Help with Open Uni qu??

[TAC]

LOLOL, gotta be worth a try :)

"A classical Cepheid variable in a distant galaxy has the same period as a classical Cepheid variable known (from trigonometric parallax) to be at a distance of 3300 pc. The flux density F received from the more distant Cepheid id 5.0 x 10^5 times less than that of the near Cepheid. Calculate the distance to the distant galaxy in parsecs"

........Anyone doing S281???? I haven't got a clue! Any hints? NB: Assignment is due in on Fri :eek:

[SteveCarter200]

42.871

[SteveCarter200]

Jesus!! You may as well have written that in Klingon.:D:D:D

[Billy]

It's (5.0 x 10^5) x whatever the flux-density gradient per parsec is.

Isn't it? :confused:

Can you tell I'm guessing yet? :)

I know Cepheid variables are used for measuring distance, so it's pretty fundamental stuff. :(

I'm not doing S281, I just watch strange things on telly a lot....:rolleyes:

[TAC]

LOLOL, I haven't a clue! I'm hoping that one of u guys can poiint me in the right direction :)

[Billy]

In that case...

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...you're fecked. :(


:D:D:D

[Billy]

I've had a dig around and apparently it 1650000000 pc (1.65 x 10^9). It's the difference in flux density (or brightness) times the known star's distance. It's a linear relationship, I think.

I found this (http://zebu.uoregon.edu/~js/ast123/lectures/lec14.html) if it's any use....


Must get a life! :rolleyes:

[Goblinslayer]

If

L=4pi(D)^2*S

L= Luminosity
D=Distance
S=Flux Density

and as the period is directly related to it's luminosity

then
4pi(3300)^2*S=4pi(D)^2*(S/5*10^5)
(3300)^2*S=D^2*(S/5*10^5)
(5*10^5)*(3300)^2*S=D^2*(S)
(5*10^5)*(3300)^2=D^2
(5*10^5)*(10890000)=D^2
5.445*10^12=D^2

so D=2333542

There or thereabouts.

Although I could be wrong.......

:rolleyes:

[RichSeal]

Originally posted by Goblinslayer
If

L=4pi(D)^2*S

L= Luminosity
D=Distance
S=Flux Density

and as the period is directly related to it's luminosity

then
4pi(3300)^2*S=4pi(D)^2*(S/5*10^5)
(3300)^2*S=D^2*(S/5*10^5)
(5*10^5)*(3300)^2*S=D^2*(S)
(5*10^5)*(3300)^2=D^2
(5*10^5)*(10890000)=D^2
5.445*10^12=D^2

so D=2333542

There or thereabouts.

Although I could be wrong.......

:rolleyes:

:eek: :eek: :eek: :eek: :eek: I thought the answer was yellow!! Doh! :p :D

[Goblinslayer]

Ah as the luminosity and flux density are calculated from the spectrum colours and even the velocity (which isn't taken into account in this question), then yellow could be an equally valid answer...

God I must be bored :o

So....

Distance and velocity are related in cosmology, the further something is away from us the faster it is going, and as the way we see this is the positions of the elemental absorbtion in the spectrum (doppler shift) we can take from your "yellow" answer that you mean a shift in the absorbtion lines to the yellow part of the spectrum, which can be translated into velocity and therefore distance, so I agree, yellow, if in a somewhat roundabout way, is equally valid, if leading to a somewhat large variance in the actual distance.....

Could also be a more mauvey shade of torpe....
;)

[siranui]

I think the answer is.....




'Lemon sorbet.'

Or it might be 'Tuesday next' as a second guess.

[XEB]

is it "get a bigger telescope"

[shadowninja]

Hmm I reckon you need a flux capacitor. :D

[AL]

more than a tank of petrol in anyones 200:D

[TAC]

Thanks guys :D:D

And, Billy, that was a well-interesting link you posted - thanks for that, matey :)

If the relationship's linear then I can probably bluff my way through, but I'll copy down Goblinslayer's wokring just in case I can't manage it myself ;)

I "only" have that question and a 500-word essay (an introduction to cosmology & discussion of the hot Big Bang theory) to finish, then I'm done :) The essay is proving problematical because I've done 800 words already and not even got on to the Big Bang stuff :eek: :rolleyes:

Never mind, I'll take a long lunch tomorrow to finish it off, then it's a nice cruise up to oxford to hand-deliver it to my tutor :D:cool:

[Leon]

Originally posted by TAC
hot Big Bang theory

doesn't that one start with a dozen roses and a bottle of Moet?

[shadowninja]

TAC, I certainly look forward to you starting that maths degree... don't expect any more useful answers either :D

[SteveCarter200]

Big Bang theory? Easy.

"The universe was one big lump of stuff ages ago and then it exploded making smaller lumps of stuff, much like putting dynamite inside a melon"

See?:D

[TAC]

Yep, Steve, that's pretty much it, in a nutshell :D

All done and dusted now, thanks guys :D Did the run to Oxford n back in 1½ hours :cool: Now it's sit back & relax until the exam in October :)