# Astrophysics questions help

WatchPage 1 of 1

Go to first unread

Skip to page:

I'm stuck on question c can someone please help me out I don't know how to do it because that all have different magnitudes so I can't equal them which is an example in the textbook. I did A and B but C has thrown me off

Three stars X, Y and Z have surface temperatures of 4000 K, 8000 K and 20 000 K respectively and absolute magnitude −2, +4 and +10 respectively

A) List the stars in order of increasing

B) state the evolutionary stage of each star, giving your reason for each

C) Calculate the ratio of the diameter of X and of Y relative to Z.

Three stars X, Y and Z have surface temperatures of 4000 K, 8000 K and 20 000 K respectively and absolute magnitude −2, +4 and +10 respectively

A) List the stars in order of increasing

B) state the evolutionary stage of each star, giving your reason for each

C) Calculate the ratio of the diameter of X and of Y relative to Z.

0

reply

Report

#2

(Original post by

I'm stuck on question c can someone please help me out I don't know how to do it because that all have different magnitudes so I can't equal them which is an example in the textbook. I did A and B but C has thrown me off

Three stars X, Y and Z have surface temperatures of 4000 K, 8000 K and 20 000 K respectively and absolute magnitude −2, +4 and +10 respectively

B) state the evolutionary stage of each star, giving your reason for each

C) Calculate the ratio of the diameter of X and of Y relative to Z.

**221loki**)I'm stuck on question c can someone please help me out I don't know how to do it because that all have different magnitudes so I can't equal them which is an example in the textbook. I did A and B but C has thrown me off

Three stars X, Y and Z have surface temperatures of 4000 K, 8000 K and 20 000 K respectively and absolute magnitude −2, +4 and +10 respectively

**A) List the stars in order of increasing**B) state the evolutionary stage of each star, giving your reason for each

C) Calculate the ratio of the diameter of X and of Y relative to Z.

For A, they should be listed in increasing order of what?

0

reply

(Original post by

Your questions seem incomplete.

For A, they should be listed in increasing order of what?

**nebelbon**)Your questions seem incomplete.

For A, they should be listed in increasing order of what?

0

reply

Report

#4

(Original post by

Oh sorry yeah increasing order of power output

**221loki**)Oh sorry yeah increasing order of power output

0

reply

(Original post by

What equations do you know about power output?

**nebelbon**)What equations do you know about power output?

0

reply

Report

#6

Part A you can complete if you know the relationship between luminosity and absolute magnitude. luminosity can be taken as the same as power output in this instance.

Part B you can complete with some knowledge of the H-R diagram and stellar evolution.

what are low temperature stars with high luminosity

what are high temperature stars with low luminosity

Part C first work out the ratio of the luminosity (i.e. power output) of X and Y to Z

rearrange M

then you can work out the ratio of the surface areas using the Stefan-Boltzman law and the supplied temperatures

then you can work out the ratio of diameters using the formula for the surface area of a sphere to get the final answers

Part B you can complete with some knowledge of the H-R diagram and stellar evolution.

what are low temperature stars with high luminosity

what are high temperature stars with low luminosity

Part C first work out the ratio of the luminosity (i.e. power output) of X and Y to Z

rearrange M

_{x}-M_{z}=-2.5 log(L_{x}/L_{z})then you can work out the ratio of the surface areas using the Stefan-Boltzman law and the supplied temperatures

then you can work out the ratio of diameters using the formula for the surface area of a sphere to get the final answers

0

reply

(Original post by

Part C first work out the ratio of the luminosity (i.e. power output) of X and Y to Z

rearrange M

**Joinedup**)Part C first work out the ratio of the luminosity (i.e. power output) of X and Y to Z

rearrange M

_{x}-M_{z}=-2.5 log(L_{x}/L_{z})
0

reply

Report

#8

(Original post by

Thanks for the reply! So when i rearrange it am I trying to calculate the logx - logz ?

**221loki**)Thanks for the reply! So when i rearrange it am I trying to calculate the logx - logz ?

You'd like to get L

_{x}/L

_{y}on its own

i.e.

L

_{x}/L

_{z}= *something you can calculate from the given magnitudes*

hopefully it's clear that L

_{x}/L

_{z}is the ratio of the power output of X to Z

repeat to get L

_{y}/L

_{z}

then you can work out what the ratio of surface areas needs to be using Stefan-Boltzmann

and from that you can get the ratio of diameters.

it is quite a bit trickier than the first 2 sections imo.

1

reply

(Original post by

Lx is the luminosity of X, Mx is its absolute magnitude

You'd like to get L

i.e.

L

hopefully it's clear that L

repeat to get L

then you can work out what the ratio of surface areas needs to be using Stefan-Boltzmann

and from that you can get the ratio of diameters.

it is quite a bit trickier than the first 2 sections imo.

**Joinedup**)Lx is the luminosity of X, Mx is its absolute magnitude

You'd like to get L

_{x}/L_{y}on its owni.e.

L

_{x}/L_{z}= *something you can calculate from the given magnitudes*hopefully it's clear that L

_{x}/L_{z}is the ratio of the power output of X to Zrepeat to get L

_{y}/L_{z}then you can work out what the ratio of surface areas needs to be using Stefan-Boltzmann

and from that you can get the ratio of diameters.

it is quite a bit trickier than the first 2 sections imo.

0

reply

X

Page 1 of 1

Go to first unread

Skip to page:

### Quick Reply

Back

to top

to top