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Questions tagged [light]

Questions regarding electromagnetic radiation in the visible spectrum.

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1answer
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How to find the source of the light

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 ...
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2answers
159 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 ...
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1answer
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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 ...
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3answers
134 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 ...
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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
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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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3answers
218 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
59 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
49 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/...
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3answers
155 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
19 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 ...
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1answer
84 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 ...
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2answers
42 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 ...
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1answer
44 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 ...
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1answer
110 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 ...
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70 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
104 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 ...
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1answer
63 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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36 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
97 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 ...
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1answer
83 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
106 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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2answers
141 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.
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2answers
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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 ...
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3answers
161 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
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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 ...
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5answers
13k 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
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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 ...
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2answers
227 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 ...
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1answer
136 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 ...
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1answer
204 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 ...
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1answer
302 views

Are there any examples where the transverse doppler effect is applied in astronomy?

Are there any astronomical examples where the transverse doppler effect(Horizontal doppler effect) is applied (Derives a meaningful result)?
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1answer
129 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 ...
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1answer
91 views

Light pollution and apparent magnitude of objects in solar system

Dust along the ecliptic scatters light, causing “light pollution” throughout the orbital plane of the solar system. If an object like, say, the sun's corona, had its brightness measured from above the ...
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2answers
54 views

Source of mirror reflectivity data

I am trying to find a source of mirror reflectivity versus wavelength for the typical protected overcoat Aluminum mirrors used in astronomy. I need this to cover the whole visible range (300-1200nm) ...
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0answers
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What is the advantage of taking monochrome photographs in standard lenses

I've readen "When photographing faint objects monochrome photos will resolve more than RGB pics" Is this really a thing? If yes, how?
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2answers
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Existence of a “reflecting” star [closed]

Wasn't even sure about what the title should be, but I had a thought and I wonder whether it may be possible or not. Is it possible that there is a star which acts as a mirror and reflects back the ...
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1answer
142 views

Looking at ourselves with a powerful telescope?

Could a small curved mirror and/or lens in Earth's orbit be aimed at a different hemisphere from where you are be be viewed with a powerful telescope to see the ground through the mirror? Would a more ...
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1answer
573 views

Does Time Exist for Photons? [closed]

If time slows down the closer you get to the speed of light, does it follow that time does not exist for photons. Do photons - even if they travel across billions of light years of space - arrive at ...
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1answer
64 views

What unit is used for region Surface brightness in DS9?

The value of the surface brightness is in what unit? I hope it is in Rayleighs. Is that true?
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0answers
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Almost unseeable light moving over nightsky. What is it? [duplicate]

Sometimes when I look up at the sky at night, I can see something moving. It’s so small that I barely can see it, but I can’t see it when I look directly at it. I need to look beside it to see it. It ...
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1answer
912 views

Strange bright light in the sky flying fast [closed]

I was out with my dad on our porch watching the stars with our telescope. after awhile of looking and taking pictures I noticed something strange in the sky. There were two airplanes flying close to ...
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2answers
299 views

Does the edge of the Universe travel faster than the speed of light?

The Universe is expanding faster than the speed of light then does that mean matter at the edge of the universe is also traveling at the speed of light or are ether opposite sides of the universe are ...
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1answer
83 views

With all the stars in the universe, why isn't the sky saturated with light? [duplicate]

Space is dark. But if we direct telescopes to seemingly dark portions of sky, we see that it is filled with galaxies. If the universe is theoretically infinite, wouldn't an infinite number of photons ...
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2answers
123 views

Are galaxies expanding away from us at more than the speed of light? [duplicate]

If you go to the following video, at this certain time: https://youtu.be/Iy7NzjCmUf0?t=435 you will see that the narrator says: "We simply don't know what else is out there because the light from ...
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2answers
116 views

How far away is this galaxy?

Arp 299 is in the news, with most sources reporting it as 140 or 150 million light-years away. But what kind of distance is this? The paper which is trhe source for the news item has Supplementary ...
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1answer
217 views

How much do starlight and artificial light illuminate the Moon?

The Moon receives most of its light from the Sun, either directly through sunlight or indirectly through Earthshine. However, there are many other dimmer sources of illumination. Starlight. This is ...
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2answers
117 views

What's the difference of the oldest light and newest light?

Excuse an amateur question, as inspired by this question: "How old is the oldest light visible from Earth?", how to determine the age of light? Does light get old? Does light have characteristic ...
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1answer
61 views

Scattered Intensity of Light vs Angles of Incidence and Emission

So I just derived an expression for the scattered intensity of light from an atmosphere with ideal isotopic scattering: $I/F=\frac{cos(i)}{4(cos(e)+cos(i))}$, where $I$ is intensity, $F$ is flux, $i$ ...
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5answers
13k views

How old is the oldest light visible from Earth?

Because light can only travel so fast, all of the light we see in the sky was emitted at a previous moment in time. So if for example we see a supernova or some other great stellar event, by the time ...