Questions tagged [light]

Questions regarding electromagnetic radiation in the visible spectrum.

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104 views

What does the filter name I+z' mean

On the TRAPPIST telescope, the filter wheels are described to have a filter with the following description: NIR Luminance I+z' (>700nm) After a bit of googling, I wasn't able to find what the ...
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177 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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339 views

Does the cosmic microwave background recede at the speed of light?

Does the cosmic microwave background recede at the speed of light? Is it possible it recedes even faster because of the stretching of space?
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128 views

traveling past the speed of light [closed]

According to the theory of relativity (If I understand correctly), nothing is supposed to be able to travel faster then the speed of light. I believe, to my limited knowledge and grasp of the concept, ...
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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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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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1answer
73 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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2answers
1k 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 ...
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1answer
391 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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1answer
64 views

Light distorsion/ilusion when looking at bright objects [closed]

What's the name of the phenomenon when you look at a bright object (e.g. the moon) and see some perpendicular "beams" going top-down and right-left (bare eye observation, also slightly visible on ...
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1answer
109 views

How did we differentiate lights from stars?

I got this question while watching the COSMOS TV series. I couldn't find the right answer in google. I read about Stellar classification and it states that we can classify the stars based on their ...
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191 views

Has the velocity of photons coming from black holes already been measured?

Has the velocity of photons, which are coming from black holes, already been measured? I am not aware of such measurements. The reason for the question is the following: If space-time near black ...
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1answer
110 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
150 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 ...
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1answer
156 views

Strange light in the sky [closed]

A few weeks ago my daughter phoned me to say she was looking at a very large bright object in the sky in the direction of the Preseli hills. She wondered if it was a planet. I went out to have a look ...
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1answer
229 views

How long can you be trapped orbiting around a black hole for?

I have a story I wanna write but I want to be sure it's not completely scientifically irrelevant. I know there is black hole modelisation called the Kerr black holes, in which there is a limit ...
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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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27 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 ...
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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 ...
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59 views

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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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 ...
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61 views

I saw a light moving fast what could it be? [duplicate]

Today, at about 23:40 in Sungkyungwan University, South Korea, a friend and I spotted a bright light. It was brighter than nearby stars. Since I was looking at South, and at that time, the brightest ...
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1answer
116 views

(Thought experiment) if we put a huge mirror into space, could we see back in time to the big bang? [duplicate]

This is an addition to this question which is closed: By putting a mirror in space, would we be able to see into the past? Imagine there is a supernova a hundred years ago. Lots of people see it but ...
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45 views

Fast moving southward tracking light [duplicate]

At about 4.15 am this morning a light travelling in a southerly direction passed over Adelaide South Australia. It was travelling 10 - 15 times the speed of an Airliner. The light was constant and ...
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94 views

${\rm W/m}^2$ to Jansky [duplicate]

Lets assume I have a source and receive $8 \times 10^{-20}$ ${\rm Wm}^{-2}$ in (400-750) nm filter. How do you convert this received flux to the unit Jansky, is there a formula? (Ultimately, I want to ...
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827 views

What was James Bradley's calculation to calculate the speed of light?

Looking into the history of how the speed of light came to be determined, to what we know it to be today, James Bradley is often mentioned. He was credited with the discovery of the aberration of ...
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1k views

What is visible light colour output of different stars?

I know the colours of the stars relate to their heat, however if I were standing on a different planet identical to Earth, but orbiting a blue Bright Giant or a Red Giant, or perhaps even a Red Dwarf, ...
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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
138 views

Regarding the age / size of the Universe [duplicate]

I believe the current estimated age of the Universe is around 14 billion years. I just read in another post on here that the diameter of the Universe is around 90 billion light years. This doesn't ...
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459 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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3answers
111 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
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 ...
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154 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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2answers
89 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 ...
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1answer
162 views

Using a telescope to look at the Earth History in Some Detail [closed]

The following paragraph is a scientific fact. When we look distantly into the universe (with telescopes) we see galaxies (or whatever else you see) as they were millions years ago- in other words ...
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104 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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2answers
153 views

Why does light from objects take time to reach us? [duplicate]

Why does the light of objects such as the Sun, stars etc. take time to reach us? E.g. Why does sunlight take 8 minutes to reach us, instead of reaching our eyes as soon as it rises.
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237 views

In a finite universe, what happens when light reaches the boundary?

If a universe is finite and is not expanding at a speed equal to or greater than c, what happens when light or another form of electromagnetic radiation traveling reaches the boundary?
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2answers
158 views

Determine north just by one shadow

I am not sure if this is the right place to post at, but I tried to find the best place to do so. To my point, I wonder if it is posssible, to determine where north is, just by one shadow, that means ...
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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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75 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 ...
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1answer
53 views

An hypothetical timepiece on board of a spaceship. Please Help [closed]

On board of a hypothetical spaceship, I have a hypothetical clock consisting of 2 mirrors and a light beam is being reflected between the mirrors to measure the time. Now if we hypothetically exceed ...
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1answer
120 views

The relation between the light of full moon and the distance between the sun and the earth

If we want the full moon to be 2 times more bright,how we should change the distance between the sun and the earth? Thanks for your help.
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277 views

TIME TRAVEL-Can it be really done? [closed]

Is it posssible for us to time travel? Is light essential factor or the dark matter and dark energy?
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661 views

Does the Sun's light travel fast enough to have a straight path to Earth?

Hopefully this question isn't too silly. When we travel through space, we use a curved path following an orbit to reach our destinations. As far as I'm aware, we could take a more straight line ...
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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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1answer
7k views

I saw an orange light in the sky which changed into flashing lights, what is this? [duplicate]

It's Saturday 15th July 2017 and currently 00:44. I saw this strange object at around 00:35. I was looking out my window and spotted a bright orange light moving at a steady speed across the sky, it ...
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72 views

LLR & Orbital Motion

As I understand it, light that is emitted from a source is not imparted with the motion of the source and so always follows a "straight line". If this is correct, I am having a difficult time ...
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34 views

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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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.