91 votes
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Is there a star over my head?

Summary There's a 1 in 500 billion chance you're standing under a star outside the Milky Way, a 1 in 3.3 billion chance you're standing under a Milky Way star, and a 1 in 184 thousand chance you're ...
MichaelS's user avatar
  • 858
32 votes
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If the Sun was replaced with a sun-mass black hole, would it be visually detectable?

Yes, easily with a telescope, but not with the naked eye. It is a matter of routine to detect the 1.7 arcsecond shifts caused to stellar positions when seen near to the limb of the Sun. The removal of ...
ProfRob's user avatar
  • 152k
16 votes

Is there a star over my head?

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 ...
peterh's user avatar
  • 3,161
14 votes

Hypothetically, would we be able to see the moon from Saturn's North Pole?

First of all, at that distance seeing the Moon and seeing the Earth amounts to the same thing. At its closest, Saturn is around 3000 times as far from Earth as the Moon is, so viewed from Saturn, the ...
Mark Olson's user avatar
  • 7,650
13 votes

Could Planet X have a perihelion much closer than 300 AU and still be responsible for the gravitational interaction with 19 TNOs?

Well yes, because Brown & Batygin (2021) say the perihelion would be $300^{+85}_{-60}$ au, so there is roughly a 50% chance that the perihelion is smaller than 300 au according to their work. The ...
ProfRob's user avatar
  • 152k
13 votes

What if Earth gained 1 km/s orbital velocity?

I am assuming that by adding 1 km/s, you mean increasing the tangential speed of the Earth by 1 km/s. This would increase both the kinetic energy and the angular momentum. This is a relatively small ...
ProfRob's user avatar
  • 152k
12 votes
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Hypothetically, would we be able to see the moon from Saturn's North Pole?

Yes, if you observe Earth and the Moon at a favorable time. Near a Saturn summer solstice, e.g. between 2012 and 2022, Earth appears well above the horizon from Saturn's north pole. If the planet body ...
Mike G's user avatar
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12 votes

How would radiation pressure inside of the Sun affect an indestructible person?

Radiation force is totally negligible at the surface of the Sun - about one hundred thousandth the force due to gravity. The radiation force does grow as you move into the solar interior, but only as ...
ProfRob's user avatar
  • 152k
9 votes

Is there a star over my head?

Does "overhead" mean over the center of your head, or over some part of your head? If we assume the latter, it changes the problem! I don't want to recapitulate all MichaelS's lovely work above, so I'...
jeffB's user avatar
  • 380
9 votes

Hypothetically, would we be able to see the moon from Saturn's North Pole?

For these kind of questions, you might want to use Stellarium, a free open source planetarium. You can specify the location of the observer on many celestial bodies, including Saturn. Any time ...
Eric Duminil's user avatar
  • 1,365
9 votes
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What would the effects on or around Earth if Betelgeuse went supernova?

tl;dr - The main measurable effect may be minor climate cooling, but in day-to-day life, the only difference would be that we see a cool, bright explosion in the sky, and eventually, Orion becomes "...
Calc-You-Later's user avatar
7 votes

If the hypothesized planet behind the Kuiper belt existed, would it have a barycenter outside the Sun?

If we have two masses $M$ and $m$, which are at distances $r_1$ and $r_2$ respectively from their barycentre, then $$Mr_1 = mr_2$$ Let $d$ equal the total distance between the two bodies. That is, $d =...
PM 2Ring's user avatar
  • 14.5k
6 votes
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When might Rowan-Robinson's planet be discovered or disproved?

Essentially: probably no-one knows for sure unless a person who started the research themselves or is writing or has written a grant application to conduct the research, if at all so far. The paper ...
planetmaker's user avatar
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6 votes

What if Earth gained 1 km/s orbital velocity?

Using calculations from here: https://www.vanderbilt.edu/AnS/physics/astrocourses/ast201/orbitalvelocity.html New semi-major axis $$ a = \frac{150000000000 \cdot 0.0000000000667 \cdot 2\cdot 10^{30}}{...
Ivan Borsuk's user avatar
6 votes
Accepted

What will be the temperature on Earth when Sun finishes its main sequence?

The difference is that your analysis is assuming that the albedo stays fixed, so the surface temperature simply scales like luminosity to the 1/4 power. The Wiki entry is including feedback from the ...
Ken G's user avatar
  • 5,330
6 votes
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How could lithium burning take place in a quasi-star?

Lithium, along with Hydrogen and Helium, was one of the 3 elements created in the Big Bang. Thus, it should exist to some part in any star that hasn't burnt all of it out, and as mentioned, it's not ...
PearsonArtPhoto's user avatar
5 votes

Is there a star over my head?

Probably, maybe. There are at least two ways of answering the question. One is to ask what were your coordinates when you wrote the question and exactly what time it was. Then we'll need to draw a ...
keparo's user avatar
  • 151
4 votes
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If the hypothesized planet behind the Kuiper belt existed, would it have a barycenter outside the Sun?

The proposal is that the apparent planet 9 is, in fact, a primordial black-hole, with mass comparable to a planet and a diameter measured in centimeters. Such an object would be almost undetectable. ...
James K's user avatar
  • 122k
4 votes

If the Sun was replaced with a sun-mass black hole, would it be visually detectable?

A black hole with the mass of the sun is much smaller than the diameter of the sun, by a factor of about 200 000 (6 km vs 140 000 000 km). The sun is, to the naked eye on earth, about the same size as ...
Jasen's user avatar
  • 141
4 votes
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I am trying to find the dates for a solar eclipse where the Earth and Ceres are in line

According to Fred Espenak, aka Mr Eclipse, there's a total solar eclipse on 2117-Sep-26 00:55:42 TD (00:53:15 UT1).  Less than two days later, at 2117-Sep-27 22:07:25 UTC, Ceres is opposite the Sun, ...
PM 2Ring's user avatar
  • 14.5k
4 votes
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Is a bromine planet possible?

Possible, but very hard to form Considering the fact that the universe is infinite, anything can be possible, be it a galaxy-wide wormhole, a bromine planet, or a Type II- no, we're getting off-topic. ...
Alastor's user avatar
  • 2,659
3 votes

If the Sun was replaced with a sun-mass black hole, would it be visually detectable?

ProfRob calculated correctly but interpreted wrongly. Any star off the BH by 0.1° would also be seen thus close (4.7") to the BH. If Mercury or Venus are in opposition and close to a node, the ...
Rainald62's user avatar
  • 135
3 votes
Accepted

Earth’s rotation speed vs rate of lunar cycle

This is not a hypothetical question since the Earth's rotation rate is slowing due to tidal interactions with the Moon. Currently, the Earth rotates once every 86164 seconds (sidereal time) for about ...
Connor Garcia's user avatar
  • 16.3k
3 votes

Earth’s rotation speed vs rate of lunar cycle

In principle, nothing. There is no direct link between the length of a day, the length of a month, and the length of a year. If you have a wizard on hand to do the magic, you can change the rotation ...
James K's user avatar
  • 122k
3 votes

How could lithium burning take place in a quasi-star?

If present, lithium is burned at lower temperatures than hydrogen (protium), although at higher temperatures than deuterium. See Why does lithium fuse at lower temperatures than hydrogen? The ...
ProfRob's user avatar
  • 152k
3 votes

Can a quasi-star develop a stable crust?

If by crust you mean a solid surface, then no, it would not be possible. Wikipedia states that the surface temperature of a Quasi-Star would be around 10,000 K. However, Hafnium Carbonitride, a ...
Astrovis's user avatar
  • 465
3 votes

What would a gas giant, such as Uranus, look like if it were orbiting a sun like star at an Earthlike orbit?

Hot Neptunes are known, beginning with an exoplanet orbiting the star Gliese 436. They may be formed either at greater distances from the star and then migrate inwards (ex-situ) or at close distances ...
Oscar Lanzi's user avatar
  • 1,113
2 votes
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Interstellar bodies

The sun couldn't. The sun gives off light and a solar wind. It doesn't emit lumps of solid matter. It is possible for a small body, such as a comet to get a slingshot around a planet and be ejected. ...
James K's user avatar
  • 122k

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