# All Questions

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### Finding a Kerr Black Holes

I understand that Kerr Black Holes are purely theoretical and have not been found anywhere in the Universe. However, they are theorized for possible means of time travel. I am attempting to prove in ...
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### What must/do astronomers reveal beyond their academic papers?

Academic papers often make claims about observational data and results from computations. The papers only refer to names of data sources (such as an observatory) and of mathematical methods without ...
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### Is it possible to create an artificial Black Hole?

I am quite curious about black holes. Once I just thought whether it is possible to create an artificial Black Hole, i.e. an human made black hole. Also explain there formation if it is possible.
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### State of the stars

This question may sound silly but I'm really not pretty sure whether the stars are rotating or stationary.If they are not rotating what makes them to be stable?
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### How fast is the universe expanding?

I've hear several theories stating that the universe is expanding faster than the speed of light, others claim that the universe expands faster the further away you measure it. Which of this is ...
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### Can redshift be measured using fourier?

Are there pictures that contain high enough dynamic width, so that amateurs can use fourier spectrum analysis to observe the redshift themselves? I know pictures usually are encoded using RGB and/or ...
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### Why does a particle feel no force at radii greater than itself?

I am working through Liddle's "An Introduction to Modern Cosmology", and in a newtonian derivation of the Friedman equation he states: in a spherically symmetric distribution of matter, a particle ...
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### Does the Moon have an aurora?

If the Moon has a magnetic field and can possibly receive solar wind, then does it have an aurora? If Earth has an aurora, and Saturn has an aurora, then could the Moon possibly have an aurora?
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In a star, the fact that not all the hydrogen is used up, not all the helium is used up etc. is a little counterintuitive. Shouldn't it be that a star looses the hydrogen layer passively, in other ...
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### Age of the universe and age of stars

The age of the universe is 13.798±0.037 billion years, yet the age of HD 140283 is 14.46±0.8 billion years, how this can be the case?
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### Is it possible to see a moonrise or moonset twice in a day?

I've been wondering this for quite some time. Due to the variations in tilt from the earth we know that moonrise/moonset times vary. Is it possible that in any location on the earth one might see ...
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### Is the expansion of the universe greater than the speed of light?

If the rate of expansion of the universe is increasing , won't it eventually become greater than c? Also, after inflation, did the rate of expansion slow down and then start to accelerate again?
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### Why natural satellites (moons) of all Planets are Solid?

Why the natural satelittes (moons)of all planets including moons of Gas Giants are are Solid or Rocky and not gaseous like them?
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### the metal distribution in our solar system

The sun dominates in our solar system. I wonder whether in every aspect the sun play the most role in our system. For example, all kinds of metals are mainly located in the sun instead of the rest ...
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### During what time of the year can Centaurus be seen from Tokyo?

During exactly what dates of the year can the Centaurus constellation be seen from Tokyo, Japan? And what is the ideal date for viewing it from Tokyo? I found on a website that it can been seen ...
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### Mechanism for Brown Dwarf Fusion

I've read (at here, among other places: http://deepblue.lib.umich.edu/bitstream/handle/2027.42/55288/index.html?sequence=1) that during the Degenerate Era, star formation will end and the last stars ...
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### How do black holes evaporate?

Will black holes evaporate, if they evaporate? When and why do they evaporate? What are the conditions for evaporation? Under what principle do they evaporate?
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### How was an infrared picture of the entire universe taken?

(click to enlarge) How was this picture of the supposed entire universe taken in infrared? Also, why does it seem as though almost all of the matter is in a line formation over the center? It makes ...
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### the length of second, minute or hour, what defines the time of exo planetary bodies

we measure time based on earth and earth mass\gravity plays a role in the measurement ? so how and what would be time if not earth time on other exo planets since they will be having different ...
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### Contradiction between Theory of Relativity and Newton's Law of Universal Gravitation?

Newton's Law of Universal Gravity states that an object will accelerate constantly as it falls. Let's assume an object falling into a black hole. According to Newton's Law, when it reaches the event ...
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### Birth and Evolution of Millisecond Pulsars

How are millisecond pulsars formed, and what is the evolutionary track of a millisecond pulsar?
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### Why there are three equations governing blackbody emission?

I learnt that the spectrum of a black body can be explained using Planck distribution Rayleigh -Jeans equation and Weins displacement law Can anyone tell me why there are three different equations ...
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### Could dark energy be negative gravity?

Main question: Could dark energy (the mysterious accelerating expansion of the universe) be explained by "negative gravity"? "Spin off" questions: Does antimatter have negative gravity? If ...
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### What do we mean by space is expanding?

I know this question had often been asked on Physics.SE as well as this site but I don't get them. What do mean when we say that space is expanding? I mean that space is no physical entity that can ...
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### How big would a disc have to be to blot out the sun covering 5% of the land mass of earth?

Like this, but floating in space. I imagine that this would also be influenced by the distance of the object from the sun, and that there is some ideal distance for this object to be? (and ...
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### how steady over time are right ascension and declination values?

I understand that astronomers use right ascension and declination for the position of stars. However both these values strike me as very anthropocentric and, more importantly, unreliable over time as ...
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### A day in earth, a thousand years somewhere else

By followig the laws of physics, is it possible, that in a place far far away that one day (at that place), is counted as 1000 years in the earth. I am familiar with black holes having impact on ...
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### Why planet's orbit is not perpendicular or random ?

Why planet's orbit is not perpendicular or random ? It always seems each planet is revolving on the same geometric-plane around the star.
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### Why is Mars' atmosphere so thin?

Is it because there isn't life to exhale enough oxygen and carbon dioxide? The size of Mars is about the same as Earth, so isn't there enough gravity to hold enough air?
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### Will a new planet form if Jupiter's influence on asteroid belt will diminish in a few billion years?

I know that tidal forces are pushing Jupiter farther from the Sun, but I couldn't find exactly the yearly amount. In a few billion years would this effect (and subsequent decrease in gravity pull) ...
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### Is it dark inside a black hole?

Assuming you could be standing inside a black hole, would it be light or dark around you?
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### How would water waves behave in partial gravity?

Would an "indoor" pool of water on the Moon or on Mars behave differently than on Earth? Would the waves caused by a splash be higher or lower? Would they propagate faster or slower? Would boyance be ...
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### A curious relationship between lunar periods and the solar year

Earlier today I was exploring the astronomy features on WolframAlpha, when I stumbled upon an intriguing numerical relationship involving the values for the lunar synodic and sidereal months. Using ...
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### Black dwarf binary systems

I know black dwarf stars do not exist yet, and that they are what white dwarfs end up after a long time. The question is really simple: would it be possible to have a binary system in which one of the ...
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### If we lived in a multiverse, what would our universe most likely then be named? [closed]

For instance, we live in the Milky Way Galaxy. We don't just call it "The Galaxy", because we know there are multiple different galaxies. So if we lived in a multiverse, it wouldn't make much sense to ...
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### Heavy bombardment - Why has things cooled?

I was always taught and lead to believe that at the beginning of our solar system, there was a period of heavy bombardment, which is conceivable. Why has it just stopped and we are at peace from ...
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### traveling past the speed of light [closed]

According to the theory of relativity (If I understand correctly), nothing is supposed to be able to travel faster then the speed of light. I believe, to my limited knowledge and grasp of the concept, ...
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### What are some applicable problems with the correct usage of G?

In some fields of astrophysics, where distances are measured in parsecs (pc), velocities in kilometers per second (km/s) and masses in solar units (), it is useful to express G as approximately 4.302 ...
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### Can General Relativity indicate phase-dependent variations in planetary orbital acceleration?

In a previous question about differences in Newtonian and GTR gravitional force for the case of star-planet gravitational interactions an approximate relationship was noted between the expressions for ...
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### What happens to photons that don't interact with something?

Say a photon left one of the first stars ever created in our universe. This photon has been traveling for 13+billion years through the vastness of space without ever hitting anything. Sure, it's ...
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### How would Special relativity explain past-present-future if thinking about 13-billion-light-years distanced objects

Halo. I'm interested in how would Special relativity comment on this: Suppose there are 2 objects, A and B. They are 13 billion light years away from each other. When the light from the B object ...
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### Is there a standard mapping of symbols to terms for celestial and orbital mechanics

Is there a standard mapping of symbols to terms for celestial and orbital mechanics (and physics in general)? For example here are some ambiguities Angular Momentum: L, H, J, $\Gamma$, Orbital ...
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### Binary star not exceeding Roche Lobe?

Is it possible that a binary star doesn't exceed its Roche lobe and so when the second star becomes a red giant, instead of accreting some of its plasma onto the white dwarf that it becomes a white ...
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### Fate of the Universe

Which scenario will be worse for the ultimate fate of the Universe , forever expanding or the "Big Crunch" ? Will the Universe be destroyed in both scenarios ? At the present time does it appear that ...
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### What is the danger for Ceres of collision with other asteroids?

In the context of possible colonization of Ceres, would not such colony be totally impossible because of high probability of collision of Ceres with other asteroids in the Asteroid Belt?
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### Can a person at a photon sphere of a black hole decide where the black hole is?

A person at the photon sphere of a black hole will observe the following: The black hole surface will cover exactly half of the visible sky (say, the left half), and cosmic horizon will cover the ...
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### Can matter leave the cosmic horizon?

Cosmic horizon in the de Sitter space is a sphere, centered at the observer with finite radius where the red shift due to cosmic expansion becomes infinite. Given that no information can be ...
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### Is there any way a meteor can hit at less than escape velocity?

Note: I have figured out one case: The meteor is splash from an impact on a close-in moon. I'm looking for any path from deep space. My understanding is that anything from deep space will ...
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### Using Tully Fisher to measure Distance Problem

Can anyone explain by looking at the solution in the pic, how did the cos (i) came about? I guess they are getting this from the major-minor axis info in the question, but I am not sure about the ...
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### Requesting book references for a non-expert person with math background or just a non-expert person

I've just finished my masters degree (to be exact previous week ^_^). And I'm completing my collection of applications of my studies. During previous year I started reading about Robotics and Coding ...

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