Questions tagged [light]

Questions regarding electromagnetic radiation in the visible spectrum.

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2 votes
1 answer
95 views

What is the diameter of a telescope lens that will capture the surface of Proxima Centauri b?

I been trying to find the way I can calculate the telescope lens diameter needed to see a star by the distance of the star or the planet from the earth. Is there any mathematical relation we usually ...
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0 votes
0 answers
60 views

What is the galactocentric aberration?

At the Wikipedia about an aberration, there is the phrase: a recommended galactocentric aberration constant of 5.8 µas/yr What is the galactocentric aberration? How is it calculated correctly? An ...
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4 votes
1 answer
110 views

Could the newly discovered glow in the solar system be antimatter?

Could the newly discovered glow in the solar system be a sparse cloud of interstellar antimatter slowly annihilating with the solar wind? The glow I am talking about is discussed at: https://www.nasa....
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12 votes
3 answers
3k views

How much light would be received on a rogue planet close to the galactic center?

I was wondering if anyone has ever attempted to estimate how much solar radiation would be received on a rogue planet floating in between star systems close to the center of the milky way, compared to ...
1 vote
4 answers
124 views

Stellar aberration without relative motion between source and observer

According to SR, there should be no aberration if source and observer move uniformely (as would be the case in terrestrial aberration). In this case we should find at least some celestial bodies that ...
2 votes
0 answers
64 views

Satellites or UFOs? [closed]

Last night in Greenville MI at around 9:15pm-9:25pm (I don't know the exact time) I saw what appeared to be a satellite appear and disappear and then a few seconds later another possible satellite ...
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3 votes
1 answer
93 views

Why can't we see the far rims of our galaxy by ordinary light?

I mean what is the relationship between the empty space between stars such that it contains sparse distribution of gas and our our inability to see the rims of our galaxy. I searched too long time to ...
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5 votes
1 answer
248 views

Crossing of particle horizon and a past light cone

What does it mean when a light cone intersects a particle horizon? Like here, about 2 billion years after the big bang? Does it have any significance? I went through a few simple equations and the ...
1 vote
0 answers
44 views

How can I estimate a stars surface temperature, luminosity, radius, and lifetime only knowing it's solar mass and peak wavelength? [duplicate]

For example: if a 10 solar mass star emits light at a peak wavelength of λ = 300nm. How can I calculate a stars surface temperature, luminosity, radius, and lifetime with this infomation?
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4 votes
1 answer
168 views

What does the surface of a star look like in visible light?

False colour images of the Sun show a highly complex structure near the surface with matter ejected and suspended in magnetic fields. But are solar prominences and coronal mass ejections visible to ...
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9 votes
4 answers
5k 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 ...
  • 115
2 votes
0 answers
58 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 ...
1 vote
1 answer
88 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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4 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 ...
2 votes
1 answer
49 views

Query about the definition of photometric zeropoints

In stscl page, apparent magnitude is defined as $$m=-2.5\log{\frac{{\rm DN}}{{\rm EXPTIME}}}+{\rm ZEROPOINT}\ ,$$, DN is Data number (I cannot understand what is meant by 'Data number'... they said it ...
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2 votes
0 answers
329 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 ...
-1 votes
1 answer
99 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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-2 votes
1 answer
96 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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6 votes
2 answers
298 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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2 votes
0 answers
113 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 ...
14 votes
0 answers
287 views

How would a cooled down neutron star look when illuminated?

Assume we have a neutron star that has cooled down so far that it no longer emits visible light. If we illuminate it with a powerful external light source, what would it look like? Would it reflect ...
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1 vote
1 answer
57 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 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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4 votes
2 answers
3k 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 ...
0 votes
0 answers
71 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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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 ...
31 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.)
1 vote
1 answer
293 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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5 votes
2 answers
233 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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0 votes
0 answers
115 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?
2 votes
1 answer
101 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 ...
1 vote
0 answers
85 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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2 votes
1 answer
81 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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20 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 ...
0 votes
0 answers
220 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?
1 vote
0 answers
111 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 ...
1 vote
0 answers
939 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 ...
4 votes
3 answers
220 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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0 votes
2 answers
107 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 ...
0 votes
1 answer
83 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?
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 ...
8 votes
1 answer
230 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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3 votes
1 answer
137 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 ...
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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2 votes
0 answers
107 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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1 vote
0 answers
57 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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2 votes
2 answers
69 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?
-5 votes
3 answers
381 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 ...
3 votes
1 answer
120 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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6 votes
1 answer
110 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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