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 ...
- 7,940
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 ...
- 7,411
69
votes
Accepted
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 ...
- 11.8k
65
votes
Accepted
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 ...
- 34.7k
52
votes
Accepted
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 ...
- 107k
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 ...
- 107k
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 ...
- 32.7k
43
votes
How did the Milky Way quasar not disrupt terrestrial life?
An active galactic nucleus doesn't emit energy equally in all directions. It may form "jets", and if you are looking into the AGN at the right angle, and then nucleus is active enough, then ...
- 107k
42
votes
Accepted
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 ...
- 31k
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 ...
- 7,470
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-...
- 15.8k
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 ...
- 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 ...
- 11.7k
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 ...
- 136k
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 ...
- 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 ...
- 986
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 ...
- 6,221
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 varying length of the day is determined by the tilt of Earth ...
- 107k
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 ...
- 32.7k
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 ...
- 107k
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. ...
- 23.3k
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 ...
- 31k
26
votes
Accepted
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 ...
- 107k
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\...
- 1,362
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, ...
- 3,848
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 ...
- 14.7k
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 ...
- 31k
22
votes
Why doesn't the sun pull the moon away from earth?
Why doesn't the sun pull the moon away from earth?
Short answer: Because the Moon is much closer to the Earth than it is to the Sun. This means the gravitational acceleration of the Earth toward the ...
- 32.7k
22
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 ...
- 32.7k
Only top scored, non community-wiki answers of a minimum length are eligible