| Evolution: Laplacian Planets, Darwinian Moon||May 23, 2012 5:13 AM PDT | url | discuss | + share
Added 1 new A* page:I've been talking about wacky astronomical theories lately; did you know that for much of the period between the two World Wars, the leading theory for the formation of planets was the tidal theory, which proposed that planets formed from material drawn out of the Sun by another star passing nearby? This funky scheme temporarily replaced what had been the leading theory, the "nebular hypothesis" first proposed by Emanuel Swedenborg in way back in 1734, and further championed by Immanuel Kant in 1755 and Pierre-Simon Laplace in 1796. There was a brief interruption in 1749 when the Count of Buffon proposed that planets were matter knocked out of the Sun by comets, but Laplace managed to show that planets formed in this way would inevitably fall back into the Sun.|
Sharp guy, that Laplace! Among his many other scientific and mathematical exploits, he speculated that some nebulae seen by telescopes might actually be distant galaxies, 100 years before Edwin Hubble proved this was the case (c. 1923) by observing stars known to have a certain fixed brightness in two of the "nebulae," which we now know as the Andromeda and Triangulum
modified from an image by Hewholooks (source)
galaxies. And, closer to our particular interests, Laplace promoted the mathematically backed theory that a star of sufficient size would have such a gravitational attraction that even light could not escape; this had first been proposed by a geologist, John Mitchell, in a letter to Henry Cavendish of the Royal Society in 1783:
|If the semi-diameter of a sphere of the same density as the Sun were to exceed that of the Sun in the proportion of 500 to 1, a body falling from an infinite height towards it would have acquired at its surface greater velocity than that of light, and consequently supposing light to be attracted by the same force in proportion to its vis inertiae, with other bodies, all light emitted from such a body would be made to return towards it by its own proper gravity.|
This "dark" or "invisible" star theory was more or less dropped until people started investigating Einstein's general relativity field equations of 1915: Karl Schwarzschild used the equations to describe the gravitational fields of point and spherical masses a few months later; Subrahmanyan Chandrasekhar, in 1931, used special relativity to show that electron-degenerate matter (particles squooshed together just as tightly as quantum rules allow) above a certain mass is not stable--ie will collapse; and Robert Oppenheimer and others predicted in 1939 that although electron-degenerate matter (which makes up white dwarfs) could collapse but then stabilize as a neutron star (which is pretty much packed neutrons), above about three solar masses, nothing could stop its further collapse--and there you get a black hole, although that term was not used until the '60's, when black holes were more or less accepted as unavoidably real.
But back to Laplace and the nebular theory of planetary evolution: in '96--1796, I mean--following Kant's description of nebular collapse under gravity, he theorized that this collapse would form a star at the center with a thin disc of material spinning around it, which would eventually coalesce into planets.
Other theories came and went throughout the 1900s in particular, and it wasn't until the '70's that the nebular theory started a comeback, and not until the early '80's that it was really accepted, and this owed a lot to one star in particular: Beta Pictoris:
image by NASA, ESA, D. Golimowski (source)
In 1983, excess infrared radiation was detected coming from Beta Pictoris by the American, British, and Dutch Infrared Astronomical Satellite, or "IRAS." Beta Pictoris was known to be an A-Type star, which are supposed to radiate most of their energy at the higher-energy, blue end of the spectrum, so an unusual abundance of infrared radiation was thought to indicate the presence of some sort of cooler--energy absorbing--material in the way of the starlight, and this was verified the next year, when the first stellar disc ever seen was imaged around Beta Pictoris.
^ That image above is a 2003 Hubble view of Beta Pictoris, showing the primary disc, and a fainter, secondary disc, which may indicate a planet orbiting the star. The black circle in the center is a mask preventing the telescope's instruments from being overwhelmed by direct starlight.
Beta Pictoris is a pretty interesting star system! It's only 63.4 light years from Earth, so we have a relatively good view. The star is about 1.75 times as massive as our Sun, but that stellar disc around it is really huge: about 1800 astronomical units on one side, and 1400 AU on the other side--yeah, it's lopsided. The Earth is 1 AU from the Sun--that's the definition of an astronomical unit, which is also about 150 million kilometers, or 92 million miles. 1800 AU would be over halfway to the "inner" Oort Cloud of debris around our solar system (the "outer" goes out perhaps as far as 100,000 AU); by comparison, Jupiter is a bit over 5 AU from the Sun, Saturn about 10, Uranus 20, Neptune 30, and Pluto 40 (to be more precise, it ranges from just below 30 AU to just below 50 in its elliptical orbit).
And while that inclined fainter disc--and certain gaps or masses at multiple places in the main disc, as well as red-shifted objects apparently falling into the star--suggest the presence of multiple planets, or at least "planetesimal" proto-planets, one actual planet has been observed, or at least as well observed as you're likely to get over a distance of 63 light years with modern technology and this type of star, which apparently is difficult to study with the radial velocity method usually used to detect exoplanets--and being a young and feisty 8-20 million years old, there's a lot of "noise" making detection of bodies around the star difficult--in fact, there's so much going on there that "material from the Beta Pictoris debris disk is thought to be the dominant source of interstellar meteoroids in our solar system." !! But an object, "Beta Pictoris b," was spotted faintly in near-infrared, first in 2003 on one side of the star, then in 2009 on the other, as demonstrated in this composite diagram:
image by ESO/A.-M. Lagrange (source)
In 2003 they couldn't exclude the possibility that it was a background star--but then in photos taken in 2008/2009, it had disappeared! Only later in 2009, it reappeared on the other side, and then they knew it had to be a planet.
Here it is seen in infrared by the Very Large Telescope in 2008 (this is another composite image: the outer, disc part is reflected light seen in 1996):
image by ESO/A.-M. Lagrange et al. (source)
The estimated 8-Jupiter-masses planet appears to orbit at a distance of about 8 AU from the star. I do tend to avoid talking about exoplanet "discoveries" in general, since their "detection" usually relies on inference from exceedingly faint indirect observations. So I like that this one was actually imaged directly, even if it was really faint.
And getting back to the "giant impact hypothesis" supposed by some to explain the formation of our Moon, that idea was born from the 1898 speculations of astronomer and mathematician George Darwin,
image by J. Russell & Sons (source)
fifth child of Charles, the famed naturalist and proponent of the theory of human evolution. His son George's theory of Moon-volution said that the Moon "spun" off the early, molten Earth as a result of the centrifugal force of Earth's rotation; this gained ground during the Space Race, when American and Soviet lasers bounced off lunar ranging targets showed very precisely that the Moon was in fact slowly moving away from the Earth, something George Darwin had predicted as part of his theory.
That theory couldn't quite explain the tremendous force required to get the Moon off of Earth, though, so in the meantime--1946--Harvard professor Reginald Aldworth Daly proposed that it was launched by an impact rather than centrifugal force--this wasn't really taken up until the mid-70's, however.
I still think it's silly, but there is some of the history of it!
I got to the art supply store today! This is the University of Washington Bookstore, to be more specific, and man they've got an amazing selection: not only did they have the specific "Cretacolor Ergonomic" 5.6 mm lead holder I pointed out online yesterday, they had two other models as well, and even a crayon holder! The crayon holder, as I suspected, was indeed even bigger, which is no good; the other two models were a round-wooden-handled Cretacolor, which wasn't as comfortable, and a triangular Koh-I-Noor.
So I got the Ergonomic home and tried jamming an old Raphael 8404 size 4 brush into it so that the lead holder could serve as a thicker, easier-to-hold handle. The brush didn't quite fit, of course
which I had known would happen :D. That's all right, because I could cut the brush handle down to a smaller size to fit into the holder; the fullest width of the handle couldn't quite fit through the holder--not to mention that the handle was too long, but in fact you can screw off the end of the holder, revealing the hollow tube, so that might not have been a problem in itself. The real problem with this scheme, though, turned out to be that the sturdy gripping metal teeth of the holder can't maintain a firm hold on the metal ferrule of the brush--that's the shiny part between the bristles and the wood handle that you actually hold while using the brush--and that's a problem because as a result the closest you can hold the brush with the lead holder is by the wood handle at the end of the ferrule, at which point your hand is too far back from the brush head for precise work. I'd suspected something like that might be the case even if the teeth could hold on the ferrule, but I still think it was worth a shot. Anyway I can take the lead holder back. :)
I don't think I'll need such contrivances anyway though because I also got a new drawing board, and after using it to support drawing today's A* page, found my wrist was quite happy! Yay! I was afraid at first that the board, a 20"x26" "Airlite," the smallest they had, was too big; it's nearly as big as my drawing table!
But that size means that I can work on an A* page sideways (tall), if necessary, and still have the whole thing easily supported across the board's surface. And even though it's large in size, this board is way lighter than my old ~10"x17.5" particle board board dredged up from scrap wood in the basement, because it's hollow! See it isn't a real board, but a construct of wood edges and some kind of firm but very thin woody surface stretched over them--it looks pretty much exactly like the photo of another brand seen close-up here (I paid nearly twice as much for the Airlite >_< which was a bit of sticker shock at the register since they didn't have a price tag on it, buuuut it doesn't have any of the construction problems mentioned by reviewers of those "Helix"-brand boards, so maybe it's a get-what-you-pay-for type of thing (I hope :P)).
So it's a pretty sweet board so far. I do find it curious though that the only two kinds of drawing boards I can find being sold now are this relatively thick, hollow kind, and a thin sort which seems like the more obvious construction, except it's got a big hole carved along one edge for a handle, and huge metal clamps along the opposite edge that are suppose to hold your paper--like these. How about not putting holes and things in it and just giving us a good thin board? Man. Art supplies can be silly.
Oh that reminds me, the UW Bookstore is actually having a 20%-off sale on fancy writing instruments, and I was tempted into trying out some of the lower-end fountain pens, like the relatively inexpensive ($20-$30) yet well-regarded Kaweco Sport and Lamy Safari. I've been sort of lusting after a fountain pen for a while--after conceiving the notion that I might be able to do A* art with something like one somehow, without scratching the paper as much as a standard dip pen, although subsequent research showed they wouldn't really be useful for scratching and ink reasons, among others--so I was excited to try them out after reading so much about these things online, and...I was underwhelmed. Yeah they've got a kind of smoothness to them that regular pens don't have, except that they do sometimes just decide not to draw part of your stroke--and there's all the fussing with ink and so forth. To show just how undeveloped my actual appreciation for fine writing instruments is, though, I actually liked the $3 cheap plastic Platinum Preppy fountain pen they had there better. :P Still I really have no use for such things, so when it comes to fountain pens I won't really use, I'll just stick with my Platinum Carbon Desk Pen, which never seems to have that not-writing problem, and with its waterproof pigment ink could even, theoretically, be used in actual A* artwork...but probably won't be.
Oh yeah, and that Tom Richmond guy whose article on inking I linked yesterday, from which I got the idea of getting a different drawing board? Well it just so happens a podcast I'd downloaded earlier that day and just got around to listening to today--Tall Tale Radio Episode 133 (TTR is a webcomic/comic podcast)--has an interview with him, and apparently he's, like, the president of the National Cartoonists Society, which is the thing to be in if you're one of those rare syndicated cartoonists. (They're sort of realizing they need to branch out, though, and the interview covers Richmond's spearheading of getting a category of their "Reuben" award dedicated to webcomics.)