasses or look away right before the sun reappears; you don’t want to look straight into the sun at that moment.
Time and Date is a great resource for getting the timing of the eclipse for your specific location, accurate to within a few seconds.
$As with any astronomical observation, no guarantee is made that the skies will be clear of clouds. I have spent many a night at observatories wishing for the sky to clear and obsessively refreshing the satellite maps to discern when it might do so. It doesn’t help – it’s almost as if nature doesn’t care that we want to witness one of its greatest displays. So my advice is to go where you can and don’t sweat the weather forecast. Either the sky cooperates or it doesn’t.
I’ve agreed to serve on a discussion panel about the eclipse on campus, so I’ll be here in Cleveland. We are right in the path of totality, but the weather statistics here are… not good. To make matters worse for the superstitious, April 8 is also the home opener for the Cleveland Guardians. Opening day is always a joyous time with a packed stadium, but the weather is inevitably miserable. Nevertheless, all we need is a brief opening in the clouds at just the right time. At an observatory we would call a that a sucker hole – a gap in the clouds big enough to get the inexperienced observer to run around prepping the instrument and the telescope, an intense amount of work, to open up and observe just in time for the clouds to cover up the sky again. Come Monday, I’ll happily accept a well-timed sucker hole.
It’s for me very interesting that you note all the myths and religious interpretations. No explanation from science for me removes the possibility that rare ubiquitous events may have some religious significance. Usually this is based on superstition, and Trump supporters are very superstitious.
But to explain how this might not really be superstition if the person who believes it very critically examines his belief, consider the 1911 eclipse where Einstein’s theory was confirmed. It gave extra foundation for Einstein to believe his 1926 credo “God does not play dice”.
Of course quantum physicists now claim Einstein was proven wrong by the Bell tests. But philosophically their approach is unacceptable: they propose a theory describing reality while denying realism of quanta before they have been measured. I personally think it’s much more logical to assert that quantum wavefunctions are the reality and that their internals can be nonlocalized, their density can be nonzero at more places at once (entanglement).
Only with measurement the wavefunction collapses to a point (classical) state, probably due to decoherence putting the unknowable quantumness into the state of the measurement device. This way I think realism can be preserved and locality is weakened to apply only to separable states (non-entangled states).
I’ve seen 745 moons. I’ve seen partial solar eclipses and both full and partial solar eclipses, but never a full solar eclipse. A sense of wonder seems appropriate, even to these old eyes.
One’s first total eclipse is always a memorable experience, even if, as in my case I was clouded out in North-East France in 1999. The rapid reduction of the sky brightness in the last few minutes before totality and the way that the colour seems to drain from the scenery are noticeable even if cloud covers the eclipsed Sun. I went on to see good total eclipses in 2006 and 2010, before completing the set with the annular “ring of fire” eclipse in 2012.
I’ve seen a few more moons than you, and yeah my first total solar eclipse. I’m praying to the weather gods for one good sucker hole near Buffalo NY.
I’ll be watching the eclipse with my girlfriend in Gardner, Massachusetts, where there will be almost 95% coverage of the sun’s disc. But now I’ve got to scramble to find eclipse glasses. As a backup in case I can’t purchase eclipse glasses in time, I’ll bring a magnifying glass and an appropriate sized sheet of metal painted white, propped up on the ground or non-flammable surface. But I’ll still make sure we both wear at least sun glasses if we don’t have eclipse glasses in hand.
Sunglasses are not adequate. What works well is a colander. All the holes act as little pinhole cameras, and will project nice multiple images of the partial eclipse on the ground. It gets pretty good when the eclipse is above 80%, at which point you may notice the same effect is provided by tree leaves.
Thanks, Stacy, I’ll bring one of those. So far the weather looks good for this region on Monday.
I forgot to say we’ll only look at the image projected on the white painted metal surface, if we don’t have eclipse glasses, and even then wear sunglasses. A few days ago I read about the Allais Effect, where pendulums act strangely during solar eclipses. But it’s controversial according to Wikipedia with no effect seen by a NASA team, while others reported anomalies.
Regardless of the fact that probably vast majority of readers of this blog have either witness at least one or are set to witness this one, just in case there’s any doubt, this is one of the events that stays with you for the rest of your life.
I’ve had no major trauma, no children born, have not been shelled, shot or stabbed. Can barely imagine any such thing but still I stand by placing experiencing totality right up there with any of that. All of a sudden you realise how insignificant one is in the grand design that is the universe and at the same time how glorious one is to be there, looking at something like TSE and having an organ capable of interpreting what eyes can see and ears can’t hear. Yes, animals go silent. If you’ve spent any time outdoors the silence will be equally shocking. So don’t be in a crowd.
There are many guides and instructions on how to watch it. I would add one more; when it happens, don’t forget to also look around. At the world. Might be different for you but for me the way environment changed in a way brain can’t even comprehend at first was the most impactful thing of it all.
People want to find significance, the only possible one I can see is that the sun and moon look the same size in the sky, due to an unlikely cancellation between size and distance. it’s pretty accurate, but this is obviously not a universal, and there may be a lot of critters out there in all those galaxies. But still, for our particular psyche it has had an effect, and perhaps they represent two sides of the same coin to us.
From the imagery of the eclipse, I have seen so far there is a nice prominence at about 5-o’clock (visible in H-alpha).
It looks beautful from Arizona…. only a partial eclipse here, but in a pinhole camera, we can see the moon coming across, amazing….
Stacy (and others along the path), can we get an update? How was it??
It was awesome.
Words really can’t do it justice. We could see the shadow sweep in on the thin cirrus clouds we had, which were just enough to cause a rainbow ring around the sun but not obscure anything. Totality is just stunning. The corona shimmers like a phantasm of white silk around the dark circle of the moon; it is so mesmerizing you’d think it overdone if it were a special effect. We could see a prominence near the bottom of the disk from our perspective: a band of plasma entrained in the magnetic field of sunspots like cosmic iron filings that glow in the pinkish Balmer lines of hydrogen. Venus and Jupiter were easily visible; some folks saw Saturn as well. Saturn was over towards the horizon; I didn’t look that far aside for 3 minutes and 49 seconds. Pictures really don’t do it justice. They seem ill-suited to illustrate the extend of the corona without overexposing the prominences.
You literally had to see it to appreciate it.
Amazing description!
I browsed some youtube videos to try to see what it was like but you’re right, the cameras do too much autoadjusting to the darkness and contrast that you can’t get a sense of it. Actually the best part of videos, I think, is the audio — the spontaneous shrieks and gasps of the crowd give you a taste of the excitement.
could you consider this
arXiv:2404.06537 (astro-ph)[Submitted on 9 Apr 2024]Exploring the nature of dark matter with the extreme galaxy AGC 114905Pavel E. Mancera Piña, Giulia Golini, Ignacio Trujillo, Mireia Montes
AGC 114905 is a dwarf gas-rich ultra-diffuse galaxy seemingly in tension with the cold dark matter (CDM) model. Specifically, the galaxy appears to have an extremely low-density halo and a high baryon fraction, while CDM predicts dwarfs to have very dense and dominant dark haloes….we explore different mass models in the context of CDM, self-interacting dark matter (SIDM), fuzzy dark matter (FDM) or Modified Newtonian Dynamics (MOND). We find that the latter does not fit the circular speed of the galaxy,”
https://doi.org/10.48550/arXiv.2404.06537
I wrote about this object before: https://tritonstation.com/2022/01/10/the-curious-case-of-agc-114905-an-isolated-galaxy-devoid-of-dark-matter/comment-page-1/
The problem then is the problem now: the inclination. It is not a matter of data quality, which do appear to have improved. I believe the authors when they say the shape of the fitted ellipses implies an inclination of 31 degrees. I don’t believe the assumption implicit in making this determination, which is that this object would appear round when see perfectly face-on.
This is a Magellanic Irregular: a messy morphology with a blobby bar. This morphology is very common among low mass field galaxies. The bar-like structure is an indication of an intrinsically triaxial structure: this object isn’t a simple oblate disk, and there is probably no angle from which it would appear perfectly round. This causes one to overestimate (but never underestimate) the inclination, a systematic error that I’ve discussed many times, e.g., https://arxiv.org/abs/1107.2934.
Kinematic inferences are very sensitive to the inclination correction for nearly face-on objects. There is a world of difference between 1/sin(i) for i = 31 and i = 11 as far as the kinematics are concerned but almost none for the photometry that constrains i. So even if the random error is only +/- 2 degrees, the important error is the systematic cause by the intrinsic shape of this messy object not being a simple circle when seen face on.
Now, let’s suppose the inclination is indeed 31, and the rotation speed is as slow as that implies. Then MOND is wrong. More generally, this object would be an exception to the empirical Tully-Fisher relation, which is also strange, and is bad news for whatever explanation we have for it in ANY theory. Dark matter-based theories are more tolerant of outliers, but that’s just because they’re more flexible and don’t really make a clear prediction for this. So it just is whatever it is shruggy emoticon. A theory is not better because it survives a test for which it doesn’t make a prediction.
If you read the abstract, the authors pretty much say that. MOND doesn’t work, but neither does anything else. DM theories look less bad only because they don’t make as strict a prediction. CDM looks bad because it does predict what ballpark the halo parameters should be in, and it ain’t this. The other types of DM predict even less.
You know what would give a good fit? A pseudo-isothermal halo of the type we always used to use to fit rotation curves in the days before CDM simulations gave us NFW. The pseudo-isothermal halo is a very flexible fitting function, so I’m sure it would work just fine. It has nothing to do with the predictions of cosmology (NFW is not the same) so the halo parameters can be whatever they need to be. Does the good fit that ensues better? Or just meaningless?
very interesting. so does not dark matter and no MOND, just newtonian gravity and baryons explain the extreme galaxy AGC 114905?
could it perhaps not be a real galaxy, but just a random cluster of gravitationally bound stars, or some variation such as 2 small dwarf galaxies that collided, and what you observe is debris
Rotating galaxies without dark matter (or MOND) are violently unstable. This has been known for half a century, and was one of the early motivations to invoke dark matter in the first place. So this is another reason that the nominal inclination simply cannot be correct: with the negligible amount of dark matter the low rotation speeds imply, this object would self-destruct in a tiny fraction of a Hubble time.
One can, in principle, strip dark matter in tidal interactions. However, that or a collisional origin seems unlikely: this object is pretty isolated; there is nothing around to collide with. Collisions generally make a train wreck, and destroy gas disks like the one observed. So it would take lots of special pleading to arrange the initial conditions: there happened to be two dwarfs that collided in what is otherwise the middle of nowhere (that’s like colliding with the only other car for a hundred miles) AND the collision had to be arranged just so that you don’t have a car wreck but instead merge to form a super-car.
interesting
are there any cluster of gravitationally bound stars that doesn’t rotate ?
Sure: globular clusters. Stability is only an issue for rotating disks.
I see their paper addresses all these issues. They make an argument that this thing has sorta barely enough dark matter to be stable. I’m skeptical of that, but I’d have to look into it more closely to say more. I can see at a glance that the parameters of their DM halos are silly, which they say themselves, so nothing really works here.
is their conclusion strong and MOND is wrong ?
so what do you conclude is going on with galaxy AGC 114905?
If the galaxy is as they say it is, *everything* is wrong, not just MOND.
They say “we assume we are seeing a circular disc at a given inclination rather than a non-circular disc” which is what I said at the beginning. The data are not the problem, but rather this specific assumption. I think the most probable interpretation is that the inclination is more face-on than they infer. This allows the disk to be stable with dark matter, saving both it and MOND.
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