# Questions tagged [light]

Questions regarding electromagnetic radiation in the visible spectrum.

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176 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 (...
87 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 ...
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 ...
30 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 ...
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/...
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### 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 (...
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 ...
93 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....
330 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 ...
110 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 ...
25 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 ...
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 ...
1k 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...?
352 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 ...
65 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 ...
130 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 ...
138 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?
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 ...
206 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 ...
82 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 ...
161 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 ...
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 ...
53 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+...
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### 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?
76 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 ...
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/...
172 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 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 ...
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 ...
111 views

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 ...
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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 ...
132 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 ...
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 ...
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 ...
71 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 ...
55 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?
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 ...
87 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 ...
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.
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### 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.
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### 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 ...
177 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 ...
83 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 ...
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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### 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 ...
305 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 ...
198 views

### Is there enough light to grow plants in the ocean of Europa?

What is the underwater temperature of Europa? I know Jupiter emits infrared light but does it emit any light able to support plant life of any type on near by Moons? Can under water volcanic activity ...
224 views

### What is the underwater temperature of Europa?

If Europa has an oxygen atmosphere with a water mantle, is it possible that there could be life under the crust of Europa ice on the ocean where it is warmer? What could be the temperature under the ...