What is Hubble's Luminosity Law?

[angela6884]

Problem Statement: Please help me understand the variables for the equation, 5 log(R) = -m + k.
Relevant Equations: 5 log(R) = -m + k

Here is the link to where I found the equation. I know it's on wikipedia but I checked the Hubble's paper and it seems to be credible. I'm trying to make theoretical graphs by testing different inputs for the equation. Would it be dumb to get rid of the "k" in the equation? Sorry I'm in high school so I'm still learning the ropes of how to make an analysis paper. Also I'm a new member so sorry if I posted on the wrong page!

 

[Drakkith]

Would it be dumb to get rid of the "k" in the equation?

No, as 'k' just represents the sensitivity of your detector. All it does if you graph the equation is move the entire graph up or down. If you're just interested in the overall shape of the graph and what it means, you can ignore the 'k'.

Setting k=0 and plotting the magnitude on the y-axis shows you that the apparent magnitude of the star increases (gets more negative) as the angular size of the nebula increases. Or, rather, that if reflection nebula are indeed illuminated by reflecting light from a nearby star, their angular size should be proportional to the magnitude of the star.

The reason for this is a bit unclear for me. I'm not sure if it has something to do with the way that angular size and magnitude change as distance from Earth changes, or if it is because of how parts of a nebula further away from a star will reflect less light, since they lie further from the star and the light is more spread out by the time it reaches that part of the nebula and reflects. I'm leaning towards the latter.

 

[angela6884]

No, as 'k' just represents the sensitivity of your detector. All it does if you graph the equation is move the entire graph up or down. If you're just interested in the overall shape of the graph and what it means, you can ignore the 'k'.

Setting k=0 and plotting the magnitude on the y-axis shows you that the apparent magnitude of the star increases (gets more negative) as the angular size of the nebula increases. Or, rather, that if reflection nebula are indeed illuminated by reflecting light from a nearby star, their angular size should be proportional to the magnitude of the star.

The reason for this is a bit unclear for me. I'm not sure if it has something to do with the way that angular size and magnitude change as distance from Earth changes, or if it is because of how parts of a nebula further away from a star will reflect less light, since they lie further from the star and the light is more spread out by the time it reaches that part of the nebula and reflects. I'm leaning towards the latter.

Oh okay that makes sense! And yes I think you're latter inference makes sense but, Ill try to read Hubble's paper and get you your answer! Thank you for your assistance!