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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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170 votes
2 answers
42k views

Why do sunbeams diverge even though the sun is much more than a few kilometers away?

Consider this picture of sun beams streaming onto the valley through the clouds. Given that the valley is only (at a guess) 3km wide, with simple trigonometry and the angles of the beams, this gives ...
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106 votes
8 answers
21k views

Why does the Sun's (or other stars') nuclear reaction not use up all its "fuel" immediately?

The temperature and pressure everywhere inside the Sun reach the critical point to start nuclear reactions - there is no reason for it to take such a long time to complete the reaction process. Just ...
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81 votes
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Why is the sky not purple?

I realise the question of why this sky is blue is considered reasonably often here, one way or another. You can take that knowledge as given. What I'm wondering is, given that the spectrum of ...
Warrick's user avatar
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65 votes
3 answers
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Do sunrises and sunsets look the same in a still image?

A question that popped into my head: if I see a picture of the sun close to the horizon, in an unknown place, can I know if it was taken at sunset or sunrise? Do sunrises and sunsets look the same in ...
AlonMln's user avatar
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63 votes
5 answers
17k views

The Sun is giving us a low entropy, not energy

While I was watching a popular science lecture on YouTube, I came across this sentence "Sun is giving us a low entropy, not energy" which was said by Prof. Krzysztof Meissner. I am not a ...
janusz's user avatar
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63 votes
3 answers
13k views

Why is the Sun almost perfectly spherical?

Relatively recent measurements indicate that the Sun is nearly the roundest object ever measured. If scaled to the size of a beach ball, it would be so round that the difference between the widest ...
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63 votes
4 answers
35k views

Why does moonlight have a lower color temperature?

Moonlight has a color temperature of 4100K, while sunlight has a higher color temperature of more than 5000K. But objects illuminated by moonlight don't look yellower to the eye. They look bluer. ...
Kartick Vaddadi's user avatar
59 votes
8 answers
13k views

Is it possible to send all nuclear waste on Earth to the Sun?

If we neglect the danger of unsuccessful lift-off of the rocket and the cost, would it be physically possible to send all nuclear waste on Earth to the Sun? Will there be an obstacle that prevents ...
Mubin Icyer's user avatar
55 votes
5 answers
7k views

What is happening when magnetic field lines snap or break?

In discussions of sun spots and auroras on Earth, magnetic field lines are often described as "snapping" or "breaking", with the result of releasing charged particles very ...
Robert's user avatar
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55 votes
1 answer
4k views

What causes the Sun to appear to be in front of a building in this picture?

I took this photograph a few days ago, during sunrise, using my smartphone camera and digital zoom: It seems that the sun is in front of the building. How is this explained?
Lior's user avatar
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52 votes
3 answers
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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 ...
Jeff's user avatar
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46 votes
6 answers
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Can the apparent equal size of sun and moon be explained or is this a coincidence?

Is there a possible explanation for the apparent equal size of sun and moon or is this a coincidence? (An explanation can involve something like tide-lock effects or the anthropic principle.)
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45 votes
4 answers
15k views

What would happen if Jupiter collided with the Sun?

This question is inspired by a similar one asked on Quora. Let's say a wizard magicked Jupiter into the Sun, with or without high velocity. What happens? The Quora question has two completely opposed ...
Allure's user avatar
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43 votes
5 answers
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Why is a new moon not the same as a solar eclipse?

Forgive the elementary nature of this question: Because a new moon occurs when the moon is positioned between the earth and sun, doesn't this also mean that somewhere on the Earth, a solar eclipse (...
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42 votes
4 answers
6k views

How far out from the Sun is visible light still sufficient to read a book?

Recent pictures from the New Horizons spacecraft, shown below, seem to indicate that, at Pluto's distance, we are entering a twilight zone, with a distinct lack of colors, although that could be due ...
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41 votes
7 answers
9k views

Why does the full Moon appear?

I know that the full Moon appears when Sun, Moon and Earth are in a straight line, but if we consider that they are in straight line, why is the Moon illuminated? I mean to say that Earth should ...
Awesome boy's user avatar
41 votes
3 answers
12k 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 ...
Peter4075's user avatar
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41 votes
2 answers
18k views

Why is the sun brighter in Australia compared to parts of Asia?

Background: I've lived in Philippines for several years, and visited other parts of Asia occasionally (Singapore, Indonesia, Hongkong). I just moved to Western Australia a few months ago and I ...
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40 votes
3 answers
10k views

Why wouldn't the part of the Earth facing the Sun a half year before be facing away from it now at noon?

The Earth takes 24 hours to spin around its own axis and 365 days to spin around the Sun. So in approximately half a year the Earth will have spun around its axis 182.5 times. Now take a look at the ...
O S's user avatar
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39 votes
4 answers
6k views

Does the sun rotate?

As implied from the question, does the sun rotate? If so, do other stars not including the sun also rotate? Would there be any consequences if the sun and other stars didn't rotate? Me and my friends ...
yuritsuki's user avatar
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37 votes
6 answers
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If the moon had a mirror surface, would the earth be equally illuminated as by the sun during full moon, or would it require a different mirror shape?

Suppose the apparent diameters of the sun and the moon are exactly the same (which in fact very close to the real situation). If the moon had a perfect mirror surface, would the reflected visible ...
Deschele Schilder's user avatar
35 votes
7 answers
37k views

Is the light from the Sun the same as the light from a bulb?

I'm arguing with a friend of mine on whether the light emitted from the sun is of the same type of that emitted by a bulb. Her insistent ignorance is laughable, unless I'm wrong... She's talking ...
Tobi's user avatar
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34 votes
3 answers
7k views

Do rainbows show spectral lines from the sun?

I'm aware of a similar question being asked in Do rainbow shows spectral lines?: The response to this question is that the body producing the light is not the water droplet that merely diffracts it ...
Mario's user avatar
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33 votes
3 answers
3k views

Can the Sun capture dark matter gravitationally?

I think my title sums it up. Given that we think the dark matter is pseudo-spherically distributed and orbits in the Galactic potential with everything else, then I assume that its speed with respect ...
ProfRob's user avatar
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31 votes
5 answers
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Can the sun cast a shadow?

The sun's light can cast the shadow of another object, but does it ever cast its own shadow?
TreeKing's user avatar
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31 votes
3 answers
4k views

Parker Solar Probe passing extremely close to the Sun; what relativistic effects will it experience and how large will they be?

note: This is a question about relativistic effects. I've included some detail about the spacecraft and its orbit for background, but the question is about relativistic effects and their observability....
uhoh's user avatar
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30 votes
5 answers
15k views

Why is the Sun called an "average star"?

This is a statement (presumably in mass, longevity, energy output) many people that I've met have heard in school, and it is known in pop culture. However, according to Wikipedia, about 75% of the ...
Ovi's user avatar
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30 votes
5 answers
19k views

How do those T-shirts that change color in the sun work?

When I was a kid, I asked my dad about them and he said (not in so many words) that it was because sunlight and artificial light have different spectrums and they picked colors that reflect only the ...
Devsman's user avatar
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28 votes
2 answers
10k views

How long until we fall into the Sun?

As a planet moves through the solar system, a bow shock is formed as the solar wind is decelerated by the magnetic field of the planet. Presumably the creation of this shock wave would cause drag on ...
tpg2114's user avatar
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27 votes
1 answer
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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 ...
Sidney's user avatar
  • 1,066
27 votes
5 answers
7k views

Why isn't the sunset/sunrise rainbow-colored

When the sun is rising/setting, it goes through a phase where the light is bending from the atmosphere. I believe this image will explain much better than I ever could. Now, if light goes through a ...
David Starkey's user avatar
27 votes
1 answer
526 views

The transit of Venus and solar neutrino rates

The following question was posed at the end of Maury Goodman's June 2012 long-baseline neutrino newsletter. During the Venus transit of the sun, were more solar neutrinos absorbed in Venus, or ...
dmckee --- ex-moderator kitten's user avatar
25 votes
9 answers
5k views

Are the physical structures in our sun of comparable complexity to those in the human brain? [closed]

The writings of Rupert Sheldrake tend to provoke strong emotions, be they ridicule, curiosity, outrage, sympathy, disgust, or otherwise. While Physics SE is not an appropriate forum in which either to ...
Tom Hosker's user avatar
25 votes
4 answers
6k views

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? ...
Ubelt6's user avatar
  • 251
25 votes
3 answers
4k views

What causes our Sun to oscillate around its mean Galactic orbit?

According to this answer on Astronomy.SE, The Sun executes oscillations around its mean orbit in the Galaxy, periodically crossing the Galactic plane. I borrowed this illustration (not to scale!) ...
Earth is a Spoon's user avatar
25 votes
2 answers
4k views

How fast is the Earth-Sun distance changing

This is inspired by Evidence that the Solar System is expanding like the Universe?, which referenced an article by G. A. Krasinsky and V. A. Brumberg, "Secular Increase of Astronomical Unit from ...
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22 votes
2 answers
3k views

Are there Higgs bosons in the Sun?

To find the Higgs boson, we had to build the biggest machine mankind has ever built: the LHC with a collision energy of up to 14 TeV. Inside the sun there is a huge pressure and temperature, but is ...
M.Herzkamp's user avatar
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22 votes
3 answers
18k views

Looking at the sun through heavy fog, do invisible wavelengths get through?

This morning it was particularly foggy and my son was excitedly looking at the sun through the fog, since of course he normally can't look directly at it and see the disk. I told him to stop looking ...
T.J. Crowder's user avatar
22 votes
3 answers
18k views

Why does sunset over a body of water cause a path of light stretching towards the horizon?

Have you ever notice the sunset's image in the sea? It's like long light path to the end of the horizon! I've attached a sample of this: How can we explain this? I know that it can happen even in ...
jack's user avatar
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21 votes
4 answers
14k views

How come the Sun's gravity can hold distant planets in orbit, but cannot rip humans off Earth?

The sun is strong enough to keep gas giants close, but why not people?
World Walker's user avatar
21 votes
7 answers
5k views

Finding how much time it takes for a complete Earth revolution around the Sun

Long story short, my brother made a joke about how stupid it is to celebrate the Earth making one "trip" around the Sun: New Year's Eve. So I got curious and was wondering: how could the first ...
Loïc's user avatar
  • 320
21 votes
7 answers
5k views

What can we deduce by the fact that mirrors cannot get a ray hotter than Sun's surface?

I think it is quite counter-intuitive that some lenses or mirrors focusing sunlight to a single spot cannot produce a temperature higher than Sun's Surface. What could a scientist deduce from that ...
CoffeDeveloper's user avatar
21 votes
3 answers
14k views

Why do materials change color when exposed to the sun for a long time?

I have a lot of solid objects that were exposed to the sun for many years and "obviously" they changed their color. I write obviously because I know it empirically and from other people, but what is ...
Physther's user avatar
  • 564
21 votes
4 answers
45k views

How is Earth protected from the gamma rays generated by the Sun?

The Sun is generating energy by nuclear fusion. This nuclear fusion will emit energy in the form of gamma rays. Normally, the earth's ozone layer filters the ultraviolet radiation while the earth's ...
sugunan's user avatar
  • 694
20 votes
2 answers
5k views

Why does the Sun appear white through clouds?

Why does the Sun appear white through clouds? It seems there should not be any absorption of, say, the reddish component, as this would not produce a white colour. So what is going on? Am I right that ...
Janko Bradvica's user avatar
20 votes
2 answers
6k views

Sun light takes 1,000/30,000/100,000/170,000/1,000,000 years bouncing around inside to then reach the Earth

When light (photon particle) is generated inside the Sun, it takes a long time to bounce around inside to later escape and travel outwards. Neutrinos escape immediately. The numbers for the years ...
Prem's user avatar
  • 460
20 votes
3 answers
671 views

What happens to the electron companions of cosmic ray protons?

If primary cosmic rays are made mostly of protons, where are the electrons lost, and does this mean that the Earth is positively charged? Does the sun eject protons and electrons in equal number?
Anarchasis's user avatar
  • 1,343
19 votes
3 answers
5k views

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 ...
Atominator's user avatar
18 votes
3 answers
7k views

Do solar panels act as an electrical load on the sun?

We know that the sun uses nuclear fusion to generate sunlight and heat energy. If we are using solar panels to harvest solar energy, aren't we putting some electrical load(resistance) on the sun? If ...
user18398875's user avatar
18 votes
1 answer
3k views

Why is the Sun made of light elements only?

Since the entire solar system inherits its heavy elements from supernovae unrelated to our star, I fail to understand why, while capturing most of said system's matter, the sun only contain light ...
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