Questions tagged [brightness]

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5 votes
1 answer
125 views

What's the brightest magnitude that the ISS can appear from Earth's surface?

Heavens-above indicates that this evening, it will fly almost over my head (79°) with a sizzling magnitude of -3.9. What is the maximum brightness it can have? Is there a formula to calculate its ...
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2 votes
1 answer
139 views

How bright would Betelgeuse's supernova appear?

Popular science articles suggest that when Betelgeuse goes supernova, for some days it would appear as bright as the full moon. But I have no intuition about a celestial point source that bright. ...
1 vote
1 answer
90 views

Conservation of specific intensity

I am trying to understand the proof of the conservation of specific intensity. Here we are trying to prove that specific intensity at dσ1 and dσ2 along the ray emitted by a source is the same. I don't ...
2 votes
1 answer
172 views

Why are galaxies thought to get bigger with distance in an expanding universe model?

In an expanding universe model. In addition to galaxies getting fainter with distance, they are also thought to get bigger. Thus the surface brightness of the object should decrease with distance. ...
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3 votes
1 answer
182 views

Flashes in the Sky

Short Version: went camping into a very dark, remote location with clear air, no moon. Was able to see everything from the Pleiades and Orion, to the Southern Cross and the Magellanic Clouds (I live ...
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4 votes
1 answer
98 views

Brightness and flux density

The alpha star in a constellation has the highest brightness, but does that mean it has the highest flux density among the other stars in the constellation?
5 votes
2 answers
407 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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0 votes
1 answer
66 views

Question about calculating the ratio of volumes of two components of an eclipsing binary star

I'm trying to solve this task: At the maximum, the eclipsing binary star has a brightness of 6^m, and at a minimum of 8^m. Considering the eclipse to be central and the companion to be dark, find the ...
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1 vote
1 answer
484 views

What would shadows look like on a planet with two suns?

On planet Tatooine which has two (main-sequence I guess) suns people still have one shadow only. Tatooine's suns seem quite close to each other, so it may actually be the case that the two shadows are ...
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1 vote
1 answer
100 views

How to calculate apparent brightness in relation to the sun

I know that we can determine the apparent brightness of an object in our solar system using the following formula: $$B=\frac{A\cdot L_S\cdot R^2}{D^2\cdot d^2}$$ $B$ = Brightness of observed object in ...
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0 votes
1 answer
102 views

How can the author of this article conclude that earth-shine on the moon is 100 times brighter than moon-shine on earth? [duplicate]

I don't understand the reasoning of the author of this article, on page 26. How can he conclude that full earth-shine on the moon is 100 times brighter than full moon-shine on earth?
18 votes
1 answer
1k views

Exoplanet dip in transit light curve when the planet passes behind the star

In the animation below, I don't understand why the brightness slightly decreases when the planet is behind the star. Where does this effect come from?
5 votes
1 answer
162 views

Why is T Tauri So Dim?

I'm looking at stellar objects and doing some math here and... Now, I can't find these values directly listed, but from it's relative magnitude and distance, (10.27, 471ly,) I calculate T Tauri to ...
8 votes
3 answers
605 views

Can we visually perceive exoplanet transits with amateur telescopes?

Is it possible for an amateur astronomer to visually perceive an exoplanet transit by the change of brightness of the star via observations spaced over time, or is the variation of the brightness too ...
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2 votes
0 answers
44 views

What is the average luminance of the star background?

What is the luminance of the star background, i.e. of all the objects outside of the Solar system? E.g. if we measured average luminance of the sky from the far side of the Moon (so that solar and ...
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2 votes
1 answer
60 views

Why do brighter stars/planets appear physically larger?

Look at Sirius and then some 2nd magnitude star. Sirius appears physically larger despite both stars subtending approximately the same angular diameter. Callisto is far enough from Jupiter at its ...
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2 votes
1 answer
141 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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4 votes
0 answers
73 views

In terms of power delivered to Earth, what is the brightest object in the sky?

I was reading about TXS 0506+056, a distant blazar. The Wikipedia article mentions it is one of the brightest objects in the sky at both gamma and radio frequencies. This got me wondering — if we ...
4 votes
1 answer
291 views

Can a telescope ever increase the apparent luminance of an extended object?

From what I know about common telescope designs, telescopes don't increase the apparent luminance of extended objects compared to the luminance seen with the naked eye. In this sense extended objects ...
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2 votes
1 answer
98 views

Strip Brightness in a Spherical System

My question concerns the following problem, published in Galactic Dynamics by Binney and Tremaine and based on a work by Schwarzschild. Specifically, I am having difficulties in deriving the given ...
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1 vote
1 answer
74 views

How imperceptible will the 4-July-2020 penumbral lunar eclipse be?

Wikipedia's July 2020 lunar eclipse; Visibility says: It will be visible from some parts of North America during moonrise, South and North America, the extreme part of Namaqua Land in South Africa ...
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1 vote
1 answer
300 views

Is it possible to calculate how much a star's brightness dims when a planet transits in front of it from a viewer's perspective?

Last night I got to thinking about what would happen if Jupiter and Venus suddenly switched places. Since Venus comes the closest to Earth than any other planet and Jupiter is much larger, does that ...
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4 votes
1 answer
2k views

How do we measure the brightness of the stars?

How do scientists measure the brightness of so distant stars?