Let's discuss Mathematics

[PlutonianEmpire]

I read a space article, although I am unsure if I got the math right:

In fact, small, terrestrial planets can form around stars nearly four times more metal-poor than our own sun, researchers said.

When I read that, I immediately thought of: 100% / 4 = 25%. Is this correct? If not, what is the correct way to visualize that in a math equation?

[Atticus]

The wording is in my opinion a little poor, but that's the only way to understand it, I think.

Another way could have been 100% - (4*100%)=-300%, but that won't do, since a star can't have a negative amount of metal.

"Metal poor" doesn't make it any better: they are speaking of how much metal there is, so if there's less it, the star is more metal poor. It leads to similar misunderstandings which made me spoil the food in the fridge when I tried to make it colder by turning the switch to smaller number. Yes, I'm stupid.

This is more about language than maths, although teachers and such have to struggle with these kinds of things all the time. I'm not a native English speaker, so don't take my word as authoritative.

[peter grimes]

I think in this case they might be using a metric like 'what fraction of the mass of the star is metal', and taking a fourth of that?

Or perhaps it's a parts-per-million?

Who know. Yet another example of terrible science writing.

[nc-1701]

I'm pretty it means 4 times less metal, so if for example the sun was 4% metal the star they are referring to would be 1% metal. The wording isn't great, but no other interpretations make sense.

[PlutonianEmpire]

That equation smack in the middle? (The one with the word "eccentricity.") How do I punch that in into Windows 7 calculator?

[dutchfire]

Why use windows calculator? Why not use for example Wolfram Alpha?

[Mise]

even google... https://www.google.co.uk/#q=sqrt(1-0.4%5E2)

[PlutonianEmpire]

Originally Posted by dutchfire

Why use windows calculator? Why not use for example Wolfram Alpha?

Because a) my internet access is NOT 24/7, and b) wolfram requires you to pay to use some features, and I am VEHEMENTLY opposed to paywalls.

[Lord Olleus]

There is no part of Classical Mechanics I hated studying more than elliptical orbits and their geometry. I am pretty sure it is the most vile thing ever invented. Too many possible lines to draw which have too many names and too many relations between them. I can feel my blood boiling already.

[PlutonianEmpire]

Originally Posted by Lord Olleus

There is no part of Classical Mechanics I hated studying more than elliptical orbits and their geometry. I am pretty sure it is the most vile thing ever invented. Too many possible lines to draw which have too many names and too many relations between them. I can feel my blood boiling already.

You'll have to take it up with God then.

[Kaiserguard]

Does someone here know of a good (re)introductionary text on mathematics? While I used to study Computer Science, I've changed studies since, and my math skills have grown rusty somewhat.

[dutchfire]

Any specific subjects you want to learn about?

[peter grimes]

I'm not a math guy, but I've been reading this:
Mathematics for the Non-Mathematician by Morris Kline
http://books.google.com/books/about/...d=f-e0bro-0FUC

I've found it to be an excellent guide for a second time around. I never pursued math beyond pre-calc (big regrets), and this book is a helpful way to re-learn or just re-acquaint myself with the fundamentals.

I'd love to hear some titles from people more knowledgeable.

[sanabas]

http://mathworld.wolfram.com/ is a website, not a textbook, but is still a pretty good resource.

http://www.amazon.com/Calculus-Compl.../dp/0201828235 is a good basic calculus text.

[Kaiserguard]

Originally Posted by sanabas

http://www.amazon.com/Calculus-Compl.../dp/0201828235 is a good basic calculus text.

Interestingly, I went to my university's mathematics department not too long ago, and read exactly the book you suggested in the quote, except I wasn't aware of the fact you had.

Thanks anyway!

[sanabas]

You weren't a fan of it?

[Jouzou]

Originally Posted by Kaiserguard

Does someone here know of a good (re)introductionary text on mathematics? While I used to study Computer Science, I've changed studies since, and my math skills have grown rusty somewhat.

I recently discovered Khan Academy. It's video lessons instead of text, but it's all free. I have watched some of them and I think they're pretty good.

[PlutonianEmpire]

I was reading up on Roche Lobes on Wiki, and when I looked at the formulas, I got confused by the syntax/format, so had my father bring me up to speed, and while helping me remember the important stuff, he noticed an apparent peculiarity, but didn't know if it was a typo or something else.

The mass ratio is indicated by this graphic:

(0.3 and 20)

but the graphic above it shows different numbers:

(0.38 and 0.2)

Were they supposed to be the same numbers, or were we misunderstanding the formulas?

[Mise]

No, you're misunderstanding the formulas. The r1/A = ... formula gives an approximation for the radius of the sphere when the mass ratio is between 0.3 and 20. That's what it says in the wikipedia article. There are other approximations listed in the wikipedia article, which you can use for mass ratios outside of this range.

[PlutonianEmpire]

Originally Posted by Mise

No, you're misunderstanding the formulas. The r1/A = ... formula gives an approximation for the radius of the sphere when the mass ratio is between 0.3 and 20. That's what it says in the wikipedia article. There are other approximations listed in the wikipedia article, which you can use for mass ratios outside of this range.

Ok, that makes a little bit more sense, although I am unsure as to what the 0.3 and 20 represent? The mass of the bodies given a specified unit (Msun, Mearth, etc)?