30 votes

What's the brightness of Alpha Centauri from Proxima Centauri?

Not close to being able to read by. Proxima Centauri is about 13,000 AU from the two binary Centari stars. Together they have about twice the luminosity of the sun but at 13,000 AU, that's roughly ...
userLTK's user avatar
  • 23.9k
9 votes
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What is the ugriz magnitude system?

"ugriz" is short for U-band, G-band, R-band, I-band, and Z-band, detailed on the Wikipedia article on photometric systems: $$\begin{array}{|c|c|} \hline \text{Band}&\text{Effective Wavelength ...
HDE 226868's user avatar
  • 36.3k
9 votes
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Can we see the stars at the edge of the Milkyway?

Take a look at the HR-diagram. You have forgotten to take into account that stars come in vastly different luminosities. For example, we can barely see all red dwarves out to a distance of 10pc, ...
AtmosphericPrisonEscape's user avatar
8 votes
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Snowball Earth brightness

Earth is already pretty bright due to cloud cover, with a typical albedo of .3-.35 -- that is, it reflects about a third of the visible light that hits it. That means it couldn't get more than about ...
jeffB's user avatar
  • 380
7 votes
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Superscript-subscript uncertainty notation

When quoted like this they would usually be the most likely value (peak of the probability distribution) or the median value (where half the distribution is above or below), and then the superscripts ...
ProfRob's user avatar
  • 149k
7 votes
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Sky surface brightness vs magnitude limit visibility

The human eye has an angular resolution of about 1 arcmin. This means that the light coming from point like stars would be visible if it significantly exceeds the luminance of the sky over an area of ...
Ritesh Singh's user avatar
6 votes
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Stars magnitude

As @RobJeffries mentions, you can calculate the difference from the equations which define magnitude and flux. But this particular case is even covered in the Wikipedia article on apparent magnitude: ...
Glorfindel's user avatar
  • 4,790
6 votes
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Can you subtract magnitude of constant source to get magnitude of variable source?

The magnitudes don't sum and subtract that way: consider two 0.00 magnitude stars closely together. Is their combined magnitude 0.00? Actually, it is -0.75. This paper might help you with the ...
User123's user avatar
  • 2,879
5 votes
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What's the difference between apparent brightness and apparent magnitude? Are they the same?

Yes, $B$ and $I$ are the same things in this context. The $\Delta m$ you derived goes by the name "distance modulus" when one of the distances is set to $10\operatorname{pc}$. The thing to be careful ...
Sean Lake's user avatar
  • 2,946
5 votes
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How is the difference of bolometric magnitudes not dependent on the stars' radii?

The R in that equation is the distance from the star to observer, not the star radius. The light emitted from the star is distributed uniformly on a sphere of radius R, and when the light arrives to ...
prody's user avatar
  • 88
4 votes
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Understanding "dex"

The "Schechter-like" Equation 3 in that paper is meant to give the value of black-hole mass density in units of "number of black holes of a particular mass per volume per log black hole mass", with ...
Peter Erwin's user avatar
  • 16.7k
4 votes

What is the difference between albedo, absolute magnitude or apparent magnitude?

Albedo is a measurement of reflected light. It varies between 0 and 1, with 0 being completely black (reflecting no light) and 1 being completely white (reflecting all light). The albedo of coal is ...
Ingolifs's user avatar
  • 4,157
4 votes

Venus' magnitude during inferior conjunction

As the phase angle of Venus changes, so does its distance to Earth. More about modeling the phase angle dependence of apparent magnitude can be found in this answer to Calculating the apparent ...
uhoh's user avatar
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4 votes
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Venus' magnitude during inferior conjunction

I found references which indicate that Venus usually goes dark. Check out the graphs in this paper for one example. The exceptions happen when Venus' orbit, which is slightly out of the ecliptic, ...
Carl Witthoft's user avatar
4 votes
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Distance to star using color index

There is a relationship between $E(B-V)$ and the reddening in any other colour. The exact value depends on the type of dust, the extinction value itself and the intrinsic spectrum of the star (as does ...
ProfRob's user avatar
  • 149k
4 votes

Converting Light curve to Luminosity

To calculate a "luminosity light curve" from a time series of V-band photoetry, you need two things. You need to know the distance. The distance to Betelgeuse is uncertain and that means ...
ProfRob's user avatar
  • 149k
4 votes

When does a solar eclipse become noticeable?

It's hard to say because the situation is very similar to this question: How much of the Sun's disk must be covered for a visible shadow to be cast? The major problem lies in the sensitivity of ...
Geographos's user avatar
4 votes

Formula to calculate the apparent magnitude of Earth from arbitrary distances

The absolute magnitude of the Earth is about $H = -3.99$. This means, from $1$ AU away from the Sun and the Earth, the Earth has an apparent magnitude of $-3.99$. Voyager 1 is $152.26$ AU from the ...
WarpPrime's user avatar
  • 6,633
4 votes
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How can I convert a GAIA-magnitude "G" to Johnson "V"?

There is no function that converts $G$ to $V$ because the conversion depends on stellar temperature/colour. For Gaia EDR3 data the most useful transform for you is $$G-V=-0.02704 +0.01424(G_{bp}-G_{rp}...
ProfRob's user avatar
  • 149k
4 votes
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How to Determine Absolute Magnitude of a Galaxy using HST FITS Image

This was already answered by a post I initially ignored as I thought it didn't pertain to my problem. It literally answers everything, if you have found yourself in a similar boat to me, read the ...
Ataaamic's user avatar
  • 111
3 votes

How to get the zeropoint magnitude?

Magnitude is defined relative to a standard flux of a magnitude 0 object $F_0$. $$M = -2.5\log(F/F_0)$$ if the error is $F_E$, then $F =F_0\pm F_E$, so the magnitude M is $$ -2.5\log((F_0+F_E)/F_0) ...
James K's user avatar
  • 119k
3 votes

Ratios of magnitudes instead of differences

Consider for example these bright stars (V and B-V values from Yale Bright Star Catalog). Near V=0, B/V is ill-behaved, and B*V is near 0. ...
Mike G's user avatar
  • 18.6k
3 votes
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Finding luminosity of a star with magnitude

The ugriz values are just measures of the stellar brightness taken in 5 bands from the near ultraviolet u through to the near infrared z. You need the distance to the star to convert the apparent ...
ProfRob's user avatar
  • 149k
3 votes

Finding the lens diameter of a telescope by magnitude

The unaided eye can typically see mag 6 objects. With your telescope, you can see an additional 8 magnitudes. This requires a factor of $100^{8/5}$ of additional light gathering power (since 5 ...
Dr Chuck's user avatar
  • 4,304
3 votes

Graph of apparent magnitude of Mars through time from around 2000 to present?

TheSkyLive's Mars information page has graphs of its distance and apparent magnitude from Earth. If you set the same year range for each, you can see how the quantities are related. They provide ...
Mike G's user avatar
  • 18.6k
3 votes

Formula to calculate the apparent magnitude of Earth from arbitrary distances

The Earth has an absolute magnitude of -4 This means that from 1 AU and at zero phase ("full Earth") it would have a magnitude of -4. Of course the only place that satisfies those two ...
James K's user avatar
  • 119k
3 votes
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How do you carry errors for brightness magnitudes

You need to do what is called “propagation of uncertainties”. You can search to get more information on that, but briefly if you have some function $f(x)$ that depends on variable $x$, then the ...
Eric Jensen's user avatar
  • 4,864
3 votes
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Question about calculating the ratio of volumes of two components of an eclipsing binary star

You are using the formula in an incorrect way. The meaning of the formula is the following: the flux we receive on Earth is $$F = \frac{L}{4\pi d^2}$$ where $L$ is the total luminosity of the star and ...
Prallax's user avatar
  • 4,431
3 votes

Can you subtract magnitude of constant source to get magnitude of variable source?

In addition to @User123 answer, and assuming you are subtracting luminosities and not magnitudes, there is usually one more obstacle: the catastrophic cancelation. In short, if the difference between ...
fraxinus's user avatar
  • 2,839
3 votes
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Is there a difference between Vis and V when analyzing the magnitudes of stars?

For AASVO, Vis refers to estimates made visually by an observers eyeball. The best observers get to 0.1 magnitude accuracy, but mostly 0.2. V is for the V band in the Cousins/Johnson system. If you ...
TazAstroSpacial's user avatar

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