Questions tagged [light]

Questions regarding electromagnetic radiation in the visible spectrum.

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1answer
79 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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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 ...
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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 ...
11
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4answers
8k views

Why is twilight longer in summer than winter and shortest at the equinox

I recently decided to set my alarm clock to wake me up when it is "dark" out. In the end, I decided to set my clock to the earliest time that nautical sunrise is in my state (Illinois) and stick with ...
2
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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 ...
7
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2answers
370 views

Why isn't the moon orange all the time?

Since the night two days ago, the moon here in Israel appears to be orange as it rises, and then gradually becomes white as it continues travelling across the sky. This phenomenon has a great timing ...
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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 ...
2
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1answer
52 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 ...
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0answers
254 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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3answers
10k views

What happens to the 99.9 % of the sun-rays that do not fall on any planets or any other celestial body?

I assume that about 99.9% of the sun-rays that do not fall on any planet or any other celestial body keep on traveling farther and farther unto infinity. Apparently such rays get lost. Keeping in mind ...
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2answers
796 views

What is the difference between albedo, absolute magnitude or apparent magnitude?

What is the difference between albedo, absolute magnitude or apparent magnitude? I can’t really tell what’s the difference between them.
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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 ...
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2answers
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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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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 ...
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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.)
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0answers
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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 ...
17
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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 ...
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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
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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 ...
7
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1answer
285 views

How does V838 Monocerotis look today? Any subsequent light echo images, or is the party over?

This answer to the question V838 Monocerotis “light-echo” images morphed into nice video, but why so few original images? contains the following information below. There are other answers and more ...
2
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1answer
230 views

Why weren't the Hubble light-echo images of V838 Monocerotis supplemented by ground telescopes?

Drawing from this answer to V838 Monocerotis “light-echo” images morphed into nice video, but why so few original images? The V838 Monocerotis expansion (not a supernova) and the observation of the ...
2
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2answers
195 views

V838 Monocerotis "light-echo" images morphed into nice video, but why so few original images?

This NYTimes video shows what I think is a series of real Hubble images which have been "morphed" artistically to appear to be continuously expanding. (also see The V838 Monocerotis Star Still Has ...
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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 ...
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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?
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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-...
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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 ...
2
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3answers
530 views

Do photons slow down as they approach the event horizon of a black hole?

So, if a black hole is so dense, that light cannot escape, what happens to the photons as the approach and go past the event horizon (or some other horizon, about which I am ignorant)? Do photons ...
21
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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 ...
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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 ...
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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?
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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 ...
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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 ...
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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 ...
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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?
3
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1answer
879 views

Does the Sun's light travel fast enough to have a straight path to Earth?

When we travel through space, we use a curved path following an orbit to reach our destinations. As far as I'm aware, we could take a more straight line approach but it would require much more deltaV ...
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1answer
1k views

How high does light pollution reach into the sky?

I want to know how high does light pollution typically reach into the sky straight up? Has anyone ever researched this because I wonder if being at 10000ft elevation would reduce the amount of light ...
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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 ...
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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 ...
2
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0answers
55 views

How to calculate the light energy of a supernova? [closed]

I have been given a distance, an average flux, and a time period. How do I find the light energy emitted of a supernova over that time period?
6
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1answer
533 views

How bright are the outer planets, when at close range?

Seven probes have passed by or orbited outer planets. I wonder how their photos differ from the naked eye view one would have if one were actually there. Saturn is 10 AU from the Sun, which means ...
4
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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
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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 ...
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5answers
17k views

If light has no mass, why is it affected by gravity?

Light doesn’t accelerate in a gravitational field, which things with mass would do, because light has a universally constant velocity. Why is that exception?
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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
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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 ...
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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
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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?
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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
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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
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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. ...

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