Ah, so I found it. rho_crit = (pi G H_0^2)^-1 *3/8, around 4.7 10^-30 g/cub.cm. That would be 4.7 * 10^-26 g/cubic metre

The mass of a hydrogen atom is 1.7 * 10^-24 g.

So "1 Hxdrogen atom per cubic metre" would be around 36 times too much.

Is that it? If not please solve the question. Shovelling around formulae is not one of my strrengths. :-? :-? :-?

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Non sunt multiplicanda entia praeter necessitatem.

I'm just totally lost on these last couple of pages...too much thinking and formulae. :P

with regards

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Sign up to sue the Sun

Well, champion munch, I think we have killed most of the outstanding questions:

The litographer/atronoomer - solved (=D> =D> =D> melusine!)
The SN/NS/BH mass question - solved.
The neutrino/Photon question - solved, by way of visitng the BA website.
The critical density thing - solved or at least exhausted
The pulsation variable that changes its radius by >60 % - several attempts at a solution, jury still out.

However, Tobin Dax's seccond question is still open:
So as I see it, melusine, minbari and Robert Anderson could all have a go (maybe only one of them, to avoid more confusion). If nothing appears within the next three hours, I''ll think of something having tried to tackle the critical density and pulsation variable questions. As for the Roche lobe, not the foggiest idea. :-k Would you maybe like to solve, Tobin, Dax?

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Non sunt multiplicanda entia praeter necessitatem.

My Roche Lobe question:
I know someone can answer this. Minbari was correct when he said that the mass ratio helped to determine the *relative* sizes of the Roche Lobes. So, what other quantity from the binary system is needed to determine that actual sizes of the Roche Lobe? (Would it help if I asked what the maximum limit is on the sum of the radii of both Roche lobes?)

The seperation ... units of your choice.

Ding Ding Ding- we have a winner. Yup, the orbital separation between the stars will give you the actual, physical sizes of the Roche lobes. (I didn't explicitly mention a circular orbit assumption, did I. #-o That's what I get for this becoming second nature.)

So now, I think we're still waiting for confirmation on answers to the critical density question and the variable star question, right?

Dang nice work

I avoided answering

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I agree (and TobinDax, naming stars is about astronomy, too :wink: ).

My question, simple enough:

What was the name of the lunar rock brought back by Apollo 15 and how old is it approximated to be?

edit typo

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Sunset

Die Sonne scheidet hinter dem Gebirge. In alle Täler steigt der Abend nieder
mit seinen Schatten, die voll Kühlung sind.

"Naming stars" is precisely what "Astro-nomy" means. (I hope no one wanted to use that as a question.)
[/hijack]

Nomos in Greek means law.

I repeat my question:

What was the name of the lunar rock brought back by Apollo 15 and how old is it approximated to be?

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Sunset

Die Sonne scheidet hinter dem Gebirge. In alle Täler steigt der Abend nieder
mit seinen Schatten, die voll Kühlung sind.

The "Genesis rock" (dated at 4Byr.s)?

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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.

[quote="George"]Sounds good enough to me...I have it at ~4.15m, 0.5 billion years younger than the generally accepted moon age, but what's a few years either way? :wink:

Your turn for a question.

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Sunset

Die Sonne scheidet hinter dem Gebirge. In alle Täler steigt der Abend nieder
mit seinen Schatten, die voll Kühlung sind.

Ok the answer is
Betelgeux -
"the giant's shoulder" of the Orion constellation
'The Armpit of the Central One'

Other Names
===========
Alpha Orionis
Alpha Orion
Betelguese
Betelgeus
HR2061

Some Info
===========
Harvard Revised (HR) number: 2061
Location: DEC +07 24 25, RA 05 55 10.3
Distance: 427 ± 92 ly
Spectral type: M1-2Ia-Iab
Apparent magnitude: 0.1-0.9
Color index (B-V): 1.85

Also known is various other names: Betelguex, Betelgueze, Beteiguex, or in Arabic, Al Mankib, meaning the shoulder. These names are related to the Arabic phrase Ibt al Jauzah, meaning 'The Armpit of the Central One'. Betelguese is a red super giant with a diameter about 650 times that of the Sun, large enough to swallow up the whole orbit of the Earth if it is placed at the position of the Sun.

It is a vriable star with no set period. During pulsation, the diameter can vary as much as 60%.

Tid Bit
=======
Betelguese is the first star to be directly imaged by a telescope.

Betelgeux reveals a huge ultraviolet atmosphere with a mysterious hot spot on the stellar's surface.

The bright spot is ten times the diameter of the Earth, with a temperature of 2000 K hotter than the surface of the star. (Credit: HST, A. Dupree (Harvard-Smithsonian CfA), R. Gilliland (STScI), NASA and ESA)

Betelguese is believed to have arrived the end of its main sequence lifetime in the stellar evolution. The hydrogen fuel at its core is depleted and the star contracts. This results in hydrogen burning that ignites at the outer shell of its core, cause the star to expand.

http://www.betelgeux.com/hubble.htm

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Ok. While on the subject....

What surprising color were the crystals Schmidt kicked-up that showed vulcanism (dated about 3.4 Byrs. old).


[BTW, Eroica, your Weins Law use to derive $6.74 was off by only 1 penny. Using Plancks equation for 4300K puts it at the actual price for my one and only astronomy text book in college at $6.75. (It cut me deep they would use an old textbook for introductory astronomy with only b&w pictures. I dropped the course. Of course, the price was right so I saved the book. ) Also, I am quite surprised the simple Wein's Law equation works so well when compared to the hairy Planck equation.]

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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.

How are you using Planck's equation to get the maximum? Just plotting it out, calculating it?

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I did a spreadsheet using Plancks equation for each wavelength increment for the Sun's Color experiment. I set it up to handle any temperature and locate the peak wavelength. In comparing it to Wein's peak, it seems to be right about .17% variation (tested from 1000K to 1,000,000K). Does it strike you odd that something so simple (Wein's law) would work this way with something so messy as Plancks BB equation? I understand, but could be wrong, that Wein's Law existed before Planck's BB equation.

Don't you want to guess the color of the lunar volcanic material that is the same color of the drink used during Apollo (so I can go to bed and not stall the quiz )?

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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.

Great, everyone is outside wathching the impact. :-?

Dang, if someone would just pick up on that last hint about the color of the drink made famous during Apollo (not to mention a somewhat less subtle embedded hint), then I wouldn't have to hang ....

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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.

Its a bit rude isn't it

Looks like P

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