Questions tagged [luminosity]

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

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Double Schechter luminosity function for the Milky Way

I would like to calculate the density of MW-like galaxies using the double Schechter luminosity function: $ \Phi(m) d m=\left[\phi_1\left(\frac{m}{m_*}\right)^{\alpha_1}+\phi_2\left(\frac{m}{m_*}\...
0 votes
0 answers
35 views

How can I convert luminosity from [erg/s/Hz] to [erg/s]

I have the dust-corrected luminosity in the Ks band in the unit erg/s/Hz. I want to convert it to erg/s. I would like to know which method is correct: $L[erg/s]=L[erg/s/Hz]\times(C/\lambda)$ $L[erg/s]...
1 vote
1 answer
91 views

Is there a specific constant name for the fifth root of 100?

I understand that each scale you go up on the absolute magnitude scale, the luminosity decreases by the fifth root of 100, or around 2.512. Is there a name for the constant 2.512, or not. Also, is the ...
15 votes
6 answers
4k views

What's the issue with Olbers' paradox?

I'm not quite grasping the reasoning behind Olbers' Paradox, or why an eternal, non-expanding and spatially infinite universe would be incompatible with a dark sky. For simplicity, let's suppose that ...
4 votes
1 answer
123 views

Wien's law gives two different results?

Say I have a star with radius $R$ and luminosity $L$. I want to find the frequency of its peak emission. Taking the star as a perfect blackbody, we can use Stefan-Boltzman to see that $$L = 4\pi R^2\...
1 vote
0 answers
47 views

Calculate Luminosity of a star from the Hipparcos catalogue

Is it possible to calculate the star's luminosity based on the data in the Hipparcos catalogue? Currently I'm using this algorithm, I have even fitted the bolometric correction to the Johnson V band (...
1 vote
0 answers
69 views

Calculating the absolute magnitude of a solar system body

I am trying to calculate the absolute magnitude of a solar system object, given its albedo, and assuming all of its luminosity comes from reflecting light from the sun. Using $L_{sun}$ = solar ...
2 votes
1 answer
41 views

Standard definitions (ISO?) about subjects related to light emitted by stars

I'm a big fan of astrophysics and astronomy. However i'm quite confused by reading these last years plenty of books on the subject with various definitions (vocabulary) and notations for the same ...
2 votes
2 answers
1k views

Confusion over habitable zone

I am confused over the habitable zone, as I calculated the expected temperature of Earth (minus greenhouse effects), and it would be -17 C. Which is below the freezing point of water. I also made a ...
1 vote
1 answer
199 views

Is luminosity distance related to both heliocentric redshift and CMB restframe redshift?

The luminosity distance $$d_l=(1+z)r(z)\ ,$$ where $r(z)$ is given by $$r(z)=cH^{-1}_0\int_{0}^{z}\frac{dz'}{E(z')}\ .$$ When I use the SNe dataset "Pantheon", I find there are two redshifts:...
1 vote
1 answer
255 views

Is there a way to calculate a star's luminosity from its apparent magnitude?

I was wondering if there's a way to calculate a star's luminosity from apparent magnitude data.
3 votes
1 answer
152 views

Period-Luminosity Relation of Cepheids via Gaia Data

I was trying to verify Leavitt's Law of Period Luminosity Relationships of Cepheid Variables using Gaia data. To do this I calculated the period using the Lomb Scargle Periodogram for 1450 stars and ...
1 vote
0 answers
22 views

Using Gaia Passbands with L_nu coordinates

I am trying to find the coordinates of my bundles of gas on the gaia ($G, G_{bp}-G_{rp}$) hr diagram. I have its spectrum in $\nu L_\nu$ coordinates. Thus far, my attempts have mainly been to ...
4 votes
1 answer
69 views

What's the relation between the parallax distance and the luminosity distance?

I have read that Riess and his team are able to measure $H_0$ from supernovae calibrated using Cepheid in a model independent way. from what I have gathered they find the absolute luminosity of ...
1 vote
1 answer
338 views

Help converting Jansky/beam to erg s^-1

I have some radio observation data in jansky/beam from NVSS at 1.4GHZ, and I want to convert these values into luminosity values (erg/sec). I have the distance data and I made a formula to convert it: ...
1 vote
1 answer
399 views

How to convert Flux Density to Flux?

I have a radio catalogue with flux density values. (Jy/bm) I'm confused converting this value to flux. Because I want to calculate luminosity, I need flux values. The unit made me confused. Since I ...
6 votes
1 answer
5k 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 $...
3 votes
1 answer
57 views

Protoplanetary disk luminosity - looking for a sanity check please

I've been told to "consider an Earth-mass of interplanetary grains (roughly spherical with a radius of a few microns) in a protoplanetary disk. Let the particles be in a torus with a cross-...
1 vote
0 answers
50 views

Magnitude cuts in different bands/surveys

I have data on around 142,000 galaxies. Some of these galaxies have apparent magnitude data in different bands. For example, many of my galaxies have SDSS PSF data in ugriz bands,GALEX FUV, GALEX NUV, ...
4 votes
2 answers
198 views

Brightness and flux density

The alpha star in a constellation has the highest brightness, but does that mean it has the highest flux density among the other stars in the constellation?
3 votes
0 answers
115 views

What is the average and the median mass and luminosity of a star?

I've heard in many places that the Sun is an average star, but in Wikipedia it says that about 75% of stars are M-type stars that are way less massive and fainter that the Sun. So how massive and ...
3 votes
1 answer
107 views

How do I determine the Luminosity with a half-life decay?

I know there is a proportionality between the luminosity and $\frac{dN}{dt}$, but I am not sure why they are proportional and why there is a need for an initial mass to compute the luminosity if the ...
5 votes
2 answers
545 views

What is the infrared self-luminosity value of Jupiter and Saturn?

I'm looking for these data to apply them to the Kelvin-Helmholtz mechanism but I can't find the values. Or at least if there is an order of magnitude compared to the solar luminosity.
9 votes
2 answers
2k views

How bright will Alpha Centauri A be from Earth when it becomes a red giant?

As of right now, both stars from Alpha Centauri are in their main sequence stages, but eventually Alpha Centauri A is going to quickly expand in a matter of time, and I’m pretty sure its luminosity is ...
34 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 ...
1 vote
0 answers
45 views

How can I estimate a stars surface temperature, luminosity, radius, and lifetime only knowing it's solar mass and peak wavelength? [duplicate]

For example: if a 10 solar mass star emits light at a peak wavelength of λ = 300nm. How can I calculate a stars surface temperature, luminosity, radius, and lifetime with this infomation?
2 votes
1 answer
400 views

How can I calculate the luminosity and mass of a star only knowing it's peak wavelength and it's subtended angle?

For example if a certain star subtends an angle of 32 arcminutes at the Earth’s orbit and it's light has a peak wavelength of 500 nm, how can I find the luminosity and mass of that star?
1 vote
3 answers
525 views

Calculating the luminosity of a comet

Assuming a 9-km comet is heading towards the Earth and it is at distance 5.2 AU away from the Sun, what is its luminosity? Assume that it has an albedo of 0.5? For now, I have calculated the Sun's ...
2 votes
1 answer
104 views

Change in Luminosity of a planet

When viewed from the sun, the brightness of the planet with a given size and albedo changes according to the fourth power of inverse distance. I found the statement in one encyclopedia but I can't ...
3 votes
1 answer
169 views

On finding the magnitude of Stars

I am wondering how I would be able to predict the Magnitude of fictional stars, given we know enough about them. As the formulae I can find online are mostly getting overly high values that don't seem ...
3 votes
0 answers
594 views

DIY Sky Quality Meter: Conversion between Illuminance and Luminance

I am trying to create a homemade Sky Quality Meter (SQM) using a TSL2591 light sensor. This sensor measures Illumination (lux), but SQMs measure Luminance (mpsas). I have seen that there are many ...
0 votes
0 answers
114 views

How luminous does a brown dwarf have to be to illuminate an Earth-sized planet with 0.5 lux at 2,000,000 kilometers away?

A brown dwarf is a deuterium-fusing substellar object, and, in the cases of the larger ones, a lithium-fusing one. They often emit electromagnetic radiation in frequencies that humans cannot see. ...
2 votes
1 answer
69 views

Total luminosity of total population of galaxies!

I'm trying to get the total luminosity of a total population of galaxies. I have the Schechter Function like $$\Phi(L) = \frac{\Phi^{*}}{L^{*}} \left(\frac{L}{L^{*}}\right)^{\alpha} \exp \left(\frac{...
2 votes
2 answers
128 views

Finding stellar radii

Is apparent magnitude of star, distance(in pc) and effective temperature enough to calculate its stellar radii or we need some extra information?
7 votes
1 answer
496 views

Measuring the mass of the luminous matter in a galaxy

The mass of total matter in a galaxy can be measured using the rotation curve of the galaxy. However, how do people determine the mass of luminous matter in the galaxy, as a function of the distance ...
9 votes
2 answers
8k 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. ...
-1 votes
1 answer
232 views

How to find luminosity from a light curve? [closed]

I am currently trying to find the luminosity from the light curve. I have the data about the distance, counts/sec and the energy range in which it is measured for an object. What equation can be used ...
5 votes
3 answers
1k views

Could a black hole's accretion disk be bright through natural means?

This question is based on this description of the Cormoran Supermassive Black Hole in the Orion Arm's website: Surrounding this event horizon is an (apparently artificial) accretion disk about 4AU in ...
5 votes
1 answer
199 views

What does a + (plus) mean in stellar classification?

I've noticed some stellar classifications might look like this: A0IV+G: (HD 70003) F3IV+F0IV (HD 82434) ...
2 votes
2 answers
609 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 :) Clarification: Luminosity is inversely ...
11 votes
1 answer
1k views

Spectral class and luminosity of hydrogen bomb explosions?

Since hydrogen bombs detonating are like tiny little stars, I wonder what luminosity and spectral classification they would get if one were to categorize them like this. E.g. Starfish Prime and the ...
2 votes
0 answers
267 views

How to calculate rest-frame luminosity in a specific wavelength band?

For instance, I have a set of templates whose y is in Jy and x is in Angstroms. I have both of their rest-frame and obs-frame wavelength (i.e. redshift). I want to know their luminosity in one ...
4 votes
1 answer
219 views

Is it dangerous to look at an L-type brown dwarf from too close?

Are some L-type brown dwarves bright enough so that it would be dangerous to the eyes if one looked at them from habitable distance or closer? If not, are the weakest M-type stars undangerous to look ...
5 votes
2 answers
2k 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 ...
3 votes
1 answer
133 views

How is the difference of bolometric magnitudes not dependent on the stars' radii?

The difference of 2 bolometric magnitudes is given by: $$M_{bol, ★} - M_{bol, ☉} = -2.5 \cdot \log \left( \frac{L_★}{L_☉} \right)$$ But Pogson's equation is: $$M_{bol, ★} - M_{bol, ☉} = -2.5 \cdot \...
4 votes
1 answer
2k 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 ...
1 vote
1 answer
211 views

HR diagram x-axis (color) and redshift?

I've read several articles and watched some videos on the HR diagram, but no-one seems to mention the effect of redshift on the color of a star. Is there some calibration step that needs to be applied ...
2 votes
1 answer
152 views

Strip Brightness in a Spherical System

My question concerns the following problem, published in Galactic Dynamics by Binney and Tremaine and based on a work by Schwarzschild. Specifically, I am having difficulties in deriving the given ...
4 votes
1 answer
1k views

Estimating a star's radius, temperature, and luminosity based on its mass

(See updated figure and description below.) I've been trying to generate ballpark estimates for the radius, temperature and luminosity of stars in the main sequence based solely on their masses (...
1 vote
1 answer
90 views

Is something wrong with my luminosity calculation?

A few million years after a white dwarf forms, its surface temperature reaches $100000\text{K}$, while its radius is $0.01R_\odot$. Would this mean that its luminosity is $\Big(\dfrac{100000}{5778}\...