Quote:
|
Originally Posted by [url=http://www.badastronomy.com/phpBB/viewtopic.php?p=154237#154237
JohnD[/url]]I'm beginning to clutch at straws to answer your point about the equal bulges
|
Yes, and that is why I would disagree with
your comment that "This way of thinking about tides is more useful". Rather, I think it adds unnecessary complication.
Quote:
|
but I suspect it is to do with equal radial velocity. Although a point on the Earth's surface away from the Moon is travelling faster than a point on the 'near' side, it is also further away from the CoM.
|
The points are traveling at the same velocity (velocity, not speed) and their orbit is not centered at the CoM, but offset somewhat. They are at the same distance from the centers of their respective orbits.
Quote:
|
Originally Posted by [url=http://www.badastronomy.com/phpBB/viewtopic.php?p=154487#154487
Eroica[/url]]I've been thinking more about your tidal theory, JohnD, and I think it's largely correct as far as the solar tides are concerned but requires some modification to explain lunar tides. The point I want to make in this post is that the rotation of the Earth about its axis is largely irrelevant to the question of solar tides, but is vitally important in explaining lunar tides.
|
If you are doing things right, there should be no real difference between the solar case and the lunar case.
Quote:
|
Solar Tides: Let's ignore the Moon for the moment and start with solar tides. In his book the BA says that he relied heavily on Mikolaj Sawicki's Myths About Gravity and Tides.
|
Interesting! Sawicki posted
his comments about gravity in March, but I don't remember seeing him referenced in the book before. Perhaps it was added after?
Quote:
|
Sawicki's explanation of solar tides, you'll be happy to know, is exactly the one you gave.
|
Sawicki's post has a link to an online version of that paper. JohnD
characterizes his (JohnD's) view as the "different orbit" explanation--but I don't see any aspect of that in Sawicki's paper.
Quote:
The Earth's centre of mass (CoM) is in free-fall about the barycentre of the Earth-Sun system (which is located near the centre of the Sun), orbiting at 108,000 kph, just the right speed to stay in orbit.
The point on the Earth's surface closest to the Sun is also travelling about the Earth-Sun barycentre at this speed
|
No, it follows a similar path, but it is not centered on the barycenter. It is centered on a point that is offset from the barycenter by the radius of the Earth. Of course, when the Earth completes a half revolution about the Sun, the point will no longer be the closest to the Sun, but will be the farthest.
Quote:
|
Unfortunately he does not go into any greater detail than this. I contend that the lunar tidal situation differs from the solar one in two crucial ways:
|
That's the problem with that sort of analysis.
Quote:
There are two things about this explanation which worry me, though:
[1] Neither Sawicki nor the BA mention any of this in their explanations. As they're the experts and I'm the plodder, I suspect that I have made some fundamental error in all of this.
|
They don't mention it because they are using a different approach to the problem. I contend, one that is much simpler to understand and easier to use.