# Questions tagged [magnitude]

Questions regarding the brightness of objects in a defined passband.

18 questions with no upvoted or accepted answers
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### Conversion of Magnitude to flux using zero point in AB Magnitude

I want to calculate the flux of the 5 sigma limited magnitude. It is given that the zero point magnitude of NB964 is 28.77 and 5sigma magnitude is 25.45. The following example is from A large, deep ...
47 views

### What is the Chołoniewski method of estimating galaxy luminosity functions?

This paper describes a method to estimate the reddening of AGN using various methods, mostly to do with the intensity ratios of different absorption lines. It also mentions the Chołoniewski method, ...
• 2,517
48 views

I'm considering doing research on SDSS spectral classification (STAR, GALAXY, QSO) with machine learning for my school dissertation. Not sure if this is an appropriate place for these kinds of ...
70 views

### starting from SSP spectra to evaluate galaxy spectrum and observed mag

I know that the galaxy spectrum, namely the flux per unit wavelength versus the wavelength, is the sum of the Simple Stellar Population (SSP) spectra at a fixed redshift (e.g. similar to eq. 1 in ...
• 51
134 views

### Why does spectral class and U-V colour correlate slightly differently for main sequence, giant and supergiant stars?

In this diagram the $x$-axis is spectral type for stars and the $y$-axis is B-V colour. Taking Series 1 as the Main Sequence, Series 2 as Giants and Series 3 as Super-giants. Why the spectral class ...
• 31
1 vote
66 views

### magnitude calculation if a blackbody's radius and temperature are provided

I know it is necessary to convolve its spectrum with the transmission curve of a filter. Are there any online tools or codes available for calculating a BB's magnitude in any specific band (e.g., ...
• 3,137
1 vote
136 views

### Photometry in SExtractor vs Python

I wanted to find stars in the dwarf Spheroidal (dSph) galaxy. I performed photometry using SExtractor and in Python using DaoStarFinder and other astropy packages. However, while extracting the ...
1 vote
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, ...
1 vote
147 views

### How to calculate absolute magnitude of planets?

Knowing: Star's radius $r_s$ , luminosity $L_s$, and absolute magnitude $V$ Planet's radius $r_p$ , albedo $a$ , and distance $d_s$ How can you calculate the absolute magnitude of a planet in a ...
• 11
1 vote
99 views

### Errors in photometric magnitudes from SDSS DR16

I'm playing around with the data in the SDSS DR16, but the magnitudes have huge uncertainties: ...
• 2,517
1 vote
43 views

### What magnitude stars are visible during a quarter moon, during nautical twilight?

Assuming I'm looking for stars at least 50° from the quarter moon, is there any way to determine what magnitude stars would be visible to the naked eye, in a sky without light pollution, during ...
• 1,467
1 vote
138 views

### Binned of phase-folded light curve

How I can bin a magnitude phase-folded lightcurve? I take mean values magnitudes and it's uncertainties but this is wrong.
1 vote
41 views

### How can I get the fluxes of fetch_imaging_sample? - astroML

I'm working with astroML in Python and I need to get the fluxes from the magnitudes in r band of fetch_imaging_sample(). ...
• 11
1 vote
126 views

### Regression line in a colour-colour diagram

A colour-colour diagram (CCD) like this compares the difference in magnitudes at different wavelengths. The trend in the pattern of colour-colour comparisons tells us about what type of source the ...
• 2,517
1 vote
126 views

### Relation between phase and magnitude

Given the phase of a planet or satellite, I can find the area illuminated visible to us, if we consider a 2D surface. But how do I find the percentage of illuminated area visible considering it a 3D ...
44 views

### converting rms to limit flux

My question is simple: if I have an RMS value (the standard deviation for my background) at 1 sigma, and I also have the zero point of my observation, how can I transform that value into the limiting ...
101 views

### Calculating the Flux density through different photometric filters

For a project I wrote the following python script for calculating the flux density. My question is: If the user enters for example magV = 22 and the user selects the B filter instead of the V filter ...
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