Questions tagged [light]
Questions regarding electromagnetic radiation in the visible spectrum.
263
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1answer
48 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 ...
0
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0answers
30 views
What were the moving lights in the sky tonight? [duplicate]
Tonight we saw moving lights in the sky south east of Orion's belt. Anyone any ideas what they were? About 20 of them all going in the same direction east.
3
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0answers
44 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?
40
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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
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2answers
188 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 (...
5
votes
2answers
93 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
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0answers
67 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
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0answers
31 views
line of at least 20 lights moving across the sky [duplicate]
We watched a line of at least 20 satellites moving in a line across the sky. They were visible to the naked eye. Could they be Starlink satellites? We are in Sandbach, Cheshire. It was about 18.00 ...
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0answers
60 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
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1answer
97 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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0answers
26 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
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1answer
94 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
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0answers
331 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 ...
1
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1answer
111 views
How much starlight do black holes absorb?
Can it be calculated how much light from other stars a black hole of certain sizes would absorb? And how long will it take for the number of active stars to decrease to the point where Hawking ...
2
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1answer
26 views
Does The ISW Effect Predict Net Redshift Over Distance?
The Integrated Sachs–Wolfe (ISW) effect is concerned primarily with the study of the Cosmic Background Microwave Radiation (CMBR), but seems to demonstrate that photons passing through voids suffer a ...
3
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1answer
55 views
Beneficial astronomical uses of satellite constellations like Starlink?
Has any thought been given to software that would use predictable occultations by Earth-orbiting satellites to improve (rather than degrade) astronomical observations?
Potential challenges I could ...
6
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3answers
2k views
Chromatic aberration in lens
Is there a way to prevent chromatic aberration without using an achromatic lens in refracting telescopes or in any other instruments...?
6
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1answer
400 views
Is the resulting light from a supernova a product of photons bouncing around in the Sun?
I was thinking about how photons formed in the centre of the Sun take quite a long time to exit the surface. And it occurred to me that at the end of a star's life (during a supernova, given that it's ...
5
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1answer
70 views
What is the intensity distribution of visible light over the solar disk?
What is the distribution of the visible spectrum over the solar disk?
Images of the Sun using the visible spectrum suggest that the light emmitted from the edge is almost equal to the light emmited ...
6
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1answer
136 views
Does light from the sun reach the surface of Venus
I am aware we have images from the surface of Venus from the Venera missions but I am not sure if those images are taken using the visible spectrum the human eye can see. This is why I was wondering ...
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1answer
139 views
What is the final destiny of a photon?
What happens with a photon when it moves ouit of a galaxy into the 'infinity void', where there's nothing but 'darkness'? Does the photon decay in the end when there are no interactions?
1
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1answer
133 views
How to find the source of the light? [closed]
There are millions of galaxies out there in the entire universe. When a telescope is set to a direction to to identify the stellar objects, it can capture all lights from all the objects. How do we ...
6
votes
2answers
211 views
What's the actual speed of electromagnetic radiation in space?
The speed of EM radiation is very slightly less than $c$, because space is not quite a vacuum. Say EM travels at $(1-\varepsilon)c$.
For example, this results in a slight delay between receiving a ...
5
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1answer
86 views
Do all stars of a given age and mass have relatively the same emission spectrum?
My understanding is that much of the visible light that we see during the day is given off from the Sun, and that means that most of the colors that we see are dictated by (with the exception of ...
4
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3answers
162 views
How do we measure distance in space?
I know that you can calculate the distance to another star for example, by using the phenomenon redshift to determine how much it has redshifted because of the expansion of the universe. But how do ...
0
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0answers
45 views
really fast moving star-like light [duplicate]
I don't know ANYTHING about astronomy but I know what I saw and 2 of my siblings saw it too. I initially thought it was a shooting star, but a Google search quickly made it clear that it wasn't.
it ...
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0answers
54 views
How is “surface brightness dimming” derived from redshift in the NED extragalactic database
I have several questions regarding “Surface Brightness Dimming” in the “Quantities Derived from Redshift” section of the Nasa/ipac Extragalactic Database.
As an example, please use quasar IRAS F08279+...
3
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3answers
250 views
Why doesn't it hurt to look at stars?
If I stare at the sun, it's bright and blinding. However, if I look at a star in the sky, it doesn't hurt. What causes this loss of energy that would otherwise damage one's eyes?
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1answer
77 views
how to define the universe itself is expanding greater than than the speed of light?
since we observe galaxies and other steller objects in very tiny tiny scale, and how we can understand that the speed of expansion on universe is higher than the speed of light ?
even using the ...
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0answers
50 views
Could Hubble's Law simply be light's frequency decaying over time? [duplicate]
Is it proven that the frequency of EMR does not decay (at all, ever), and if not, could the observations that led to Hubble's Law simply be that the frequency of light decays over very large durations/...
2
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3answers
176 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 ...
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0answers
21 views
Polarization of an emission line
Say I have a flux density spectrum of a galaxy, as well as polarization spectra for the object in U, Q, and P. I want to find the polarization of some emission line in the spectrum. First, I can fit a ...
0
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1answer
104 views
Could an object, assuming possible, escape black hole by travelling above constant speed? [closed]
I am always hearing that after travelling inside a given BH's event horizon, the escape velocity is greater than c, which makes it impossible to escape.
Suppose an ship is inside a BH. Assume it is ...
2
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2answers
122 views
Radiative Flux, Irradiance and Luminosity confusion
First of all I know there is a similar question here, but I feel is wasn't answered at all.
My question is that I have seen many texts which says that Radiative Flux is equal to the Irradiance of a ...
2
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1answer
58 views
How do radio telescopes gather information about visible light?
Is the first image of a black hole that was captured by the Event Horizon Telescope what would be seen with a large enough optical telescope (or with the naked eye from a proper distance of the black ...
0
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1answer
133 views
If a black hole does not emit light, how can one take a picture of the black hole itself?
There's some discussion that the image composed by the Event Horizons Telescope is really just an accretion disk. To "take an image" of something, you need the light reflecting off of the surface of ...
5
votes
1answer
145 views
What is the actual visual characteristics of a black hole?
Is there a safe distance in which a black hole can be observed with the human eye? What is a safe distance?
I have seen many computer simulated and artist renditions, and I am not sure if they ...
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3answers
110 views
If FTL travel is possible can i look back in time to a younger earth? [closed]
For this question assume that.
We found a way to go faster than light.
I build a ship that could go faster than light and go to another planet with this ship in the span of mere hours. The ship was ...
1
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1answer
73 views
Was is the angle needed to see a glory (a rainbow-like effect) from space off the Earth? [closed]
What positions would the Earth, Sun and viewer need to be to see a glory (a rainbow-like effect) from space?
What position would they need to be in to reproduce this picture?
Source: Gizmodo (NASA ...
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0answers
60 views
Definition of the light that is projected by a celestial body/luminary [closed]
I'm creating an application which will simulate the light created by sun or moon on a 3d topographic map of Earth. Something like this:
Is there a word or definition for this light/light projection?
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1answer
108 views
Possible to use tachyons to explore black hole?
I read on a Wikipedia article lately that tachyons are theoretical particles which always travel at or above the speed of light. That means that when one passes us, we see two images, a blue shifted ...
2
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1answer
89 views
Are there any ways in which the light time difference between the center and the edge of the solar disk is noticeable?
In the ABC News video New space discovery has astronomers buzzing at about 02:30 Dr. Hakeem M. Oluseyi explains that the shortness of FRBs (before dispersion) suggests a compact source size and ...
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1answer
108 views
Can light be curved due to heavy gravitational force?
Lets suppose there is a huge planet having large amount of gravitational pull, then will the light passing through the planet get attracted towards it.
2
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2answers
317 views
What is the difference between albedo, absolute magnitude or aparent magnitude?
What is the difference between albedo, absolute magnitude or aparent magnitude? I can’t really tell what’s the difference between them.
5
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2answers
104 views
What is the difference between the way light travels in a gravitational field and the way it travels through an expanding universe?
A photon is travelling through space. As it travels, the space through which it travels is expanding
Does this describe
A - a photon travelling from a distant galaxy to earth
B - a photon travelling ...
6
votes
3answers
180 views
Universe isn't infinite theory
Forgive me if any of my terminology is off I am no physicist but I have wondered about this question for a while.
I have read in various books that if the universe was infinite, and uniformly created ...
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2answers
98 views
Why is it that night has a almost a bluish tint to it instead of red?
From my understanding/been told, the color red has the ability to travel the farthest in our atmosphere, being the reason why we have red sunsets and such. But with this in mind, why is it that at ...
53
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5answers
14k 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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0answers
58 views
Can you go blind if you look at the sunrise and sunset? [duplicate]
Everyine knows its dangerous to look directly at the sun, but can you look safely at sunrises and sunsets without going blind? Because the uv radiaton and the light is much weaker. Or is it still very ...
2
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2answers
319 views
What fraction of starlight, seen from Earth, is actually reflected light?
Thanks to reflected starlight, many planets and comets in the Solar System have been visible to humans since long before the development of modern astronomy.
Some of the starlight from outside the ...
