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# Questions tagged [sun]

The Sun is an almost perfectly symmetric yellow dwarf star [spectral class G2V] which is at the center of our Solar System.

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### Solar neutrino Spectrum - Why are there discrete energies for Be and pep?

What is the reason why some reactions give a continuum for the energy of the released neutrinos and others give only a discrete value ($\ ^7B$ and $pep$ )? Thanks for your help. Please feel free to ...
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### What's the timescale for the formation of a coronal mass ejection?

How quickly does the sun form and release a coronal mass ejection? If we were watching the right part of the sun closely, how long would it take us to go from "nothing seems to be happening" to "...
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### Estimating the temperature of the sun using Wien's displacement law

After previously deriving the frequency distribution of photons as $$u(\omega,T) = \frac{\omega^3\hbar}{\pi^2 v^3}\frac{1}{e^{-B K_B T} - 1}$$ I have been asked to estimate the temperature of the ...
619 views

### Is it possible to collimate a point source of concentrated light?

So I am wondering whether it would be possible to create an optical system that does and consists of the following: Use a Fresnel lens to concentrate direct sunlight to a point focus. I assume that ...
51 views

### Extra figure in photo of sun [closed]

I just captured a photo of sun in my mobile camera. And see the pic. Where there is an extra sun or a shape similar to it just below on the right side. What is this?
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### For how much energy does the heat generated in earth's interior account in earth's total energy budget? [duplicate]

I imagine the sources of earth's total energy budget to be The sun The sun deposits about $\sim 1400 \frac{\mathrm{kW}}{\mathrm{m^2}}$ via radiation on earth$^1$. Eventually, this is the source of ...
2k views

### Why isn't the Sun blue?

If I believe right, blue flames are hotter than red ones and if I recall correctly it's because blue tend to ultraviolet. Then why is the sun, which's capable of warming whole planets, red instead of ...
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### Do all materials get warmed by the sun, or do there exist materials which reflect the major part of the IR radiation?

Once upon a time, on a hot day, (in a country far, far away, where the internet doesn't exist) I was wondering when I felt that all things around me on which the sun shined were feeling warm: Do all ...
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### Can a perfect Earth-sized lens between the Earth and the sun darken parts of the Earth (so in that parts the sky looks like the night sky)? [closed]

Suppose an Earth-sized (convex) perfect lens is placed between the sun and the Earth (with the center of the lens on the line between the center of the Earth and the center of the sun, and the lens ...
157 views

### Water molecules on the Sun? How does that work?

I've been reading about water on the Sun. The water they talk about is supposedly in a gaseous state because the Sun is so hot. But I'm wondering how even that could exist. Wouldn't the extreme ...
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### Why can my camera see the Sun when I can't?

There was a lot of smoke blowing high over the west coast of the United States last summer due to forest fires. It was thick enough that near the horizon, the Sun was all but invisible. It could ...
109 views

### If we could withstand the temperature of Sun then could we actually stand on it? Does it have a solid surface or not?

If the sun's temperature were lower or we could withstand it, could we actually stand still on a solid surface or would we fall through into the depth of the sun? Is the sun's surface gaseous with ...
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### What accelerates the solar wind?

The question is in the title. A bit of background info: the escape velocity at the photosphere of the Sun is ~ 620 km/s, but the mean speed of the solar plasma there (inferred from the temperature) ...
465 views

### How many photons does our sun emit in a second? [closed]

How many photons does our sun emit in a second? I would assume that given that the earth receives about 1350 W/m^2 from the sun there is some calculation involving the size of the sun (radius 696,000 ...
1k views

### What will happen if the nuclear reactions in the Sun stop suddenly? [closed]

If all nuclear reactions inside the Sun would have stopped somehow for ever then what all will be the consequences? My Attempt at the Question: Since the reactions were a source of Sun's ...
6k views

### Sun's power density compared to a compost heap

According to Wikipedia the Sun's "power density" is "approximately 276.5 $W/m^3$, a value that more nearly approximates that of reptile metabolism or a compost pile than of a thermonuclear bomb." My ...
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### Why does the speed of sun play a role in dark matter detection

I'm reading the book supersymmetry and beyond from Gordon Kane and got a bit confused at the point where he started explaining how we can check whether the signal we got at a detector is truly because ...
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### If gravity can be disrupted by larger forces, why does the moon orbit the Earth instead of the Sun? [duplicate]

I read an thread on this site about how a larger gravitational pull can overpower a smaller gravitational pull. I took this to mind, and I started wondering why the moon orbits the Earth instead of ...
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### Measuring temperature of a solar object at different distances to its core

I recently was taught about the composition of the Sun, and that the temperature we know about it is its surface temperature. I find it hard to accept this. There has to be a way in which ...
33 views

### Reason for borexino pep flux confidence level error

At the TAUP conference in 2011, the Borexino collaboration presented an analysis of electron-neutrino elastic scattering events in their liquid scintillation detector to claim the first observation of ...
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### What if the Sun became a black hole?

Upon talking to someone about the concepts of black holes, a question arised that I did not know the answer to. If the Sun became a black hole, but the mass remained the same as it is now, the Earth ...
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### Where will the Goldilocks zone be when the Sun becomes a red giant?

In about 5 billion years, when our Sun expands into a red giant making our planet uninhabitable, where will the new Goldilocks zone be? Could life form on a new planet in the Goldilocks zone? ...
135 views

### Another way to find the energy diffusion time in the Sun?

I was surprised when I first heard that the energy produced at the Sun's core takes a long time to escape the Sun. The process is often explained as a photon traveling a "drunkard's walk" based on ...
1k views

### Why is the sky blue and the sun yellow?

The blue color of light of the sky is due to Rayleigh scattering. But the sun itself appears yellow in color whereas the scattered sunlight itself appears blue. Why does this happen? Should the sun ...
416 views

### What is the viscosity of Sun surface?

It should be possible to compute value from hydrodynamics of Solar prominence. What is the current estimate of Solar surface viscosity?
269 views

### How can we see the Sun if it is made up of only gas?

So I'm researching if the sun is transparent or not and have found that it is made up of gases. From what I know the gases the sun is made from are transparent. So why can we see the sun if it's made ...
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### Interaction energy of stuff in the suns core

There is a post where CR Drost calculates the interaction engery in the center of the sun using only the density $\rho$ of the sun at it's center. Assuming that all the mass comes from protons we get ...
629 views

### How much light does the sun emit in the violet spectrum? [closed]

According to wikipedia: "UV radiation constitutes about 10% of the total light output of the Sun, and is thus present in sunlight" It also states that "at ground level sunlight is 44% visible light, 3%...
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### Is the orbit of Earth currently decaying?

As we know, interplanetary space is not completely empty. This would cause a drag to Earth, spiralling it towards the sun in a long enough timescale, which appears to be what has happened for many ...
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### As the sun expands, will its Roche limit also expand?

So my friend and I had a debate. He stated that we don't have to worry about the sun consuming the Earth ─ we'll already be broken apart by then. He states that as the sun expands, its Roche limit ...
218 views

### Does Blue Light Really Have a Dark Side?

I was reading the following article on Wikipedia which discusses the dangers of blue light: Blue-light hazard is defined as the potential for a photochemical-induced retinal injury resulting from ...
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### Model to predict temperature of the Sun?

In a homework problem, we were to assume the Sun is a sphere with uniform density and use the hydrostatic equilibrium equation to compute the pressure at the center of the Sun? Upon doing this, I was ...
1k views

### Why does the sun appear yellow? [duplicate]

I read an article by NASA in which the following assertion was made: The sun, in fact, emits light in all colors, but since yellow is the brightest wavelength from the sun, that is the color we ...
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### How can the color of the sun be measured?

As the sun sets it changes color, sometimes first becoming orange, then red, for example. The device typically used to measure color is a colorimeter, but all of the colorimeters I have seen only ...
229 views

### Are the sun rays incident on earth's surface parallel to good approximation?

If so how can an image of the sun be formed using a pinhole camera (for e.g. sun diameter estimate), the rays incident on the pinhole can't all be parallel and at least for this case the approximation ...
251 views

### why do total solar eclipses vary in length?

Quoting https://www.mnn.com/earth-matters/space/blogs/why-2024-total-solar-eclipse-may-outshine-2017, For the 2017 eclipse, the duration of totality will last between 20 seconds (over Kansas City,...
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### Is looking at an eclipse worse than looking at the sun? [duplicate]

I understand why looking at the sun is bad. I also understand that looking at the eclipse is bad. Is it more dangerous to glance at an eclipse than the sun, assuming you avert your eyes right very ...
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### What speed should I maintain on land or in the air in order to experience the whole path of total solar eclipse?

What speed should I maintain on land or in the air in order to experience the total path of total solar eclipse? And What other factors are taken into account for calculating that speed? For e.g. ...
118 views

### Very old photons from the Sun

While watching the rebooted Cosmos series, I heard Tyson say that a photon arriving to the Earth from the Sun might be millions of years old. If I understood correctly, once it's emitted inside the ...
645 views

### How does the Sun burn a crescent shaped scar in your eyes during a solar eclipse?

I was listening to NPR this morning and a man talking about the solar eclipse said that you cannot look at even a sliver of the sun because it could still damage your eyes. He noted he's even had ...
24k views

### Why aren't 100% UV blocked sunglasses safe to view an eclipse with?

I am not planning on staring into the sun during an eclipse or any other time. I have been reading about how no variety of regular sunglasses are safe enough to view the eclipse with. I'm not talking ...
111 views

### Total eclipses becoming rare soon?

Given that the moon is receding from the earth and that the average angular size of the moon is approximately equal to the angular size of the sun at the moment, what is the current rate at which ...
1k views

### Why can I look at the sun with my sunglasses but not at the solar eclipse?

Is the problem with seeing an eclipse that you have a sudden change between penumbra and regular sun? If that's the case, why can I look to the sun with my sunglasses on but I can't do it in an ...
531 views

### What percentage of sunlight isn't scattered by air molecules?

The sky looks blue because of scattered photons. Our Sun looks often yellow because the photons we receive in ours eyes 'are' yellow. Now is the yellow light we receive in our eyes when looking ...
4k views

### Why does the Sun appear larger during the sunrise and sunset?

Why does the Sun appear larger during sunrise and sunset compared to its size during midday even though its distance from the Earth remains fixed all the day? It is only during the Winter when the Sun ...
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### First method to observe solar prominences without an eclipse

What was the first method used to observe solar prominences without an eclipse? I understand that Helium was first discovered in the Sun, separately by Pierre Janssen and Norman Lockyer, in 1868, ...
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### How can a full moon be seen south of an observer's location?

I know this seems like a simple question, but I'm trying to debate with a flat earth theorist. I asked him to explain why can the ISS visibly be seen orbiting the Earth with the naked eye, and he put ...
138 views

### Solar Activity Confined to a belt around the Sun, Why?

The "photo" image shown below was posted today on Facebook by Fifth Star Labs. It shows the accumulation of one year's worth of solar activity in one photo image. So, I see that this solar activity ...