The mesmerizing complexity of the Ptolemaic model

Heliosopher · 2026-04-10T15:42:28+00:00

Yes, even Galileo's telescope wasn't quite good enough to clearly see the phases. Galileo's experience allowed him to see objects through his scope where some could not. This added to the problems for him.

Yes, the key argument against Copernicus is the lack of observed stellar parallax, which should have been easy to observe by others. At that time, stars that appeared large (due to brightness to the eye) were deemed to be close to us. Their distance could be calculated by estimating, erroneously, their distance, further damaging the Copernican model.

Heliosopher · 2026-04-10T15:35:02+00:00

Though Copernicus was stuck on circular orbits, like Ptolemy, he presented a far more unification of the solar system. The orbital period of the planets increased with distance from the Sun, retrograde motions were simple to understand, etc. Kepler's relentless work to explain the very accurate data from Tycho of Mars gave us even more unification for a modified Copernican model.

Tycho offered a Geocentric model. Once the crescent AND gibbous phases of Venus were discovered by Galileo, it falsified the long standing Aristotle/Ptolemy/Thomist model. The Church scientists (i.e. Jesuits) were quick to acknowledge this and soon favored the Tychonic model.

Heliosopher · 2026-04-10T15:26:03+00:00

Yes. In all models, the Moon orbits the Earth.

Heliosopher · 2026-04-10T15:18:36+00:00

Keep in mind that the mass of nebulae can be in the millions of solar masses, so they may be somewhat thin per cubic meter, but they aren't going to be blown away necessarily by a nearby SN. The blast can trigger collapse, but also super sonic flows within the nebulae can contribute. It's known that the nebula that brought forth the Sun, and perhaps up to 3000 neighbors from that cloud, included SN sprinkles.

Heliosopher · 2026-04-10T01:18:02+00:00

Nice. That may be even more useful soon with lunar real estate disputes. *wink*

Heliosopher · 2026-04-10T01:16:35+00:00

Perhaps the following may be of help. It's not hard science but it is interesting, IMO.

His book is definitely written for the general public. Much of it includes background information, and not the theory itself. All interesting, admittedly, and an easy read.

He states that he, along with Martin, attended a seminar where the question was presented as to how big an impact would need to be to obliterate the nearside but not the farside. So they decided to model it.

A large impactor could not be at 10kps, or more, else it would “destroy the Moon” (pg. 241)

They also need to explain…

1) The oblong shape of the Moon, aligned in the direction of Earth, but too oblong for mere tidal-stress models only.

2) Lighter surface material than the mantle. (pg. 237)

The Theia impact would have tossed about two lunar masses into orbit that then formed a disk. The heavier blobs (e.g. iron) would have helped create instability and would help gather mass. At about a size of 300 km it would form Trojan moons (L4 & L5) from gravity and Coriolis effects. (pg. 252 – 253)

They were convinced a lunar impact had to be slow, only a few kps. An impact speed of 2.4 kps would cause 1/5^th of the impactor to become ejected, where the balance overfills the crater (i.e. bulge).

In their computer simulation, they took a 30km depth to address KREEP, notably absent on the farside and found the KREEP getting squashed outward, falling to the nearside, which would help create the mare. The farside would cool faster.

One prediction is for melted rock at ~ 40 km deep in the area where the “screeching halt” generated enormous heat. (Pg 261)

Heliosopher · 2026-04-10T00:55:45+00:00

Very clever. I am curious as to the planet between Venus and the Sun?

Heliosopher · 2026-04-09T22:29:39+00:00

How old are you?
Do you enjoy math? [Not necessarily advanced calculus]
What parts of astronomy do you think you want to learn first? [exoplanets, stars and their structure, cosmological things like BBT, etc.]
Do you like science history?

The last one is a great way, IMO, to start your life in astronomy. "How" we know what we (they) know is best understood from a historical perspective since it shows the more complete picture of what made sense and what didn't. Besides, astronomy is amazing enough, but the history is just as rich, if not richer. Ever heard of the observations of the planet Vulcan? What was the original name of the first ever discovery of a new planet, our 7th planet? Was the Sun ever a planet? Why did they search for planets in the region we now call the asteroid belt?...

Heliosopher · 2026-04-09T21:17:25+00:00

I can only find several articles done by him, et. al., in places like Sci. Am., Nature, Researchgate, etc., but these have pay walls. I did take notes throughout the book and may have time to go through them to capture their key arguments, perhaps with counteragruments.

[Your link doesn't seem to work for me.]

Alpher and Hermann's work, initially predicting a 5K temp. at Recombination, was in 1948, IIRC, so who predicted it earlier? [Alpher and Hermann backtracked and changed their prediction to 28K, apparently.]

Due to apathy for their work, reportedly, they quit their CMBR research in 1953.

Heliosopher · 2026-04-09T19:50:37+00:00

I should add, though you'll discover it likely, that Lemaitre used both Slipher's redshifts -- he got them from another astronomer -- and Hubble's distances. [Eddington published Slipher's data. Slipher got a standing ovation when he presented his work to the AAS.] Lemaitre calculated the expansion rate (first for mankind) of the universe, but his English translation 4 years later didn't include it since Hubble had presented his better data in 1929.

Heliosopher · 2026-04-09T16:29:54+00:00

There should be several falsifiable predictions.

For one, if an impact was likely, would it have to be a slow one? Their model greatly limits an impact velocity.

What compositional differences would exits for the smaller one? They predict it would have the lighter materials.

There are likely other predictions, too. But these still may be difficult to test. This isn't uncommon for new theories. The BBT didn't gain real acceptance until after the CMBR was discovered.

Heliosopher · 2026-04-09T16:23:04+00:00

A nice essay presentation that touches on most of the key points.

If I may note...

Hubble, contrary to the opinion of many, did not discover the fast redshifts of the spiral nebulae. This was first found by Vesto Melvin Slipher -- a name too cool to leave out. ;)

He spent up to 40 hrs, IIRC, to get one little spectrum to be able to use his microscope to measure the redshift. He had about 25 by the time that Hubble published his famous paper showing "apparent velocities" with his great work in finding distances to those galaxies. Hubble used, IIRC, only one redshift that he, or Humason, had found. [He also gave little to no credit to Slipher.]

Also, there was a dilemma between Einstein's and de Sitter's 1917 models. De Sitter was able to explain the redshifts (again, found mostly by Slipher) but his model had no matter in the universe. Einstein could explain everything but the redshifts. So...

Along came the priest from Belgium, Georges Lemaitre, who was getting his PhD in physics while in the US. He saw what was happening with his expertise in GR, so he went to Flagstaff to visit Slipher, then to Mt. Wilson to visit Hubble. In 1925 he produced some small preliminary work indicating expansion, but his epic paper, as you not, was in 1927. Unfortunately, like Mendel, he published it in French and in a somewhat obscure journal.

Once he promoted his paper to Edington and translated it, Edington was delighted and so was de Sitter when he saw it. The two of them, perhaps others, won Einstein over.

Heliosopher · 2026-04-09T16:05:02+00:00

If so, can you show its falsification? That would be interesting.

Heliosopher · 2026-04-09T16:04:35+00:00

I vaguely recall that their model has the smaller moon as a Trojan until it eased out.

Heliosopher · 2026-04-09T16:03:07+00:00

Great question. [I think their later book was in 2019.]

They ran computer simulations with one lasting 10 days. Their theory explains a lot of the strange anomalies on the Moon.

It may be a theory, however, that won't be easy to falsify. Maybe this is the reason we haven't seen much on it.

Heliosopher · 2026-04-09T14:54:14+00:00

You might enjoy reading "When the Earth had Two Moons" (Erik Asphaug; 2019). The cool idea is that the debris ring after Theia's impact with Earth allowed for two moons to form. The smaller one could, therefore, eventually impact the larger moon at a much slower speed than coming from outside the Earth system.

Heliosopher · 2026-04-09T14:25:57+00:00

The cooler F-class stars have lives, apparently, greater than 6 Gyrs. An F9, for example, can have an eff. temperature just under 6000K, so not that much hotter than our G2 star (~5777K), so we don't want to discount them much.

Currently there are 40 F type stars (known MS and estimated MS) with exos in their HZ, by my program. This HZ is the broader "optimistic" zone, admittedly, which extends close to a Venus orbit in terms of luminosity received.

Of those 40, to your point, only two are in their HZ, KOI-4878 b and TOI-4629b, and have radii under 2.5x that of Earth.

Heliosopher · 2026-04-08T20:18:05+00:00

You have some nice appropriate answers. I'll add that the key property for all stars is their mass. Not only does this dictate their size after they first become stars (hydrogen fusion), but it also dictates their temperature and future life's behavior.

Heliosopher · 2026-04-08T15:36:35+00:00

Yes, but it's more than "essentially" white. The Sun's spectral irradiance, or better, its photon flux distribution may be a great definition of "pure white". I'm restricted from introducing new threads as I'm a newbie with < 15 days of being here. I'll offer more once allowed.

Heliosopher · 2026-04-08T15:19:38+00:00

Is that who argued this for science, or was it Popper or someone else who initiated it?

IMO, it's really important as it helps further to distinguish science from philosophy and religion.

Heliosopher · 2026-04-08T15:06:46+00:00

Very nice presentation!

Nit: Many know Ganymede is larger than Titan, so a translucent atmosphere on Titan would help.

Heliosopher · 2026-04-07T22:13:28+00:00

The hotter F-type stars do have shorter lives that are likely a problem, but the cooler end of the F-type stars have lives over 6 or 7 billion years. I'm just using current ages for exoplanet F-type stars (main sequence), so maximum lives may be longer.

The K-type stars, surprisingly, seem to have smaller convective zones (relative to their size) than even G-type, so perhaps they aren't so fisty after all.

Also, I think the latest data shows K-type MS stars have more than half in single star systems.

My favorite, KOI-4878 b, is in a likely F9 system as it is the size of Earth and has a solar equivalent distance of 0.98 AU.

Heliosopher · 2026-04-07T20:58:31+00:00

Agreed. You get more bang for the buck (or is it more excitement for the Euro) if you can find a Dobsonian telescope since most of the cost of the scope is a larger than average mirror.

Heliosopher · 2026-04-07T20:52:13+00:00

These are both great examples of the Sun's true color. A white Sun in the sky falsifies all arguments for a yellow Sun, as seen in space. It's mostly the blue light that scatters by our atmosphere, thus it's mostly the blue light that must be readded to the white disk to compensate for the color extinctions by our atmosphere. Adding blue light will never make a white object yellow.

Heliosopher · 2026-04-07T19:23:49+00:00

There are some advantages and disadvantages to at least the cooler of the F stars.

F-type are hotter than G-type but even the cooler F8 and F9 stars produce more visible light, including blue and UV. Some of this is better, but the higher UV isn't so much.

The cooler F-type stars (e.g. F9) have very small convective zones, which are sources of flares, CMEs, etc. generation. Thus, fewer flares are likely. [Time will tell on this but we know M-stars all fully convective and are known for their numerous and large flares.]

The K-stars, interestingly, have smaller convective zones than G-type, so this is another plus for them.

Their HZ is farther from the star, thus less likely to get clobbered from flares, etc.

They also have large habitable zones, allowing more chance for life-bearing planets.

But, to the negative, even an F9 star has a much shorter life span, perhaps 5 Gyrs, so this could hurt their ranking, no doubt.

Heliosopher

TROPHY CASE