Questions tagged [luminosity]
Questions regarding the amount of energy produced by an object per unit of time.
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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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How to find the accretion rate required to power the Sun?
If The potential energy of the Sun is:
Ep =3GM^2/5R
PROVIDED that the density is constant.
prove that the accretion rate required to power the Sun is:
dM/dt = 2 ...
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1answer
35 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
53 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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2answers
138 views
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
945 views
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 $...
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1answer
78 views
Is it possible that quasars are not powered by black holes but some other kind of compact, massive object?
AFAIK, objects in the universe thought to be black holes show evidence of radiatively inefficient accretion flow. But is this the case with Quasars? If not, is there a possibility that the core of a ...
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1answer
414 views
How bright would it be on the “face” of Titan
If you were planing a maned mission to Titan and wanted to find a landing site that would get the most visible light for the longest amount of time, your first logical choice would be the dark side of ...
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1answer
49 views
Two lights roughly 5 minutes apart about as bright as Mars or maybe Saturn
I'm in the Minneapolis/St. Paul area and around 9:30 on August 4th 2017 I saw a bright light that got dimmer moving from the tree line to the east up and to my left fairly slowly, and steadily getting ...
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1answer
198 views
How to shift AGN x-ray spectrum to rest frame from
I have limited information to shift a spectrum (in the x-ray 0.5-10 keV bandpass) at redshift z=2 to rest frame. I have a plot of normalized (photon) counts s$^{−1}$ keV$^{−1}$ by energy (keV), and so ...
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0answers
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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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Mass-luminosity relation for a fully convective star
I'm trying to show that the mass-luminosity for a fully convective star is
$$L \propto M^{\frac{113}{66}}$$
I know that the energy generation is via pp-chain and the opacity is due to $H^{-}$ ions ...
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1answer
313 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
180 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
134 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
528 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
164 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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1answer
994 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
628 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
854 views
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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533 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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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
508 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
77 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
90 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
97 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
45 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
2k 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
109 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
101 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
321 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
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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
102 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
179 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
107 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
898 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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306 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
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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.
...
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1answer
416 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
335 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
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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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114 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_{...
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1answer
595 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
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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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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 ...
