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

Just before the planet goes behind the star, we see the light directly from the star as well as the light reflected from the planet's surface. When the planet is behind the star, we no longer see the ...
Connor Garcia's user avatar
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25 votes

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

We can use the expression that is commonly used to estimate the apparent magnitude of a planet or asteroid in the Solar System: $$\boxed{m=5 \log \frac{1329}{d \cdot \sqrt p}+5 \log (D_s \cdot D)-2.5\...
Albert's user avatar
  • 2,182
24 votes

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

Bayer didn't sort the stars strictly by brightness. He classified them as "first magnitude", "second magnitude" (and so on) following the traditional magnitudes assigned to stars ...
James K's user avatar
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22 votes

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

tl;dr: There's about a 1.4 mag oscillation due to $1/r^2$ effects and only a very tiny residual due to illumination angle. I went to JPL's Horizons and extracted the distances between Jupiter and the ...
uhoh's user avatar
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18 votes
Accepted

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

Jupiter appears particularly bright because it is close to Earth at the moment, it is also high in the sky (in the Northern Hemisphere). However its brightness doesn't vary that much. Jupiter reached ...
James K's user avatar
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17 votes

Can we visually perceive exoplanet transits with amateur telescopes?

Amateur equipment is good enough. But you cannot detect it with a naked eye. The change in flux for a passing exoplanet in transit is roughly 1%...2% at most for the larger exoplanets - and it is a ...
planetmaker's user avatar
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16 votes
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Which is brighter, Mars as seen from Earth, or Earth as seen from Mars?

At it's brightest, Earth is a rather impressive magnitude -2.5 when viewed from Mars1 (the maximum brightness depends on how favourable the elongation is, but it isn't usually brighter than -2) At the ...
James K's user avatar
  • 125k
11 votes

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

Without much math, the answer is relatively simple when we look at two facts: Earth is bigger than Mars. Size of the cross-section (or rather illuminated area) matters for brightness. The path of the ...
planetmaker's user avatar
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9 votes
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Brightest Stars (by its Apparent Magnitude) List beyond 300

The Yale Bright Star Catalogue lists stars brighter than about magnitude 6.5. It is available as a compressed text file documented in the readme file I've also made a google sheets version sorted by ...
James K's user avatar
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9 votes

Why is T Tauri So Dim?

According to Herczeg & Hillenbrand (2014) the intrinsic bolometric luminosity of T Tau is about $7L_\odot$ (for an assumed distance of 479 light years). The main difference between their estimate ...
ProfRob's user avatar
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9 votes
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Why are sometimes the brightest star of a constellation not named alpha?

It's true that stars are lettered in order of brightness. So, in a constellation the brightnest star is (Alpha), the second brightest (Beta) and so on. That is why most of the First Magnitude Stars ...
Nilay Ghosh's user avatar
  • 4,695
8 votes

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

Setting up the problem Here is a little picture of our geometry (nothing to scale): Here, $i$ is the phase angle, $v$ is the distance from the Sun to Venus, $e$ is the distance from the Sun to Earth ...
Connor Garcia's user avatar
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7 votes

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

Mars at its brightest as seen from Earth can be brighter than Earth at its brightest as seen from Mars. But it's complicated because of the relatively large eccentricity of the orbit of Mars, so the ...
PM 2Ring's user avatar
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7 votes

Flashes in the Sky

Interesting! Could you provide a few more details: what date/time? roughly where in the sky (nearest constellation, as well as how near to the horizon/which cardinal direction would be helpful)? It ...
Keyan Gootkin's user avatar
7 votes
Accepted

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
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7 votes
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How do we measure the brightness of the stars?

The term brightness, or apparent brightness, is used to describe how bright a star appears to us from Earth. The term luminosity is used to describe how bright the star is physically, also called ...
sbjartmar's user avatar
  • 186
5 votes

Can we visually perceive exoplanet transits with amateur telescopes?

Can exoplanet transits be detected visually with amateur equipment? No. The magnitude change is too small. With proper equipment, transits can be detected by amateurs. For example, American ...
JohnHoltz's user avatar
  • 8,032
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
3 votes

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

The ISS maximum brightness is reported at about -5.9, sometimes -6. I guess you could technically estimate it analytically by considering how much light it receives, but I imagine that would be messy ...
Marco Leonardi's user avatar
3 votes
Accepted

How bright would Betelgeuse's supernova appear?

A typical Type II supernova has a peak absolute magnitude of -17. Betegeuse is ~170 pc away, so its supernova would be 289 times dimmer, corresponding to a magnitude increase of 6.15, so its apparent ...
WarpPrime's user avatar
  • 6,683
3 votes

Brightest Stars (by its Apparent Magnitude) List beyond 300

It's serious overkill, but https://www.usno.navy.mil/USNO/astrometry/information/catalog-info lists many catalogs and their current recommended/usability status. Unfortunately, it's not 100% complete ...
Guest's user avatar
  • 31
3 votes

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

The author says that the difference between the factor of 100 and the geometric increase due to area and albedo is because of "atmospheric absorption and directional effects". The former is ...
ProfRob's user avatar
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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
  • 4,441
3 votes
Accepted

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

Can there be no telescope design... that makes extended objects appear "brighter"... than with the naked eye, by somehow overcoming the limitation of the observer's pupil? I've left out all ...
uhoh's user avatar
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3 votes
Accepted

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

Completely imperceptible except to instruments. Space.com reports In general, most people don't notice the penumbral shadow projected on the moon until at least 70% of its diameter is covered. Some ...
James K's user avatar
  • 125k
3 votes

Can we visually perceive exoplanet transits with amateur telescopes?

Of course transits are observable with telescopes; this is the main method for detecting exoplanets, see Wikipedia's Methods of detecting exoplanets; Transit photometry. Unfortunately, they can do ...
User123's user avatar
  • 2,879
3 votes

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

I think your last sentence summarizes perfectly units in astronomy: it seems like a huge mess. Your table shows correctly some various units for measuring "things that emit light", but there ...
pela's user avatar
  • 38.7k
3 votes
Accepted

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

Let's collect some data: Earth has an absolute magnitude of -3.99 Venus has an absolute magnitude of -4.4 (Source Wikipedia Venus and Wikipedia Earth) Absolute magnitude equals the apparent ...
Ralf Kleberhoff's user avatar
3 votes

Human Brightness perception and contrast

After some time I found the answer: Actually the CIELAB definition in Figure 1 in my question and the Grayscale standard display function in Figure 2 are quite similar, if the x and y axes of the ...
Charles Tucker 3's user avatar
3 votes
Accepted

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

The (boldly titled) omnicalculator can do luminosity calculations. At 500 trillion solar luminosities, this object would have an absolute magnitude of -32, and if placed at 26000 light years distance,...
James K's user avatar
  • 125k

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