Questions tagged [light]

Questions regarding electromagnetic radiation in the visible spectrum.

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9 votes
4 answers
2k views

Huge galaxies seen from earth

How do we see whole galaxies or even the whole sun? The photons of light travelling from the sun cover a vast distance, so shouldn't we only see the bit that hits the earth and the rest would be ...
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  • 91
2 votes
0 answers
20 views

Slow moving pulsing light

I was looking at the stars as it was clear tonight. I saw a slow moving and slow pulsing star like object. It moved across the sky turning on and off a ‘light’ only being visible when lit and it was ...
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1 vote
1 answer
62 views

Lunar sky brightness

Looking at the report "The Measurements of Sky Brightness on Lunokhod-2"1, I read that the day time visible light sky brightness was so large that it was off the scale. Unfortunately I have ...
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  • 41
3 votes
2 answers
2k views

Is it possible to block the surrounding light in a solar eclipse if we made the moon bigger or closer to the earth?

Is it possible to block the surrounding light in a solar eclipse if we made the moon bigger or closer to the earth? In an eclipse, you always see a ring of light surrounding the moon, but I am ...
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  • 149
1 vote
1 answer
31 views

About photometric zeropoint: Why is the definition like $m=-2.5\log{\frac{DN}{EXPTIME}}+ZEROPOINT$?

In stscl page, magnitude is defined as $m=-2.5\log{\frac{DN}{EXPTIME}}+ZEROPOINT$, DN is Data number(I can not understand what's mean of 'Data number'.. they said it is 'one count', but count for what?...
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  • 109
2 votes
0 answers
132 views

DIY Sky Quality Meter: Conversion between Illuminance and Luminance

I am trying to create a homemade Sky Quality Meter (SQM) using a TSL2591 light sensor. This sensor measures Illumination (lux), but SQMs measure Luminance (mpsas). I have seen that there are many ...
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  • 21
-1 votes
1 answer
92 views

How come we see something xx light years away? [duplicate]

If we are at point A in the universe and something is say 13 billion light years away, wouldn’t we have to travel wayyyy faster than the speed of light from the Big Bang in order to turn around from ...
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  • 1,002
-2 votes
1 answer
86 views

Speed of light in cosmic voids [closed]

If temperature affects the speed of light (a contentious issue, I gather) then is it possible that the speed of light outside our solar system or galaxy, which might be minimally warmer than the ...
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  • 5
6 votes
2 answers
123 views

color of stars and temperature

I recently got questioned on why stars are the color they are. I know the color of a star depends on its surface temperature where hotter stars produce more light towards the blue side of the spectrum ...
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  • 61
2 votes
0 answers
68 views

Formula for calculating if an object can cast a visible shadow on the ground or not

I know that we can see the shadow cast by the light of Venus on the ground. I also talk with one person who said they were able to see the shadow even from Jupiter. Recently I've read something like ...
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  • 216
1 vote
1 answer
37 views

Calculation of time delay in NASA's STEREO project

I'm trying to solve this task: Astronomers recently managed to get an image of the entire surface of the Sun for the first time. This became possible thanks to the STEREO project. In 2006, two ...
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  • 1,017
1 vote
0 answers
49 views

What color would stars have with an apparent magnitude of ~-30? [duplicate]

The light of the Sun is white because our eyes are evolved to work with it as the primary light source. Other stars look white in the night sky because they are too faint to activate the color ...
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  • 187
4 votes
2 answers
2k views

How can we know if a star which is visible in our night sky goes supernova?

Let's say there is a star about 3000 light-years away from earth visible in our night sky. If this star were to go supernova tomorrow(not relative to earth's night sky), we would know about it 3000 ...
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0 votes
0 answers
69 views

How can a black hole stop light from being emitted when all observers see light traveling at the same speed? [duplicate]

Quite literally every science show talks about black holes with a similar phrase: so dense that nothing, not even light, can escape. Let's say I am in space a safe distance from an object. I drop an ...
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  • 119
1 vote
0 answers
36 views

From where the light comes? [duplicate]

Gravitational field of a supermassive blackhole is so strong that even light cannot escape from it (eg. black hole in the core of M87). In this case when a blackhole tears a star,a bright disk of ...
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30 votes
6 answers
10k views

Why does light accelerate instantaneously to c, while no other phenomena do it? [closed]

In physics, it always takes some time for a particle to move from rest to some speed. However, photons (light particles) accelerate instantly from zero to c. How? (A visualization would be helpful.)
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1 vote
1 answer
62 views

Nightsky observation : a light/star suddenly disappeared, why?

For starter, I'm a beginner/noob in astronomy so it might be an obvious answer but I keep asking it to myself I was watching the sky in the night looking for shooting stars, there was plenty of them, ...
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  • 113
5 votes
2 answers
117 views

Why would someone choose a lower resolution grating over a higher one when performing spectroscopy?

The higher spectral resolution grating would reduce the spectral range. Besides that, would a higher resolution grating reduce the signal per pixel? I thought I heard someone mentioned this to me a ...
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  • 1,051
0 votes
0 answers
85 views

Volume of the observable universe [duplicate]

What about the volume of the observable universe? Can we find it? And what is the result in cubic light years?
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2 votes
1 answer
98 views

Spectra of different stellar classes?

I'm beyond an amateur, but I've been failing to find this information and it makes me think I'm missing something. Anyway: I am trying to write a procedurally generated simulation that includes ...
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1 vote
0 answers
81 views

Is it likely there are more rogue planets than brown dwarfs, and that we just can't see them because they're too dim?

Among celestial bodies revolving around the galactic center directly, it seems the bodies of lowest mass (brown and red dwarfs) are the most abundant. However, when it comes to even less massive Y-...
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  • 1,538
2 votes
1 answer
72 views

How do the stars in the near-infrared (NIR) radiate?

Let's say we are studying the integrated near-infrared (NIR) light of a distant spiral galaxy. We would expect most of this light to be dominated by red giants stars and dwarfs. I assumed these stars ...
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  • 1,051
19 votes
5 answers
6k views

Is it suspicious that gravitational waves propagate at the speed of light?

Thinking about gravitational waves and the fact that they propagate at the speed of light, I was wondering if it isn't suspicious - the speed of light I mean. Does it perhaps point to something ...
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0 votes
0 answers
98 views

Astronomical data bases express spectra in flux density, e.g. ergs/s/cm2/Angstrom( or Hz) how can I calculate the flux, i.e. ergs/s/cm2?

I have light spectral data from astronomy data bases in flux density (flux/Angstrom or flux/Hz) and would like to calculate the flux. How can I calculate the flux from the flux density?
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1 vote
0 answers
101 views

Where does the energy of the decaying CMB go?

I would expect that energy of photons in the Cosmic ray Microwave Background gets less and less because their wavelengths are stretched due to the expansion of space. How can this be possible? Does it ...
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1 vote
0 answers
280 views

Bright light in sky that slowly faded away [closed]

North Carolina June 5th 2021 at about 1:45 a.m. my boyfriend walked to me to my car just to see a bright like just above the tree line. Didn’t think anything of it. Finished our goodnight talk and ...
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4 votes
3 answers
185 views

What escape velocity would quark stars have?

Quark stars are hypothetical compact stars that are denser than neutron stars and maybe the last stage of upholding matter before stars that collapse into a singularity. Neutron stars have escape ...
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  • 145
0 votes
2 answers
56 views

Seeming conflict between most distant objects and age of universe (both estimated)

There was a recent article on bbc.com for laypeople like me titled "The mystery of how big our Universe really is", which prompted me to post the following question in their comments section ...
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0 votes
1 answer
74 views

Traversing a proton within the Planck time

If I could travel a super small distance (proton) in an even smaller time (Planck time), how long would it take me to cross the observable universe?
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16 votes
2 answers
2k views

How distorted will our galaxy be if we are viewing it from several thousand light years away?

I saw this answer and read this sentence regarding the distortion of our galaxy when viewed above the galactic plane: Once you got to a point where the entire [sic] galaxy was within your vision, the ...
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8 votes
1 answer
195 views

The physical processes of emission lines in cosmic nebula

I think I understand how absorption lines in cosmic bodies occur. But after reading about the emission lines in quasars I am wondering more and more about the physical processes causing the emission ...
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  • 293
3 votes
1 answer
128 views

Could photons orbit a black hole if fired at the correct angle?

My experience with Kerbal Space Program gives me the impression that it's impossible to transfer from a stable orbit of one body to the stable orbit of another without deceleration. But is this true ...
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13 votes
1 answer
2k views

Does bending of light around the Sun depend on the wavelength?

If the energy of light is high, does its curvature differ from that of low-energy light around the Sun? In other words, if the wavelength of the light is shorter than another wavelength of light, then ...
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  • 179
2 votes
0 answers
98 views

I have a scientific paper on gravity, how do I publish it, and will my research benefit me? [closed]

I read a lot about gravity and discovered a hole in it, and I want to publish that hole, but I am not good at mathematics. To show that gap, what should I do? Should I use Newton's equations which are ...
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  • 179
1 vote
0 answers
51 views

What happens to the Fourier Transform of the Measured Spectrum?

What happens when you double the width of the entrance slit of a spectrograph, in turn letting in twice as much light, would there be an improvement in the Fourier transform of the measured spectral ...
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  • 303
2 votes
2 answers
65 views

Will the night sky ever be more stars than darkness? [duplicate]

Given enough time, will enough light from distant stars reach Earth so that our night sky will be more than 50% stars?
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-5 votes
3 answers
223 views

Why do people say travelling at the speed of light or faster is impossible? [closed]

Impossible assumes we know everything there is to know about, well, everything. There was a time when everything mad knew said that traveling faster than the speed of sound was impossible. These same ...
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3 votes
1 answer
75 views

How much does the equivalent width of a line change by the introduction of 5% scattered light?

How much does the equivalent width of a line change by the introduction of 5% scattered light? We know the equivalent width is defined as $W = \int_{-\infty}^{\infty} \bigg(\frac{1-F_{\nu}}{F_c}\bigg) ...
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  • 303
6 votes
1 answer
85 views

Looking for methods to preserve night vision

Does anyone have a method to preserve night vision so that a car or other passing light source does not ruin it? I have a dark location to observe the sky; however, it is near a rarely used dirt road. ...
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  • 1,519
0 votes
2 answers
331 views

Does a photon need to have EXACTLY the right energy to be absorbed by a gas molecule?

From an answer to this question, https://physics.stackexchange.com/questions/281660/how-does-an-electron-absorb-or-emit-light, Absorption of a photon will occur only when the quantum energy of the ...
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  • 13.8k
1 vote
0 answers
401 views

Slow moving, flashing star-like object in the sky. What could it be? [closed]

The sky was particularly clear last night and I noticed an extremely bright star. I thought it was venus possibly but it was too low down and was flickering craziy. That meant that it couldn't be a ...
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  • 11
9 votes
4 answers
734 views

Is there a term for "path of the Sun at a given point of the Earth"

I want to buy a house and I'm asking myself what quantity of daylight the various sides of the house receive. I know the house is roughly oriented in the east-west direction. But I'd like to know the ...
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4 votes
3 answers
216 views

Starlight: are the rays that we see here on Earth parallel?

Are the rays of light emitted from stars that are perceived by an eye here on Earth parallel? Do they travel in a straight line from the star to the eye, never crossing, and equidistant? Do they ...
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0 votes
1 answer
284 views

If it only takes 8 minutes for that light to reach the Earth, what took up most of the time? [closed]

If it only takes 8 minutes for that light to reach the Earth, what took up most of all that time to get to the Earth?
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  • 1
2 votes
0 answers
37 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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  • 606
4 votes
2 answers
104 views

How much light comes from quasars in an AGN?

From what I've been able to gather, the very bright spot at the center of galaxies is produced by both the central quasar and a dense cluster of millions of stars that surround it. How much of the ...
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3 votes
6 answers
3k views

If an exoplanet transit we are seeing is 13000 light years away, are we seeing a 13000-year-old orbit? [duplicate]

If a star is 13000 light years away, doesn't that mean we are seeing 13000-year-old light? If it does, then does that mean when we discover a planet with dimming star light, we are seeing a planet ...
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  • 177
16 votes
4 answers
3k views

Can a star emit heat but no visible light?

Can a star emit enough heat to allow human life on its planets, however emit no visible light? If so, what problems would this pose?
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  • 169
0 votes
1 answer
132 views

Faster than light?

From what popular science tells us, if I travel at close to the speed of light, I'd age slower. So if I travel at 99% of SOL and travel the distance of one light year, for other people one year has ...
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  • 557
2 votes
1 answer
282 views

How do the sun's light rays come to the world?

How do they come to the world? One of my friends who is a flat earther told me about how the rays seem to gather at one point, which sort of proves that the sun is close to us and not very big, in his ...
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