66 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 (...
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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 ...
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  • 471
54 votes
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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 ...
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52 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 ...
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38 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 ...
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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 ...
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35 votes
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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 ...
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33 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 ...
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33 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 ...
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27 votes
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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 ...
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25 votes
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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 ...
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25 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 ...
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24 votes

How does the evolution of a solar system not break the second law of thermodynamics?

The total entropy actually increases, as the molecular cloud shrinks under gravity. It may seem that as the molecules are getting closer, they are more ordered, which means less entropy. That is ...
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24 votes
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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 ...
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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 ...
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20 votes

How does neutron star collapse into black hole?

Just to focus on one part of your question. Whilst it might be possible for a neutron star to accrete material, or for two neutrons stars to collide, in order to form black holes, this kind of event ...
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20 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 ...
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20 votes
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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 ...
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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 ...
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20 votes
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How to be an astrophysicist?

In addition to the answer of James K, who outlines the most straight forward way into astrophysics, there's many paths. Some others include: There are people who did a BSc and/or MSc in Engineering ...
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18 votes
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Is any consensus forming on the solution to the "Lithium Problem"?

There is no absolute consensus and nothing proven beyond doubt, but there are favourite explanations. The discrepancy between the predicted big bang nucleosynthetic abundance of Lithium 7 and the ...
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18 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 ...
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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 ...
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17 votes
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Problem regarding the absorption lines of the sun

Possibly you are labouring under the misapprehension that the number of photons is somehow a conserved quantity? That isn't true, there are more photons at any given wavelength when you are deeper ...
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16 votes
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Circular formation around the moon

That sounds very much like a 22° halo. It's not an astrophysical phenomenon; it results from the refraction of light by ice crystals in Earth's atmosphere. If this is what it is, it should be a ...
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16 votes

Why doesn't the Earth's rotation throw us off the surface?

OK, the reason we don't get flung off the surface of the Earth is that the rotational forces are not large enough to do it. Keep in mind that Earth formed because material was pulled together by it's ...
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16 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 ...
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16 votes
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How is the Hubble constant determined from gravitational waves?

If you measure the gravitational waveform from an inspiralling binary, you can at any point measure the amplitude, instantaneous frequency and the rate of change of frequency. The last two give you ...
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16 votes
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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 ...
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