Questions tagged [light]

Questions regarding electromagnetic radiation in the visible spectrum.

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1answer
2k views

Is there a simple, analytical formula for the lunar phase brightness curve?

Brightness of the lunar disk varies as a function of phase angle. This phenomenon is very well established, as is the increase in brightness at low phase angles. Is there a simple analytical formula ...
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1answer
35 views

Light levels on other celestial bodies

What I'm trying to achieve For a series of realistic renders I am currently working on I am trying to calculate the light level on different celestial bodies, in terms of the luminous flux (in lumens)...
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0answers
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What was up with the lights in the sky tonight? [duplicate]

I and my boyfriend where looking up in the sky tonight around 8:30 am. We noticed about 17 or more things, that looked like stars. They was perfectly spaced, and just vanished they was heading east. ...
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1answer
229 views

What is length of the universe on lights perspective

According to Einsteins theory of special relativity, when something is travelling close to light speed, travel path is contracted. When the traveller is light itself, does it see the travel path ...
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22 views

Light profile fitting related questions

I am computer scientist and now I'm working with some astrophysical projects. During this work I accumulated some questions and maybe here I would be able to find some answers or advice where to look ...
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1answer
74 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 ...
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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.
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1answer
402 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 ...
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1answer
1k views

How much illumination do the background stars provide?

I'm trying to get a better understanding of what things look like in "outer space." The main problem I'm trying to solve right now, is how much illumination is provided by the background stars. Is it ...
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4answers
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How can a supermassive black hole cause so much energy to enlighten its matter when its massive gravity prevents light to escape?

To cite the German newpaper article Astronomen beobachten erwachendes Schwarzes Loch: Das Materie-Monster sitzt den Angaben zufolge im Herzen der 42 Millionen Lichtjahre entfernten Polarring-...
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5answers
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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 ...
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1answer
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Constructing a periscope/telescope - trouble with lenses

Not sure if this is the best place for this, maybe physics would be a better fit, but I'm trying to build a periscope and am running into an issue. Traditional mirror periscopes work well, but when ...
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2answers
191 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 (...
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1answer
148 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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2answers
95 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 ...
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0answers
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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 ...
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1answer
218 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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0answers
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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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1answer
99 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
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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6answers
14k views

By putting a mirror in space, would we be able to see into the past?

I only ask this because of how fast light travels. The question remains in the title. Why, or why not, would this work?
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1answer
231 views

Speed of light through the ISM and Wavelength

Articles written about fast radio bursts describe the signal's short-wavelength components arriving before its longer-wavelength components, suggesting energy-dependent time delays in the interstellar ...
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0answers
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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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1answer
958 views

How did New Horizons take such well-lit pictures of Pluto?

The photos of Pluto from New Horizons are truly beautiful. But considering that Pluto is so far away from its nearest start - our Sun - how is it so well lit up? Did the New Horizons have a massive ...
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1answer
96 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....
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1answer
239 views

minimum size for a black hole to capture a photon

If a photon is moving past a black-hole, what is the minimum size of the black-hole that will capture the photon and prevent the photon from going onto orbit around the mass? Do black-holes exist that ...
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1answer
115 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 ...
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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 ...
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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 ...
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1answer
58 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 ...
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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...?
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6answers
2k views

Could light be dark matter?

Is it possible that light itself is dark matter? I am speaking of photons (e.g. visible light, infrared, ultraviolet, etc...). I realize light is understood to be massless, but it is obvious it at ...
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1answer
75 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 ...
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7answers
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Does Sun have a reflection on Earth?

The new Google Maps1 presents an actual view of Earth, with the current position of Sun illuminating half part of Earth in real time. It is quite an exquisite view. My question is based on the ...
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3answers
1k views

Does Absolute Velocity Exist?

It seems everyone is on the same page about there being no "absolute velocity" due to the fact that everything is relativistic. However, this leaves me confused. This seems to be disconnected with the ...
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1answer
139 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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2answers
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Is the age of the universe relative to an observer's location in that universe?

According to Wiki the age of the universe is 13 billion years old, and I was taught that background radiation made the universe uniform in all directions. Doesn't this define a sphere of space in the ...
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1answer
140 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?
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1answer
158 views

Does the sky darken proportionally during a partial solar eclipse?

During a solar eclipse, some of the visible area of the sun is obscured by the moon. The exact percentage varies with time and with the observer's location. My question is, does the sky darken by ...
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1answer
135 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 ...
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2answers
212 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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3answers
163 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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1answer
88 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 ...
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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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1answer
497 views

How long would a near-light-speed trip to proxima centauri take from the traveler's and the earth-observer's perspectives?

Lets say the spaceship is traveling at .9c to Proxima Centauri. How long does this trip take from the observational standpoint of the passenger vs. the observer from Earth?
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3answers
267 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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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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1answer
78 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
51 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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