peterh
  • Member for 7 years, 7 months
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Is there any orbit at which the Roche limit can be "felt"?
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24 votes

Roche limit happens where the gravity of the object, trying to pull the object together, becomes smaller than the tidal force (trying to pull the object apart). But the astronaut is bound by not ...

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Is there a star over my head?
15 votes

In short: no one knows for sure, but currently it looks that the probability is 1. Longer: On our current understanding, the Universe is probably infinite in space. This depends on the recent WMAP ...

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Can a system of three stars exist?
15 votes

It is possible in a Trojan configuration: In the place of the "Planet" on the image, also a small star could exist. The third star would be at $L_4$ or at $L_5$. This configuration could be made ...

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Satellite in orbit in front of and behind the Moon
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11 votes

Yes. Trojan orbits (60° before or after the Moon) are even stable in most cases. These points are called the L₄ and L₅ points, which are two of the five Lagrangian points. These orbits are mostly ...

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Is there anything like a supermassive white hole? How are they formed? And where are they present?
11 votes

White holes are a theoretical construction of General Relativity. Despite extensive searches, nothing has been found: not a supermassive white hole, not a stellar-sized white hole, nothing. Thus, the ...

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How well would the Moon protect the Earth from an Asteroid?
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8 votes

The Moon orbits the Earth from $\approx$ 380000 km, but its radius is only $\approx$ 3500 km. The sky has 41253 sq degrees, and the Moon covers only $\approx$ 0.25 sq degree from it. Thus, the ...

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Lunar orbit distance
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8 votes

It depends on where we observe it from. There is no absolute velocity reference. For example, the most distant quasars are moving away from us at nearly the speed of the light. They "see" our Moon ...

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If the Sun disappeared, could some planets form a new orbital system?
7 votes

No. The 8 planets would go into 8 different directions. It is because their relative velocity to each other is much higher than the escape velocity, even from their smallest distance. If it would not ...

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How much solid matter is in the observable Universe?
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7 votes

Any non-star is negligible, their volume is practically zero. Most matter in the Universe is gravitationally bound plasma, resulting that they do not have a well-specifiable volume, because their ...

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How is dark matter different from ordinary (visible) matter?
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6 votes

Nobody knows it for sure. What is known: it interacts gravitationally it doesn't interact electromagnetically "Dark" doesn't mean "black" here, it means here "invisible". There are many ...

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If the Universe is infinite, why isn't it of infinite density?
5 votes

Your assumption is not true. For example: if the probability density function of the atoms decreases quadratic exponentially (i.e. $e^{-r^2}$), then their sum will be finite even in an infinite ...

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antimatter annihilation in stars
5 votes

They are not replaced. Fusion in ordinary stars means actually many processes, neutrinos are involved most commonly in these: $p + p \rightarrow D + \nu_e + e^+$ $T \rightarrow He_3 + \nu_e + e^+$ ...

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Would two Earth-like planets on opposite sides of a Sol-like star at about 1 AU be a stable configuration?
5 votes

It would not be a stable configuration, but it wouldn't be too far from the stability. The are 5 points where a third body could have a semi-stable orbit in a 2-body system: The Earth is the blue ...

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Could Black holes forge heavier elements that have yet to be discovered?
5 votes

The problem of the superheavy elements is not that we can't forge them. Their problem is that they decay very quickly. For example, Oganesson, the heaviest element synthetised until now, has a half ...

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I need to study space, planets and black holes, how do I study them on my own
4 votes

I am sorry to say, but the best resources are still books. If it is really a no-go, read further. It is very likely, that you can find and buy astronomy books on Arabic on the Internet. First start ...

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If the whole observable Universe is as big as planet Earth, how big would Earth be?
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4 votes

The radius of the observable Universe is 41.5billion light years (ref). A light year is $9.5\cdot10^{12}$ km. The radius of the Earth is 6371 km. So the answer is $6371 km \cdot \frac{6371 km}{41.5\...

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What is the closest candidate for Dark Matter currently?
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4 votes

This arxiv post says if there is dark matter in the solar systems, its density should be below $\approx 1.4\cdot 10^{-20} \frac{g}{cm^3}$. They tried to find the dark matter in the solar systems by ...

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How deep in Mars would a person not need insulation and pressure?
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4 votes

According to this paper, there are various but enough good estimations for the temperature gradient of the Martian soil. Note, direct measurements will we have first with the next Martian lander, the ...

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Why does the moon not leave its orbit around the earth due to the gravitational force from the sun?
4 votes

The speed of the Earth (and Moon) around the Sun is $\approx 29.8 \frac{km}{s}$. The speed of the Moon around the Earth is $\approx 1.05 \frac{km}{s}$. The result is that the Moon has a nearly ...

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Small changes to Earth's orbit caused by a large impact on the Moon
3 votes

No. A short calculation: the Moon orbits the Earth with with 1022m/s. The mass of the Earth is 81 times bigger than of the Moon. That means, that also the Earth orbits the common center of mass of the ...

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any proof that stars are born, and die?
3 votes

An analogy You can not sit in a forest, and watch as the trees grow, mature and die. You have no time for that, because the trees live typically longer than you. However, if you are a forester, then ...

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Is it possible to revive the Mars geodynamo?
3 votes

I think a superconducting cable system around the Martian equator is far more easy. To get an Earthian $\rm B$, which is $\approx 4 \mu T$, from a Martian radius ($\approx \rm{3000 km}$), we would ...

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How can you verify the theories presented on TV shows like "How the Universe Works" is current and/or valid?
3 votes

Use other, more scientific sources. You have no way to test them by some home measurements - science was tuned to pass even more sophisticated tests. Popular media is often not very exact. They try ...

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From what distance would our sun have an angular diameter of 7 arc seconds?
3 votes

From us, the Sun is visible around a half grad, which is $\approx$ 30 arc min = 1800 arc seconds. To get to 7 arc seconds, you need to go 1800/7 times farther away, so the result is around 250 AU.

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If the Higgs field only formed after the Big Bang, how was hydrogen formed?
3 votes

After the Big Bang, matter has formed in many steps. These are calles epoches. Their length grows typically exponentially. A more detailed description can you read here. The Higgs field always ...

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How loud would a black hole be?
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3 votes

Nothing comes out from the BH (well, with a single known, very small exception). The accretion disk of the Black Holes most likely has various streams, pressure differences and so in it. Calculating ...

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Can a black hole be torn apart by SMBHs?
3 votes

No. The total mass of the Black Hole is in the point in its center, but there is no return from passing the event horizon. The Area theorem (from Hawking) says, that the total area of the event ...

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Is there any way to tell which way is the next universe?
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3 votes

There is no way to know, if any other "different Universe" exists. There is also a terminologic problem with it. Universe means, on latinic, something what "contains everything". If there is no way ...

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What is the relative time difference between us and a star system in outer layer of our galaxy?
3 votes

Your third question has a very well known answer here: What means, that although a big time difference had to exist, there is a much smaller one, and in the opposite direction. This is considered the ...

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How many light years away is Earth from the closest outer edge of the black hole at the center of the Milky Way?
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3 votes

As @Py-ser already said, there is the very clear information about that, although his link correctly is here. As we can read there, the distance of this is around 25000 light years, with a precision ...

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