# What is Hubble's Luminosity Law?

• angela6884
In summary, the equation, 5 log(R) = -m + k, is found on wikipedia and states that as the angular size of a reflection nebula increases, the magnitude of the star that it reflects decreases.
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!

angela6884 said:
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
Drakkith said:
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!

## 1. What is Hubble's Luminosity Law?

Hubble's Luminosity Law, also known as the Hubble Law, is a fundamental principle in cosmology that describes the relationship between the distance of a galaxy and its velocity of recession. It states that the farther a galaxy is from us, the faster it is moving away from us.

## 2. Who discovered Hubble's Luminosity Law?

Hubble's Luminosity Law was discovered by American astronomer Edwin Hubble in the 1920s. He observed that the light from distant galaxies was shifted towards the red end of the spectrum, indicating that they were moving away from us.

## 3. How does Hubble's Luminosity Law support the Big Bang theory?

Hubble's Luminosity Law provides evidence for the expansion of the universe, which is a key component of the Big Bang theory. The law suggests that the universe is expanding uniformly in all directions, which is consistent with the idea that the universe began with a single, explosive event.

## 4. What is the significance of Hubble's constant in Hubble's Luminosity Law?

Hubble's constant, denoted as H0, is a numerical value that represents the rate of expansion of the universe. It is an important parameter in Hubble's Luminosity Law because it allows us to calculate the distance of a galaxy based on its observed velocity of recession.

## 5. How is Hubble's Luminosity Law used to measure the age of the universe?

By using Hubble's Luminosity Law, scientists can measure the distance and velocity of galaxies, which in turn allows them to calculate the expansion rate of the universe. This information, along with other cosmological data, can be used to estimate the age of the universe, which is currently believed to be around 13.8 billion years old.

Replies
5
Views
2K
Replies
75
Views
8K
Replies
1
Views
3K
Replies
9
Views
14K
Replies
1
Views
2K
Replies
2
Views
3K
Replies
23
Views
7K
Replies
4
Views
2K
Replies
2
Views
1K
Replies
3
Views
964