Questions tagged [luminosity]
Questions regarding the amount of energy produced by an object per unit of time.
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How to convert magnitude to spectral luminosity? [duplicate]
In the Gaia catalogue I have the magnitude of several stars in the G band. I also have the distances to these stars (parallax is known). Additionally, I oftentimes have the effective temperature in ...
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I need help with an equation for figuring out the surface temperature of Red Dwarf!
Say you have a 10 billion year old, slow rotating, quiescent M5 star with a mass of 0.32 M☉ , a luminosity of 0.018 L☉ and a burning (haha) desire to figure out the surface temperature. However you ...
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1answer
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Converting the log (Stellar Luminosity/Solar Luminosity) and the log of the plus and minus variation
There are some stars in the NASA Exoplanet Archive that I am interested in but I am confused by the physical meaning of the terms.
For example, there's a star BD+15 2940 with a log10 of Solar ...
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Q: Calculating the luminosity of a galaxy
I am currently working on a project on which I am calculating the luminosity of galaxies by using the SDSS data. They use a system of asinh magnitudes, and according to their website they use a system ...
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Stars that don't fit $L=4\pi R^{2}\sigma T^{4}$?
When calculating luminosity/radius/temperature for several stars, I've noticed that while the majority of stars conform to the luminosity relationship $L=4\pi R^{2}\sigma T^{4}$, there are a few that ...
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41 views
How to calculate the distance to galaxies with standard candles?
I was wondering how the distance in Mpc could be calculated between Earth and a galaxy using the luminosity provided? Do not be shy to use all math necessary :)
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How actively is Deep Learning being used in exoplanet identification?
Papers, like this one from Google, show that Deep Learning and Machine Learning are effective in detecting exoplanets from luminosity data provided by telescopes like TESS or Kepler.
These models ...
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1answer
58 views
Eddington luminosity in various plasmas
So I know that the Eddington luminosity is given by:
$L_{Eddington} = 4\pi GMc/\kappa$.
I want to calculate this luminosity for a plasma of purely ionized helium, as well as for an electron-...
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2answers
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Radiative Flux, Irradiance and Luminosity confusion
First of all I know there is a similar question here, but I feel is wasn't answered at all.
My question is that I have seen many texts which says that Radiative Flux is equal to the Irradiance of a ...
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1answer
57 views
How to correct observed flux densities for redshift
Say I have a spectrum of a galaxy at a redshift $z$, in flux density units of erg/s/cm^2/Angstrom. I'd like to recover the spectrum (in the same flux density units) at z=0, i.e. at its rest ...
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Luminosity of the Milky Way compared to Seyfert galaxies
This page lists the total luminosity of the Milky Way Galaxy to be $4\times10^{10}$ $L_{sol}$, and $L_{sol}=3.86 \times10^{33}$ ergs.sec$^{-1}$; this gives a total luminosity for the MW of $1.54\...
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Conversion factors for flux
I have a flux value in the infrared band of 8 mJy at a wavelength of 80 microns that I want to translate into X-ray conventional ...
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1answer
84 views
What area of Proxima Centauri would need to be occluded for the effect to be observable on Earth?
One of ideas of how Breakthrough Starshot could communicate data from Proxima Centauri is to have a massive swarm of the solar sail powered craft to pivot (with their sails) synchronously, taking ...
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1answer
50 views
How can I estimate the M/L ratio from a fitted SED on a galaxy?
This answer (here in the forum) provides background to my question: https://astronomy.stackexchange.com/a/5953
I am trying to understand the process in which a stellar population synthesis (SPS) is ...
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1answer
82 views
H-R diagram, Double stars
Can someone help me? I have a case, like, we have H-R diagram and two stars on it. One of them is a blue star on main sequence, another is a red giant. They have equal luminosity. If they are in a ...
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What does this figure imply about the luminosity of pre-main-sequence stars?
Check out Figure 1 in http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1955PASP...67..154H&data_type=PDF_HIGH&whole_paper=YES&type=PRINTER&filetype=.pdf .
It seems to ...
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1answer
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How to calculate luminosity in g-band from absolute AB magnitude and luminosity distance?
How can I calculate the (non-bolometric) luminosity $L$ of a galaxy (or a star for that matter) over a given band from its AB apparent magnitude $m_{AB}$ over that band and its luminosity distance $...
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1answer
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Is it possible that quasars are not powered by black holes but some other kind of compact, massive object?
AFAIK, objects in the universe thought to be black holes show evidence of radiatively inefficient accretion flow. But is this the case with Quasars? If not, is there a possibility that the core of a ...
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1answer
771 views
How bright would it be on the “face” of Titan
If you were planing a maned mission to Titan and wanted to find a landing site that would get the most visible light for the longest amount of time, your first logical choice would be the dark side of ...
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1answer
54 views
Two lights roughly 5 minutes apart about as bright as Mars or maybe Saturn
I'm in the Minneapolis/St. Paul area and around 9:30 on August 4th 2017 I saw a bright light that got dimmer moving from the tree line to the east up and to my left fairly slowly, and steadily getting ...
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1answer
271 views
How to shift AGN x-ray spectrum to rest frame from
I have limited information to shift a spectrum (in the x-ray 0.5-10 keV bandpass) at redshift z=2 to rest frame. I have a plot of normalized (photon) counts s$^{−1}$ keV$^{−1}$ by energy (keV), and so ...
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185 views
What is the radiant intensity of the celestial sphere?
Specifically, excluding the Sun and the Moon:
How much energy, as light and other frequencies reaches a point in space on the average, if you add up all the sources like distant stars, the Milky Way, ...
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1answer
423 views
What does Eddington Limit (Eddington Luminosity) Show?
We know Eddington Limit (Eddington Luminosity) is calculated with this formula:
$$L_{Ed} \approx 3 * 10^4 * L_{sun} * \frac{M}{M_{sun}}$$
Example: For a black hole with $10^4 M_{sun}$, we get
$$L_{...
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1answer
2k views
How to convert magnitudes to bolometric luminosity? [duplicate]
If we know a star's magnitudes from several bands(say u,g,r,i,z,J,H,k) and the star's distance, how to calculate Lbol?
Let's suppose the star has a black body spectrum. Is there any manual about the ...
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2answers
239 views
Question about radiation pressure
A spaceship with mass $m = 25\:kg$ is moving toward a red giant with $M = M_{sun}$ and $L = 1000\:L_{sun}$ (L: Luminosity). It is moving on a line (so this is not an orbital question). When it gets ...
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1answer
170 views
Problem about finding distance with magnitude given
A star in Pleiades cluster has apparent magnitude of +12 ($m_{star} = +12$) determine it's distance from the sun? (We know the Sun properties such apparent and absolute magnitudes, distance from earth,...
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1answer
724 views
How to convert theoretical template spectrum from luminosity density to flux density units?
I'm working with galaxy spectral templates (e.g., Bruzual & Charlot 2003) which seem to always come with y-axis units of $L_{\odot}$/A and x-axis units of Angstroms. Thus the y-axis is a ...
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1answer
177 views
Why do different instrumental filters use different magnitude systems (Vega vs AB)?
Suppose I wanted to construct the spectral energy distribution (SED) of an object. Further suppose I observe this object through the 9 broad-band filters using the Subaru Suprimecam (just for an ...
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2answers
1k views
Difference between luminosity, luminous flux, and radiant flux?
I've looked this up, and was wondering the differences between them. Luminosity is the total energy emitted by a source, in watts. However, I'm confused about luminous flux and radiant flux. Since ...
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1answer
766 views
How to find a Cepheid's pulsation period using its graph?
Basically, I've been seeing these graphs that say: Cepheid Period-Luminosity Relation and the Period axis is supposed to be "logarithmic";
How does this graph work? Since the luminosity of a star ...
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3answers
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Calculate Luminosity of Vega
I want to calculate the Luminosity of a star e.g. Vega but can be any star and came across the formula for Luminosity at the University of Oregon (http://pages.uoregon.edu/soper/Light/luminosity.html)....
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1answer
670 views
Finding luminosity of a star with magnitude
I'm working on my assessment for Physics in the IB, and I'm planning to investigate stars in spiral galaxies and determine their ages. For this I'm going to use data from the SDSS (Sloan digital sky ...
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302 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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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
641 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
109 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 ...
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1answer
96 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
134 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
50 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 ...
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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
124 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
106 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
445 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
218 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
135 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
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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 ...
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1answer
4k 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 ...
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1answer
182 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
119 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 ...
