Questions tagged [brightness]

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Closest/farthest point where the sun stops being the brightest star?

Which is the closest point to the Sun where it's not the brightest star anymore? My intuition is that this is either on a direct line between the Sun and Alpha Centauri, or between the Sun and Sirius ...
Michael Borgwardt's user avatar
2 votes
1 answer
216 views

How bright in the night sky would J0529-4351 (brightest quasar ever found) be if it were in our galaxy?

According to this article, the quasar (black hole) named J0529-4351 is the most luminous object in the known universe, being: 500 trillion times more luminous than the Sun To put it in terms easier ...
Ahmed Tawfik's user avatar
2 votes
0 answers
94 views

Calculation of twilight sky surface brightness based on object's apparent magnitude

I would like to be able to compute the sky surface brightness, which is based on the object's apparent magnitude. We have formulas, which allow us to compute the sky surface brightness based on the ...
Geographos's user avatar
6 votes
1 answer
192 views

Human Brightness perception and contrast

This is kind of an interdisciplinary question on human brightness perception and the ability to distinguish grayscales. To be honest, I wasn't sure if the Physics, Biology or Computer graphics SE site ...
Charles Tucker 3's user avatar
16 votes
2 answers
3k views

Why was Jupiter so bright; is it the "phase"?

When I was walking in the evening (2023-12-30) in the south of Germany (roughly 49°N 12°E) I noticed a single bright object in the sky, and (not being an astronomer) I wondered what it might be. So I ...
U. Windl's user avatar
  • 273
1 vote
1 answer
56 views

Visible angular size

Is it true that given two celestial objects of the same size and at the same distance, the fainter one will appear smaller? Is there a calculation that can be made about how smaller? Is it the same ...
Kim's user avatar
  • 11
3 votes
1 answer
91 views

Does the reflected light from Earth boost Venus' apparent magnitude when it is seen transiting the Sun?

During solar transits of Venus as seen from Earth, exactly 0% of Venus' disk is illuminated by sunlight, as expected. However during these transits, Earth is at opposition and fully illuminated by the ...
user267545's user avatar
2 votes
1 answer
41 views

Standard definitions (ISO?) about subjects related to light emitted by stars

I'm a big fan of astrophysics and astronomy. However i'm quite confused by reading these last years plenty of books on the subject with various definitions (vocabulary) and notations for the same ...
Vincent ISOZ's user avatar
1 vote
2 answers
128 views

How bright would an object need to be in order to block out stars at night?

I am wondering just how bright a star or other object would have to be before it starts blocking out the night sky. I'm looking for an answer in apparent magnitude. I'll note the Full Moon gets to ...
DrZ214's user avatar
  • 1,960
0 votes
0 answers
94 views

Bright out north Idaho

It is Oct 9th 10;30- 11:00 pm. I'm in Northern Idaho and it is as bright as it would be with a full moon (or brighter). The moon is going to be new in a few days and the sliver as it is won't be out ...
Trevor Dunnett's user avatar
16 votes
2 answers
3k views

Why are sometimes the brightest star of a constellation not named alpha?

From the Wikipedia page of Alpha Ursae Majoris: Alpha Ursae Majoris, Latinised from α Ursae Majoris, formally named Dubhe /ˈdʌbiː/, is, despite being designated "α" (alpha), the second-...
Snack Exchange's user avatar
27 votes
4 answers
6k views

Which is brighter, Mars as seen from Earth, or Earth as seen from Mars?

At their closest flyby, Earth is ‘new’ and dim from Mars, and Mars is ‘full’ from Earth and brightest as seen from Earth. When Earth is 39 degrees from the Sun then Earth is brightest as seen from ...
Mark Besser's user avatar
3 votes
1 answer
247 views

Solar eclipse impact on twilight

Has anyone observed the impact of the solar eclipse on twilight? I mean mostly the extension of the totality path in the atmosphere. I mean the pattern below: I - normal situation with total solar ...
Geographos's user avatar
6 votes
1 answer
240 views

Sky surface brightness vs magnitude limit visibility

I am wondering how we can calculate the magnitude limit of the celestial object, which could be visible at the given sky surface brightness conditions. We already know that Venus and Jupiter are ...
Geographos's user avatar
1 vote
0 answers
23 views

Surface brightness of transparent vs opaque galaxies

When describing surface brightness of galaxies, I would imagine that in some wavelengths some galaxies are mostly transparent and in other wavelengths some are somewhat opaque (for example galaxies ...
user1247's user avatar
  • 121
6 votes
1 answer
179 views

Does anybody know how to solve this Earth-Venus-Sun problem?

How can I find (in terms of the angle) the moment when in the system Sun-Earth-Venus, Venus can be seen the most bright if its brightness (flow received in Earth) is proportional to the size projected ...
Miguel Gutiérrez's user avatar
5 votes
1 answer
634 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 ...
longtry's user avatar
  • 403
2 votes
1 answer
516 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. ...
Camille Goudeseune's user avatar
1 vote
1 answer
304 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 ...
radastro's user avatar
  • 115
2 votes
1 answer
283 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. ...
Tivity's user avatar
  • 129
3 votes
1 answer
374 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 ...
Curtez's user avatar
  • 31
4 votes
2 answers
198 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?
LAKSHYA ANILKUMAR's user avatar
5 votes
2 answers
558 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....
Nau's user avatar
  • 153
0 votes
1 answer
118 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 ...
ALiCe P.'s user avatar
  • 1,017
1 vote
1 answer
936 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 ...
John's user avatar
  • 1,538
1 vote
1 answer
393 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 ...
TrEs-2b's user avatar
  • 111
0 votes
1 answer
112 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?
Constantthin's user avatar
19 votes
1 answer
2k 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?
user avatar
5 votes
1 answer
225 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 ...
user1299656's user avatar
8 votes
3 answers
698 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 ...
Vitor Z.'s user avatar
  • 153
2 votes
0 answers
77 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 ...
Ruslan's user avatar
  • 967
2 votes
1 answer
69 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 ...
user177107's user avatar
  • 2,689
3 votes
1 answer
1k 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 ...
Gimcrack's user avatar
  • 179
4 votes
0 answers
79 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 ...
Riley Scott Jacob's user avatar
4 votes
1 answer
422 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 ...
Puk's user avatar
  • 223
2 votes
1 answer
152 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 ...
wrb98's user avatar
  • 231
1 vote
1 answer
98 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 ...
uhoh's user avatar
  • 30.8k
1 vote
1 answer
687 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 ...
user177107's user avatar
  • 2,689
4 votes
1 answer
3k views

How do we measure the brightness of the stars?

How do scientists measure the brightness of so distant stars?
Sazzad Hissain Khan's user avatar