Questions tagged [brightness]

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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 ...
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2 votes
1 answer
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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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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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2 votes
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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?
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5 votes
2 answers
372 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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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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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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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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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?
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18 votes
1 answer
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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?
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5 votes
1 answer
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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 ...
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7 votes
3 answers
590 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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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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1 answer
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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
126 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
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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 ...
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4 votes
1 answer
272 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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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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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 answer
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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
1k views

How do we measure the brightness of the stars?

How do scientists measure the brightness of so distant stars?
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