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106 votes
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How loud would the Sun be?

The Sun is immensely loud. The surface generates thousands to tens of thousands of watts of sound power for every square meter. That's something like 10x to 100x the power flux through the speakers at ...
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106 votes
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If Earth is tilted, why is Polaris always above the same spot?

You are correct that the axis of the Earth's rotation is tilted with respect to the plane of its orbit by 23 degrees. But it is incorrect that the direction that the axis points changes by a large ...
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68 votes
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Where in space would the Earth and Moon appear to be the same size?

When viewing a sphere of radius $r$ at a distance $d$ from the centre of the sphere, you don't see a circle of radius $r$. The extreme lines of sight are tangents to the sphere, as this diagram ...
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65 votes
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How old is the oldest light visible from Earth?

The oldest light in the universe is the cosmic microwave background. Roughly 380,000 years after the Big Bang, protons and electrons "recombined"1 into hydrogen atoms. Before this, any photons ...
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51 votes
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How does the Earth move in the sky as seen from the Moon?

Still new at stellarium but here are some quick capture gif lasting one month. Sorry about the quality- limited to 256 colors for smaller gifs. Date on lower left corner. By the way the sun is of ...
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51 votes
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Why are the time zones calculated as 360°/24 and not 361°/24 or 360°/23.933?

The Earth takes 23 hours 56 minutes to rotate once. But that is not relevant to most people. Sure, the stars will be in the same position again after 23 hours 56 minutes, but the sun will not be in ...
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47 votes
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Why is the summer solstice night shorter than the winter solstice day?

Why is the summer solstice night shorter than the winter solstice day? Aside: If you use your sunrise / sunset calculator you will see that day and night are not equal at the equinoxes. The reason ...
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  • 28.1k
42 votes

How does the Earth move in the sky as seen from the Moon?

You are correct. The Earth would always appear in approximately the same location in the sky, when viewed from a point on the lunar surface. And it would be seen to spin, the continents coming in and ...
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42 votes
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Why does the Moon appear gray when passing between the Sun and the Earth?

That's what it really would look like if you were there with DSCOVR. The albedo of the Moon is only about 0.136, about half of the Earth's average albedo. Of course the part with clouds is higher. I ...
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  • 31.5k
41 votes

Simple experimental evidence that Earth revolves around Sun

The answer is ironic: Without good instruments, there is no evidence. The people who thought that the Sun went around the Earth were perfectly correct as far as the actual evidence went until the ...
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38 votes
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Can an object from a natural process escape earth gravitation?

Yes, it is not only possible, but has almost certainly happened on Earth. The asteroid that killed the dinosaurs is thought to have produced these high velocity fragments on the order of one-...
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  • 13.8k
37 votes

What if Earth and Moon revolved around each other like Pluto and Charon?

They do, but due to the ratio of masses being vastly different, they seem like they would not to do so as moon seems to rotate just around (the centre of) Earth. The ratio of Earth and Moon's masses ...
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  • 556
37 votes

Why are there no stars visible in cislunar space?

It is a matter of exposure and dynamic range. A sensor like a camera can only handle inputs in a certain range of intensities, and much of photographic skill (or smart presets) is about mapping the ...
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37 votes
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Was the Geocentric Model correct at all?

Ptolemy's epicyclic, geocentric model, in use until the Renaissance, was very accurate in terms of predicting the positions of planets and the times of eclipses. What it couldn't account for were ...
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  • 115k
34 votes
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Is it a coincidence that both the Sun and the Moon look of same size from the Earth?

The coincidence isn't so much that they appear very similar sizes from Earth, but that we are alive to see them at the point in time in which they appear very similar sizes. The moon is slowly moving ...
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32 votes
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Official degrees of earth’s rotation per day

First, we need to decide which definition of "day" to employ. There are several types of days: Apparent solar day: the time between two successive culminations of the Sun (apparent Noon) from an ...
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31 votes

Is it at all possible for the sun to revolve around as many barycenters as we have planets in our solar system?

The short answer is no; there is only one barycenter. Yes, you can count the Sun/Jupiter barycenter or the Sun/Saturn barycenter, or whichever barycenter you want, but the net effect of all Solar ...
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30 votes

How loud would the Sun be?

While Sir Cumference's post is a very intriguing answer, but I'm afraid it's wrong. The sun's surface is clearly in motion, but that does not necessarily result in the radiation of audible sound, even ...
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  • 401
30 votes

Why are perihelion and the shortest day in the northern hemisphere different?

We have "days" because the Earth is rotating. The shape of the orbit has little effect on the daily cycle of light and dark. The length of the day is determined by the tilt of Earth to the orbit of ...
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29 votes
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Will Earth lose the Moon before the Sun goes into supernova?

As HDE 226868 noted in his answer, the Sun is not going to go supernova. That's something only large stars experience at the end of their main sequence life. Our Sun is a dwarf star. It's not big ...
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  • 28.1k
29 votes

Why is the L3 Lagrangian point not perfectly stable? And why is the Earth-Sun L3 point a bit less than one A.U.?

L1, L2 and L3 are saddle points in the effective potential of the gravitational field in a rotating frame of reference. That is if you combine gravity (of Earth and Sun) with the centrifugal force on ...
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28 votes
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Did we ever actually see the earth revolving around the sun? Is the geocentric model completely disproved?

What you're asking, basically, is whether there are any proofs for the heliocentric model of the Solar System. A literal naked-eye observation of the Earth revolving around the Sun would be rather ...
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28 votes

Why are the time zones calculated as 360°/24 and not 361°/24 or 360°/23.933?

We teach the students: Sidereal day: In 23 h 56 min the earth rotates 360° Solar day: In 24 h the earth rotates 361° You should not teach your students that. You should instead teach your students ...
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  • 28.1k
28 votes

If suddenly "knocked" or perturbed from its orbit, would gravity eventually return the Earth to its original orbit?

There's a few parts to this question so there's more than one answer. Earth gets knocked a little bit out of its orbit all the time by gravitational influence of other planets in our solar system. ...
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  • 22.9k
27 votes

Why would it be very light out at 3 AM?

I come from a similar latitude and enjoyed the night skies and two things that can add to "the amount of light in the sky" that I can think of. The first is the near-full moon as mentioned ...
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26 votes
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How many planets have we discovered that can support human life?

There is currently only one planet known to be capable of supporting human life, and you're on it. Several planets have been found in the region in which we expect water to be liquid on much of the ...
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25 votes
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Does the Earth have another moon?

Not strictly satellites/moons, but certainly companions are 2010 TK7 with a diameter of ~300 m, an Earth trojan at the L4 point, and the ~5 km 3753 Cruithne in a peculiar orbit locked to the ...
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23 votes

Did the earth form outside the solar system?

The chance happenstance that Earth happened to be floating along and got captured is minuscule. How did Earth wind up floating through space? There's no established mechanism for terrestrial planets ...
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23 votes
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If Theia really crashed into Earth, did it impact Earth's axial tilt?

TL;DR: Yes Long answer: Theia is a hypothesized ancient planet in the early Solar System that, according to the giant-impact hypothesis, collided with the early Earth around 4.5 billion years ago, ...
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