Questions tagged [light]
Questions regarding electromagnetic radiation in the visible spectrum.
300
questions
20
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5answers
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
0answers
46 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?
3
votes
0answers
89 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
0answers
32 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
3answers
97 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 ...
0
votes
2answers
46 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
1answer
62 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
2answers
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
1answer
160 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 ...
3
votes
1answer
124 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 ...
14
votes
1answer
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 ...
2
votes
0answers
83 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 ...
1
vote
0answers
48 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 ...
2
votes
2answers
63 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
3answers
101 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
1answer
52 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) ...
6
votes
1answer
77 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. ...
0
votes
2answers
199 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 ...
0
votes
0answers
88 views
Slow moving, flashing star-like object in the sky. What could it be?
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 ...
9
votes
4answers
711 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 ...
4
votes
3answers
114 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 ...
0
votes
1answer
151 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?
2
votes
0answers
29 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 ...
4
votes
2answers
88 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 ...
3
votes
6answers
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 ...
16
votes
4answers
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?
0
votes
1answer
114 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 ...
2
votes
1answer
116 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 ...
0
votes
3answers
86 views
Absorption of light by matter
What determines whether or not photons can be absorbed by matter? Intuitively, the answer is that a charged particle can absorb photons (whether it's positively or negatively charged), and neutral ...
17
votes
2answers
937 views
Problem regarding the absorption lines of the sun
Some of the wavelengths of light that are emitted from the sun will be absorbed by atoms in the outer layer of the sun and also the atmosphere of the sun, and we see this as absorption lines in the ...
2
votes
2answers
84 views
How dark/bright are polar nights?
During the polar night directly at the pole the Sun sets once and—after a period of twilight—stays down for months at a time.
The only sources of non-human-made light are the stars, the auroras, and ...
0
votes
1answer
90 views
how long a light year on earth will seem [closed]
First of all, sorry if this is not the right StackExchange to ask this question, but i don't know a better place (open to suggestion in case).
So, the question:
Suppose that for some reason, we can ...
1
vote
2answers
117 views
Events I cannot explain
In the last few days I experienced two events I cannot explain. I watch the sky since I was a child so I'm aware of most events like satellites, ISS, Iridium flares, etc...
First event
It was about 22:...
1
vote
1answer
130 views
At what distance wouldn't the Sun cast a visible shadow anymore? [closed]
How far from the Sun would a (dwarf) planet have to be so that the Sun is dim enough that it doesn't cast a shadow when you're standing on the planet? What magnitude is the border in brightness beyond ...
2
votes
0answers
51 views
Is cosmological redshift caused due to expansion of space or distance traveled by light?
If the universe wasn't expanding, would light still be redshifted after traveling some distance?
Is there a way of being sure that it's the expansion that causes light to redshift and not just a ...
0
votes
1answer
79 views
First Confirmed Visual Observation of Gravitational Lensing
Is it possible to identify the first direct observation of the gravitational lensing?
What object was lensed, and where did the energy detected fall on the electromagnetic spectrum?
2
votes
1answer
52 views
Light levels on other celestial bodies
What I'm trying to achieve
For a series of realistic renders I am currently working on I am trying to calculate the light level on different celestial bodies, in terms of the luminous flux (in lumens)...
1
vote
0answers
35 views
What was up with the lights in the sky tonight? [duplicate]
I and my boyfriend where looking up in the sky tonight around 8:30 am. We noticed about 17 or more things, that looked like stars. They was perfectly spaced, and just vanished they was heading east. ...
1
vote
0answers
23 views
Light profile fitting related questions
I am computer scientist and now I'm working with some astrophysical projects. During this work I accumulated some questions and maybe here I would be able to find some answers or advice where to look ...
0
votes
1answer
88 views
If a black hole pulls every object in the universe, why there is a light around it?
I've seen some black hole images and I've seen some movies about it e.g(interstellar). I wonder why it has a light around it. Even if I know that light can't escape through it. Can someone enlighten ...
3
votes
0answers
47 views
If the distance between galaxies is increasing and the speed of light is constant will the most of the light from the universe ever reach us?
Will the light from other galaxies ever reach us if the universe is expanding?
42
votes
5answers
10k views
Are photons aged?
If a star is at a distance of one lightyear, how old are its photons when they reach earth (from the photons’ perspective)? If time dilation is near zero at light speed, can we assume that the light ...
-2
votes
2answers
245 views
Is Olbers' Paradox Nonsense? [closed]
Ok, this is a bold question, I know. But, let me explain: After first hearing about Olbers' paradox, I found that something seemed 'off' about it, so I looked into the subject as much as my skills (...
6
votes
2answers
132 views
Why is blue light extincted more strongly than red?
We know that blue light suffers extinction more strongly than red (examples include ISM, atmosphere etc.), but why? Is it a property of the shorter wavelength itself? Can someone provide a conceptual ...
2
votes
0answers
75 views
Did a galaxy get discovered more than 30 billion light-years away? How does one observe light older than the estimated age of the universe? [duplicate]
I'm more into questioning mainstream science and pseudo-science to remain open-minded.
Why is it that we are seeing light 30 billion light years away; when the estimated age of the universe is much ...
0
votes
0answers
61 views
can gravity be faster than light in some specific cases? [duplicate]
This is a follow up question from
If an event occurs at a point in space time what will an observer experience first, it's gravity or the light from it?
This https://en.wikipedia.org/wiki/...
4
votes
1answer
104 views
If an event occurs at a point in space time what will an observer experience first, it's gravity or the light from it?
Let's assume a person is close enough to an object in space time to be able to observe it's gravitational effects and the light coming from it.
If that object suddenly pops out of existence (...
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vote
0answers
30 views
If interstellar medium was dense plasma and light slowed down, would things appear to move slower far away?
Voyager 2 recently left the solar system and registered an increase in plasma density. If light moved slower in this dense plasma, would it appear like events in other solar systems played out slower ...
2
votes
1answer
99 views
How much photon is still in flight?
Since space is mostly empty, one might first think that the majority of the photons, e.g. emissions from the stars since the beginning of the universe, are still in flight and not absorbed by anything....
4
votes
0answers
335 views
Why the space is so dark even there are billions of stars and many quasars emitting light [duplicate]
In our galaxy itself, there are millions of stars, and there are many more other galaxies in our local group and billions in the observable universes.
For sure they all emit a lot of light, still why ...
