Okay, Phil, I just couldn't resist.

I got my copy of the book today -- Mr. Postman actually put it in my hands at the front door. I've read the first five chapters, plus selections from other parts of the book.

I'm enjoying it, but of course, as a regular here and at the web site, there's not much in it that I didn't already know. So I've been able to do a bit of "meta-reading", thinking about the style and tone, and the like.

I think the style and tone are great, by the way, very friendly and conversational. Most of the arguments you make are good common-sense approaches, put in terms that the average Joe or Jane can understand. Well done!

But I do have a couple small quibbles, things I think your proofers and editors missed. I'll mention them here at the risk of offending your most loyal followers...

1. Page 16: "...the yolk is really the embryo of the chicken and shouldn't get jostled too much."

Bad biology! The yolk (deutoplasm) isn't the embryo. In fact, commercial chicken eggs are unfertilized and have no embryos (or at most, very tiny ones). The yolk is a sac of rich nutrients that are there to feed the embryo (if there was one).

Page 250-251: "The light that left M31... started its journey when Australopithecus Africanus was the most highly evolved creature on the planet."

Bad evolution! Australopithecus may have been the closest human ancestor (if indeed it was an ancestor of ours), but that doesn't make it the "most highly evolved species", or even the brainiest at the time.

Evolution isn't directed; humans are not the ultimate goal of evolution, just one little twig on a vast branching bush, with each branch's history highly contingent on the environment and even natural catastrophes like volcanism and meteorite impacts. It's incorrect to call the primates "more highly evolved" than, say, cockroaches or T. Rex.

Quibbles? Maybe... but in a book dedicated to correcting misconceptions about science, we shouldn't be echoing or introducing other misconceptions, even if they are outside our own field of expertise. Right, BA?

I'll bet your eagle-eyed readers will find more of these. Perhaps, if the book is a hit, you'll have an opportunity to correct these things in the second edition.

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<font size=-1>[ This Message was edited by: Donnie B. on 2002-03-02 17:51 ]</font>

First, thanks for the kind words about the style. I appreciate that!

I'll grant you the yolk line. Nuts. I even knew that, but got it wrong.

I think I still like the phrase "highly evolved". As you say, there is no goal in evolution, but in my opinion it's better to be adaptive than to be restrictively evolved to fit one niche. If that niche were to disappear, so would the species. So in that case, "more highly evolved" has a meaning.

The problem with the phrase is that it is a bit prejudiced. I'll grant that too! If I get a chance to fix anything, I'll change that line to "most highly evolved primate" which would be more technically correct.

Thanks!

Oops, I think I found another, and possibly two (sorry, BA)...

Page 70: "The time between high and low tides changes every day by about half an hour."

Shouldn't this be "fifteen minutes"?

The time of the "same" high tide advances by about an hour a day. With two tides per day, the time between subsequent high tides advances about a half hour. So the time between high and low tide advances by about 15 minutes, relative to when it would occur with a stationary moon.

Or did this old salt misunderstand?

By the way, has anyone investigated whether the fact that we (typically) measure time in two daily 12-hour cycles, rather than one 24-hour cycle, has anything to do with the fact that there are two tidal cycles per day? Many early civilizations were coastal...

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The other possible "oopsie" I'm not so sure about. On page 75, you discuss tidal exchanges of matter between binary stars. You describe the explosion of such a matter accumulation as a supernova. Last time I knew, such an outburst was called a nova, not a supernova; the latter has a totally different mechanism (gravitational collapse of a massive star that has exhausted its nuclear fuel).

I'm less certain of this one, as technical terms sometimes get redefined, and I'm not an astronomy professional.

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Still enjoying the book, though. I stumbled a little when you introduced the barycenter to help explain the double tides. Other writers have used different approaches to this crucial point, sometimes by looking at the Earth's tides on the Moon (where the barycenter can be ignored, being pretty close to the Earth's center from the Moon's perspective). That allows the idea of the oppositely-directed tidal force to be introduced first (usually by showing that the outer and inner edges are trying to be in "different orbits" than the Moon's center); then the barycenter can be invoked to show why the Earth has the same effect.

It is a tricky concept, no matter how you describe it. I imagine you'll lose a few of the less-savvy readers there. But they can always pick up a tide table and see for themselves...

There are several types of supernovae. The gravitational collapse of a massive star that has exhausted its nuclear fuel is known as a type II supernova. When the accretion of matter on the white dwarf of a binary system results in a supernova, it is known as a type Ia supernova. These are considered to be "standard candles" that can be used to determine the distance to galaxies, since they always occur when the mass of the white dwarf reaches a certain point.

__________________
Any day you wake up on "the right side of the dirt" is a good day.

T. Anderson

I don't have my copy yet, so I may have lost some of the context, but what does that mean anyway? "The time between high and low tides" changes? Is that the length of the interval between the two tides, or is it the actual time of the particular tide? It seems to refer to the former, but I would have thought it would be the latter.

Our time convention seems to be derived from the Sumerians, via the Egyptians, but tides in the Mediterranean area are small, some say negligible [1], [2], [3], [4].

The chapter describes how tides work, as you have inferred. It begins with simple ideas (tides are caused by the moon's gravity), and proceeds to explain why there are two high tides per day, not just one.

This particular paragraph adds the next complication. If the moon were stationary, the tides would occur at the same time each day (say, highs at noon and midnight, lows at 0600 and 1800). It's the moon's orbital motion that causes subsequent tides to be stretched to 12.5 hour spacings rather than 12 hour. (Numbers approximate.)

So my point was, the time from high tide to the subsequent low tide is 6:15, rather than 6:00 as would be expected without taking the moon's orbital motion into account. The text seems to be trying to say that this interval is 6:30.

Of course, the wording of the text is somewhat ambiguous, and can be read to mean that each day the interval from high to low tide grows by 30 minutes, e.g. if today's high-to-low interval is 6 hours, tomorrow's will be 6:30, and the next day's 7:00. I'm sure this is not what Phil intended, and not what I'm criticizing. Although if you fix the error, BA, you might want to reword it to avoid the ambiguity.

Perhaps something like, "So the time from one high tide to the next is about a half-hour longer than you'd expect if the moon weren't moving; this makes the time of high and low tide change from day to day."

Well, I might still argue the question of what we mean by "highly evolved". However, since this is a peripheral topic, and just an illustration, I'd be happy with your proposed wording.

Okay, it seems my terminology is out of date. Correctly or incorrectly, I learned (way too many years ago) to call this phenomenon a "nova". But if it's properly known as a "Type Ia supernova", I withdraw my tentative criticism.

As I understand it, both terms are used. There's a standard nova, where the accreting star undergoes a big explosion, but afterwards sticks around to continue the process again. Then there's the Supernova, where the star accretes so much that it literally blows itself up completely.

Somebody correct me if I'm wrong here (or confirm it if I'm right). [img]/phpBB/images/smiles/icon_smile.gif[/img]

__________________
...And that, my liege, is how we know the Earth to be banana-shaped. --Sir Bedevere

Hi, BA,

You haven't responded to my issue of the timing of the tides. Was this a catch, or not?

I have another question about a statement in Chapter 19. On page 192, when discussing why young-Earth creationist DeYoung is wrong about the age of the moon, you write,

First of all, when a satellite (artificial or otherwise) slows in its orbit, it gets closer to the Earth, not further away. If that weren't true, retro-rockets would boost you to a higher orbit instead of causing reentry!

Furthermore, this seems to directly contradict what you say earlier, in the chapter on tides (which I believe to be correct): that the moon's orbit gets higher when its energy is increased by the tidal tug of the ocean bulges (thus slowing the Earth's rotation rate, and boosting the Moon further away from us).

Furtherfurthermore, you're trying to argue that the moon took longer to get out to where it is, yet you're saying that there's a force pushing it outward that DeYoung didn't account for. So you're making the moon even younger than he is!

It seems to me that, if you are correct that the effect of friction takes energy out of the Moon's orbit, then this effect counteracts the "boosting" force of the tidal bulge, slowing the rate of recession. Therefore the moon took longer to get out to where it is than a first-order calculation would suggest.

Correct?

As tidal drag slows the Earth's rotation, the Earth loses rotational energy. By conservation of momentum, that energy has to go somewhere. It goes into increasing the orbital energy of the Moon. This causes the Moon's orbital distance to increase. As the Moon's orbital distance increases, its orbital speed decreases.

__________________
Any day you wake up on "the right side of the dirt" is a good day.

T. Anderson

Hmmm, yes, I need to reread what I wrote. The Earth loses rotational energy, giving it to the Moon's orbital energy. This makes it moves out, which is why it moves more slowly. I had my effects switched in order, making it look like the cart was before the horse.

Abotu tide timing: High tide to subsequent high tide should be half of the 25 hour tidal period, so high to low is half of that, or fifteen minutes. Bleah. Now I'll need to check to make sure all those numbers are right.

I hate things like that.

OK, I'm just glad I wasn't totally confused.

Sorry if I spoiled your afternoon.

BTW I've just about finished the book... so you probably won't be getting any more of these from this direction.

Sorry, Donnie B., but I'm going to have to steal this one from you. I just got up to page 70 (I'm a slow reader!).

First, the quotation is wrong, at least in my copy, which reads "The time of high and low tides changes every day by about a half hour."

The tides are very complicated (some places only have one high tide a day) but as far as the timing is concerned, I think that the point is that the tide times advance each day in a regular fashion, in the ideal case. If you experience a high tide at 6:00am, then the next morning, the high tide will be at around an hour later, closer to 7:00am.

So, it's not a half-hour, nor fifteen minutes--it's an hour.

I think if you look at the whole paragraph preceding that sentence in the book, this is clearer:

"... the Moon rises about an hour later every day, because as the Earth spins, the Moon is also orbiting the Earth. The Moon moves during that day, so we have to spin a little bit extra every day to catch up to it. So instead of there being 24 hours bnetween successive moonrises, there are actually about 25. That means there is a little extra time between high tides; half of that 25 hours, or 12.5 hours."

If you have a high tide at 1:00 a.m., the next day that morning high tide will be 2:00 a.m. That in turn means the second high tide of the day will be 12 hours + half that difference after the first one, or 1:30 p.m. on the first day and 2:30 p.m. the second.

I edited a dumb typo, changing the word "afternoon" to "morning"

<font size=-1>[ This Message was edited by: The Bad Astronomer on 2002-03-07 11:34 ]</font>

Yes, in those cases (the link I set previously would show tides at Nawiliwili, Hawaii, that only have one high tide a day) the times of the high tides advance by a half hour if you ignore the "AM" and "PM" designations. 1:00am, 1:30pm, 2:00am, 2:30pm.

So, you can say "The time of high and low tides changes every half day by about a half hour," or you can say "The time of high and low tides changes every day by about an hour."

Okay, I'll buy that. What led me astray was that you started out talking about high tides exclusively, then suddenly switched to "high and low tides", which made me think you meant the interval between high tide and its subsequent low tide.

And I know tides are complicated, especially way up at the north end of Naragansett Bay, where I keep my boat. [img]/phpBB/images/smiles/icon_smile.gif[/img]