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Questions tagged [magnitude]

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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 ...
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2answers
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What is the difference between albedo, absolute magnitude or aparent magnitude?

What is the difference between albedo, absolute magnitude or aparent magnitude? I can’t really tell what’s the difference between them.
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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 ...
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3answers
53 views

Ratios of magnitudes instead of differences

The color index in the photometric system is defined by the differences in magnitudes between two wavelength filters, which gives the ratio of intensities. For example, to determine the B-V index, you'...
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2answers
69 views

Can I take logarithms of magnitudes (which are already log) [closed]

I'm investigating the relationship between the magnitude of quasars in various wavelengths, and their redshift $z$. I've found that if I take the $log$-$mod$-transform ($L_{mag}$) of the magnitudes, ...
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1answer
54 views

What are the apparent visual magnitudes of Spica A and Spica B?

What would be the (theoretical) apparent visual magnitudes of Spica A and Spica B (since they are too close together to be resolved telescopically)? The Spica System is 77 parsecs away, and the ...
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1answer
219 views

How to get the zeropoint magnitude?

I'm working with some data and I have some values named fluxmag0 and fluxmag0err that should correspond to the zero point values ...
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1answer
63 views

Stars magnitude

I have a question: assume two identical stars, but one is 10 times farther than the other from the earth. If the nearest star has a relative magnitude of 5, what is the relative magnitude of the other?...
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2answers
247 views

Can we see the stars the at the edge of the Milkyway?

This question proved much more difficult to formulate than I initially imagined. It concerns how far out in the Milky Way that we actually see with different telescopes. I know the Milky Way disk is ...
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1answer
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What's the brightness of Alpha Centauri from Proxima Centauri?

Self-explanatory, but I would like a comparison as well. Is the light enough to see by? How disrupted will the pitch darkness on the spot opposite of the 'solar pole' be?
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1answer
438 views

Finding the lens diameter of a telescope by magnitude

We have a telescope that can see stars with about +14 magnitude. how to find its lens (or mirror) diameter? (I mean the $D$ in formula $\theta = 1.22 \lambda / D $) I don't know whether I can assume ...
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1answer
149 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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0answers
53 views

How to derive uncertainty on photometric magnitudes of extended objects?

Suppose I have an astronomical image in some bandpass and I do photometry of an extended source (i.e., a galaxy). I measure an enclosed magnitude within my aperture or galaxy profile. What is a ...
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1answer
166 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
1k views

Absolute Magnitude and Absolute Bolometric Magnitude

What is the difference between Absolute Magnitude and Absolute Bolometric Magnitude, is it a case of multiply one by a constant to get the other? Can you give an example for a star, say Vega?
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1answer
573 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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0answers
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${\rm W/m}^2$ to Jansky [duplicate]

Lets assume I have a source and receive $8 \times 10^{-20}$ ${\rm Wm}^{-2}$ in (400-750) nm filter. How do you convert this received flux to the unit Jansky, is there a formula? (Ultimately, I want to ...
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1answer
1k views

What is the ugriz magnitude system?

While studying photometric redshifts, I came across the ugriz (or u'g'r'i'z) system for classifying magnitudes of galaxies, but I didn't find much information on the internet about how it works. Can ...
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1answer
1k views

What's the difference between apparent brightness and apparent magnitude? Are they the same?

I know that the equation for the difference in apparent magnitudes can be represented as: $\Delta m=-2.5\log\left(\dfrac{I_{1}}{I_{2}}\right)$ and the apparent brightness of a celestial object is ...
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1answer
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Why is the magnetic reconnection(of sun) effect many orders of magnitude faster than predicted by standard models?

Why is the sun's magnetic reconnection effect many orders of magnitude faster than predicted by standard models?
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1answer
662 views

Understanding “dex”

Hi I am trying to understand the concept of dex and how to use it in calculations. The usual definition is that it is the order of magnitude, so $10^{0.1}$ is $0.1$ dex. I want to do a simple ...
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2answers
436 views

How many stars are in the constellation Canis Minor?

I've read Wikipedia and found a list of stars in Canis Minor, and counted the number of stars in the list. I came up with 56 stars, a surprising number. I did some more research and found that Canis ...
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0answers
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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 ...
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1answer
950 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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1answer
282 views

What is the brightest star (relative magnitude) in M31?

I am wondering what the brightest individual star is in M31, the Andromeda Galaxy. Specifically, brightest as seen from Earth (so relative magnitude).
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1answer
827 views

What is the brightest star (by absolute magnitude) that we can see by naked eye?

Is it Rho Cassiopeiae or Mu Sagittarii? I see in the Stellarium 0.13.0 that Mu Sagittarii has absolute magnitude -11.43!!
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1answer
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Question about total absolute magnitudes of galaxies - negative or not?

I have seen this in a couple of places, but when the authors in the paper - http://chandra.as.utexas.edu/~kormendy/kfcb-accepted.pdf - wrote: "All 10 of our ellipticals with total absolute ...
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A question about stellar magnitude and the pogson's equation

Well surely the eye has different sensitivity to various wavelengths... will the pogson's equation not be affected if say I compare Betelgeuse and Rigel( both having a marked difference in spectral ...
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1answer
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What is the apparent magnitude limit for the naked eye?

If you only read the question, you will answer: ''That depends on the light pollution''. Yes, it does, but if you are in the darkest night sky (Bortle class 1), what magnitude would have the faintest ...