# All Questions

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### Where to obtain Tycho Brahe's data?

I would like to obtain Tycho Brahe's data on Mars. What would be an authoritative source? One source I could find is this page (the data is given as an Excel file) but I have no idea can that be ...
188 views

### Weight of a celestial body

How do astronomers find out the correct weight of a planet even though there isn't any direct means to weigh them? What technique do they use? Just curious!
636 views

### What would we find if we could travel 786 trillion light years in any direction

I've sometimes heard of galaxies that are millions or billions of light years away but if we could instantly travel 786 trillion light years in any direction, what are we likely to find? And what if ...
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### Is the sun too small to self-ignite?

I recently heard in a discussion that the sun is not massive enough to self-ignite via core-pressure. It simply has not enough mass to "generate" the gravitational force needed for that. The reason ...
168 views

### Can the Universe be spatially closed and expand forever?

In the lambda-CDM model, the Universe is spatially flat, and will expand forever. Is possible that a spatially closed Universe expands forever?
137 views

### How should one rationally deal with the issue of space travelling alien civilizations?

What kind of reasoning is appropriate to understand the as of today unanswered question of whether there are (other) interstellar space travelling civilizations in the Milky Way? We have already sent ...
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### Equations for coordinates of solar system objects

I would like to write a program that visualizes the solar system. To do this, I would need equations for calculating the coordinates of each solar system object at a given time. Where could I obtain ...
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### Can you assume atmosphere height for the purpose of surface pressure calculation?

Given that by definition of scale height an atmosphere thins by a factor of 1/e^x where x is elevation in terms of scale height multiples (See the table here: Definition of Scale Height), can we ...
33 views

### Are there any works discussing planetary bodies being forms of life?

I'm searching for works or individuals that consider and discuss the idea of planetary bodies being considered stand alone living creatures, rather than objects either capable or incapable of ...
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### How much do the mascons on the moon affect surface gravity?

The gravity anomalies on the moon (generally accepted to be caused by mascons) are powerful enough to affect the orbit of satellites. I'm trying to determine how much effect they would have on a ...
46 views

### Source of high energy cosmic particles

Earth receives shower of both solar and cosmic radiations every seconds. The Sun put up a heliosphere around the solar system and thus foreign high energy charged particles could not penetrate easily. ...
123 views

### Statistics of elements abundance in exoplanets

Recently, I encountered the concept of carbon planets - planets, which would be, unlike the Earth, formed mostly by carbon, instead of oxygen, silicon and magnesium. (I am not counting iron, which is ...
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### Why is the Boomerang Nebula colder than the CMB?

An earlier answer on temperature mentioned that the temp of the CMB is 2.4K and the temp of the Boomerang nebula as 1K. How did the nebula cool faster than the CMB?
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### If the 24 microarcsec parallax precision of the Gaia spacecraft is a 1-sigma value, what is the smallest parallax…?

If the 24 microarcsec parallax precision of the Gaia spacecraft is a 1-sigma value, what is the smallest parallax that could be measured to a 3-sigma confidence? What distance, in kiloparsecs, does ...
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### How far apart is the dust in the Sombrero Galaxy's dust lane?

In his answer to this question, TildalWave made this remark: I think that first, we have to properly appreciate the size of the Sombrero Galaxy. It is roughly 50,000 light years (15 kilo parsecs) ...
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### Is there any practical use for astronomy?

Although astronomy is very cool and the things we are learning are awesome, is there really any practical use to knowing the things we know about the universe? Do other fields of science draw from ...
157 views

### Is it certain that dark matter consists of particles? (And not just curved space)

The main idea about dark matter today seems to be supersymmetry. That there exists a set of yet undiscovered fundamental particles which (in a mathematically most convenient way) mirror the particles ...
26 views

### Orbital Elements Mars near June 2014

do you know any website in which I could obtain orbital elements of planets at some date? For instance, I'm now needing the orbital elements of Mars around June, 2014. Thanks!
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### Is there any astronomical phenomena that could emit strong radio waves with multiples of a discrete frequency?

In the New Scientist article Is this ET? Mystery of strange radio bursts from space, it is reported that several times since 2001, astronomers have detected fast radio bursts that seem to have a ...
730 views

### Why do objects burn when they enter earth's atmosphere?

Why do all objects burn when they enter our atmosphere? is this because of our atmosphere composition? and does this happen on other planets as well?
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### Is it true that chaotic inflation is the most popular inflationary model nowadays?

Old inflation was ruled out, and I think that Linde's New inflation has its problems. There's an astonishing number of inflationary models out there (more than 100?) and they're all too technical for ...
326 views

### What would happen if a body were to fall into a neutron star?

We know neutron stars as a very massive object with extremely strong gravitational forces that composes mostly of neutrons. I couldn't help but wonder, what would happen if an object fell into a ...
66 views

### Collision of asteroid and gaseous planet - what would happen

What happens when asteroids (or other small bodies) "collide" with a gas planet? In my head it would either go through it or just stay "inside" it due to the strong gravity. I tend to believe in the ...
17 views

### Why is MRI important in disc formation?

I understand the principle of the magneto-rotational instability, but why is it so important for disc formation? Does it cause large scale turbulence that helps the evacuation of angular momentum? If ...
15 views

### SDSS: Inclination of a Field?

I am working with the Sloan Digital Sky Survey CasJob service. I am trying to determine the ellipticity of a galaxy using the stokes parameters $U$ and $Q$ from which I can deduce $e$ and $\phi$. But ...
184 views

### How do we find the exact temperature of a star?

This is a very basic question, but I am a little confused. As far as I know, the temperature of a star is analyzed based on the color of the light it emits. So, if a star is moving away from us, then ...
136 views

### Why aren't brown dwarfs the dark matter?

There seems to be not enough matter to account for the fact that the speed of some stars located far from the Galaxy center is almost the same speed as those stars found nearer to the center of the ...
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### Is there a publicly available Gliese Star List

Is there a publicly available list of the Gliese catalogue of nearby stars with their constellations? or a Gliese to Hipparcos List ?
280 views

### Calculate Distance To Stars

I was just watching a lecture from Carl Sagan. He talked about figuring out the distance to the stars; it got me interested in learning more about the subject. As far as I know, the Inverse square ...
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### How much mass does an object in space need to keep a human on its surface?

Assume there were a roughly spherical object in space like a meteorite or a comet. If I weighed 80kg on Earth, how much mass would be required for an object in space so that I could stay on its ...
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### How do we know the universe's expansion is speeding up?

Please forgive my ignorance, I am not an astronomer, just an interested layman. The further away a galaxy is from us, the faster it is moving away from us. But the galaxies we see exist in the ...
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### What uncertainty does an error bar signify in astronomy?

When an astronomer talks about her/his topic and shows an X/Y-plot with error bars. What should one assume that those error bars represent? 1 standard deviation? Or 2? Or some specific significance ...
347 views

### What happens when star spins too fast?

Some stars such as a neutron star can spin very fast around 600 times a second, wouldn't the star be ripped apart? Although the gravitational pull is very strong but gravity is the weakest of all ...
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### Life planets orbiting black-holes. Can/Do they really exist?

So, I watched Interstellar and if you watched it too you know that there's a planet orbiting a black-hole, they call it Miller's Planet. According to the movie, every hour on Miller's Planet is ...
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### Does the mass of the universe ever change?

First do we have anyway to even estimate the mass of the entire universe? And then is there any data that shows mass being gained or lost? Would we ever know if someone was playing with the til.
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### what is a Friedmann model?

Can you explain what is a Friedmann model to a layman? And also give some examples of Friedmann models, specially I would like to know if the lambda-CDM model is considered a Friedmann model.
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### What could be the utmost lowest temperature in the universe/multiverse?

What could be the utmost lowest temperature in the universe/multiverse?
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### How can I calculate how the debris of an object ripped apart at the Roche limit will spread out?

Let's say I have a moon orbiting a planet at a distance $d$. Eventually, $d \leq d_R$, where $d_R$ is the Roche limit of the moon-planet system. I can figure out the mass of both bodies by experiment, ...
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### Can we observe what objects exist at the L3 positiion of planets of our solar system?

From what I understand Earth's L3 is obscured by the Sun, so is that true for our viewpoint of the other planets? Or, are there times when other planets are on the other side of the Sun from Earth and ...
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### Total solar eclipse, supermoon, and spring equinox all happening at the same time: anything special about this?

Today (March 20, 2015) is seeing a rare combination of the spring equinox, a total solar eclipse, and a supermoon. I am wondering if there is anything special astronomically about all three of these ...
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### Binary stars system ultimate fate

I read an article mentioning that when two stars orbiting each other they'll produce gravitational waves that can carry away energy into space. These phenomenon increases the speed of the two orbiting ...
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### Naming of the planets of the solar system

Planets of the solar system have been named with Roman mythology gods names. I have a few questions on my mind concerning that subject for a while: Who decided to name them like this? When did the ...
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### death of a red dwarf star / minimum mass needed for a white dwarf?

OK, first, I know there's a variety of sizes and types of red dwarf stars and the universe is too young for any of them to have reached the end of their main sequence phase yet, so it's all ...
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### Can ground based telescopes use a starshade in space?

1) Could a starshade in orbit be used by ground based telescopes? If so, what kind of orbit should it have? 2) Could the same starshade be used by two different space telescopes, or does the ...
1k views

### Why doesn't Earth's axis change during the year?

My understanding is that the Earth's axis points in the same direction in space during its entire orbit around the sun. And this is what causes our seasons. My question is why doesn't the axis follow ...
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### infrared telescopes, magnitude and observations

Currently 22-23mag could be the limit to make a spectrum for ground based 10m class telescopes, 21-22may may be easy for them. 4m class telescopes could handle 20mag? I am not sure. 2m could be ...
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### how to tell an optical spectrum is featureless or just with a low S/N?

A featureless spectrum and a spectrum low S/N are very similar. Is there a way to tell them?
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### Is it possible to use the stars to determine the passage of time?

I'm writing a science fiction short story which involves a group of people being in suspended animation for a very long period of time, on the order of thousands of years. My question is, would an ...