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That should be from 6.7 miles/second to 47.0 miles/second.
This takes into account:
- energy gained falling into the Earth's gravity
- speed of the Earth's orbit compared to that of the rock's orbit
- the fact that some comets orbit backwards.
- the fact that some metoriods come from near Earth sources.

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What's a mile?

Translating into units I understand, your range runs from 10.78 km/sec to 75.6 km/sec. I guess those are close enough to my source to be acceptable. My source (Meteors and Meteorites: Origins and Observations by Martin Beech) gives a range of 11.2 - 72.8 km/s.

Beech's explanation of the velocity range is as follows:

Your explanation is close enough to that, I think! Take it away, antoniseb.

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I vaguely recall that the estimate was about a trillion objects based on the rate of comets with large inclinations.

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Lighten up! This is a stellar board! Author: duh.

"The Sun, with all the planets revolving around it, and depending on it, can still ripen a bunch of grapes as though it had nothing else in the universe to do..." Author: Galileo supposedly.

The most quoted mass for the Oort cloud is about 40 earth masses, estimated from the assumption that Halley's comet is a typical long period comet and the number of long period comets entering the solar system is (a) constant and (b) representative of the total population of the Oort cloud.

The upper limit to the mass is around that of Jupiter, the lower limit is 1-2 times the mass of the earth.

As a counter-question, was this the mass of the whole cometary halo outside the Edgworth-Kuiper belt or just the circularly symmetrical outer part? ie: what is the mass of the Hill's Cloud?

That's good enough for me Ozark1. Your turn to ask a question.

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I am not sure how to continue. Shall we treat Ozark1's counter question as the active question at the moment, or is he supposed to ask a new one?

Maybe it's easiest to keep the question we already have:

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A hill is heavier than a cloud but must be climbed to reach a cloud. [no charge since it is feeble humor.]

I could be wrong, as usual, but I believe most of the mass of the Oort is contained within its inner region which is designated as the Hills Cloud. I'll guess 60% to 75% of the Oort Cloud mass is located in this "cloud" (though it is more of a belt in shape, IIRC).

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Lighten up! This is a stellar board! Author: duh.

"The Sun, with all the planets revolving around it, and depending on it, can still ripen a bunch of grapes as though it had nothing else in the universe to do..." Author: Galileo supposedly.

Sorry to take so long to reply.

I'd like to ask a better question.

Why was an Italian alchemist who was burned at the stake in renaissance Rome, not born in the 12th Century?

Because he was born in 1548 (in Nola, Campania).

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I haven't heard of Giordano Bruno as an alchemist - he was delivered into the hands of Roman justice specifically because he was not able to teach his Venetian sponsor the magic tricks that were expected of him.

I think that the designation "alchemist" would be altogether too dismissive of someone who was a fervent supporter of a Copernican astronomy and who stands at the beginning of the philosophy that was to produce the enlightenment.

By the way, burning at the stake did not start before the 13th century. It had it's heyday in the 15-17th and did not end before the middle of the 18th century (Wikipedia says).

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I doubt alchemy was the cause of the problems, either. There was a 12th century alchemist who was hung for defrauding others, IIRC.

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Lighten up! This is a stellar board! Author: duh.

"The Sun, with all the planets revolving around it, and depending on it, can still ripen a bunch of grapes as though it had nothing else in the universe to do..." Author: Galileo supposedly.

Yes, you're nearly there...right person. But this isn't the biography channel - Why wasn't he born in 1178? And OK I don't really mean "born".

Has this something to do with that crater on the Moon named after Giordano Bruno, which some people think English monks in 1178 witnessed being created?

[Edit: Wikipedia - Yep, looks like it!]

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Yes, just the Why Not bit to go now.

Ah, nice - because that would have triggered a week-long meteor shower, but didn't (NASA writes. But of course we know they're just trying to hide the Truth )

But, please, please, don't call the crater's namesake an alchimist. He did better than that, lots better!

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Exactly.

I used the description - alchemist - as intended ie: scientist. As a chartered chemist myself, the description sits well.

Your turn

Other famous alchemists

Albertus Magnus -discovered Arsenic
Thomas Aquinas
Paracelus - inventor of al-kohl
Isaac Newton

The big problems with alchemy are caused by the minor branch looking to transmute lead into gold. The guy who started that nonsense was an Arab called Geber. He is immortalised in the word Gibberish.

Excellent point, thanks - although I think philosopher is still the more apt desription even if we see the designation "alchimist" in a more positive light.

Regarding the next question, it'll take moment. I have to survive my lung doctor exam tomorrow...

See ya'll!

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I have the impression that it was started long before Geber. Do you have any source saying *he* started it?

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