# Questions tagged [luminosity]

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

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3 votes
0 answers
181 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 ...
• 273
1 vote
1 answer
2k 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 ...
• 834
0 votes
1 answer
326 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 ...
• 834
2 votes
1 answer
261 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 ...
3 votes
2 answers
394 views

• 1,344
4 votes
1 answer
645 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$_{\mathrm{I}}$ ...
3 votes
1 answer
453 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?
• 141
6 votes
1 answer
153 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_{...
• 161
3 votes
1 answer
1k 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 ...
• 41
3 votes
1 answer
2k views

### What is the Fundamental plane for Elliptical Galaxies?

An alternate explanation rather than from wikipedia is preferable.
4 votes
2 answers
95 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?
4 votes
2 answers
3k 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 ...
• 43
35 votes
2 answers
2k 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 ...
• 6,362