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110 votes
Accepted

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 ...
Sir Cumference's user avatar
107 votes
Accepted

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 ...
JohnHoltz's user avatar
  • 7,952
69 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 ...
PM 2Ring's user avatar
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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 ...
HDE 226868's user avatar
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52 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 ...
James K's user avatar
  • 118k
51 votes

Why is the solstice the first day of summer, and not the central day?

The English word "summer" means the season of the year that is associated with higher temperatures and shorter nights. There is no official "first day of summer" and different ...
James K's user avatar
  • 118k
47 votes
Accepted

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 ...
David Hammen's user avatar
  • 33.7k
44 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 ...
uhoh's user avatar
  • 31.3k
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 ...
Mark Olson's user avatar
  • 7,620
41 votes
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What does the Earth look like when viewed from Saturn?

Yes! It's a tiny blue dot of just about 1.6 arc seconds diameter. Cassini made the most famous image of the "In Saturn's Shadow – The Pale Blue Dot", in remembrance of the first such image ...
planetmaker's user avatar
  • 18.9k
38 votes
Accepted

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-...
Connor Garcia's user avatar
  • 16.3k
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 ...
Anders Sandberg's user avatar
37 votes
Accepted

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 ...
ProfRob's user avatar
  • 149k
34 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 ...
Hilmar's user avatar
  • 441
32 votes
Accepted

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 ...
FSimardGIS's user avatar
  • 1,006
32 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 varying length of the day is determined by the tilt of Earth ...
James K's user avatar
  • 118k
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 ...
Pierre Paquette's user avatar
30 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 ...
James K's user avatar
  • 118k
29 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 ...
David Hammen's user avatar
  • 33.7k
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. ...
userLTK's user avatar
  • 23.9k
28 votes

Safest Place on Earth from Falling Meteorites

Robertson et al. (2021) (note the erratum) provide a very comprehensive answer to your question. Surprisingly (to me) the asteroidal flux (impacts per unit area) is slightly higher at the poles (by 8%)...
ProfRob's user avatar
  • 149k
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 ...
uhoh's user avatar
  • 31.3k
26 votes

How did the Earth come to be in orbit around the sun?

The picture was so much cleaner 20 to 25 years ago. I'll present that nice clean picture first. Stars form from the gravitational collapse of huge clouds of interstellar gas. Those gas clouds ...
David Hammen's user avatar
  • 33.7k
26 votes

Which is brighter, Mars as seen from Earth, or Earth as seen from Mars?

We can use the expression that is commonly used to estimate the apparent magnitude of a planet or asteroid in the Solar System: $$\boxed{m=5 \log \frac{1329}{d \cdot \sqrt p}+5 \log (D_s \cdot D)-2.5\...
Albert's user avatar
  • 1,910
26 votes
Accepted

Would the Earth and Moon still have tides after the Earth tidally locks to the Moon?

There won't be significant lunar tides. The moon will become fixed at one location above the Earth. The tidal forces that drive the resonant water flows that we call "tides" will be fixed. ...
James K's user avatar
  • 118k
25 votes

How one can establish that the Earth is round?

Observer the shadow of the Earth on the moon. It is circular, no matter where the moon is in the sky. Observe that the position of the stars in the sky changes as you travel north or south. In ...
James K's user avatar
  • 118k
24 votes
Accepted

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, ...
Nilay Ghosh's user avatar
  • 4,436
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 ...
zephyr's user avatar
  • 15k
23 votes

Can a satellite stay in one place but not above equator?

To add to @Planetmaker's concise yet complete answer: In order to keep at least one satellite in the sky over Russia (or any other high N or S latitude area) at all times, the Molniya orbit was ...
uhoh's user avatar
  • 31.3k

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