Questions tagged [absolute-magnitude]

Use this tag for questions that are about the brightness of a celestial object as seen from 10 parsecs away.

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3 votes
2 answers
1k views

Gaia Gbp - Grp: why does it get larger as star gets redder?

As an enthusiastic amateur scientist, I'm plowing my way through a cool Gaia DR2-based paper, "An Empirical Measurement of the Initial-Final Mass Relation with Gaia White Dwarfs". I'm doing all right, ...
4 votes
2 answers
302 views

Good source for the relationship between absolute magnitude, diameter, and albedo?

In this answer I have rearranged an equation from somewhere, and now I can not relocate the source. My re-aranged form is: $$M_{Abs} = 5 \left(\log_{10}(1329) -\frac{1}{2}\log_{10}(\text{albedo}) -\...
-5 votes
2 answers
117 views

What is 5 in 5log10 the value of?

I know what 2.5 stand for in $2.5 \log_{10}$, but what does the number 5 in $5\log_{10}$ stand for and what application does it have. Thus, why is the number a five and not a four, or a three, or ...
2 votes
1 answer
87 views

E(B-V) , the color excess between B and V bands, for galaxy at redshift 0

Following Mo et al. 2010 (page 479), the quantity $E(B-V)$, called the color excess between B and V bands, is equal to: $$E(B-V) = A_B - A_V = (B - V) - (B - V)_0 = (m_B - m_V) - (M_B- M_V)$$ where $...
3 votes
1 answer
783 views

How can you determine the distance of a star using the magnitude equation?

In high school we are undergoing a short course about astronomy. It is stated that you can use the apparent and absolute magnitude (m, M) to get a distance (D) of a star, with the formula $$m - M = 5 \...
3 votes
1 answer
71 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
233 views

Given that a color index ($B-V$) of star A is lower than that of Star B, What can we say about the stars?

The color index $B-V$ of the star is defined as $$B-V\equiv M_B-M_V$$ Let us suppose it's given $$(B-V)^{(A)}<(B-V)^{(B)}\Rightarrow M_B^A-M_V^A>M^B_B-M^B_V$$ The notations are a bit confusing, ...
2 votes
0 answers
28 views

Is it possible that absolute magnitude for two stars is equal for some wavelength?

The title explains the questions. I don't find any problem with it. As If the two stars A and B do have equal absolute magnitude for some wavelength $\lambda_0$ then $$M_A=M_B$$ $$-5(\log d_A-1)+m_A=-...
2 votes
1 answer
54 views

When calculating absolute magnitudes of distant objects, do you use the light-travel distance or the comoving distance?

I want to calculate the absolute magnitude of GN-z11. Its light-travel distance is 13.4 billion ly (4.1 Gpc), its comoving distance is 32 billion ly (9.8 Gpc), and its apparent magnitude is $25.8$. ...
0 votes
2 answers
1k views

Conversion of UBVRIJHK magnitudes to luminosity?

So, I know that the standard for conversion from bolometric magnitude to luminosity established in 2015 equates to: L = 10^(-0.4 * magnitude) * 3.0128e28 Easy ...
4 votes
4 answers
4k views

What spectral type of star has an absolute magnitude of exactly 0?

We know that Vega is the star that serves as the zero point for the UBV color scale, and has an apparent magnitude of nearly zero (+0.02). But its absolute magnitude is +0.58, making it rather far ...
1 vote
1 answer
639 views

Calculate the absolute magnitude for a multi-star system

We know that the absolute magnitude of a single star can be calculated with the formulae: $$M_{\rm bol} = 4.75 -2.5 \log_{10} \left(\frac{L_*}{L_{\odot}}\right)\ ,$$ $$M = -2.5 \log_{10}(L_* / L_0),$$...
3 votes
2 answers
848 views

Is there a formula for absolute magnitude that does not contain an apparent magnitude term?

I have a star that I need to calculate the absolute magnitude of. I am given the temperature, luminosity, radius, mass, and distance in light-years. So I am wondering, what is the formula to compute ...
2 votes
0 answers
68 views

Apparent magnitude of a spherical body with specular, rather than diffuse reflectivity? How bright were Sputnik 1 and Vanguard 2?

How bright are geostationary satellites due to reflected sunlight? and Did Sputnik 1 tell us more than “beep”? What science was improved by information gained from its orbiting the Earth? now have me ...
1 vote
0 answers
445 views

Which star has the lowest absolute magnitude?

I have seen many lists of stars with the most luminosity, mass, and temperature, but I have never seen one that is about absolute magnitude. So I'm wondering, which star has the lowest absolute ...
0 votes
0 answers
120 views

Distance and absolute brightness

This is an exercise from a text, I’m learning from and I can’t understand it so I’m asking just to develop my knowledge: The explosion of V603 Aql (Nova Aquilae) took place in June 1918. The nova ...
3 votes
2 answers
217 views

Best way to simulate star sizes to scale in celestial sphere

Using the Hipparcos catalogue, I am trying to create a celestial sphere. As all the stars are a fixed distance from the centre of this sphere, the only way to differentiate the distances and magnitude ...
3 votes
2 answers
5k views

Calculating star radius from temperature and absolute magnitude - what am I missing?

In an attempt to visualise nearby stars, I've tried to get the star radius (measured in solar radii) using the equation provided on the following site: http://cas.sdss.org/dr4/en/proj/advanced/hr/...
2 votes
1 answer
188 views

Is there a relationship between stars' absolute magnitude, spectral class and relative location in a cluster?

I am interested to know whether a pattern has been observed with regard to the characteristics of a star (in particular, its absolute magnitude and spectral class) and its location relative to others ...
2 votes
1 answer
353 views

Distance to star using color index

I'm doing the following question: A star is observed with UBV magnitudes $m_u = 16.31$, $m_b = 14.52$, $m_v = 13.76$. Spectral analysis gives $M_{bol} = 7.31$, $BC = -1.02$, $(U − B)_0 = 1.222$. ...
3 votes
1 answer
441 views

How to convert luminosity at rest frame wavelength of 1450 A to absolute magnitude at 1450 A?

How do I convert the luminosity (erg sec$^{-1}$ Hz$^{-1}$) of a quasar at a rest frame wavelength of 1450 Angstroms to absolute magnitude at the same wavelength? I know that the bolometric ...
0 votes
2 answers
273 views

Rendering stars in 3D space - AbsMag to OpenGL scale values

I am using the AMNH's Digital Universe stars.speck file to render stars in 3D space. The speck contains parsec-scale coortinates, where our Sun is at 0,0,0. It also lists the AbsMag values - i.e the ...
2 votes
1 answer
58 views

How to interpret error of absolute magnitude of a star given data from wikipedia?

This Wikipedia page contains information about the star Spica in the rightmost table. A small snapshot of this table is below. In this table, the absolute magnitude is given as ...
3 votes
1 answer
164 views

Snowball Earth brightness

The Earth likely froze over almost completely about 700 million years ago. This increased its albedo significantly, and I wonder if that would have a considerable effect on its apparent magnitude from ...
1 vote
1 answer
114 views

Relationship between Hubble paramater and absolute magnitude

I have a set of data that is absolute magnitude of a star and its redshift. Is there any way to compute the value of the hubble parameter given that magnitude and redshift?
0 votes
0 answers
61 views

Is albedo ever greater than unity? How is it calculated for various surface diffusivities and specular reflection? [duplicate]

I'm trying to understand how albedo would be calculated for a body with well-characterized surface reflectance properties, so that it's absolute magnitude could be defined. One could argue that this ...
3 votes
2 answers
2k views

Table of absolute magnitudes of stars by spectral type and photometric band

I would like to find a table where I can, say, look for K5 dwarfs and read off that stars of that type have on average an absolute magnitude of X.XX in the infrared L band and Y.YY in the G band. I've ...
3 votes
1 answer
505 views

Absolute magnitudes with dust extinction

I have a distant $z\sim3$ galaxy with absolute AB magnitudes $M_B$ and $M_I$, where the central wavelengths of the $B$ and $I$ passbands are $\sim0.4\,\mu\text{m}$ and $\sim0.8\,\mu\text{m}$, ...
4 votes
0 answers
43 views

In the JPL small body browser, why is uncertainty on absolute magnitude "N/A"?

In the JPL small body browser, orbital elements are all provided with uncertainties and even a covariance matrix, such as for 2013 LA2. Very good. But underneath, the absolute magnitude is reported ...
4 votes
0 answers
70 views

Is there an acceptable value for the absolute magnitude of horizontal branch stars?

I'm writing a test for a gen-ed level astronomy class that I teach, and would just like a good reliable number to use as the basis for a distance calculation question. And yes, I know that real ...
1 vote
1 answer
80 views

Mass-magnitude relation of evolved stars

In short: what mass is appropriate for absolute magnitude $M_V \sim -7$? Some context: I'm processing the observational data (supernova light curve) and curve fitting gives me about $0.4M_\bigodot$ ...
5 votes
1 answer
4k 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 $...
1 vote
1 answer
1k 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 ...
31 votes
3 answers
6k views

Is the Sun visible from Proxima Centauri to human eyes?

I know that the light coming from Proxima Centauri is not bright enough to make it naked-eye visible from the Earth. Is the Sun naked-eye visible from Proxima Centauri?
1 vote
1 answer
125 views

Absolute/apparent magnitude and distance for HIP31978 inconsistent?

EDIT: I am still following up, but here's the latest response from Wolfram: Paclet servers are updated and optimized for each version of Mathematica, so I suspect you may be working on an older ...