Questions tagged [light]
Questions regarding electromagnetic radiation in the visible spectrum.
314
questions
-1
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1answer
82 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 ...
-2
votes
1answer
85 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 ...
6
votes
2answers
72 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 ...
2
votes
0answers
60 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 ...
1
vote
1answer
33 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 ...
1
vote
0answers
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 ...
4
votes
2answers
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 ...
0
votes
0answers
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 ...
1
vote
0answers
35 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 ...
29
votes
6answers
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
1answer
47 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, ...
4
votes
2answers
64 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 ...
0
votes
0answers
74 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
1answer
90 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
0answers
79 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-...
2
votes
1answer
66 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 ...
21
votes
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
61 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
0answers
99 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
169 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
165 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
51 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
71 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
175 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
127 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
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
93 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
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 ...
2
votes
2answers
64 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
154 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
62 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
79 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
249 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 ...
1
vote
0answers
255 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 ...
9
votes
4answers
727 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
161 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
248 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
32 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
90 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
127 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
241 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
124 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
986 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
123 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
103 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
153 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
178 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 ...