Luminosity is the energy radiated from a body per second.
Questions tagged [luminosity]
113 questions
41
votes
2 answers
Why does laser light not affect glowing materials?
I have this childrens rubber ball which glows in the dark after it's exposed to light. I "charge" it with a flash light then play with my dogs at night. I thought to try a very intense green laser, and see how the ball reacted.
The laser light had…
Michael
- 800
18
votes
1 answer
Olbers' paradox in a closed space
I'm looking for a proper interpretation of the following, which is a variant of the Olbers' paradox.
Consider a spatially closed empty universe ($k = 1$) with a positive cosmological constant $\Lambda$ (closed deSitter universe). It is easy to…
Cham
- 8,015
17
votes
5 answers
What is "white light" ? Uniform wavelengths or uniform frequencies ?
Suppose you have a mixture of electromagnetic waves of wavelengths spreaded on the visible spectrum only (from $\lambda_{\text{min}} \sim 400 \, \text{nm}$ to $\lambda_{\text{max}} \sim 700 \, \text{nm}$). At some ideal detector, the light spectral…
Cham
- 8,015
12
votes
3 answers
What part of the photons emitted from a star are from black body radiation and what part originate from fusion reactions?
What part of the photons emitted from a star are from black body radiation and what part originate from fusion reactions?
To my understanding these are the two sources of luminosity for a star, so I'm just wondering which phenomena accounts for the…
Miika Vuorio
- 223
11
votes
1 answer
Eclipse of the sun - Intriguing luminosity curve
I've just recorded the luminosity during the sun eclipse, here is the resulting curve :
Only green curve is relevant, blue curve should be ignored (it's actually the temperature).
The sky was uniformly cloudy, so even if I couldn't see the eclipse…
Harijoe
- 211
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9
votes
2 answers
How will the luminosity of the current very near supernova Ia "PTF 11kly" develop in the next weeks and why?
Currently there is a unique chance for amateur astronomers to observe a very near type Ia supernova, named PTF 11kly.
As standard candles are very important to measure distances in the universe, can you give a brief overview of how the luminosity of…
Hauser
- 721
7
votes
3 answers
Binary stars' apparent magnitude
If you plot the apparent magnitude of a binary system (so you are unable to see 2 distinct stars) against time, it gives a repeating 'M' effect.
(from http://accessscience.com/)
Assuming one star is brighter (and bigger in size) than the other.…
Jonathan.
- 7,057
7
votes
3 answers
Explain relationship between angular diameter distance and luminosity distance, Etherington Theorem
I have a question relating to the Etherington Theorem.
The luminosity distance is defined by the equation for flux, i.e.
$F=\frac{L}{4\pi D_L^2}$
where flux is in units energy per unit time (luminosity) per unit area.
The angular diameter distance…
ShanZhengYang
- 907
7
votes
2 answers
Position of Neutron Stars in H R diagrams
Why is that neutron stars are never depicted in a Hertzsprung-Russell diagram? They can be placed in the bottom left corner but you will never find any diagram in literature showing neutron stars.
seeking_infinity
- 1,586
7
votes
3 answers
Why is moonlight less colourful than yellow light?
Just what the title states; and this isn't an original question:
On full-moon, moonlight is almost as bright as mid-dawn; yet there is hardly any colour visible. This is not the case with sunlight.
I'm curious to know why this is the case.
Everyone
- 4,741
7
votes
1 answer
Question on luminosity of a radiant source and its dependence on temperature, and involvement of Doppler Effect
A few days ago, I happened to go through the chapters on Radiation, and Photometry, studying them at quite an elementary level. I studied Wien's displacement law, and the dependence of luminous flux of a radiant source on the total radiant flux of…
abstract
- 501
6
votes
2 answers
How many watts of light do instruments in modern telescopes need?
I just calculated that if the European extremely large telescope(978 m^2 area) would be pointed at the Andromeda galaxy once it is built, it will only get mere 1.2*10^-6 Watts of power from Andromeda.
And I didn't account for atmospheric factors or…
Aayush Mahajan
- 277
6
votes
2 answers
What is the luminosity per square meter hitting the Earth's surface from the Sun?
So I know that the Sun's luminosity is $3.839 \cdot 10^{26}$.
What I want is the luminosity per square meter at the Earth's surface. So this is what I have got so far:
I know the distance to the Earth from the Sun is $149.60 \cdot 10^9$ m. So…
capcom
- 165
5
votes
1 answer
Why is the relation between luminosity distance $d_L$ and comoving distance $\chi$ $d_L=\chi/a$?
The textbook (Scott Dodelson, Modern Cosmology, Section 2.2 Distance, Page 35-36) states the following:
Another way of inferring distances in astronomy is to measure the flux from
an object of known luminosity. Recall that (forgetting about…
Wang Yun
- 529
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5
votes
2 answers
How does the Hertzsprung-Russell Diagram allow us to calculate the distance to stars?
I understand how to interpret an H-R diagram, in the sense that I know that the upper right top corner is occupied by cool stars, but they are very luminous so they must be big; and the bottom left corner is hot stars, not luminous, so they are…
ScienceGirl1234
- 193