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 ...

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 ...

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 ...

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 ...

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 ...

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 ...

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 ...

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 ...

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 ...

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 ...

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 ...

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

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 ...

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 ...

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 ...

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 $6371 km \cdot \frac{6371 km}{41.5\... View answer Accepted answer 4 votes This arxiv post says if there is dark matter in the solar systems, its density should be below$\approx 1.4\cdot 10^{-20} \frac{g}{cm^3}$. They tried to find the dark matter in the solar systems by ... View answer Accepted answer 4 votes According to this paper, there are various but enough good estimations for the temperature gradient of the Martian soil. Note, direct measurements will we have first with the next Martian lander, the ... View answer 4 votes The speed of the Earth (and Moon) around the Sun is$\approx 29.8 \frac{km}{s}$. The speed of the Moon around the Earth is$\approx 1.05 \frac{km}{s}$. The result is that the Moon has a nearly ... View answer 3 votes No. A short calculation: the Moon orbits the Earth with with 1022m/s. The mass of the Earth is 81 times bigger than of the Moon. That means, that also the Earth orbits the common center of mass of the ... View answer 3 votes An analogy You can not sit in a forest, and watch as the trees grow, mature and die. You have no time for that, because the trees live typically longer than you. However, if you are a forester, then ... View answer 3 votes I think a superconducting cable system around the Martian equator is far more easy. To get an Earthian$\rm B$, which is$\approx 4 \mu T$, from a Martian radius ($\approx \rm{3000 km}$), we would ... View answer 3 votes Use other, more scientific sources. You have no way to test them by some home measurements - science was tuned to pass even more sophisticated tests. Popular media is often not very exact. They try ... View answer 3 votes From us, the Sun is visible around a half grad, which is$\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.

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 ...

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 ...

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 ...

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 ...