The Observant Astronomer

The passing scene as observed by an observant Jew, who daylights as an astronomer.

Tuesday, November 29, 2005

Seasonal Notice

So, it is The Season once again. Yes, that time of year when long-suffering non-Jews bend over backwards to be as inclusive as possible while celebrating their Holiday. So important is it, that they cannot bear to think that there are those of us who simply don't care what they are doing in late December. The Boston Holiday Tree is typical. The Season used to bother me, until I spent a couple of fin Decembers in Eretz Yisrael. Now I find it to be just so much background noise.

The flyer for the department's annual "Holiday Party" appeared in my mailbox last week, RSVP requested. So I informed the department secretary that, once again, I won't be attending their Christmas Party. But if they were really sincere in their quest for inclusiveness, they wouldn't be holding it on a Friday evening.

Then there was the kindly British Professor who made it his business to see that all the foreign members of the department had somewhere to go for Christmas Dinner. He invited me. I declined. He invited the Israeli post doc. He also declined, and added, for good measure, that he'd be coming into work that day.
"But, but," protested the Prof, "What about your wife?"
Responded the puzzled Sabra, "She'll be at home."
"At home!?", inquired the aghast Professor.
"Well that's where she generally is when I go to work."

Do they get overtime if the hurricane season goes into December?


The Incredible Jerusalem Compass

An advertisement for this device just came across my desk. It is for a patented, non-electronic, compass that is guaranteed to point towards Jerusalem. Indeed, according to Rav Moshe Halbershtam, "It is a fine device—mainly, that it points directly towards Eretz Yisroel, directly towards Jerusalem, directly towards the holy site of the Beis HaMikdash, directly towards the Holy of Holies—just as is taught in the Gemora."

So, until now facing in the general direction of Jerusalem has been good enough. Suddenly we need to face precisely? Is this a great circle route, or a straight line through the Earth? Will we need to reorient all our shuls? And, can you change the location it is pointing to? Does it do, say, Mecca?

UPDATE: I asked the advertiser about the claimed patents and they just directed me to the manufacturers website at There, we find, that there are only "international patents pending" and that it was invented by "Moshe" a "married student in one of Jerusalem's popular Yeshivahs". It is claimed to "defy the laws of nature". Too good to be true, I think. Anyway, anyone have $25 to blow on this and see if it really works? Additional finances for either extensive travel, or postage will be required for a full test.

FURTHER UPDATE: I have located what is apparently the patent application in question. The inventor is indeed Moshe, but he now apparently lives in New Jersey. It is listed as a "Novelty Item". As one of the anonymous commentators speculated, it is indeed a standard compass with the magnetized needle hidden and another, non-magnetized, needle suspended above it set to point east. At point 14 it points out that similar devices could be made for other locations ". For example, a compass indicating South can be marketed in Finland and Russia," etc. At point 16, it is designed to "appear to defy the laws of physics" by minimizing the space for the magnetized needle.

So, it will only work from one location. It does not point any more accurately to Jerusalem than any other compass. It just saves you having to turn 90 degrees. It is indeed incredible. Literally, too good to be true. Further commentary is left to the reader.

ANOTHER COMMENT: Correspondence seems to indicate that the advertised item moves beyond the linked patent application. Josh Waxman on parshablog has some related thoughts on how it might actually work, which also occurred to me. See my comment there for further thoughts.

Wednesday, November 23, 2005

Experts talking off the cuff

No need to belabor the obvious on this
A leading constitutional expert says it has been more than a century since a federal government was defeated on a stand-alone non-confidence motion.

“It wouldn't have been in the 20th century – it would have to be before,” said Ned Franks, professor emeritus at Queen's University.[Globe and Mail]
but the closest was King's motion in 1926 that Meighen's governement was illegally constituted. Other than that, since confederation, no motion like this has ever been passed. (My earlier summary on the issue)

Tuesday, November 08, 2005

Manned spaceflight

In this post I commented on the relative roles of men and robots in space exploration. The linked article emphasizes a point I make there in passing. What is needed is a change of focus from science to colonization. Then men win hands down.

Sunday, November 06, 2005

Geocentrism is not geocentric
(The Great Divide: Methodology)

Back in March, when I last wrote on this subject we saw that the Pre-SR astronomers wanted to predict the positions of the planets in the sky. But how did they go about it? Post-SR astronomers do it by using the tools of calculus, i.e. they write down the appropriate differential equations, apply some initial conditions, and integrate the combined system. In practice, given the uncertainties inherent in observations, rather than only one initial position and velocity, a large number of past observed positions are used to constrain the solutions of those equations so that the error in their post-diction of those observations is the minimum possible. Then things are integrated forward to get predictions of future positions, in three dimensions. For the state of the art visit the Solar System Dynamics pages at JPL. The underlying assumptions are, for the most part, Newton's Three Laws of motion, and his Law of Gravitation---General Relativity is required for Mercury's orbit. Comets suffer from additional forces due to their losing mass---but the principle is the same: Sum up all the forces acting on a body and this is its acceleration. Integrate the acceleration to get the velocity, and the velocity to get the position.

Pre-SR astronomers worked from a different set of assumptions. In their view, the planets moved exclusively on circles which turned at constant angular rates. This restriction posed something of a difficulty since the observed planets don't move at constant rates in the sky. The superior planets (Mars, Jupiter, and Saturn) even, at times near opposition, move backwards on the sky, which is hard to explain with constantly rotating circles. So, the Pre-SR astronomers had to employ a variety of schemes to get variable apparent motions from their constant true motions. Epicycles were small circles containing the planet and were carried around but the large circle. The large circles, deferents, themselves were placed off center (eccentric) with respect to the Earth so that their apparent motions would be faster when they were closer to the Earth and slower when they were more distant. This works even better when the planet moves at a constant speed not as seen from the center, but from the equant point placed symmetrically on the opposite side of the circle's centre from the Earth. This last device, however, represents a step away from a uniformly rotating circle and proved controversial for that reason.

What is striking about all this is just how non-geocentric this geocentric model really is. The Earth is contained within the region where the planet (including the Sun) travelled, but it is not at the centre of any of the circles of motion. In the case of the Sun, the centre of the deferent is offset by 1/24th of its radius. Further, different eccentricities are needed for different planets, so the deferents don't have a common centre about a fictitious point, never mind the Earth. About the only thing that is geocentric is the spherical annulus containing all this apparatus. All planets have their closest and furthest points from the Earth (perigee and apogee). The apparatus for a planet necessarily lies between a pair geocentric spheres with the radii of perigee and apogee for that planet. The motion of the planet itself is not geocentric at all.

In this period all the calculations of planetary motion were expressed in terms of angles on circles of relative sizes, since no one knew how far away any of the planets were. There were some inaccurate estimates as to the relative distances of the Moon and Sun, but that was about as far as things went. Even the order of the planets was a matter of conjecture. Indeed, this subject was about the only thing Ptolemy didn't settle in the Almagest. He did produce an ordering in a later work called Planetary Hypotheses, but there wasn't any observational evidence to support it. (Quite frankly, the whole subject was of secondary importance since it had no practical affect on their objectives.) Once an order has been chosen, and on the assumption that the spherical annuli were tightly nested, the relative distances of the planets, and the stars, immediately follow. But these distances are entirely arbitrary. Consequently, anyone wanting to resurrect a geocentric model of this type has his work cut out for him.

NASA can send spacecraft around the solar system on a complicated trajectories shaped by passages by several other planets along the way. Ptolomaic astronomers would be entirely incapable of doing this successfully in the event they had been able to even conceive of it. Let the modern geocentric astronomer produce a physical model able to replicate this feat, and we'll have something to talk about.