Questions tagged [light]
Questions regarding electromagnetic radiation in the visible spectrum.
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What is the ring of light around the moon and which star seen near it?
In this amatuer photograph, the following are to be noted:
There is a faint ring of light around the moon. What is the distance we see this at. From the ground it looks like a hundred meters.
There ...
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Why is the H-alpha line slightly shorter in wavelength (656.28 nm) in air than in vacuum (656.46 nm)? Shouldn't it be longer?
Perhaps this is a question better suited for Physics SE, but since the H-alpha line is so important in astronomy, I'm posting this here....
I would, naively, assume that wavelengths would be longer, ...
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Distance of the Crab nebula and the speed of light
I am watching a youtube video that says that, there is plenty of historic records that shows that the star, that turned into the Crab nebula, blew up in 1054. According to the video, it is located ...
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How much of the surface of other planets is lit by the sun?
Since the sun is much larger than the earth, it should ideally light up a considerable portion of the earth rather than only half of it.
However the sun lighting only half of the earth can be ...
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Why speed of light is considered to be the fastest?
According to Hubble's law, as things move further and further away from one another, there might come a point when their speed gets faster than the speed of light. So, why is it that the speed of ...
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Why does earthshine fade out when night comes and reappear on the next evening?
While watching the Moon in the thin-crescent phase (a few days after new Moon), I often noticed that the earthshine becomes noticeable near the end of civil twilight, and very noticeable during ...
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How can redshifted light be detected?
I've been reading about redshifts and it got me really curious. Basically, I want to figure out how we know light is redshifted and what's the original emitted light.
I found the following question ...
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Cosmic background radiation - what frequency tells us?
I understand that cosmic microwave background radiation is remnant of the universe after 380,000y of the origin.
To me, this radiation is still a wave which has a microwave frequency and I also ...
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What is the diameter of a telescope lens that will capture the surface of Proxima Centauri b?
I been trying to find the way I can calculate the telescope lens diameter needed to see a star by the distance of the star or the planet from the earth. Is there any mathematical relation we usually ...
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What is the galactocentric aberration?
At the Wikipedia about an aberration, there is the phrase:
a recommended galactocentric aberration constant of 5.8 µas/yr
What is the galactocentric aberration? How is it calculated correctly? An ...
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Could the newly discovered glow in the solar system be antimatter?
Could the newly discovered glow in the solar system be a sparse cloud of interstellar antimatter slowly annihilating with the solar wind?
The glow I am talking about is discussed at: https://www.nasa....
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How much light would be received on a rogue planet close to the galactic center?
I was wondering if anyone has ever attempted to estimate how much solar radiation would be received on a rogue planet floating in between star systems close to the center of the milky way, compared to ...
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Stellar aberration without relative motion between source and observer
According to SR, there should be no aberration if source and observer move uniformely (as would be the case in terrestrial aberration). In this case we should find at least some celestial bodies that ...
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Satellites or UFOs? [closed]
Last night in Greenville MI at around 9:15pm-9:25pm (I don't know the exact time) I saw what appeared to be a satellite appear and disappear and then a few seconds later another possible satellite ...
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Why can't we see the far rims of our galaxy by ordinary light?
I mean what is the relationship between the empty space between stars
such that it contains sparse distribution of gas and our our inability to see
the rims of our galaxy.
I searched too long time to ...
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Crossing of particle horizon and a past light cone
What does it mean when a light cone intersects a particle horizon? Like here, about 2 billion years after the big bang? Does it have any significance? I went through a few simple equations and the ...
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How can I estimate a stars surface temperature, luminosity, radius, and lifetime only knowing it's solar mass and peak wavelength? [duplicate]
For example: if a 10 solar mass star emits light at a peak wavelength of λ = 300nm.
How can I calculate a stars surface temperature, luminosity, radius, and lifetime with this infomation?
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What does the surface of a star look like in visible light?
False colour images of the Sun show a highly complex structure near the surface with matter ejected and suspended in magnetic fields. But are solar prominences and coronal mass ejections visible to ...
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Huge galaxies seen from earth
How do we see whole galaxies or even the whole sun? The photons of light travelling from the sun cover a vast distance, so shouldn't we only see the bit that hits the earth and the rest would be ...
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Slow moving pulsing light [closed]
I was looking at the stars as it was clear tonight. I saw a slow moving and slow pulsing star like object. It moved across the sky turning on and off a ‘light’ only being visible when lit and it was ...
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Lunar sky brightness
Looking at the report "The Measurements of Sky Brightness on Lunokhod-2"1, I read that the day time visible light sky brightness was so large that it was off the scale. Unfortunately I have ...
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Is it possible to block the surrounding light in a solar eclipse if we made the moon bigger or closer to the earth?
Is it possible to block the surrounding light in a solar eclipse if we made the moon bigger or closer to the earth? In an eclipse, you always see a ring of light surrounding the moon, but I am ...
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Query about the definition of photometric zeropoints
In stscl page, apparent magnitude is defined as
$$m=-2.5\log{\frac{{\rm DN}}{{\rm EXPTIME}}}+{\rm ZEROPOINT}\ ,$$, DN is Data number (I cannot understand what is meant by 'Data number'... they said it ...
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DIY Sky Quality Meter: Conversion between Illuminance and Luminance
I am trying to create a homemade Sky Quality Meter (SQM) using a TSL2591 light sensor. This sensor measures Illumination (lux), but SQMs measure Luminance (mpsas). I have seen that there are many ...
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How come we see something xx light years away? [duplicate]
If we are at point A in the universe and something is say 13 billion light years away, wouldn’t we have to travel wayyyy faster than the speed of light from the Big Bang in order to turn around from ...
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Speed of light in cosmic voids [closed]
If temperature affects the speed of light (a contentious issue, I gather) then is it possible that the speed of light outside our solar system or galaxy, which might be minimally warmer than the ...
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color of stars and temperature
I recently got questioned on why stars are the color they are. I know the color of a star depends on its surface temperature where hotter stars produce more light towards the blue side of the spectrum ...
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Formula for calculating if an object can cast a visible shadow on the ground or not
I know that we can see the shadow cast by the light of Venus on the ground. I also talk with one person who said they were able to see the shadow even from Jupiter.
Recently I've read something like ...
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How would a cooled down neutron star look when illuminated?
Assume we have a neutron star that has cooled down so far that it no longer emits visible light. If we illuminate it with a powerful external light source, what would it look like? Would it reflect ...
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Calculation of time delay in NASA's STEREO project
I'm trying to solve this task:
Astronomers recently managed to get an image of the entire surface of the Sun for the first time. This became possible thanks to the STEREO project.
In 2006, two ...
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What color would stars have with an apparent magnitude of ~-30? [duplicate]
The light of the Sun is white because our eyes are evolved to work with it as the primary light source. Other stars look white in the night sky because they are too faint to activate the color ...
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How can we know if a star which is visible in our night sky goes supernova?
Let's say there is a star about 3000 light-years away from earth visible in our night sky. If this star were to go supernova tomorrow(not relative to earth's night sky), we would know about it 3000 ...
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How can a black hole stop light from being emitted when all observers see light traveling at the same speed? [duplicate]
Quite literally every science show talks about black holes with a similar phrase: so dense that nothing, not even light, can escape.
Let's say I am in space a safe distance from an object. I drop an ...
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From where the light comes? [duplicate]
Gravitational field of a supermassive blackhole is so strong that even light cannot escape from it (eg. black hole in the core of M87). In this case when a blackhole tears a star,a bright disk of ...
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Why does light accelerate instantaneously to c, while no other phenomena do it? [closed]
In physics, it always takes some time for a particle to move from rest to some speed.
However, photons (light particles) accelerate instantly from zero to c. How? (A visualization would be helpful.)
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Nightsky observation : a light/star suddenly disappeared, why?
For starter, I'm a beginner/noob in astronomy so it might be an obvious answer but I keep asking it to myself
I was watching the sky in the night looking for shooting stars, there was plenty of them, ...
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Why would someone choose a lower resolution grating over a higher one when performing spectroscopy?
The higher spectral resolution grating would reduce the spectral range. Besides that, would a higher resolution grating reduce the signal per pixel? I thought I heard someone mentioned this to me a ...
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Volume of the observable universe [duplicate]
What about the volume of the observable universe?
Can we find it?
And what is the result in cubic light years?
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Spectra of different stellar classes?
I'm beyond an amateur, but I've been failing to find this information and it makes me think I'm missing something.
Anyway: I am trying to write a procedurally generated simulation that includes ...
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Is it likely there are more rogue planets than brown dwarfs, and that we just can't see them because they're too dim?
Among celestial bodies revolving around the galactic center directly, it seems the bodies of lowest mass (brown and red dwarfs) are the most abundant. However, when it comes to even less massive Y-...
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How do the stars in the near-infrared (NIR) radiate?
Let's say we are studying the integrated near-infrared (NIR) light of a distant spiral galaxy. We would expect most of this light to be dominated by red giants stars and dwarfs. I assumed these stars ...
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Is it suspicious that gravitational waves propagate at the speed of light?
Thinking about gravitational waves and the fact that they propagate at the speed of light, I was wondering if it isn't suspicious - the speed of light I mean. Does it perhaps point to something ...
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Astronomical data bases express spectra in flux density, e.g. ergs/s/cm2/Angstrom( or Hz) how can I calculate the flux, i.e. ergs/s/cm2?
I have light spectral data from astronomy data bases in flux density (flux/Angstrom or flux/Hz) and would like to calculate the flux. How can I calculate the flux from the flux density?
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Where does the energy of the decaying CMB go?
I would expect that energy of photons in the Cosmic ray Microwave Background gets less and less because their wavelengths are stretched due to the expansion of space.
How can this be possible? Does it ...
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Bright light in sky that slowly faded away [closed]
North Carolina June 5th 2021 at about 1:45 a.m. my boyfriend walked to me to my car just to see a bright like just above the tree line. Didn’t think anything of it. Finished our goodnight talk and ...
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What escape velocity would quark stars have?
Quark stars are hypothetical compact stars that are denser than neutron stars and maybe the last stage of upholding matter before stars that collapse into a singularity. Neutron stars have escape ...
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Seeming conflict between most distant objects and age of universe (both estimated)
There was a recent article on bbc.com for laypeople like me titled "The mystery of how big our Universe really is", which prompted me to post the following question in their comments section ...
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Traversing a proton within the Planck time
If I could travel a super small distance (proton) in an even smaller time (Planck time), how long would it take me to cross the observable universe?
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How distorted will our galaxy be if we are viewing it from several thousand light years away?
I saw this answer and read this sentence regarding the distortion of our galaxy when viewed above the galactic plane:
Once you got to a point where the entire [sic] galaxy was within your vision, the ...
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The physical processes of emission lines in cosmic nebula
I think I understand how absorption lines in cosmic bodies occur. But after reading about the emission lines in quasars I am wondering more and more about the physical processes causing the emission ...
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