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Questions tagged [light]

Questions regarding electromagnetic radiation in the visible spectrum.

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1answer
75 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 ...
2
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1answer
68 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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0answers
43 views

7 to 8 moving lights across the sky [duplicate]

I have seen 7 to 8 faint lights moving very quickly from north to south over Ramsbottom in Bury, UK. They were definitely not satellites and some appeared to move around one another. They were as far ...
1
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1answer
32 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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0answers
26 views

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
66 views

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 ...
-1
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1answer
127 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 ...
4
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1answer
536 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
28 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
52 views

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 ...
2
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1answer
318 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
126 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
73 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 ...
2
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2answers
99 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
votes
2answers
91 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 ...
6
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1answer
185 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 ...
5
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2answers
107 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 ...
2
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1answer
30 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, $i$ ...
37
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5answers
12k 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 ...
3
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2answers
99 views

Bright light in the sky, in the '90s, what could it have been?

Sometime in the summer months during the years from 1993 to 1998, my friend and I saw what looked like a gamma-ray burst (or what looked like an artist's impression of it). It looked like a star that ...
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2answers
356 views

Sunlight intensity during a day

What simple mathematical function would reasonably well simulate sunlight intensity (disregarding weather) from dawn till dusk in relative numbers, 0-100 %. Are there significant differences (apart ...
4
votes
1answer
151 views

Can light be trapped in orbit?

Could rays of light be ever trapped in a constant orbit around a black hole if approached from a certain angle ? Like light hitting a glass or liquid with critical angle.
2
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1answer
54 views

Spectrum of star

I constructed a telescope and fixed my mobile's camera to the eye lens. I then viewed the sky via the mobile and I captured this image. This is the magnified version of it: I'm not sure if this ...
26
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1answer
3k views

How did Ole Christensen Romer measure the speed of light?

How did Ole Christensen Rømer, who in 1676, shortly after Galileo's death, was said to have measured the speed of light as 220,000 km/s by timing the orbits of Io around Jupiter? My only guess is ...
4
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3answers
145 views

What would a terraformed Mars look like from Earth?

Question in the title. Currently, Mars is a small orange dot in the sky. But what if green, blue, and some white were added? I wouldn't expect it to be too different- a large portion of it will remain ...
2
votes
1answer
145 views

What is the light that we see from a neutron star come from?

What hold the electrons in orbit? Is it gravity or the atomic attraction between the protons and neutrons? I asked this question on Physics SE I hope I improved on the quality enough to do better ...
8
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1answer
3k views

Why do stars twinkle but the Sun doesn't (I'm asking this because the Sun is also a star) [duplicate]

My friend asked me "Sun is also a star then why doesn't it twinkle like other stars" I brought this question here so that I have (and have more) infomation on this topic.
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0answers
30 views

Space expansion speed vs Light speed [duplicate]

How is the space expanding at a speed greater than the speed of light, while nothing is moving faster than light?
3
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1answer
57 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 ...
2
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0answers
43 views

How do I measure occultation for the upcoming lunar eclipse?

I'm trying to simulate the lunar eclipse on Jan. 31, similar to this simulation I made of last year's solar eclipse, using Three.js. I have the minute-by-minute coordinates for the Sun and the Moon in ...
3
votes
0answers
71 views

What is the science behind the polar light shapes

Is there any scientific explanation that causes polar lights (aurora borealis/australis) to have their unique shapes? Specifically: Rayed Arcs Dual Bands Corona (Images on NASA Pdf) This site (by ...
4
votes
1answer
383 views

How bright would it be on the “face” of Titan

If you were planing a maned mission to Titan and wanted to find a landing site that would get the most visible light for the longest amount of time, your first logical choice would be the dark side of ...
1
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1answer
97 views

Are there clouds/clusters of gas in space that have red and blue color adjescent to one another?

In artistic renditions of space scenes, there were stunning depictions of gasses or galaxies with bold red and blue colors immediately adjacent to one another, in contact as water is with oil in a ...
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0answers
37 views

Finding individual band magnitudes: Why and how is the integration of individual flux values for each wavelength used?

What differentiates the distance modulus equation to find the difference between two apparent magnitudes? For example, $$ m_1 = -2.5\cdot log_{10}\left(\frac{F_1}{F_2}\right) + m_2$$ leads to the ...
2
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2answers
115 views

How close to a brown dwarf would a planet need to be to receive as much light as Earth?

How close to a brown dwarf would an orbiting planet need to be in order to receive as much sunlight as Earth receives from the Sun?
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3answers
148 views

Will we be able to see our galaxy if we travel far enough?

Will we be able to see our galaxy if we travel far enough? When we leave earth far enough, we'll be able to see Earth from distant, is it same with the galaxy? if we travel far enough, will we see the ...
3
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3answers
385 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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2answers
131 views

A [very basic?] question about light scattering and colors

Since the night two days ago, the moon here in Israel appears to be orange as it rises, and then gradually becomes white as it continues travelling across the sky. This phenomenon comes in a great ...
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2answers
256 views

Is an expanding universe equivalent to a universe in which everything is shrinking?

Why do we always think of the universe as expanding? Surely, from our perspective an expanding universe would look exactly the same as a universe in which everything is shrinking away from ...
2
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2answers
566 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 ...
8
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2answers
596 views

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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6answers
12k views

How do we have photos of galaxies so far away?

A possible answer for this is that, light emitted from the galaxies travelled a billion miles all the way to earth, where the hubble space telescope picked up this light through its sensors, and was ...
0
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1answer
113 views

A real light source, or an artifact?

I was taking shots of the 2017 eclipse using my D7200 camera with a 1000 ND filter. As I was going through the pictures after downloading them to a pc, I noticed that there's what appears to be a tiny ...
0
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1answer
64 views

why there is a circle of light surrounding Sun and Moon?

One day when I was playing basketball I saw a circle around the bright Sun. It is a perfect circle with a radius of about 20-30 km. Why does this circle of light form? I have seen the same also ...
0
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1answer
89 views

is this really true that speed of light is same as we look from different parts of universe?

According to the theory of relativity. The speed of light is same for every observer. But how can we know that this applies to more than a local region? What if light travelled to us from a distant ...
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4answers
959 views

Is there an example of a star that is already dead, but can still be seen on earth?

While looking up at the stars I wondered, what are the odds that some of them are already dead. I did some research and found a very interesting article here. It states that the odds are rather small, ...
3
votes
1answer
102 views

Why is it not always light? [duplicate]

Hopefully this is not a silly question, but I was wondering why earth is not always in the light (and any other planet for that matter). I mean, we have billions of stars just in our galaxy that all ...
3
votes
1answer
104 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
2k views

Please help explain this unknown light in the sky. Not ISS. Not a star or comet. Too slow [duplicate]

So a few nights ago I walked outside on my front lawn and sat down on the tailgate of my truck. I was facing north. I was looking down and towards the house across the street. Out of no where a bright ...
2
votes
1answer
76 views

How do I know what I'll be able to see?

So I live in a suburb in Victoria, Australia. Less than an hour away from the city and I guess there is a bit of light pollution because from my backyard I can probably only see about 15 - 20 stars (...