70
votes
What happens to the 99.9 % of the sun-rays that do not fall on any planets or any other celestial body?
The light from the Sun spreads, at least initially, in a roughly isotropic fashion into the universe.
As it gets further from the Sun, some of that light will interact with the interstellar medium (...
- 146k
58
votes
Why can't we feel the Earth's revolution?
You do, but it's too small to really notice
First, it's not correct to say that we don't feel Earth's rotation because it's rotating at a constant speed.
Think about driving a car, or riding in an ...
- 471
54
votes
Accepted
How do scientists know that the distant parts of the universe obey the physical laws exactly as we observe around us?
We don't know in general but to the extent we can measure, the laws seem to be the same, even if conditions are not.
For example radioactive decay: We know how fast various elements decay, and we can ...
- 116k
53
votes
If all stars rotate, why was there a theory developed that requires non-rotating stars?
In a similar way, we could ask...
No beams can be exactly 1 meter long. No beams can be exactly
straight. The material making up a beam cannot be truly isotropic.
So why should we bother ...
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47
votes
If all stars rotate, why was there a theory developed that requires non-rotating stars?
All models are approximations, we judge a model on how useful it is.
Understanding the collapse of a non-rotating star to a black hole gives insight into the nature of gravitational collapse. Much of ...
- 116k
40
votes
What happens to the 99.9 % of the sun-rays that do not fall on any planets or any other celestial body?
You want nature to be frugal and efficient. You want all the energy of the sun to have a purpose. However what you want nature to be like has no bearing on what it is.
The light from the sun is a ...
- 116k
38
votes
What would happen to a polished marble statue left in space for a million years?
There are three main space weathering processes that will affect the surface of the marble.
Cosmic rays, high energy particle from the sun and beyond, will hit the surface. This can change the ...
- 116k
36
votes
Accepted
Why don't (or can't) stars be more than 325 or so times the mass of the sun? What limits their size?
There is basically an upper limit to the mass of a star because their luminosity is so great that the radiation pressure prevents the accretion of further mass.
However, the upper limit depends on the ...
- 146k
34
votes
Why is the Moon's orbit so complicated?
The moon is so big that the processes that circularize and reduce the equatorial inclination would take much longer. The moon is big because of how it formed: a huge collision in the early solar ...
- 116k
34
votes
Why are there no gamma-ray bursts detected in our galaxy?
All models of gamma-ray bursts involve extremely energetic phenomena: particular types of supernovae, the coalescence of binary compact objects, strong magnetar flares, or tidal disruption events. It ...
- 36k
34
votes
Why doesn't dark matter clump strongly in the center of galaxies, since it doesn't feel either radiation pressure or the Pauli exclusion effect?
The reason is the fact that dark matter is non collisional. The dark matter particles interact only gravitationally, they feel no pressure, right, but they also feel no drag! No drag, no friction, ...
- 4,371
28
votes
Accepted
Quantum Mechanics after the detection of Gravitational Waves
No more than the observation of light waves disproves quantum mechanics.
Light has properties of both a particle and a wave. At low energies, the particle nature of light is hard to detect: radio ...
- 116k
26
votes
How to be an astrophysicist?
Different education systems differ, however
At school you would take maths and physics courses, at least covering calculus.
As an undergraduate, taking (or majoring in) physics. Also probably doing ...
- 116k
25
votes
Accepted
Why does the sensitivity to GWs drops off inversely proportional to the distance?
EDIT I'm leaving the original, highly upvoted answer below, but I've had a fundamental rethink about this, prompted by questions from Keith McClary and a helpful clarification from a Physics SE ...
- 146k
25
votes
Is Dark Matter possible if there is dynamical friction?
Dynamical friction is considered in the study of dark matter.
The timescale for dynamical friction to cause a significant loss of kinetic energy is roughly
$$\tau \sim \frac{10^{5}}{\sqrt3 \ln \Lambda}...
- 146k
24
votes
Accepted
Why can't we feel the Earth's revolution?
Firstly the speeds are massively different (about 1000 mph (1610 kph) on the equator for Earth's rotation and 70,000 mph (112,654 kph) for the revolution), so the change is not large. Secondly, the ...
- 10.2k
24
votes
Is there anything currently 46 billion light years away from Earth that we can see?
The CMBR came from a sphere of matter with an extrapolated comoving radius of around 46 billion ly. That's the most distant thing we can see. The observable universe is sometimes defined to end there, ...
- 3,498
23
votes
How can astronomers pinpoint the location of the source of a neutrino?
You correctly state that neutrinos do not interact too often. The physical parameter describing that is the effective cross-section. So what you observe in a detector is not the neutrino itself, but ...
- 5,526
23
votes
Do these results mean that I have found this exoplanet?
It could be an exoplanet transit (but that doesn't mean it is).
The star in question, TIC92352620, is an F8 main sequence star, which would be much larger than any plausible planet. If a planet ...
- 146k
21
votes
Quantum Mechanics after the detection of Gravitational Waves
The impact of this measurement on the status of quantum gravitation is exactly zero.
The proper statement of the incompatibility of general relativity and quantum mechanics is that the quantum field ...
- 311
21
votes
Accepted
How to be an astrophysicist?
The main way into astrophysics is - as James K outlines in his answer well - to study physics with an emphasis on astrophysics or astronomy. The entry into these academic careers are easier for those ...
- 17.5k
20
votes
Accepted
If all stars rotate, why was there a theory developed that requires non-rotating stars?
Another consideration is that the physics that describe a rotating black hole was much harder to develop.
The maths describing the Schwarzschild (uncharged, non-spinning) black hole was developed in ...
- 4,137
20
votes
Gravitational Properties of Asteroids
Of course you would need to specify who the person is - an Olympic athlete? Let us assume so and then you can scale downwards accordingly.
So an Olympic high jumper can jump hard enough to raise ...
- 146k
19
votes
Quantum Mechanics after the detection of Gravitational Waves
Another question, how can we identify the ripple's origin (let's say that if it's the result from the big bang or another big event)?
(I'm just answering this part of the question, as James has ...
- 2,467
19
votes
Is there anything currently 46 billion light years away from Earth that we can see?
We don't see stars and galaxies at a proper distance of 46 Gly, because this distance corresponds to a light travel time of 13.7 billion years, or very shortly after the big bang.
When we look into ...
- 116k
18
votes
Is there a possibility that a white dwarf can turn into a neutron star or a black hole?
The answer is: to a neutron star - possibly; to a black hole, no.
The process whereby a neutron star is formed is known as an accretion induced collapse and is being seriously debated, especially in ...
- 146k
18
votes
Has anyone back-calculated previous close encounters between the Apophis asteroid and Earth?
The JPL Small Body Database lists Apophis close approaches dating back 100 years before discovery.
Three fairly close ones were:
1907-04-13, 0.029 au
1949-04-14, 0.028 au
1990-04-14, 0.033 au
While ...
- 18.2k
17
votes
Accepted
Have I nearly found the event horizon of a black hole?
This is the Newtonian model of gravity. It is a very good model, it is used for accurate calculating the motion of objects in the solar system to a very high degree of accuracy.
However, for very ...
- 116k
17
votes
Accepted
Problem regarding the absorption lines of the Sun
Possibly you are under the misapprehension that the number of photons is a conserved quantity? That isn't true, there are more photons at any given wavelength when you are deeper into the star because ...
- 146k
17
votes
Accepted
Why isn't most hydrogen in the universe molecular (diatomic), instead of atomic (monoatomic)?
Yes, the atomic hydrogen is probably mostly left over from the Big Bang. [Edited to add: Not sure how much that is true and how much present-day atomic hydrogen is the result of recombination.] And, ...
- 16.4k
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