Questions tagged [apparent-magnitude]
Questions regarding how bright an object appears to be.
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questions
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1answer
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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 $...
5
votes
2answers
317 views
Brightest Stars (by its Apparent Magnitude) List beyond 300
I've been observing the stars and I have found some lists on internet that sort them by its apparent magnitude (m), so you end up with lists of brightest-stars like this one: https://www.star-facts....
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0answers
38 views
Estimate the shape of an object based on flux curve
Is there an aproximation to know the shape of a dust cloud,etc based on the magnitude/flux curves of stars they transit? Example, can I know if the shape is (at least in 2 dimensions) elliptical, ...
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1answer
90 views
Apparent Magnitude of First quarter Moon [closed]
Given
Apparent magnitude of moon is -12.5.
Distance of moon and earth is 384400 km.
Diameter of Moon is 31 arcmin.
Phase of moon is 0.5.
Find the apparent magnitude of first quarter moon.
1
vote
1answer
35 views
Why must all magnitude systems have a reference point?
Let $f_*$ and $f_0$ be the observed flux of a star and a reference flux in a particular spectral band, and let $m_*$ and $m_0$ be their respective apparent magnitudes. Then the star's magnitude is ...
1
vote
1answer
56 views
Has lunar opposition surge ever been observed from Earth? From Earth orbit?
This thorough answer to How long does lunar opposition surge last? Are there measurements of the full Moon getting suddenly brighter? details observations of lunar opposition surge by the Clementine ...
2
votes
1answer
43 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 $25.8$. ...
5
votes
1answer
157 views
How long does lunar opposition surge last? Are there measurements of the full Moon getting suddenly brighter?
Wikipedia's opposition surge is a short article and forwards shadow hiding and coherent backscattering as proposed mechanisms, but it doesn't really explain how much the brightness of the Moon ...
2
votes
1answer
47 views
Limiting magnitudes for different telescopes
I live in an extremely light polluted place. On a new moon night, magnitude 3.5 stars are at the limit of naked eye visiblity on clear nights, and the Orion nebula is visible as a smudge through my ...
3
votes
1answer
76 views
How to compute for Distance Modulus' uncertainty/ies?
This is rather a short question. As we know of;
Distance Modulus (DM) $\mu = 5 \log d - 5$
If $d = 168_{-14.9}^{+27.5}$ pc ($3\sigma$ value), how can I possibly compute for $\mu$'s uncertainty?
P.S. ...
10
votes
1answer
284 views
If Planet Nine indeed exists, how large a impact event there should be to be seen from Earth?
Recently I've found this news article, A meteorite crashed into the Moon during total lunar eclipse in January, about a collision into the moon that happened while a lunar eclipse was under way. ...
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0answers
26 views
How to calculate the luminosity of a quasar?
Is there a relation between the distance ($d$) and the apparent bolometric magnitude ($m_{bol}$) of a quasar and its luminosity ($L$) in watt? If so, what is that relation?
Thanks in advance!
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vote
1answer
58 views
How was Mars' very noticeable change in apparent magnitude explained by the Geocentric Model?
In the geocentric model, the Sun, the Moon, and the 5 naked-eye planets (Mercury, Venus, Mars, Jupiter, Saturn) all orbited Earth.
Today we know that the planets orbit the Sun, and thus they come ...
5
votes
1answer
180 views
How much dimmer is a partial solar eclipse that goes from -26.71 to -25.89?
Based on what I found in Stellarium, for Vlissingen, Netherlands, on July 2, 1666 there was a partial eclipse with a change of apparent brightness -26.71 to -25.89.
Is it valid to say based on the ...
3
votes
1answer
77 views
How to convert between AB and Vega magnitudes?
This might be a bit silly, but I'm really struggling with a conversion.
I have apparent AB magnitudes: $$m_{AB} = -2.5 \log_{10}(f_\nu [\mu Jy]) + 25$$ that I would like to convert to Vega magnitudes, ...
2
votes
2answers
76 views
Formula to calculate the apparent magnitude of Earth from arbitrary distances
I would like to calculate the apparent magnitude of Earth from various distances, say from the Voyager probe at this moment or from various stars in the sky. I know there must be a formula that I can ...
8
votes
1answer
100 views
How many photons does it take to determine the existence of a distant object?
This applies to any object, but I see the recent discovery of the oldest, most distant galaxy and it started me wondering what the limits are. Presumably you can do better with a bigger telescope and ...
3
votes
1answer
98 views
Approximate spectral type and luminosity given apparent magnitude and distance
I am looking at the data acquired from the Gaia DR2 survey. I found that most of the stars had their distance and apparent magnitude catalogued, but not their spectral type and luminosity class. Is ...
1
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0answers
57 views
How many streetlights should we turn off to decrease light on the ground by about 2.512 times?
I am looking for some guidance for a back-of-the-envelope-calculation to show that turning off street lights can make a difference for light pollution in the style of a Fermi problem.
My first step is ...
0
votes
1answer
42 views
Is it possible to calculate a star's apparent magnitude in another photometric band knowing its visual magnitude?
Or, in other words, is it possible to know a star's luminosity in a certain photometric band?
Proxima Centauri's Wikipedia page provides the apparent magntiude in each UBVRIJHK band (getting ...
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0answers
90 views
How long would it take to first detect a new object in the night sky given its apparent magnitude?
If an object as bright as the star Polaris (Apparent Magnitude +1.8) showed up in the night sky, it would be detected almost instantly by stargazers. If an object as bright as Pluto (Apparent ...
3
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2answers
59 views
Graph of apparent magnitude of Mars through time from around 2000 to present?
I tried to search online but failed to find a graph of the apparent magnitude of Mars over time from 2000 to present.
From Wikipedia:
Mars made its closest approach to Earth and maximum apparent
...
2
votes
1answer
166 views
A double star consists of two stars of equal brightness at equal distance from the Earth. What is the apparent magnitude of the combined object?
The magnitude of each star in the V-band is mV= 8.34. If these stars are so close together that they appear as one object, what is the apparent magnitude of the combined object?
I just want someone to ...
2
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1answer
100 views
When does a solar eclipse become noticeable?
For a human viewer located on Earth, is there an approximate apparent magnitude at which a solar eclipse becomes apparent in the form of a noticeable change in ambient brightness?
Assume normal ...
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0answers
41 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 ...
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votes
2answers
244 views
How bright are geostationary satellites due to reflected sunlight?
We are all familiar with seeing low-Earth orbit satellites scooting across the sky in a couple of minutes. Many of them are bright and readily identifiable with the naked eye. Geostationary satellites ...
3
votes
1answer
596 views
What is the "lunar irradiance" received by the Earth from the full Moon?
The solar irradiance received by the Earth is 1361 $W/m^2$. What is the lunar irradiance received by Earth from the full Moon in the same units? My first thought was to work it out via apparent ...
4
votes
3answers
584 views
Apparent magnitude of Milky Way?
We have apparent magnitude of stars, planets, DSOs. What about the apparent magnitude of Milky Way?
Can it be estimated?
3
votes
1answer
96 views
What is wrong with my calculations of Jupiter's apparent magnitude?
I was searching for a formula to calculate the apparent magnitude of a planet knowing its physical characteristics and stumbled upon this answer.
The final formula given is:
$$m_{planet} = V_{planet} +...
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vote
1answer
57 views
apparent and absolute magnitude of meteors and space debris
I have a question regarding the apparent and absolute magnitude of space debris objects or meteors reentering the earth's atmosphere. I already understand the difference between apparent and absolute ...
3
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2answers
196 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 ...
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1answer
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How is Comet SWAN C/2020 F8 doing? Will it become easily visible by eye?
The New York Times article How to See Comet SWAN in Night Skies says:
Astronomers have their fingers crossed that the comet will keep brightening in the coming weeks as it heads north, passing 52 ...
9
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1answer
1k views
Determining the extinction by counting stars?
Hi I'm a highschool student studying astronomy at school.
I learned that one can determine how much a luminosity of a star is reduced by counting stars, but I can't understand how it works. My ...
2
votes
1answer
243 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$. ...
4
votes
1answer
244 views
Total apparent magnitude of eclipsing binary system
This is a question from the 2016 USAAAO national exam, for which no solutions are given:
An eclipsing binary system has a magnitude $m_p$ = 14.2 during the
primary transit and $m_s$ = 13.7 during ...
2
votes
0answers
47 views
Minimum apparent magnitude of galaxy
currently I'm working on astronomy problem which deals with finding redshift of a galaxy. But the first part asks to derermine apparent magnitude of a galaxy:
Find what should be the minimum ...
0
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1answer
34 views
Extinction and reddening dataset
Where can I find a dataset containing the interstellar reddening and extinction values for all globular clusters, preferably in the HST/WFC3 system.
4
votes
1answer
100 views
Why is there "modulus" word in the "distance modulus" term?
The difference of apparent (m) and absolute (M) magnitudes of an object is called "distance modulus", which is related to the distance $d$ to the object in parsecs with equation
$$m - M = 5 \log \Big(...
3
votes
0answers
84 views
What is the apparent magnitude of the faintest stars visible during a full moon?
Assuming the viewer is far from any light pollution, it is a cloudless night, and humidity is very low. What is the faintest apparent magnitude of stars visible to the naked eye during a full moon (...
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vote
1answer
44 views
Estimating the abundance of type-Ia supernovae using magnitude limited survey
I would like to estimate the fraction of type-Ia supernovae in a magnitude limited survey (only including those supernovae that are brighter than a certain than a given fixed apparent magnitude).
I ...
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0answers
112 views
Apparent Magnitude / Apparent Brightness relationship help
I'm a high-school student that is currently working on a project that describes, using mathematical notation and explanation, how scientists can find the values of each of the properties of stars, ...
3
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1answer
160 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 ...
4
votes
1answer
78 views
Comparing different magnitudes. Is this statement correct?
I have two methods which allow for a detection of a signal that is at most of magnitude x. If method 2 can detect signal that are half a magnitude larger, i.e. fainter, let's say x.5 mag, is it ...
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vote
1answer
77 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 ...
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0answers
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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 ...
4
votes
1answer
129 views
Would one have to be more than halfway to the Oort Cloud for the Sun to appear as bright as the full moon?
Is this correct? If the Sun is 400,000 times brighter than the full moon am I correct in figuring that one would have to be about 632AU from the Sun for it to appear as bright as the full moon. If ...
4
votes
2answers
169 views
Galactic mass estimation from apparent magnitude and distance
Can we estimate the order of the total mass of any galaxy from the apparent magnitude and its distance to us? Just like
\begin{equation}
M_{galaxy}=c\times 10^{8}M_{\odot },
\end{equation}
where $c$ ...
2
votes
1answer
108 views
Light pollution and apparent magnitude of objects in solar system
Dust along the ecliptic scatters light, causing “light pollution” throughout the orbital plane of the solar system. If an object like, say, the sun's corona, had its brightness measured from above the ...
2
votes
1answer
329 views
What is the planet relative to earth that shows the greatest change in apparent brightness?
What is the planet relative to earth that shows the greatest change in apparent brightness?
I think the answer is Mars, and a quick google search reveals it is Mars.
I have my reasoning here, but I ...
2
votes
1answer
119 views
How would a flat mirror on the Moon reflect sunlight
I was solving a task that said (paraphrasing):
There is a flat mirror on the Moon, whose reflection coefficient is 100%, and observers on the Earth observe it as a star whose apparent magnitude is $...
