30 votes
Accepted

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 ...
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16 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 ...
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9 votes
Accepted

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 ...
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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 ...
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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 ...
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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 ...
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  • 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 ...
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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 ...
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  • 216
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 ...
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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 ...
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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 ...
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  • 2,686
3 votes

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 ...
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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 ...
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  • 2,660
2 votes

Why do brighter stars/planets appear physically larger?

It is an optical illusion. Our brains associate brighter with bigger. This is how software like stellarium are able to make convincing views of the night sky: they play this in reverse and use larger ...
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2 votes
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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 ...
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2 votes

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?

You answer your question basically yourself with the calculation - that's the right way to approach it, your math is correct. Stars and planets are big enough, that simple geometric optics work well ...
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1 vote
Accepted

Conservation of specific intensity

The rays that come from area 1 and pass through area 2 (and hence the power emitted from area 1 that passes through area 2) will be emitted into a solid angle given by the (projected) area of area 2 ...
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1 vote

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

It's actually due to the Angular Diameter distance. I still don't understand the exact mechanism, but I can shed some light on it. The angular diameter distance can be written as $$d_A = \frac{\chi}{1+...
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  • 546
1 vote
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What would shadows look like on a planet with two suns?

You will have two half-shadows, and maybe an overlapping part where no direct light reaches the ground. Thus there will be a shadow where light of neither reaches the space. There will be a partial ...
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1 vote

How to calculate apparent brightness in relation to the sun

If you're just looking for an equivalent expression, but relative to the sun, the modification is pretty simple. Let's start with the original expression: $$B=\frac{A \cdot L_S \cdot R^2}{D^2 \cdot d^...
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1 vote

Strip Brightness in a Spherical System

It is the luminosity in a straight strip like this: (Credit: West 29 / CC BY-SA from here) where the center of the strip passes a distance $x$ from the center of the circle at closest approach. So ...
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