Questions tagged [light]

Questions regarding electromagnetic radiation in the visible spectrum.

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9
votes
3answers
183k views

Star like light moving in the sky, what could it be? [closed]

I was camping this weekend away from the city, so my friends and I decided to spend one of the nights watching the sky, since it's impossible to see anything around where we live. After a little while,...
19
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6answers
13k 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?
34
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2answers
7k views

Why doesn't the moon twinkle?

Stars twinkle because their light has to squeeze through several different layers of the Earth's atmosphere. So why doesn't the moon twinkle as well?
17
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3answers
3k views

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-...
3
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3answers
653 views

How can the universe be expanding faster than speed of light? [duplicate]

So the story goes like this: A long time ago, 13.799±0.021 billion years to be exact, something happened. It was a big bang, loud explosion and universe came to existence. It grew and grew, and now ...
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3answers
3k views

How does gravity interact with a photon?

If photon is mass-less and gravity can interact only with matter, then how does gravity alter the trajectory of light?
33
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3answers
9k 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 ...
25
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3answers
5k views

Why can't light escape from a black hole?

I've heard that light can't escape from a black hole. Can it? If not, why?
24
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6answers
19k views

Is the light we see from stars extremely old?

Our nearest star Proxima Centauri is 4.243 light years away from Earth. Does that mean we are seeing light that is 4.243 years old everyday?
11
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3answers
887 views

How does light affect the universe?

When light is emitted by for example a star, that star loses energy - which causes it to reduce its gravity. Then that energy begins a journey for potentially billions of years, until it reaches some ...
2
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2answers
143 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 ...
1
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1answer
171 views

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

Drawing from this answer The V838 Monocerotis expansion (not a supernova) and the observation of the subsequent "spectacular" light echo was quite a notable event! From Nature 422, 405-408 (27 ...
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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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2answers
4k views

Why is the speed of light 299,792,458 meters/sec?

Ok, I am majoring in physics (4th year) and I never understood this fundamental (kinda) question. Maybe I haven't explored it enough. For example, why does it take 8min20sec for the light from the ...
8
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1answer
285 views

Sunsets: Mars/Earth

I understand why our sky is blue and turns red when the sun sets or rises. I know why the sky on mars is red, but why does it turn blue during sunsets and rises? Shouldn't this actually not work due ...
5
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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 ...
4
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1answer
96 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 (...
2
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1answer
801 views

What is the faintest magnitude a telescope can see?

This website claims: The space telescope can detect objects as faint as 31st magnitude... It's referring to Hubble, but does not cite any source or math. How do you calculate the faintest (...
14
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4answers
6k views

How do scientists determine the age of stars?

I was Googling about the oldest galaxies in the Universe. Everywhere is written that their age is known by the light. Referring to this line "Since light travels at a set speed, if you look at a star ...
29
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1answer
4k views

If dark matter bends light, how do we know the stuff in the sky is where we think it is?

We measure movement, position, and many other things of an object in space because of its light and what we can measure with it. But as far as I know there's supposed to be a HUGE amount of dark ...
24
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8answers
11k views

Why can't we see distant galaxies with the naked eye?

If light keeps travelling in a straight line, why can't we see distant galaxies with the naked eye? Surely if you stared long enough, the light from them would eventually hit your eye? I apologize if ...
30
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4answers
3k views

Why does the Moon appear gray when passing between the Sun and the Earth?

Shouldn't the Moon appear as bright as a full Moon seen at midnight from Earth? The photo was taken by DSCOVR at Lagrange point 1. In the picture, The Moon appears dark gray. Of course the Earth ...
42
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5answers
14k 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 ...
17
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4answers
3k views

What is Gravitational Lensing?

What is the effect known as gravitational lensing? How does it work? What objects would be able to cause this effect?
15
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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 ...
11
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3answers
6k 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 ...
10
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2answers
471 views

Is there a place in the known universe that there would be no visible light from other stars/galaxies?

Is there a place in the universe where, with the naked eye, you wouldn't see any stars, galaxies or light emitting phenomena? From what I understand at some point into the far future in Earth's ...
3
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2answers
2k views

Difference between luminosity, luminous flux, and radiant flux?

I've looked this up, and was wondering the differences between them. Luminosity is the total energy emitted by a source, in watts. However, I'm confused about luminous flux and radiant flux. Since ...
2
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1answer
172 views

What is the ratio of cosmic microwave background radiation to normal radiation?

I would like to know the ratio of cosmic microwave background radiation to normal radiation in the universe. I am considering cosmic microwave background radiation to include the microwave, and any ...
10
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2answers
4k views

How bright is the full Earth during the lunar midnight?

At lunar midnight (i.e. the new moon as seen from Earth), the Earth is in its full phase with its entire disk in sunlight, and it is the brightest object in the lunar sky. How bright is it, and how ...
7
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1answer
353 views

How is it known that Pillars of Creation are destroyed?

We can observe Pillars of Creation with 7000 years delay, but it is destroyed only 6000 years ago. How do we know that? How the information about explosion reached the Earth before light do?
6
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2answers
207 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 ...
6
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1answer
203 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 ...
6
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1answer
892 views

When we say a galaxy is 200 million light years away, does this account for the expansion of space in the time it took it's light to reach us?

When we see a distant galaxy, the light we are watching started it's journey millions of years ago. In all that time, space has been expanding, so if the initial distance was A, right now the distance ...
6
votes
1answer
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 ...
5
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1answer
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 ...
3
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1answer
1k views

Is there light on the surface of Venus?

A simple question: is there light on the surface of Venus?
3
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1answer
155 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 ...
2
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3answers
211 views

If the expansion of the universe is speeding up, how long until everything nears the speed of light, and what would happen?

Since dark energy is causing everything to speed up infinitely, wouldn't everything near the speed of light? And since it's nearing the speed of light, wouldn't all kinds of strange things start ...
2
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2answers
95 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) ...
2
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2answers
137 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 ...
2
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1answer
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 ...
2
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2answers
713 views

How much light would be reflected from Jupiter to Europa (in Europas night)?

Suppose Europa is found habitable and humans start living on it. Europa is close to Jupiter and during the night Jupiter would be reflecting light to Europa, just like our full moon reflects light to ...
2
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1answer
534 views

Is it possible that we see our solar system as a star?

A few days ago I just read here that our galaxies (one of which we are part of) move or expand faster than light, And read here that light we see from stars is extremely old, maybe more than several ...
2
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1answer
53 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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2answers
290 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.
1
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1answer
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 ...
0
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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/...