Questions tagged [luminosity]

Questions regarding the amount of energy produced by an object per unit of time.

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2
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0answers
353 views

What characteristics or patterns do galaxies have on color-luminosity chart? [closed]

For the following graph, I have some confusions: How do galaxies rank by mass? We know that on main-sequence, more luminous stars are also more massive, so I guess it also applies to galaxies. Do red ...
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0answers
139 views

What is the spectral power output of a typical galaxy?

I'm looking for a function which gives the typical isotropic spectral power of light emitted by an entire galaxy on the whole electromagnetic spectrum (in watts per frequency unit), as a function of ...
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1answer
942 views

Flux density to flux

The definition of flux and flux density is fairly straightforward. However, I'm musing over the practical usage of it. For one thing, if you observe a source through a filter, how would one go from ...
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1answer
157 views

From color index to luminosity

Given two colorindices LX and LY, such that the color X-Y is given by X-Y = -2.5 log(LX/LY) is there a way to infer the luminosity in X (or Y)? I'm think not ...
2
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1answer
105 views

Solar luminosity proportional to $G^7$?

A book I recently purchased describes Dirac's proposed variation of Newton's G, and why that specific proposal wouldn't work because the earth would have been too hot for the known history of life. A ...
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2answers
203 views

Deriving phase of a pulsating star from list of Julian date values of observing brightness

I want to convert the list of Julian date values of observing brightness of a Cepheid variable into its phase. The equation I found in the Internet is the following: $$\mathrm{Phase}= \frac{\mathrm{...
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0answers
53 views

Change in angular diameter of Cepheid variables

I'm a highschool student and in the process of writing a research paper of deriving period-lumniosity relation of Cepheid variable independently of the pre-existing PL relation. Thus, I need to derive ...
4
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1answer
3k views

How can I convolve a template spectrum with a photometric filter response spectrum?

Suppose I have a template stellar population spectrum (say, from Bruzual & Charlot 2003) which runs from like 1000 Angstroms to 160,000 Angstroms and which has x-axis wavelength units of Angstroms ...
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1answer
135 views

Finding Mass of Star with only Luminosity [closed]

Estimate the mass of the star given this formula: $$\frac{L}{L_\mathrm{\odot}} = \left(\frac{M}{M_\mathrm{\odot}}\right)^{3.5}$$ Given $L= 2.752\times10^{28}\,\mathrm{W}$, how do I find the mass of ...
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1answer
122 views

The relation between the light of full moon and the distance between the sun and the earth

If we want the full moon to be 2 times more bright,how we should change the distance between the sun and the earth? Thanks for your help.
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2answers
547 views

What would be the apparent magnitude of Betelgeuse if it were as close to Earth as Sirius?

How large and bright would Betelgeuse appear if it were as close to Earth as Sirius, before and after it goes supernova?
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2answers
418 views

Color of planets

I am developing an astronomy software and need to know the color of each planet in the Solar System, when observed with the naked eye. I cannot find that information after googling for a while. Is ...
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1answer
151 views

Red dwarf variation in Luminosity

I recently saw this video. The creator of the video says that one of the reasons for non-existence of life on planets around red dwarfs might be that these stars can increase luminosity roughly by a ...
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2answers
2k views

What is the frequency distribution for luminosity classes in the Milky Way Galaxy?

I'm working on a game concept that does some mild simulation of realistic stellar classes and luminosities. In particular, I'd like to roughly model the general frequencies of the classes and ...
14
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1answer
5k views

Is the Sun really a medium size star?

It is often said that the Sun is a medium size, or even dim star. Is this true? According to this list of stars within 21 light years, there are, out of the closest 121 stars, only six brighter than ...
3
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1answer
187 views

If the Sun were bigger but colder, Earth would be hotter or colder?

That is the question. I know the concepts of luminosity $(L=4\pi R^2F)$ and the flow $F=\sigma· T^4$, with $T$ the temperature in its surface. But how I use that to know if the Earth would get warmer ...
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1answer
158 views

What is the illuminance of Tau Ceti?

As part of my physics project, I investigated the relationship between a light bulb's illuminance and the distance from the measuring device to it. Illuminance was measured in flux, and distance in ...
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1answer
1k views

Conversion of magnitudes to Jansky and MAGPHYS?

I'm a bit puzzled and not an observer, so please bear with me if I'm being stupid here. The code MAGPHYS specifies Jansky (Jy) as the input unit for flux through ...
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0answers
394 views

How to use spectral profiles to determine luminosity class?

I know the luminosity classes are: Ia-0 ( Hypergiants ), Ia ( bright supergiants ), ... , VII ( white dwarf ). I also have learned that you can use the presence of absorption lines ( ie. use spectral ...
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2answers
4k views

Why does the Hertzsprung–Russell diagram's x-axis go from large temperatures to lower?

In my textbook, the H–R diagram’s y-axis is $\log(L/L_{\odot})$ and values are higher as we go higher on the scale, but the x-axis is $\log(T_\text{eff})$ and gets smaller as we proceed to the right. ...
4
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1answer
530 views

Luminosity Schechter function for galaxies

Just a question I am having trouble understanding. I have the Schechter luminosity function for galaxies, given as: $$\Phi(L)dL=\Phi_{0}\left({\frac{L}{L_{\star}}}\right)^{\alpha}e^{-\frac{L}{L_{\...
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1answer
474 views

How is the Lithium Depletion Boundary used to determine the age of a stellar cluster?

According to my understanding of Soderblom et al. (2014), lithium ages of stars are determined as follows: Determine lithium abundance from equivalent width measurement of Li$_{\mathrm{I}}$ ...
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1answer
100 views

How do you determine which star, between two, is more luminous?

For example, if star 1 is 4x bigger than star 2 but both are the exact same temperature how do you determine which is more luminous?
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1answer
132 views

What happens to the Gas Pressure when working out the Eddington Luminosity?

I am looking at how the Eddington Luminosity is derived and I do no understand why we only care about $P_{rad}$? When working out $L_{Edd}$ you take the ratio between $dP_{rad}/dr$ and $dP_{...
3
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1answer
812 views

Instrumental magnitude to “real” magnitude - Photometry with not enough data?

I have a lot of data taken in R, B, V, Luminance and Halpha-bands which I want to analyse photometrically (one target in the frame). The frames are already reduced (with flats, darks etc.) and have a ...
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1answer
1k views

What is the Fundamental plane for Elliptical Galaxies?

An alternate explanation rather than from wikipedia is preferable.
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2answers
87 views

Can solar luminosity & activity be predicted?

Can a star's luminosity and its activity, solar flares and sunspots, be predicted? If so, with what accuracy & precision?
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2answers
2k views

Stellar mass of galaxies

Given the magnitudes (in the i-band) of certain galaxies, I would like to calculate their stellar mass (in terms of solar masses). So far, I have calculated their absolute magnitudes and gotten to ...
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1answer
1k views

How could a hobbyist astronomer determine apparent magnitude of a star?

Apparent magnitude is a rather complex way to determine the brightness of a star. Quoting the introduction text from the linked to Wikipedia page: The apparent magnitude (m) of a celestial body is ...

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